Adding upstream version 1.64.0+dfsg1.upstream/1.64.0+dfsg1

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

6 files changed, 3669 insertions, 0 deletions

diff --git a/src/tools/rust-analyzer/crates/hir-ty/src/infer/closure.rs b/src/tools/rust-analyzer/crates/hir-ty/src/infer/closure.rs
new file mode 100644
index 000000000..3ead92909
--- /dev/null
+++ b/src/tools/rust-analyzer/crates/hir-ty/src/infer/closure.rs
@@ -0,0 +1,82 @@
+//! Inference of closure parameter types based on the closure's expected type.
+
+use chalk_ir::{cast::Cast, AliasEq, AliasTy, FnSubst, WhereClause};
+use hir_def::{expr::ExprId, HasModule};
+use smallvec::SmallVec;
+
+use crate::{
+    to_chalk_trait_id, utils, ChalkTraitId, DynTy, FnPointer, FnSig, Interner, Substitution, Ty,
+    TyExt, TyKind,
+};
+
+use super::{Expectation, InferenceContext};
+
+impl InferenceContext<'_> {
+    pub(super) fn deduce_closure_type_from_expectations(
+        &mut self,
+        closure_expr: ExprId,
+        closure_ty: &Ty,
+        sig_ty: &Ty,
+        expectation: &Expectation,
+    ) {
+        let expected_ty = match expectation.to_option(&mut self.table) {
+            Some(ty) => ty,
+            None => return,
+        };
+
+        // Deduction from where-clauses in scope, as well as fn-pointer coercion are handled here.
+        let _ = self.coerce(Some(closure_expr), closure_ty, &expected_ty);
+
+        // Deduction based on the expected `dyn Fn` is done separately.
+        if let TyKind::Dyn(dyn_ty) = expected_ty.kind(Interner) {
+            if let Some(sig) = self.deduce_sig_from_dyn_ty(dyn_ty) {
+                let expected_sig_ty = TyKind::Function(sig).intern(Interner);
+
+                self.unify(sig_ty, &expected_sig_ty);
+            }
+        }
+    }
+
+    fn deduce_sig_from_dyn_ty(&self, dyn_ty: &DynTy) -> Option<FnPointer> {
+        // Search for a predicate like `<$self as FnX<Args>>::Output == Ret`
+
+        let fn_traits: SmallVec<[ChalkTraitId; 3]> =
+            utils::fn_traits(self.db.upcast(), self.owner.module(self.db.upcast()).krate())
+                .map(to_chalk_trait_id)
+                .collect();
+
+        let self_ty = TyKind::Error.intern(Interner);
+        let bounds = dyn_ty.bounds.clone().substitute(Interner, &[self_ty.cast(Interner)]);
+        for bound in bounds.iter(Interner) {
+            // NOTE(skip_binders): the extracted types are rebound by the returned `FnPointer`
+            if let WhereClause::AliasEq(AliasEq { alias: AliasTy::Projection(projection), ty }) =
+                bound.skip_binders()
+            {
+                let assoc_data = self.db.associated_ty_data(projection.associated_ty_id);
+                if !fn_traits.contains(&assoc_data.trait_id) {
+                    return None;
+                }
+
+                // Skip `Self`, get the type argument.
+                let arg = projection.substitution.as_slice(Interner).get(1)?;
+                if let Some(subst) = arg.ty(Interner)?.as_tuple() {
+                    let generic_args = subst.as_slice(Interner);
+                    let mut sig_tys = Vec::new();
+                    for arg in generic_args {
+                        sig_tys.push(arg.ty(Interner)?.clone());
+                    }
+                    sig_tys.push(ty.clone());
+
+                    cov_mark::hit!(dyn_fn_param_informs_call_site_closure_signature);
+                    return Some(FnPointer {
+                        num_binders: bound.len(Interner),
+                        sig: FnSig { abi: (), safety: chalk_ir::Safety::Safe, variadic: false },
+                        substitution: FnSubst(Substitution::from_iter(Interner, sig_tys)),
+                    });
+                }
+            }
+        }
+
+        None
+    }
+}
diff --git a/src/tools/rust-analyzer/crates/hir-ty/src/infer/coerce.rs b/src/tools/rust-analyzer/crates/hir-ty/src/infer/coerce.rs
new file mode 100644
index 000000000..f54440bf5
--- /dev/null
+++ b/src/tools/rust-analyzer/crates/hir-ty/src/infer/coerce.rs
@@ -0,0 +1,673 @@
+//! Coercion logic. Coercions are certain type conversions that can implicitly
+//! happen in certain places, e.g. weakening `&mut` to `&` or deref coercions
+//! like going from `&Vec<T>` to `&[T]`.
+//!
+//! See <https://doc.rust-lang.org/nomicon/coercions.html> and
+//! `librustc_typeck/check/coercion.rs`.
+
+use std::{iter, sync::Arc};
+
+use chalk_ir::{cast::Cast, BoundVar, Goal, Mutability, TyVariableKind};
+use hir_def::{expr::ExprId, lang_item::LangItemTarget};
+use stdx::always;
+use syntax::SmolStr;
+
+use crate::{
+    autoderef::{Autoderef, AutoderefKind},
+    db::HirDatabase,
+    infer::{
+        Adjust, Adjustment, AutoBorrow, InferOk, InferenceContext, OverloadedDeref, PointerCast,
+        TypeError, TypeMismatch,
+    },
+    static_lifetime, Canonical, DomainGoal, FnPointer, FnSig, Guidance, InEnvironment, Interner,
+    Solution, Substitution, TraitEnvironment, Ty, TyBuilder, TyExt, TyKind,
+};
+
+use super::unify::InferenceTable;
+
+pub(crate) type CoerceResult = Result<InferOk<(Vec<Adjustment>, Ty)>, TypeError>;
+
+/// Do not require any adjustments, i.e. coerce `x -> x`.
+fn identity(_: Ty) -> Vec<Adjustment> {
+    vec![]
+}
+
+fn simple(kind: Adjust) -> impl FnOnce(Ty) -> Vec<Adjustment> {
+    move |target| vec![Adjustment { kind, target }]
+}
+
+/// This always returns `Ok(...)`.
+fn success(
+    adj: Vec<Adjustment>,
+    target: Ty,
+    goals: Vec<InEnvironment<Goal<Interner>>>,
+) -> CoerceResult {
+    Ok(InferOk { goals, value: (adj, target) })
+}
+
+#[derive(Clone, Debug)]
+pub(super) struct CoerceMany {
+    expected_ty: Ty,
+}
+
+impl CoerceMany {
+    pub(super) fn new(expected: Ty) -> Self {
+        CoerceMany { expected_ty: expected }
+    }
+
+    /// Merge two types from different branches, with possible coercion.
+    ///
+    /// Mostly this means trying to coerce one to the other, but
+    ///  - if we have two function types for different functions or closures, we need to
+    ///    coerce both to function pointers;
+    ///  - if we were concerned with lifetime subtyping, we'd need to look for a
+    ///    least upper bound.
+    pub(super) fn coerce(
+        &mut self,
+        ctx: &mut InferenceContext<'_>,
+        expr: Option<ExprId>,
+        expr_ty: &Ty,
+    ) {
+        let expr_ty = ctx.resolve_ty_shallow(expr_ty);
+        self.expected_ty = ctx.resolve_ty_shallow(&self.expected_ty);
+
+        // Special case: two function types. Try to coerce both to
+        // pointers to have a chance at getting a match. See
+        // https://github.com/rust-lang/rust/blob/7b805396bf46dce972692a6846ce2ad8481c5f85/src/librustc_typeck/check/coercion.rs#L877-L916
+        let sig = match (self.expected_ty.kind(Interner), expr_ty.kind(Interner)) {
+            (TyKind::FnDef(..) | TyKind::Closure(..), TyKind::FnDef(..) | TyKind::Closure(..)) => {
+                // FIXME: we're ignoring safety here. To be more correct, if we have one FnDef and one Closure,
+                // we should be coercing the closure to a fn pointer of the safety of the FnDef
+                cov_mark::hit!(coerce_fn_reification);
+                let sig =
+                    self.expected_ty.callable_sig(ctx.db).expect("FnDef without callable sig");
+                Some(sig)
+            }
+            _ => None,
+        };
+        if let Some(sig) = sig {
+            let target_ty = TyKind::Function(sig.to_fn_ptr()).intern(Interner);
+            let result1 = ctx.table.coerce_inner(self.expected_ty.clone(), &target_ty);
+            let result2 = ctx.table.coerce_inner(expr_ty.clone(), &target_ty);
+            if let (Ok(result1), Ok(result2)) = (result1, result2) {
+                ctx.table.register_infer_ok(result1);
+                ctx.table.register_infer_ok(result2);
+                return self.expected_ty = target_ty;
+            }
+        }
+
+        // It might not seem like it, but order is important here: If the expected
+        // type is a type variable and the new one is `!`, trying it the other
+        // way around first would mean we make the type variable `!`, instead of
+        // just marking it as possibly diverging.
+        if ctx.coerce(expr, &expr_ty, &self.expected_ty).is_ok() {
+            /* self.expected_ty is already correct */
+        } else if ctx.coerce(expr, &self.expected_ty, &expr_ty).is_ok() {
+            self.expected_ty = expr_ty;
+        } else {
+            if let Some(id) = expr {
+                ctx.result.type_mismatches.insert(
+                    id.into(),
+                    TypeMismatch { expected: self.expected_ty.clone(), actual: expr_ty },
+                );
+            }
+            cov_mark::hit!(coerce_merge_fail_fallback);
+            /* self.expected_ty is already correct */
+        }
+    }
+
+    pub(super) fn complete(self) -> Ty {
+        self.expected_ty
+    }
+}
+
+pub fn could_coerce(
+    db: &dyn HirDatabase,
+    env: Arc<TraitEnvironment>,
+    tys: &Canonical<(Ty, Ty)>,
+) -> bool {
+    coerce(db, env, tys).is_ok()
+}
+
+pub(crate) fn coerce(
+    db: &dyn HirDatabase,
+    env: Arc<TraitEnvironment>,
+    tys: &Canonical<(Ty, Ty)>,
+) -> Result<(Vec<Adjustment>, Ty), TypeError> {
+    let mut table = InferenceTable::new(db, env);
+    let vars = table.fresh_subst(tys.binders.as_slice(Interner));
+    let ty1_with_vars = vars.apply(tys.value.0.clone(), Interner);
+    let ty2_with_vars = vars.apply(tys.value.1.clone(), Interner);
+    let (adjustments, ty) = table.coerce(&ty1_with_vars, &ty2_with_vars)?;
+    // default any type vars that weren't unified back to their original bound vars
+    // (kind of hacky)
+    let find_var = |iv| {
+        vars.iter(Interner).position(|v| match v.interned() {
+            chalk_ir::GenericArgData::Ty(ty) => ty.inference_var(Interner),
+            chalk_ir::GenericArgData::Lifetime(lt) => lt.inference_var(Interner),
+            chalk_ir::GenericArgData::Const(c) => c.inference_var(Interner),
+        } == Some(iv))
+    };
+    let fallback = |iv, kind, default, binder| match kind {
+        chalk_ir::VariableKind::Ty(_ty_kind) => find_var(iv)
+            .map_or(default, |i| BoundVar::new(binder, i).to_ty(Interner).cast(Interner)),
+        chalk_ir::VariableKind::Lifetime => find_var(iv)
+            .map_or(default, |i| BoundVar::new(binder, i).to_lifetime(Interner).cast(Interner)),
+        chalk_ir::VariableKind::Const(ty) => find_var(iv)
+            .map_or(default, |i| BoundVar::new(binder, i).to_const(Interner, ty).cast(Interner)),
+    };
+    // FIXME also map the types in the adjustments
+    Ok((adjustments, table.resolve_with_fallback(ty, &fallback)))
+}
+
+impl<'a> InferenceContext<'a> {
+    /// Unify two types, but may coerce the first one to the second one
+    /// using "implicit coercion rules" if needed.
+    pub(super) fn coerce(
+        &mut self,
+        expr: Option<ExprId>,
+        from_ty: &Ty,
+        to_ty: &Ty,
+    ) -> Result<Ty, TypeError> {
+        let from_ty = self.resolve_ty_shallow(from_ty);
+        let to_ty = self.resolve_ty_shallow(to_ty);
+        let (adjustments, ty) = self.table.coerce(&from_ty, &to_ty)?;
+        if let Some(expr) = expr {
+            self.write_expr_adj(expr, adjustments);
+        }
+        Ok(ty)
+    }
+}
+
+impl<'a> InferenceTable<'a> {
+    /// Unify two types, but may coerce the first one to the second one
+    /// using "implicit coercion rules" if needed.
+    pub(crate) fn coerce(
+        &mut self,
+        from_ty: &Ty,
+        to_ty: &Ty,
+    ) -> Result<(Vec<Adjustment>, Ty), TypeError> {
+        let from_ty = self.resolve_ty_shallow(from_ty);
+        let to_ty = self.resolve_ty_shallow(to_ty);
+        match self.coerce_inner(from_ty, &to_ty) {
+            Ok(InferOk { value: (adjustments, ty), goals }) => {
+                self.register_infer_ok(InferOk { value: (), goals });
+                Ok((adjustments, ty))
+            }
+            Err(e) => {
+                // FIXME deal with error
+                Err(e)
+            }
+        }
+    }
+
+    fn coerce_inner(&mut self, from_ty: Ty, to_ty: &Ty) -> CoerceResult {
+        if from_ty.is_never() {
+            // Subtle: If we are coercing from `!` to `?T`, where `?T` is an unbound
+            // type variable, we want `?T` to fallback to `!` if not
+            // otherwise constrained. An example where this arises:
+            //
+            //     let _: Option<?T> = Some({ return; });
+            //
+            // here, we would coerce from `!` to `?T`.
+            if let TyKind::InferenceVar(tv, TyVariableKind::General) = to_ty.kind(Interner) {
+                self.set_diverging(*tv, true);
+            }
+            return success(simple(Adjust::NeverToAny)(to_ty.clone()), to_ty.clone(), vec![]);
+        }
+
+        // Consider coercing the subtype to a DST
+        if let Ok(ret) = self.try_coerce_unsized(&from_ty, to_ty) {
+            return Ok(ret);
+        }
+
+        // Examine the supertype and consider auto-borrowing.
+        match to_ty.kind(Interner) {
+            TyKind::Raw(mt, _) => return self.coerce_ptr(from_ty, to_ty, *mt),
+            TyKind::Ref(mt, _, _) => return self.coerce_ref(from_ty, to_ty, *mt),
+            _ => {}
+        }
+
+        match from_ty.kind(Interner) {
+            TyKind::FnDef(..) => {
+                // Function items are coercible to any closure
+                // type; function pointers are not (that would
+                // require double indirection).
+                // Additionally, we permit coercion of function
+                // items to drop the unsafe qualifier.
+                self.coerce_from_fn_item(from_ty, to_ty)
+            }
+            TyKind::Function(from_fn_ptr) => {
+                // We permit coercion of fn pointers to drop the
+                // unsafe qualifier.
+                self.coerce_from_fn_pointer(from_ty.clone(), from_fn_ptr, to_ty)
+            }
+            TyKind::Closure(_, from_substs) => {
+                // Non-capturing closures are coercible to
+                // function pointers or unsafe function pointers.
+                // It cannot convert closures that require unsafe.
+                self.coerce_closure_to_fn(from_ty.clone(), from_substs, to_ty)
+            }
+            _ => {
+                // Otherwise, just use unification rules.
+                self.unify_and(&from_ty, to_ty, identity)
+            }
+        }
+    }
+
+    /// Unify two types (using sub or lub) and produce a specific coercion.
+    fn unify_and<F>(&mut self, t1: &Ty, t2: &Ty, f: F) -> CoerceResult
+    where
+        F: FnOnce(Ty) -> Vec<Adjustment>,
+    {
+        self.try_unify(t1, t2)
+            .and_then(|InferOk { goals, .. }| success(f(t1.clone()), t1.clone(), goals))
+    }
+
+    fn coerce_ptr(&mut self, from_ty: Ty, to_ty: &Ty, to_mt: Mutability) -> CoerceResult {
+        let (is_ref, from_mt, from_inner) = match from_ty.kind(Interner) {
+            TyKind::Ref(mt, _, ty) => (true, mt, ty),
+            TyKind::Raw(mt, ty) => (false, mt, ty),
+            _ => return self.unify_and(&from_ty, to_ty, identity),
+        };
+
+        coerce_mutabilities(*from_mt, to_mt)?;
+
+        // Check that the types which they point at are compatible.
+        let from_raw = TyKind::Raw(to_mt, from_inner.clone()).intern(Interner);
+
+        // Although references and unsafe ptrs have the same
+        // representation, we still register an Adjust::DerefRef so that
+        // regionck knows that the region for `a` must be valid here.
+        if is_ref {
+            self.unify_and(&from_raw, to_ty, |target| {
+                vec![
+                    Adjustment { kind: Adjust::Deref(None), target: from_inner.clone() },
+                    Adjustment { kind: Adjust::Borrow(AutoBorrow::RawPtr(to_mt)), target },
+                ]
+            })
+        } else if *from_mt != to_mt {
+            self.unify_and(
+                &from_raw,
+                to_ty,
+                simple(Adjust::Pointer(PointerCast::MutToConstPointer)),
+            )
+        } else {
+            self.unify_and(&from_raw, to_ty, identity)
+        }
+    }
+
+    /// Reborrows `&mut A` to `&mut B` and `&(mut) A` to `&B`.
+    /// To match `A` with `B`, autoderef will be performed,
+    /// calling `deref`/`deref_mut` where necessary.
+    fn coerce_ref(&mut self, from_ty: Ty, to_ty: &Ty, to_mt: Mutability) -> CoerceResult {
+        let from_mt = match from_ty.kind(Interner) {
+            &TyKind::Ref(mt, _, _) => {
+                coerce_mutabilities(mt, to_mt)?;
+                mt
+            }
+            _ => return self.unify_and(&from_ty, to_ty, identity),
+        };
+
+        // NOTE: this code is mostly copied and adapted from rustc, and
+        // currently more complicated than necessary, carrying errors around
+        // etc.. This complication will become necessary when we actually track
+        // details of coercion errors though, so I think it's useful to leave
+        // the structure like it is.
+
+        let snapshot = self.snapshot();
+
+        let mut autoderef = Autoderef::new(self, from_ty.clone());
+        let mut first_error = None;
+        let mut found = None;
+
+        while let Some((referent_ty, autoderefs)) = autoderef.next() {
+            if autoderefs == 0 {
+                // Don't let this pass, otherwise it would cause
+                // &T to autoref to &&T.
+                continue;
+            }
+
+            // At this point, we have deref'd `a` to `referent_ty`.  So
+            // imagine we are coercing from `&'a mut Vec<T>` to `&'b mut [T]`.
+            // In the autoderef loop for `&'a mut Vec<T>`, we would get
+            // three callbacks:
+            //
+            // - `&'a mut Vec<T>` -- 0 derefs, just ignore it
+            // - `Vec<T>` -- 1 deref
+            // - `[T]` -- 2 deref
+            //
+            // At each point after the first callback, we want to
+            // check to see whether this would match out target type
+            // (`&'b mut [T]`) if we autoref'd it. We can't just
+            // compare the referent types, though, because we still
+            // have to consider the mutability. E.g., in the case
+            // we've been considering, we have an `&mut` reference, so
+            // the `T` in `[T]` needs to be unified with equality.
+            //
+            // Therefore, we construct reference types reflecting what
+            // the types will be after we do the final auto-ref and
+            // compare those. Note that this means we use the target
+            // mutability [1], since it may be that we are coercing
+            // from `&mut T` to `&U`.
+            let lt = static_lifetime(); // FIXME: handle lifetimes correctly, see rustc
+            let derefd_from_ty = TyKind::Ref(to_mt, lt, referent_ty).intern(Interner);
+            match autoderef.table.try_unify(&derefd_from_ty, to_ty) {
+                Ok(result) => {
+                    found = Some(result.map(|()| derefd_from_ty));
+                    break;
+                }
+                Err(err) => {
+                    if first_error.is_none() {
+                        first_error = Some(err);
+                    }
+                }
+            }
+        }
+
+        // Extract type or return an error. We return the first error
+        // we got, which should be from relating the "base" type
+        // (e.g., in example above, the failure from relating `Vec<T>`
+        // to the target type), since that should be the least
+        // confusing.
+        let InferOk { value: ty, goals } = match found {
+            Some(d) => d,
+            None => {
+                self.rollback_to(snapshot);
+                let err = first_error.expect("coerce_borrowed_pointer had no error");
+                return Err(err);
+            }
+        };
+        if ty == from_ty && from_mt == Mutability::Not && autoderef.step_count() == 1 {
+            // As a special case, if we would produce `&'a *x`, that's
+            // a total no-op. We end up with the type `&'a T` just as
+            // we started with.  In that case, just skip it
+            // altogether. This is just an optimization.
+            //
+            // Note that for `&mut`, we DO want to reborrow --
+            // otherwise, this would be a move, which might be an
+            // error. For example `foo(self.x)` where `self` and
+            // `self.x` both have `&mut `type would be a move of
+            // `self.x`, but we auto-coerce it to `foo(&mut *self.x)`,
+            // which is a borrow.
+            always!(to_mt == Mutability::Not); // can only coerce &T -> &U
+            return success(vec![], ty, goals);
+        }
+
+        let mut adjustments = auto_deref_adjust_steps(&autoderef);
+        adjustments
+            .push(Adjustment { kind: Adjust::Borrow(AutoBorrow::Ref(to_mt)), target: ty.clone() });
+
+        success(adjustments, ty, goals)
+    }
+
+    /// Attempts to coerce from the type of a Rust function item into a function pointer.
+    fn coerce_from_fn_item(&mut self, from_ty: Ty, to_ty: &Ty) -> CoerceResult {
+        match to_ty.kind(Interner) {
+            TyKind::Function(_) => {
+                let from_sig = from_ty.callable_sig(self.db).expect("FnDef had no sig");
+
+                // FIXME check ABI: Intrinsics are not coercible to function pointers
+                // FIXME Safe `#[target_feature]` functions are not assignable to safe fn pointers (RFC 2396)
+
+                // FIXME rustc normalizes assoc types in the sig here, not sure if necessary
+
+                let from_sig = from_sig.to_fn_ptr();
+                let from_fn_pointer = TyKind::Function(from_sig.clone()).intern(Interner);
+                let ok = self.coerce_from_safe_fn(
+                    from_fn_pointer.clone(),
+                    &from_sig,
+                    to_ty,
+                    |unsafe_ty| {
+                        vec![
+                            Adjustment {
+                                kind: Adjust::Pointer(PointerCast::ReifyFnPointer),
+                                target: from_fn_pointer,
+                            },
+                            Adjustment {
+                                kind: Adjust::Pointer(PointerCast::UnsafeFnPointer),
+                                target: unsafe_ty,
+                            },
+                        ]
+                    },
+                    simple(Adjust::Pointer(PointerCast::ReifyFnPointer)),
+                )?;
+
+                Ok(ok)
+            }
+            _ => self.unify_and(&from_ty, to_ty, identity),
+        }
+    }
+
+    fn coerce_from_fn_pointer(
+        &mut self,
+        from_ty: Ty,
+        from_f: &FnPointer,
+        to_ty: &Ty,
+    ) -> CoerceResult {
+        self.coerce_from_safe_fn(
+            from_ty,
+            from_f,
+            to_ty,
+            simple(Adjust::Pointer(PointerCast::UnsafeFnPointer)),
+            identity,
+        )
+    }
+
+    fn coerce_from_safe_fn<F, G>(
+        &mut self,
+        from_ty: Ty,
+        from_fn_ptr: &FnPointer,
+        to_ty: &Ty,
+        to_unsafe: F,
+        normal: G,
+    ) -> CoerceResult
+    where
+        F: FnOnce(Ty) -> Vec<Adjustment>,
+        G: FnOnce(Ty) -> Vec<Adjustment>,
+    {
+        if let TyKind::Function(to_fn_ptr) = to_ty.kind(Interner) {
+            if let (chalk_ir::Safety::Safe, chalk_ir::Safety::Unsafe) =
+                (from_fn_ptr.sig.safety, to_fn_ptr.sig.safety)
+            {
+                let from_unsafe =
+                    TyKind::Function(safe_to_unsafe_fn_ty(from_fn_ptr.clone())).intern(Interner);
+                return self.unify_and(&from_unsafe, to_ty, to_unsafe);
+            }
+        }
+        self.unify_and(&from_ty, to_ty, normal)
+    }
+
+    /// Attempts to coerce from the type of a non-capturing closure into a
+    /// function pointer.
+    fn coerce_closure_to_fn(
+        &mut self,
+        from_ty: Ty,
+        from_substs: &Substitution,
+        to_ty: &Ty,
+    ) -> CoerceResult {
+        match to_ty.kind(Interner) {
+            // if from_substs is non-capturing (FIXME)
+            TyKind::Function(fn_ty) => {
+                // We coerce the closure, which has fn type
+                //     `extern "rust-call" fn((arg0,arg1,...)) -> _`
+                // to
+                //     `fn(arg0,arg1,...) -> _`
+                // or
+                //     `unsafe fn(arg0,arg1,...) -> _`
+                let safety = fn_ty.sig.safety;
+                let pointer_ty = coerce_closure_fn_ty(from_substs, safety);
+                self.unify_and(
+                    &pointer_ty,
+                    to_ty,
+                    simple(Adjust::Pointer(PointerCast::ClosureFnPointer(safety))),
+                )
+            }
+            _ => self.unify_and(&from_ty, to_ty, identity),
+        }
+    }
+
+    /// Coerce a type using `from_ty: CoerceUnsized<ty_ty>`
+    ///
+    /// See: <https://doc.rust-lang.org/nightly/std/marker/trait.CoerceUnsized.html>
+    fn try_coerce_unsized(&mut self, from_ty: &Ty, to_ty: &Ty) -> CoerceResult {
+        // These 'if' statements require some explanation.
+        // The `CoerceUnsized` trait is special - it is only
+        // possible to write `impl CoerceUnsized<B> for A` where
+        // A and B have 'matching' fields. This rules out the following
+        // two types of blanket impls:
+        //
+        // `impl<T> CoerceUnsized<T> for SomeType`
+        // `impl<T> CoerceUnsized<SomeType> for T`
+        //
+        // Both of these trigger a special `CoerceUnsized`-related error (E0376)
+        //
+        // We can take advantage of this fact to avoid performing unnecessary work.
+        // If either `source` or `target` is a type variable, then any applicable impl
+        // would need to be generic over the self-type (`impl<T> CoerceUnsized<SomeType> for T`)
+        // or generic over the `CoerceUnsized` type parameter (`impl<T> CoerceUnsized<T> for
+        // SomeType`).
+        //
+        // However, these are exactly the kinds of impls which are forbidden by
+        // the compiler! Therefore, we can be sure that coercion will always fail
+        // when either the source or target type is a type variable. This allows us
+        // to skip performing any trait selection, and immediately bail out.
+        if from_ty.is_ty_var() {
+            return Err(TypeError);
+        }
+        if to_ty.is_ty_var() {
+            return Err(TypeError);
+        }
+
+        // Handle reborrows before trying to solve `Source: CoerceUnsized<Target>`.
+        let reborrow = match (from_ty.kind(Interner), to_ty.kind(Interner)) {
+            (TyKind::Ref(from_mt, _, from_inner), &TyKind::Ref(to_mt, _, _)) => {
+                coerce_mutabilities(*from_mt, to_mt)?;
+
+                let lt = static_lifetime();
+                Some((
+                    Adjustment { kind: Adjust::Deref(None), target: from_inner.clone() },
+                    Adjustment {
+                        kind: Adjust::Borrow(AutoBorrow::Ref(to_mt)),
+                        target: TyKind::Ref(to_mt, lt, from_inner.clone()).intern(Interner),
+                    },
+                ))
+            }
+            (TyKind::Ref(from_mt, _, from_inner), &TyKind::Raw(to_mt, _)) => {
+                coerce_mutabilities(*from_mt, to_mt)?;
+
+                Some((
+                    Adjustment { kind: Adjust::Deref(None), target: from_inner.clone() },
+                    Adjustment {
+                        kind: Adjust::Borrow(AutoBorrow::RawPtr(to_mt)),
+                        target: TyKind::Raw(to_mt, from_inner.clone()).intern(Interner),
+                    },
+                ))
+            }
+            _ => None,
+        };
+        let coerce_from =
+            reborrow.as_ref().map_or_else(|| from_ty.clone(), |(_, adj)| adj.target.clone());
+
+        let krate = self.trait_env.krate;
+        let coerce_unsized_trait =
+            match self.db.lang_item(krate, SmolStr::new_inline("coerce_unsized")) {
+                Some(LangItemTarget::TraitId(trait_)) => trait_,
+                _ => return Err(TypeError),
+            };
+
+        let coerce_unsized_tref = {
+            let b = TyBuilder::trait_ref(self.db, coerce_unsized_trait);
+            if b.remaining() != 2 {
+                // The CoerceUnsized trait should have two generic params: Self and T.
+                return Err(TypeError);
+            }
+            b.push(coerce_from).push(to_ty.clone()).build()
+        };
+
+        let goal: InEnvironment<DomainGoal> =
+            InEnvironment::new(&self.trait_env.env, coerce_unsized_tref.cast(Interner));
+
+        let canonicalized = self.canonicalize(goal);
+
+        // FIXME: rustc's coerce_unsized is more specialized -- it only tries to
+        // solve `CoerceUnsized` and `Unsize` goals at this point and leaves the
+        // rest for later. Also, there's some logic about sized type variables.
+        // Need to find out in what cases this is necessary
+        let solution = self
+            .db
+            .trait_solve(krate, canonicalized.value.clone().cast(Interner))
+            .ok_or(TypeError)?;
+
+        match solution {
+            Solution::Unique(v) => {
+                canonicalized.apply_solution(
+                    self,
+                    Canonical {
+                        binders: v.binders,
+                        // FIXME handle constraints
+                        value: v.value.subst,
+                    },
+                );
+            }
+            Solution::Ambig(Guidance::Definite(subst)) => {
+                // FIXME need to record an obligation here
+                canonicalized.apply_solution(self, subst)
+            }
+            // FIXME actually we maybe should also accept unknown guidance here
+            _ => return Err(TypeError),
+        };
+        let unsize =
+            Adjustment { kind: Adjust::Pointer(PointerCast::Unsize), target: to_ty.clone() };
+        let adjustments = match reborrow {
+            None => vec![unsize],
+            Some((deref, autoref)) => vec![deref, autoref, unsize],
+        };
+        success(adjustments, to_ty.clone(), vec![])
+    }
+}
+
+fn coerce_closure_fn_ty(closure_substs: &Substitution, safety: chalk_ir::Safety) -> Ty {
+    let closure_sig = closure_substs.at(Interner, 0).assert_ty_ref(Interner).clone();
+    match closure_sig.kind(Interner) {
+        TyKind::Function(fn_ty) => TyKind::Function(FnPointer {
+            num_binders: fn_ty.num_binders,
+            sig: FnSig { safety, ..fn_ty.sig },
+            substitution: fn_ty.substitution.clone(),
+        })
+        .intern(Interner),
+        _ => TyKind::Error.intern(Interner),
+    }
+}
+
+fn safe_to_unsafe_fn_ty(fn_ty: FnPointer) -> FnPointer {
+    FnPointer {
+        num_binders: fn_ty.num_binders,
+        sig: FnSig { safety: chalk_ir::Safety::Unsafe, ..fn_ty.sig },
+        substitution: fn_ty.substitution,
+    }
+}
+
+fn coerce_mutabilities(from: Mutability, to: Mutability) -> Result<(), TypeError> {
+    match (from, to) {
+        (Mutability::Mut, Mutability::Mut | Mutability::Not)
+        | (Mutability::Not, Mutability::Not) => Ok(()),
+        (Mutability::Not, Mutability::Mut) => Err(TypeError),
+    }
+}
+
+pub(super) fn auto_deref_adjust_steps(autoderef: &Autoderef<'_, '_>) -> Vec<Adjustment> {
+    let steps = autoderef.steps();
+    let targets =
+        steps.iter().skip(1).map(|(_, ty)| ty.clone()).chain(iter::once(autoderef.final_ty()));
+    steps
+        .iter()
+        .map(|(kind, _source)| match kind {
+            // We do not know what kind of deref we require at this point yet
+            AutoderefKind::Overloaded => Some(OverloadedDeref(Mutability::Not)),
+            AutoderefKind::Builtin => None,
+        })
+        .zip(targets)
+        .map(|(autoderef, target)| Adjustment { kind: Adjust::Deref(autoderef), target })
+        .collect()
+}
diff --git a/src/tools/rust-analyzer/crates/hir-ty/src/infer/expr.rs b/src/tools/rust-analyzer/crates/hir-ty/src/infer/expr.rs
new file mode 100644
index 000000000..d164e64a8
--- /dev/null
+++ b/src/tools/rust-analyzer/crates/hir-ty/src/infer/expr.rs
@@ -0,0 +1,1527 @@
+//! Type inference for expressions.
+
+use std::{
+    collections::hash_map::Entry,
+    iter::{repeat, repeat_with},
+    mem,
+};
+
+use chalk_ir::{
+    cast::Cast, fold::Shift, DebruijnIndex, GenericArgData, Mutability, TyVariableKind,
+};
+use hir_def::{
+    expr::{ArithOp, Array, BinaryOp, CmpOp, Expr, ExprId, Literal, Ordering, Statement, UnaryOp},
+    generics::TypeOrConstParamData,
+    path::{GenericArg, GenericArgs},
+    resolver::resolver_for_expr,
+    ConstParamId, FieldId, FunctionId, ItemContainerId, Lookup,
+};
+use hir_expand::name::{name, Name};
+use stdx::always;
+use syntax::ast::RangeOp;
+
+use crate::{
+    autoderef::{self, Autoderef},
+    consteval,
+    infer::coerce::CoerceMany,
+    lower::{
+        const_or_path_to_chalk, generic_arg_to_chalk, lower_to_chalk_mutability, ParamLoweringMode,
+    },
+    mapping::{from_chalk, ToChalk},
+    method_resolution::{self, VisibleFromModule},
+    primitive::{self, UintTy},
+    static_lifetime, to_chalk_trait_id,
+    utils::{generics, Generics},
+    AdtId, Binders, CallableDefId, FnPointer, FnSig, FnSubst, Interner, Rawness, Scalar,
+    Substitution, TraitRef, Ty, TyBuilder, TyExt, TyKind,
+};
+
+use super::{
+    coerce::auto_deref_adjust_steps, find_breakable, BindingMode, BreakableContext, Diverges,
+    Expectation, InferenceContext, InferenceDiagnostic, TypeMismatch,
+};
+
+impl<'a> InferenceContext<'a> {
+    pub(crate) fn infer_expr(&mut self, tgt_expr: ExprId, expected: &Expectation) -> Ty {
+        let ty = self.infer_expr_inner(tgt_expr, expected);
+        if let Some(expected_ty) = expected.only_has_type(&mut self.table) {
+            let could_unify = self.unify(&ty, &expected_ty);
+            if !could_unify {
+                self.result.type_mismatches.insert(
+                    tgt_expr.into(),
+                    TypeMismatch { expected: expected_ty, actual: ty.clone() },
+                );
+            }
+        }
+        ty
+    }
+
+    /// Infer type of expression with possibly implicit coerce to the expected type.
+    /// Return the type after possible coercion.
+    pub(super) fn infer_expr_coerce(&mut self, expr: ExprId, expected: &Expectation) -> Ty {
+        let ty = self.infer_expr_inner(expr, expected);
+        if let Some(target) = expected.only_has_type(&mut self.table) {
+            match self.coerce(Some(expr), &ty, &target) {
+                Ok(res) => res,
+                Err(_) => {
+                    self.result.type_mismatches.insert(
+                        expr.into(),
+                        TypeMismatch { expected: target.clone(), actual: ty.clone() },
+                    );
+                    target
+                }
+            }
+        } else {
+            ty
+        }
+    }
+
+    fn infer_expr_inner(&mut self, tgt_expr: ExprId, expected: &Expectation) -> Ty {
+        self.db.unwind_if_cancelled();
+
+        let ty = match &self.body[tgt_expr] {
+            Expr::Missing => self.err_ty(),
+            &Expr::If { condition, then_branch, else_branch } => {
+                self.infer_expr(
+                    condition,
+                    &Expectation::has_type(TyKind::Scalar(Scalar::Bool).intern(Interner)),
+                );
+
+                let condition_diverges = mem::replace(&mut self.diverges, Diverges::Maybe);
+                let mut both_arms_diverge = Diverges::Always;
+
+                let result_ty = self.table.new_type_var();
+                let then_ty = self.infer_expr_inner(then_branch, expected);
+                both_arms_diverge &= mem::replace(&mut self.diverges, Diverges::Maybe);
+                let mut coerce = CoerceMany::new(result_ty);
+                coerce.coerce(self, Some(then_branch), &then_ty);
+                let else_ty = match else_branch {
+                    Some(else_branch) => self.infer_expr_inner(else_branch, expected),
+                    None => TyBuilder::unit(),
+                };
+                both_arms_diverge &= self.diverges;
+                // FIXME: create a synthetic `else {}` so we have something to refer to here instead of None?
+                coerce.coerce(self, else_branch, &else_ty);
+
+                self.diverges = condition_diverges | both_arms_diverge;
+
+                coerce.complete()
+            }
+            &Expr::Let { pat, expr } => {
+                let input_ty = self.infer_expr(expr, &Expectation::none());
+                self.infer_pat(pat, &input_ty, BindingMode::default());
+                TyKind::Scalar(Scalar::Bool).intern(Interner)
+            }
+            Expr::Block { statements, tail, label, id: _ } => {
+                let old_resolver = mem::replace(
+                    &mut self.resolver,
+                    resolver_for_expr(self.db.upcast(), self.owner, tgt_expr),
+                );
+                let ty = match label {
+                    Some(_) => {
+                        let break_ty = self.table.new_type_var();
+                        self.breakables.push(BreakableContext {
+                            may_break: false,
+                            coerce: CoerceMany::new(break_ty.clone()),
+                            label: label.map(|label| self.body[label].name.clone()),
+                        });
+                        let ty = self.infer_block(
+                            tgt_expr,
+                            statements,
+                            *tail,
+                            &Expectation::has_type(break_ty),
+                        );
+                        let ctxt = self.breakables.pop().expect("breakable stack broken");
+                        if ctxt.may_break {
+                            ctxt.coerce.complete()
+                        } else {
+                            ty
+                        }
+                    }
+                    None => self.infer_block(tgt_expr, statements, *tail, expected),
+                };
+                self.resolver = old_resolver;
+                ty
+            }
+            Expr::Unsafe { body } | Expr::Const { body } => self.infer_expr(*body, expected),
+            Expr::TryBlock { body } => {
+                let _inner = self.infer_expr(*body, expected);
+                // FIXME should be std::result::Result<{inner}, _>
+                self.err_ty()
+            }
+            Expr::Async { body } => {
+                let ret_ty = self.table.new_type_var();
+                let prev_diverges = mem::replace(&mut self.diverges, Diverges::Maybe);
+                let prev_ret_ty = mem::replace(&mut self.return_ty, ret_ty.clone());
+
+                let inner_ty = self.infer_expr_coerce(*body, &Expectation::has_type(ret_ty));
+
+                self.diverges = prev_diverges;
+                self.return_ty = prev_ret_ty;
+
+                // Use the first type parameter as the output type of future.
+                // existential type AsyncBlockImplTrait<InnerType>: Future<Output = InnerType>
+                let impl_trait_id = crate::ImplTraitId::AsyncBlockTypeImplTrait(self.owner, *body);
+                let opaque_ty_id = self.db.intern_impl_trait_id(impl_trait_id).into();
+                TyKind::OpaqueType(opaque_ty_id, Substitution::from1(Interner, inner_ty))
+                    .intern(Interner)
+            }
+            Expr::Loop { body, label } => {
+                self.breakables.push(BreakableContext {
+                    may_break: false,
+                    coerce: CoerceMany::new(self.table.new_type_var()),
+                    label: label.map(|label| self.body[label].name.clone()),
+                });
+                self.infer_expr(*body, &Expectation::has_type(TyBuilder::unit()));
+
+                let ctxt = self.breakables.pop().expect("breakable stack broken");
+
+                if ctxt.may_break {
+                    self.diverges = Diverges::Maybe;
+                    ctxt.coerce.complete()
+                } else {
+                    TyKind::Never.intern(Interner)
+                }
+            }
+            Expr::While { condition, body, label } => {
+                self.breakables.push(BreakableContext {
+                    may_break: false,
+                    coerce: CoerceMany::new(self.err_ty()),
+                    label: label.map(|label| self.body[label].name.clone()),
+                });
+                self.infer_expr(
+                    *condition,
+                    &Expectation::has_type(TyKind::Scalar(Scalar::Bool).intern(Interner)),
+                );
+                self.infer_expr(*body, &Expectation::has_type(TyBuilder::unit()));
+                let _ctxt = self.breakables.pop().expect("breakable stack broken");
+                // the body may not run, so it diverging doesn't mean we diverge
+                self.diverges = Diverges::Maybe;
+                TyBuilder::unit()
+            }
+            Expr::For { iterable, body, pat, label } => {
+                let iterable_ty = self.infer_expr(*iterable, &Expectation::none());
+
+                self.breakables.push(BreakableContext {
+                    may_break: false,
+                    coerce: CoerceMany::new(self.err_ty()),
+                    label: label.map(|label| self.body[label].name.clone()),
+                });
+                let pat_ty =
+                    self.resolve_associated_type(iterable_ty, self.resolve_into_iter_item());
+
+                self.infer_pat(*pat, &pat_ty, BindingMode::default());
+
+                self.infer_expr(*body, &Expectation::has_type(TyBuilder::unit()));
+                let _ctxt = self.breakables.pop().expect("breakable stack broken");
+                // the body may not run, so it diverging doesn't mean we diverge
+                self.diverges = Diverges::Maybe;
+                TyBuilder::unit()
+            }
+            Expr::Closure { body, args, ret_type, arg_types } => {
+                assert_eq!(args.len(), arg_types.len());
+
+                let mut sig_tys = Vec::new();
+
+                // collect explicitly written argument types
+                for arg_type in arg_types.iter() {
+                    let arg_ty = match arg_type {
+                        Some(type_ref) => self.make_ty(type_ref),
+                        None => self.table.new_type_var(),
+                    };
+                    sig_tys.push(arg_ty);
+                }
+
+                // add return type
+                let ret_ty = match ret_type {
+                    Some(type_ref) => self.make_ty(type_ref),
+                    None => self.table.new_type_var(),
+                };
+                sig_tys.push(ret_ty.clone());
+                let sig_ty = TyKind::Function(FnPointer {
+                    num_binders: 0,
+                    sig: FnSig { abi: (), safety: chalk_ir::Safety::Safe, variadic: false },
+                    substitution: FnSubst(
+                        Substitution::from_iter(Interner, sig_tys.clone()).shifted_in(Interner),
+                    ),
+                })
+                .intern(Interner);
+                let closure_id = self.db.intern_closure((self.owner, tgt_expr)).into();
+                let closure_ty =
+                    TyKind::Closure(closure_id, Substitution::from1(Interner, sig_ty.clone()))
+                        .intern(Interner);
+
+                // Eagerly try to relate the closure type with the expected
+                // type, otherwise we often won't have enough information to
+                // infer the body.
+                self.deduce_closure_type_from_expectations(
+                    tgt_expr,
+                    &closure_ty,
+                    &sig_ty,
+                    expected,
+                );
+
+                // Now go through the argument patterns
+                for (arg_pat, arg_ty) in args.iter().zip(sig_tys) {
+                    self.infer_pat(*arg_pat, &arg_ty, BindingMode::default());
+                }
+
+                let prev_diverges = mem::replace(&mut self.diverges, Diverges::Maybe);
+                let prev_ret_ty = mem::replace(&mut self.return_ty, ret_ty.clone());
+
+                self.infer_expr_coerce(*body, &Expectation::has_type(ret_ty));
+
+                self.diverges = prev_diverges;
+                self.return_ty = prev_ret_ty;
+
+                closure_ty
+            }
+            Expr::Call { callee, args, .. } => {
+                let callee_ty = self.infer_expr(*callee, &Expectation::none());
+                let mut derefs = Autoderef::new(&mut self.table, callee_ty.clone());
+                let mut res = None;
+                let mut derefed_callee = callee_ty.clone();
+                // manual loop to be able to access `derefs.table`
+                while let Some((callee_deref_ty, _)) = derefs.next() {
+                    res = derefs.table.callable_sig(&callee_deref_ty, args.len());
+                    if res.is_some() {
+                        derefed_callee = callee_deref_ty;
+                        break;
+                    }
+                }
+                // if the function is unresolved, we use is_varargs=true to
+                // suppress the arg count diagnostic here
+                let is_varargs =
+                    derefed_callee.callable_sig(self.db).map_or(false, |sig| sig.is_varargs)
+                        || res.is_none();
+                let (param_tys, ret_ty) = match res {
+                    Some(res) => {
+                        let adjustments = auto_deref_adjust_steps(&derefs);
+                        self.write_expr_adj(*callee, adjustments);
+                        res
+                    }
+                    None => (Vec::new(), self.err_ty()), // FIXME diagnostic
+                };
+                let indices_to_skip = self.check_legacy_const_generics(derefed_callee, args);
+                self.register_obligations_for_call(&callee_ty);
+
+                let expected_inputs = self.expected_inputs_for_expected_output(
+                    expected,
+                    ret_ty.clone(),
+                    param_tys.clone(),
+                );
+
+                self.check_call_arguments(
+                    tgt_expr,
+                    args,
+                    &expected_inputs,
+                    &param_tys,
+                    &indices_to_skip,
+                    is_varargs,
+                );
+                self.normalize_associated_types_in(ret_ty)
+            }
+            Expr::MethodCall { receiver, args, method_name, generic_args } => self
+                .infer_method_call(
+                    tgt_expr,
+                    *receiver,
+                    args,
+                    method_name,
+                    generic_args.as_deref(),
+                    expected,
+                ),
+            Expr::Match { expr, arms } => {
+                let input_ty = self.infer_expr(*expr, &Expectation::none());
+
+                let expected = expected.adjust_for_branches(&mut self.table);
+
+                let result_ty = if arms.is_empty() {
+                    TyKind::Never.intern(Interner)
+                } else {
+                    match &expected {
+                        Expectation::HasType(ty) => ty.clone(),
+                        _ => self.table.new_type_var(),
+                    }
+                };
+                let mut coerce = CoerceMany::new(result_ty);
+
+                let matchee_diverges = self.diverges;
+                let mut all_arms_diverge = Diverges::Always;
+
+                for arm in arms.iter() {
+                    self.diverges = Diverges::Maybe;
+                    let _pat_ty = self.infer_pat(arm.pat, &input_ty, BindingMode::default());
+                    if let Some(guard_expr) = arm.guard {
+                        self.infer_expr(
+                            guard_expr,
+                            &Expectation::has_type(TyKind::Scalar(Scalar::Bool).intern(Interner)),
+                        );
+                    }
+
+                    let arm_ty = self.infer_expr_inner(arm.expr, &expected);
+                    all_arms_diverge &= self.diverges;
+                    coerce.coerce(self, Some(arm.expr), &arm_ty);
+                }
+
+                self.diverges = matchee_diverges | all_arms_diverge;
+
+                coerce.complete()
+            }
+            Expr::Path(p) => {
+                // FIXME this could be more efficient...
+                let resolver = resolver_for_expr(self.db.upcast(), self.owner, tgt_expr);
+                self.infer_path(&resolver, p, tgt_expr.into()).unwrap_or_else(|| self.err_ty())
+            }
+            Expr::Continue { .. } => TyKind::Never.intern(Interner),
+            Expr::Break { expr, label } => {
+                let mut coerce = match find_breakable(&mut self.breakables, label.as_ref()) {
+                    Some(ctxt) => {
+                        // avoiding the borrowck
+                        mem::replace(
+                            &mut ctxt.coerce,
+                            CoerceMany::new(self.result.standard_types.unknown.clone()),
+                        )
+                    }
+                    None => CoerceMany::new(self.result.standard_types.unknown.clone()),
+                };
+
+                let val_ty = if let Some(expr) = *expr {
+                    self.infer_expr(expr, &Expectation::none())
+                } else {
+                    TyBuilder::unit()
+                };
+
+                // FIXME: create a synthetic `()` during lowering so we have something to refer to here?
+                coerce.coerce(self, *expr, &val_ty);
+
+                if let Some(ctxt) = find_breakable(&mut self.breakables, label.as_ref()) {
+                    ctxt.coerce = coerce;
+                    ctxt.may_break = true;
+                } else {
+                    self.push_diagnostic(InferenceDiagnostic::BreakOutsideOfLoop {
+                        expr: tgt_expr,
+                    });
+                };
+
+                TyKind::Never.intern(Interner)
+            }
+            Expr::Return { expr } => {
+                if let Some(expr) = expr {
+                    self.infer_expr_coerce(*expr, &Expectation::has_type(self.return_ty.clone()));
+                } else {
+                    let unit = TyBuilder::unit();
+                    let _ = self.coerce(Some(tgt_expr), &unit, &self.return_ty.clone());
+                }
+                TyKind::Never.intern(Interner)
+            }
+            Expr::Yield { expr } => {
+                // FIXME: track yield type for coercion
+                if let Some(expr) = expr {
+                    self.infer_expr(*expr, &Expectation::none());
+                }
+                TyKind::Never.intern(Interner)
+            }
+            Expr::RecordLit { path, fields, spread, .. } => {
+                let (ty, def_id) = self.resolve_variant(path.as_deref(), false);
+                if let Some(variant) = def_id {
+                    self.write_variant_resolution(tgt_expr.into(), variant);
+                }
+
+                if let Some(t) = expected.only_has_type(&mut self.table) {
+                    self.unify(&ty, &t);
+                }
+
+                let substs = ty
+                    .as_adt()
+                    .map(|(_, s)| s.clone())
+                    .unwrap_or_else(|| Substitution::empty(Interner));
+                let field_types = def_id.map(|it| self.db.field_types(it)).unwrap_or_default();
+                let variant_data = def_id.map(|it| it.variant_data(self.db.upcast()));
+                for field in fields.iter() {
+                    let field_def =
+                        variant_data.as_ref().and_then(|it| match it.field(&field.name) {
+                            Some(local_id) => Some(FieldId { parent: def_id.unwrap(), local_id }),
+                            None => {
+                                self.push_diagnostic(InferenceDiagnostic::NoSuchField {
+                                    expr: field.expr,
+                                });
+                                None
+                            }
+                        });
+                    let field_ty = field_def.map_or(self.err_ty(), |it| {
+                        field_types[it.local_id].clone().substitute(Interner, &substs)
+                    });
+                    self.infer_expr_coerce(field.expr, &Expectation::has_type(field_ty));
+                }
+                if let Some(expr) = spread {
+                    self.infer_expr(*expr, &Expectation::has_type(ty.clone()));
+                }
+                ty
+            }
+            Expr::Field { expr, name } => {
+                let receiver_ty = self.infer_expr_inner(*expr, &Expectation::none());
+
+                let mut autoderef = Autoderef::new(&mut self.table, receiver_ty);
+                let ty = autoderef.by_ref().find_map(|(derefed_ty, _)| {
+                    let (field_id, parameters) = match derefed_ty.kind(Interner) {
+                        TyKind::Tuple(_, substs) => {
+                            return name.as_tuple_index().and_then(|idx| {
+                                substs
+                                    .as_slice(Interner)
+                                    .get(idx)
+                                    .map(|a| a.assert_ty_ref(Interner))
+                                    .cloned()
+                            });
+                        }
+                        TyKind::Adt(AdtId(hir_def::AdtId::StructId(s)), parameters) => {
+                            let local_id = self.db.struct_data(*s).variant_data.field(name)?;
+                            let field = FieldId { parent: (*s).into(), local_id };
+                            (field, parameters.clone())
+                        }
+                        TyKind::Adt(AdtId(hir_def::AdtId::UnionId(u)), parameters) => {
+                            let local_id = self.db.union_data(*u).variant_data.field(name)?;
+                            let field = FieldId { parent: (*u).into(), local_id };
+                            (field, parameters.clone())
+                        }
+                        _ => return None,
+                    };
+                    let is_visible = self.db.field_visibilities(field_id.parent)[field_id.local_id]
+                        .is_visible_from(self.db.upcast(), self.resolver.module());
+                    if !is_visible {
+                        // Write down the first field resolution even if it is not visible
+                        // This aids IDE features for private fields like goto def and in
+                        // case of autoderef finding an applicable field, this will be
+                        // overwritten in a following cycle
+                        if let Entry::Vacant(entry) = self.result.field_resolutions.entry(tgt_expr)
+                        {
+                            entry.insert(field_id);
+                        }
+                        return None;
+                    }
+                    // can't have `write_field_resolution` here because `self.table` is borrowed :(
+                    self.result.field_resolutions.insert(tgt_expr, field_id);
+                    let ty = self.db.field_types(field_id.parent)[field_id.local_id]
+                        .clone()
+                        .substitute(Interner, &parameters);
+                    Some(ty)
+                });
+                let ty = match ty {
+                    Some(ty) => {
+                        let adjustments = auto_deref_adjust_steps(&autoderef);
+                        self.write_expr_adj(*expr, adjustments);
+                        let ty = self.insert_type_vars(ty);
+                        let ty = self.normalize_associated_types_in(ty);
+                        ty
+                    }
+                    _ => self.err_ty(),
+                };
+                ty
+            }
+            Expr::Await { expr } => {
+                let inner_ty = self.infer_expr_inner(*expr, &Expectation::none());
+                self.resolve_associated_type(inner_ty, self.resolve_future_future_output())
+            }
+            Expr::Try { expr } => {
+                let inner_ty = self.infer_expr_inner(*expr, &Expectation::none());
+                self.resolve_associated_type(inner_ty, self.resolve_ops_try_ok())
+            }
+            Expr::Cast { expr, type_ref } => {
+                // FIXME: propagate the "castable to" expectation (and find a test case that shows this is necessary)
+                let _inner_ty = self.infer_expr_inner(*expr, &Expectation::none());
+                let cast_ty = self.make_ty(type_ref);
+                // FIXME check the cast...
+                cast_ty
+            }
+            Expr::Ref { expr, rawness, mutability } => {
+                let mutability = lower_to_chalk_mutability(*mutability);
+                let expectation = if let Some((exp_inner, exp_rawness, exp_mutability)) = expected
+                    .only_has_type(&mut self.table)
+                    .as_ref()
+                    .and_then(|t| t.as_reference_or_ptr())
+                {
+                    if exp_mutability == Mutability::Mut && mutability == Mutability::Not {
+                        // FIXME: record type error - expected mut reference but found shared ref,
+                        // which cannot be coerced
+                    }
+                    if exp_rawness == Rawness::Ref && *rawness == Rawness::RawPtr {
+                        // FIXME: record type error - expected reference but found ptr,
+                        // which cannot be coerced
+                    }
+                    Expectation::rvalue_hint(&mut self.table, Ty::clone(exp_inner))
+                } else {
+                    Expectation::none()
+                };
+                let inner_ty = self.infer_expr_inner(*expr, &expectation);
+                match rawness {
+                    Rawness::RawPtr => TyKind::Raw(mutability, inner_ty),
+                    Rawness::Ref => TyKind::Ref(mutability, static_lifetime(), inner_ty),
+                }
+                .intern(Interner)
+            }
+            &Expr::Box { expr } => self.infer_expr_box(expr, expected),
+            Expr::UnaryOp { expr, op } => {
+                let inner_ty = self.infer_expr_inner(*expr, &Expectation::none());
+                let inner_ty = self.resolve_ty_shallow(&inner_ty);
+                match op {
+                    UnaryOp::Deref => {
+                        autoderef::deref(&mut self.table, inner_ty).unwrap_or_else(|| self.err_ty())
+                    }
+                    UnaryOp::Neg => {
+                        match inner_ty.kind(Interner) {
+                            // Fast path for builtins
+                            TyKind::Scalar(Scalar::Int(_) | Scalar::Uint(_) | Scalar::Float(_))
+                            | TyKind::InferenceVar(
+                                _,
+                                TyVariableKind::Integer | TyVariableKind::Float,
+                            ) => inner_ty,
+                            // Otherwise we resolve via the std::ops::Neg trait
+                            _ => self
+                                .resolve_associated_type(inner_ty, self.resolve_ops_neg_output()),
+                        }
+                    }
+                    UnaryOp::Not => {
+                        match inner_ty.kind(Interner) {
+                            // Fast path for builtins
+                            TyKind::Scalar(Scalar::Bool | Scalar::Int(_) | Scalar::Uint(_))
+                            | TyKind::InferenceVar(_, TyVariableKind::Integer) => inner_ty,
+                            // Otherwise we resolve via the std::ops::Not trait
+                            _ => self
+                                .resolve_associated_type(inner_ty, self.resolve_ops_not_output()),
+                        }
+                    }
+                }
+            }
+            Expr::BinaryOp { lhs, rhs, op } => match op {
+                Some(BinaryOp::Assignment { op: None }) => {
+                    let lhs = *lhs;
+                    let is_ordinary = match &self.body[lhs] {
+                        Expr::Array(_)
+                        | Expr::RecordLit { .. }
+                        | Expr::Tuple { .. }
+                        | Expr::Underscore => false,
+                        Expr::Call { callee, .. } => !matches!(&self.body[*callee], Expr::Path(_)),
+                        _ => true,
+                    };
+
+                    // In ordinary (non-destructuring) assignments, the type of
+                    // `lhs` must be inferred first so that the ADT fields
+                    // instantiations in RHS can be coerced to it. Note that this
+                    // cannot happen in destructuring assignments because of how
+                    // they are desugared.
+                    if is_ordinary {
+                        let lhs_ty = self.infer_expr(lhs, &Expectation::none());
+                        self.infer_expr_coerce(*rhs, &Expectation::has_type(lhs_ty));
+                    } else {
+                        let rhs_ty = self.infer_expr(*rhs, &Expectation::none());
+                        self.infer_assignee_expr(lhs, &rhs_ty);
+                    }
+                    self.result.standard_types.unit.clone()
+                }
+                Some(BinaryOp::LogicOp(_)) => {
+                    let bool_ty = self.result.standard_types.bool_.clone();
+                    self.infer_expr_coerce(*lhs, &Expectation::HasType(bool_ty.clone()));
+                    let lhs_diverges = self.diverges;
+                    self.infer_expr_coerce(*rhs, &Expectation::HasType(bool_ty.clone()));
+                    // Depending on the LHS' value, the RHS can never execute.
+                    self.diverges = lhs_diverges;
+                    bool_ty
+                }
+                Some(op) => self.infer_overloadable_binop(*lhs, *op, *rhs, tgt_expr),
+                _ => self.err_ty(),
+            },
+            Expr::Range { lhs, rhs, range_type } => {
+                let lhs_ty = lhs.map(|e| self.infer_expr_inner(e, &Expectation::none()));
+                let rhs_expect = lhs_ty
+                    .as_ref()
+                    .map_or_else(Expectation::none, |ty| Expectation::has_type(ty.clone()));
+                let rhs_ty = rhs.map(|e| self.infer_expr(e, &rhs_expect));
+                match (range_type, lhs_ty, rhs_ty) {
+                    (RangeOp::Exclusive, None, None) => match self.resolve_range_full() {
+                        Some(adt) => TyBuilder::adt(self.db, adt).build(),
+                        None => self.err_ty(),
+                    },
+                    (RangeOp::Exclusive, None, Some(ty)) => match self.resolve_range_to() {
+                        Some(adt) => TyBuilder::adt(self.db, adt).push(ty).build(),
+                        None => self.err_ty(),
+                    },
+                    (RangeOp::Inclusive, None, Some(ty)) => {
+                        match self.resolve_range_to_inclusive() {
+                            Some(adt) => TyBuilder::adt(self.db, adt).push(ty).build(),
+                            None => self.err_ty(),
+                        }
+                    }
+                    (RangeOp::Exclusive, Some(_), Some(ty)) => match self.resolve_range() {
+                        Some(adt) => TyBuilder::adt(self.db, adt).push(ty).build(),
+                        None => self.err_ty(),
+                    },
+                    (RangeOp::Inclusive, Some(_), Some(ty)) => {
+                        match self.resolve_range_inclusive() {
+                            Some(adt) => TyBuilder::adt(self.db, adt).push(ty).build(),
+                            None => self.err_ty(),
+                        }
+                    }
+                    (RangeOp::Exclusive, Some(ty), None) => match self.resolve_range_from() {
+                        Some(adt) => TyBuilder::adt(self.db, adt).push(ty).build(),
+                        None => self.err_ty(),
+                    },
+                    (RangeOp::Inclusive, _, None) => self.err_ty(),
+                }
+            }
+            Expr::Index { base, index } => {
+                let base_ty = self.infer_expr_inner(*base, &Expectation::none());
+                let index_ty = self.infer_expr(*index, &Expectation::none());
+
+                if let Some(index_trait) = self.resolve_ops_index() {
+                    let canonicalized = self.canonicalize(base_ty.clone());
+                    let receiver_adjustments = method_resolution::resolve_indexing_op(
+                        self.db,
+                        self.trait_env.clone(),
+                        canonicalized.value,
+                        index_trait,
+                    );
+                    let (self_ty, adj) = receiver_adjustments
+                        .map_or((self.err_ty(), Vec::new()), |adj| {
+                            adj.apply(&mut self.table, base_ty)
+                        });
+                    self.write_expr_adj(*base, adj);
+                    self.resolve_associated_type_with_params(
+                        self_ty,
+                        self.resolve_ops_index_output(),
+                        &[GenericArgData::Ty(index_ty).intern(Interner)],
+                    )
+                } else {
+                    self.err_ty()
+                }
+            }
+            Expr::Tuple { exprs, .. } => {
+                let mut tys = match expected
+                    .only_has_type(&mut self.table)
+                    .as_ref()
+                    .map(|t| t.kind(Interner))
+                {
+                    Some(TyKind::Tuple(_, substs)) => substs
+                        .iter(Interner)
+                        .map(|a| a.assert_ty_ref(Interner).clone())
+                        .chain(repeat_with(|| self.table.new_type_var()))
+                        .take(exprs.len())
+                        .collect::<Vec<_>>(),
+                    _ => (0..exprs.len()).map(|_| self.table.new_type_var()).collect(),
+                };
+
+                for (expr, ty) in exprs.iter().zip(tys.iter_mut()) {
+                    self.infer_expr_coerce(*expr, &Expectation::has_type(ty.clone()));
+                }
+
+                TyKind::Tuple(tys.len(), Substitution::from_iter(Interner, tys)).intern(Interner)
+            }
+            Expr::Array(array) => {
+                let elem_ty =
+                    match expected.to_option(&mut self.table).as_ref().map(|t| t.kind(Interner)) {
+                        Some(TyKind::Array(st, _) | TyKind::Slice(st)) => st.clone(),
+                        _ => self.table.new_type_var(),
+                    };
+                let mut coerce = CoerceMany::new(elem_ty.clone());
+
+                let expected = Expectation::has_type(elem_ty.clone());
+                let len = match array {
+                    Array::ElementList { elements, .. } => {
+                        for &expr in elements.iter() {
+                            let cur_elem_ty = self.infer_expr_inner(expr, &expected);
+                            coerce.coerce(self, Some(expr), &cur_elem_ty);
+                        }
+                        consteval::usize_const(Some(elements.len() as u128))
+                    }
+                    &Array::Repeat { initializer, repeat } => {
+                        self.infer_expr_coerce(initializer, &Expectation::has_type(elem_ty));
+                        self.infer_expr(
+                            repeat,
+                            &Expectation::has_type(
+                                TyKind::Scalar(Scalar::Uint(UintTy::Usize)).intern(Interner),
+                            ),
+                        );
+
+                        if let Some(g_def) = self.owner.as_generic_def_id() {
+                            let generics = generics(self.db.upcast(), g_def);
+                            consteval::eval_to_const(
+                                repeat,
+                                ParamLoweringMode::Placeholder,
+                                self,
+                                || generics,
+                                DebruijnIndex::INNERMOST,
+                            )
+                        } else {
+                            consteval::usize_const(None)
+                        }
+                    }
+                };
+
+                TyKind::Array(coerce.complete(), len).intern(Interner)
+            }
+            Expr::Literal(lit) => match lit {
+                Literal::Bool(..) => TyKind::Scalar(Scalar::Bool).intern(Interner),
+                Literal::String(..) => {
+                    TyKind::Ref(Mutability::Not, static_lifetime(), TyKind::Str.intern(Interner))
+                        .intern(Interner)
+                }
+                Literal::ByteString(bs) => {
+                    let byte_type = TyKind::Scalar(Scalar::Uint(UintTy::U8)).intern(Interner);
+
+                    let len = consteval::usize_const(Some(bs.len() as u128));
+
+                    let array_type = TyKind::Array(byte_type, len).intern(Interner);
+                    TyKind::Ref(Mutability::Not, static_lifetime(), array_type).intern(Interner)
+                }
+                Literal::Char(..) => TyKind::Scalar(Scalar::Char).intern(Interner),
+                Literal::Int(_v, ty) => match ty {
+                    Some(int_ty) => {
+                        TyKind::Scalar(Scalar::Int(primitive::int_ty_from_builtin(*int_ty)))
+                            .intern(Interner)
+                    }
+                    None => self.table.new_integer_var(),
+                },
+                Literal::Uint(_v, ty) => match ty {
+                    Some(int_ty) => {
+                        TyKind::Scalar(Scalar::Uint(primitive::uint_ty_from_builtin(*int_ty)))
+                            .intern(Interner)
+                    }
+                    None => self.table.new_integer_var(),
+                },
+                Literal::Float(_v, ty) => match ty {
+                    Some(float_ty) => {
+                        TyKind::Scalar(Scalar::Float(primitive::float_ty_from_builtin(*float_ty)))
+                            .intern(Interner)
+                    }
+                    None => self.table.new_float_var(),
+                },
+            },
+            Expr::MacroStmts { tail, statements } => {
+                self.infer_block(tgt_expr, statements, *tail, expected)
+            }
+            Expr::Underscore => {
+                // Underscore expressions may only appear in assignee expressions,
+                // which are handled by `infer_assignee_expr()`, so any underscore
+                // expression reaching this branch is an error.
+                self.err_ty()
+            }
+        };
+        // use a new type variable if we got unknown here
+        let ty = self.insert_type_vars_shallow(ty);
+        self.write_expr_ty(tgt_expr, ty.clone());
+        if self.resolve_ty_shallow(&ty).is_never() {
+            // Any expression that produces a value of type `!` must have diverged
+            self.diverges = Diverges::Always;
+        }
+        ty
+    }
+
+    fn infer_expr_box(&mut self, inner_expr: ExprId, expected: &Expectation) -> Ty {
+        if let Some(box_id) = self.resolve_boxed_box() {
+            let table = &mut self.table;
+            let inner_exp = expected
+                .to_option(table)
+                .as_ref()
+                .map(|e| e.as_adt())
+                .flatten()
+                .filter(|(e_adt, _)| e_adt == &box_id)
+                .map(|(_, subts)| {
+                    let g = subts.at(Interner, 0);
+                    Expectation::rvalue_hint(table, Ty::clone(g.assert_ty_ref(Interner)))
+                })
+                .unwrap_or_else(Expectation::none);
+
+            let inner_ty = self.infer_expr_inner(inner_expr, &inner_exp);
+            TyBuilder::adt(self.db, box_id)
+                .push(inner_ty)
+                .fill_with_defaults(self.db, || self.table.new_type_var())
+                .build()
+        } else {
+            self.err_ty()
+        }
+    }
+
+    pub(super) fn infer_assignee_expr(&mut self, lhs: ExprId, rhs_ty: &Ty) -> Ty {
+        let is_rest_expr = |expr| {
+            matches!(
+                &self.body[expr],
+                Expr::Range { lhs: None, rhs: None, range_type: RangeOp::Exclusive },
+            )
+        };
+
+        let rhs_ty = self.resolve_ty_shallow(rhs_ty);
+
+        let ty = match &self.body[lhs] {
+            Expr::Tuple { exprs, .. } => {
+                // We don't consider multiple ellipses. This is analogous to
+                // `hir_def::body::lower::ExprCollector::collect_tuple_pat()`.
+                let ellipsis = exprs.iter().position(|e| is_rest_expr(*e));
+                let exprs: Vec<_> = exprs.iter().filter(|e| !is_rest_expr(**e)).copied().collect();
+
+                self.infer_tuple_pat_like(&rhs_ty, (), ellipsis, &exprs)
+            }
+            Expr::Call { callee, args, .. } => {
+                // Tuple structs
+                let path = match &self.body[*callee] {
+                    Expr::Path(path) => Some(path),
+                    _ => None,
+                };
+
+                // We don't consider multiple ellipses. This is analogous to
+                // `hir_def::body::lower::ExprCollector::collect_tuple_pat()`.
+                let ellipsis = args.iter().position(|e| is_rest_expr(*e));
+                let args: Vec<_> = args.iter().filter(|e| !is_rest_expr(**e)).copied().collect();
+
+                self.infer_tuple_struct_pat_like(path, &rhs_ty, (), lhs, ellipsis, &args)
+            }
+            Expr::Array(Array::ElementList { elements, .. }) => {
+                let elem_ty = match rhs_ty.kind(Interner) {
+                    TyKind::Array(st, _) => st.clone(),
+                    _ => self.err_ty(),
+                };
+
+                // There's no need to handle `..` as it cannot be bound.
+                let sub_exprs = elements.iter().filter(|e| !is_rest_expr(**e));
+
+                for e in sub_exprs {
+                    self.infer_assignee_expr(*e, &elem_ty);
+                }
+
+                match rhs_ty.kind(Interner) {
+                    TyKind::Array(_, _) => rhs_ty.clone(),
+                    // Even when `rhs_ty` is not an array type, this assignee
+                    // expression is inferred to be an array (of unknown element
+                    // type and length). This should not be just an error type,
+                    // because we are to compute the unifiability of this type and
+                    // `rhs_ty` in the end of this function to issue type mismatches.
+                    _ => TyKind::Array(self.err_ty(), crate::consteval::usize_const(None))
+                        .intern(Interner),
+                }
+            }
+            Expr::RecordLit { path, fields, .. } => {
+                let subs = fields.iter().map(|f| (f.name.clone(), f.expr));
+
+                self.infer_record_pat_like(path.as_deref(), &rhs_ty, (), lhs.into(), subs)
+            }
+            Expr::Underscore => rhs_ty.clone(),
+            _ => {
+                // `lhs` is a place expression, a unit struct, or an enum variant.
+                let lhs_ty = self.infer_expr(lhs, &Expectation::none());
+
+                // This is the only branch where this function may coerce any type.
+                // We are returning early to avoid the unifiability check below.
+                let lhs_ty = self.insert_type_vars_shallow(lhs_ty);
+                let ty = match self.coerce(None, &rhs_ty, &lhs_ty) {
+                    Ok(ty) => ty,
+                    Err(_) => {
+                        self.result.type_mismatches.insert(
+                            lhs.into(),
+                            TypeMismatch { expected: rhs_ty.clone(), actual: lhs_ty.clone() },
+                        );
+                        // `rhs_ty` is returned so no further type mismatches are
+                        // reported because of this mismatch.
+                        rhs_ty
+                    }
+                };
+                self.write_expr_ty(lhs, ty.clone());
+                return ty;
+            }
+        };
+
+        let ty = self.insert_type_vars_shallow(ty);
+        if !self.unify(&ty, &rhs_ty) {
+            self.result
+                .type_mismatches
+                .insert(lhs.into(), TypeMismatch { expected: rhs_ty.clone(), actual: ty.clone() });
+        }
+        self.write_expr_ty(lhs, ty.clone());
+        ty
+    }
+
+    fn infer_overloadable_binop(
+        &mut self,
+        lhs: ExprId,
+        op: BinaryOp,
+        rhs: ExprId,
+        tgt_expr: ExprId,
+    ) -> Ty {
+        let lhs_expectation = Expectation::none();
+        let lhs_ty = self.infer_expr(lhs, &lhs_expectation);
+        let rhs_ty = self.table.new_type_var();
+
+        let func = self.resolve_binop_method(op);
+        let func = match func {
+            Some(func) => func,
+            None => {
+                let rhs_ty = self.builtin_binary_op_rhs_expectation(op, lhs_ty.clone());
+                let rhs_ty = self.infer_expr_coerce(rhs, &Expectation::from_option(rhs_ty));
+                return self
+                    .builtin_binary_op_return_ty(op, lhs_ty, rhs_ty)
+                    .unwrap_or_else(|| self.err_ty());
+            }
+        };
+
+        let subst = TyBuilder::subst_for_def(self.db, func)
+            .push(lhs_ty.clone())
+            .push(rhs_ty.clone())
+            .build();
+        self.write_method_resolution(tgt_expr, func, subst.clone());
+
+        let method_ty = self.db.value_ty(func.into()).substitute(Interner, &subst);
+        self.register_obligations_for_call(&method_ty);
+
+        self.infer_expr_coerce(rhs, &Expectation::has_type(rhs_ty.clone()));
+
+        let ret_ty = match method_ty.callable_sig(self.db) {
+            Some(sig) => sig.ret().clone(),
+            None => self.err_ty(),
+        };
+
+        let ret_ty = self.normalize_associated_types_in(ret_ty);
+
+        // FIXME: record autoref adjustments
+
+        // use knowledge of built-in binary ops, which can sometimes help inference
+        if let Some(builtin_rhs) = self.builtin_binary_op_rhs_expectation(op, lhs_ty.clone()) {
+            self.unify(&builtin_rhs, &rhs_ty);
+        }
+        if let Some(builtin_ret) = self.builtin_binary_op_return_ty(op, lhs_ty, rhs_ty) {
+            self.unify(&builtin_ret, &ret_ty);
+        }
+
+        ret_ty
+    }
+
+    fn infer_block(
+        &mut self,
+        expr: ExprId,
+        statements: &[Statement],
+        tail: Option<ExprId>,
+        expected: &Expectation,
+    ) -> Ty {
+        for stmt in statements {
+            match stmt {
+                Statement::Let { pat, type_ref, initializer, else_branch } => {
+                    let decl_ty = type_ref
+                        .as_ref()
+                        .map(|tr| self.make_ty(tr))
+                        .unwrap_or_else(|| self.err_ty());
+
+                    // Always use the declared type when specified
+                    let mut ty = decl_ty.clone();
+
+                    if let Some(expr) = initializer {
+                        let actual_ty =
+                            self.infer_expr_coerce(*expr, &Expectation::has_type(decl_ty.clone()));
+                        if decl_ty.is_unknown() {
+                            ty = actual_ty;
+                        }
+                    }
+
+                    if let Some(expr) = else_branch {
+                        self.infer_expr_coerce(
+                            *expr,
+                            &Expectation::has_type(Ty::new(Interner, TyKind::Never)),
+                        );
+                    }
+
+                    self.infer_pat(*pat, &ty, BindingMode::default());
+                }
+                Statement::Expr { expr, .. } => {
+                    self.infer_expr(*expr, &Expectation::none());
+                }
+            }
+        }
+
+        if let Some(expr) = tail {
+            self.infer_expr_coerce(expr, expected)
+        } else {
+            // Citing rustc: if there is no explicit tail expression,
+            // that is typically equivalent to a tail expression
+            // of `()` -- except if the block diverges. In that
+            // case, there is no value supplied from the tail
+            // expression (assuming there are no other breaks,
+            // this implies that the type of the block will be
+            // `!`).
+            if self.diverges.is_always() {
+                // we don't even make an attempt at coercion
+                self.table.new_maybe_never_var()
+            } else {
+                if let Some(t) = expected.only_has_type(&mut self.table) {
+                    if self.coerce(Some(expr), &TyBuilder::unit(), &t).is_err() {
+                        self.result.type_mismatches.insert(
+                            expr.into(),
+                            TypeMismatch { expected: t.clone(), actual: TyBuilder::unit() },
+                        );
+                    }
+                    t
+                } else {
+                    TyBuilder::unit()
+                }
+            }
+        }
+    }
+
+    fn infer_method_call(
+        &mut self,
+        tgt_expr: ExprId,
+        receiver: ExprId,
+        args: &[ExprId],
+        method_name: &Name,
+        generic_args: Option<&GenericArgs>,
+        expected: &Expectation,
+    ) -> Ty {
+        let receiver_ty = self.infer_expr(receiver, &Expectation::none());
+        let canonicalized_receiver = self.canonicalize(receiver_ty.clone());
+
+        let traits_in_scope = self.resolver.traits_in_scope(self.db.upcast());
+
+        let resolved = method_resolution::lookup_method(
+            &canonicalized_receiver.value,
+            self.db,
+            self.trait_env.clone(),
+            &traits_in_scope,
+            VisibleFromModule::Filter(self.resolver.module()),
+            method_name,
+        );
+        let (receiver_ty, method_ty, substs) = match resolved {
+            Some((adjust, func)) => {
+                let (ty, adjustments) = adjust.apply(&mut self.table, receiver_ty);
+                let generics = generics(self.db.upcast(), func.into());
+                let substs = self.substs_for_method_call(generics, generic_args);
+                self.write_expr_adj(receiver, adjustments);
+                self.write_method_resolution(tgt_expr, func, substs.clone());
+                (ty, self.db.value_ty(func.into()), substs)
+            }
+            None => (
+                receiver_ty,
+                Binders::empty(Interner, self.err_ty()),
+                Substitution::empty(Interner),
+            ),
+        };
+        let method_ty = method_ty.substitute(Interner, &substs);
+        self.register_obligations_for_call(&method_ty);
+        let (formal_receiver_ty, param_tys, ret_ty, is_varargs) =
+            match method_ty.callable_sig(self.db) {
+                Some(sig) => {
+                    if !sig.params().is_empty() {
+                        (
+                            sig.params()[0].clone(),
+                            sig.params()[1..].to_vec(),
+                            sig.ret().clone(),
+                            sig.is_varargs,
+                        )
+                    } else {
+                        (self.err_ty(), Vec::new(), sig.ret().clone(), sig.is_varargs)
+                    }
+                }
+                None => (self.err_ty(), Vec::new(), self.err_ty(), true),
+            };
+        self.unify(&formal_receiver_ty, &receiver_ty);
+
+        let expected_inputs =
+            self.expected_inputs_for_expected_output(expected, ret_ty.clone(), param_tys.clone());
+
+        self.check_call_arguments(tgt_expr, args, &expected_inputs, &param_tys, &[], is_varargs);
+        self.normalize_associated_types_in(ret_ty)
+    }
+
+    fn expected_inputs_for_expected_output(
+        &mut self,
+        expected_output: &Expectation,
+        output: Ty,
+        inputs: Vec<Ty>,
+    ) -> Vec<Ty> {
+        if let Some(expected_ty) = expected_output.to_option(&mut self.table) {
+            self.table.fudge_inference(|table| {
+                if table.try_unify(&expected_ty, &output).is_ok() {
+                    table.resolve_with_fallback(inputs, &|var, kind, _, _| match kind {
+                        chalk_ir::VariableKind::Ty(tk) => var.to_ty(Interner, tk).cast(Interner),
+                        chalk_ir::VariableKind::Lifetime => {
+                            var.to_lifetime(Interner).cast(Interner)
+                        }
+                        chalk_ir::VariableKind::Const(ty) => {
+                            var.to_const(Interner, ty).cast(Interner)
+                        }
+                    })
+                } else {
+                    Vec::new()
+                }
+            })
+        } else {
+            Vec::new()
+        }
+    }
+
+    fn check_call_arguments(
+        &mut self,
+        expr: ExprId,
+        args: &[ExprId],
+        expected_inputs: &[Ty],
+        param_tys: &[Ty],
+        skip_indices: &[u32],
+        is_varargs: bool,
+    ) {
+        if args.len() != param_tys.len() + skip_indices.len() && !is_varargs {
+            self.push_diagnostic(InferenceDiagnostic::MismatchedArgCount {
+                call_expr: expr,
+                expected: param_tys.len() + skip_indices.len(),
+                found: args.len(),
+            });
+        }
+
+        // Quoting https://github.com/rust-lang/rust/blob/6ef275e6c3cb1384ec78128eceeb4963ff788dca/src/librustc_typeck/check/mod.rs#L3325 --
+        // We do this in a pretty awful way: first we type-check any arguments
+        // that are not closures, then we type-check the closures. This is so
+        // that we have more information about the types of arguments when we
+        // type-check the functions. This isn't really the right way to do this.
+        for &check_closures in &[false, true] {
+            let mut skip_indices = skip_indices.into_iter().copied().fuse().peekable();
+            let param_iter = param_tys.iter().cloned().chain(repeat(self.err_ty()));
+            let expected_iter = expected_inputs
+                .iter()
+                .cloned()
+                .chain(param_iter.clone().skip(expected_inputs.len()));
+            for (idx, ((&arg, param_ty), expected_ty)) in
+                args.iter().zip(param_iter).zip(expected_iter).enumerate()
+            {
+                let is_closure = matches!(&self.body[arg], Expr::Closure { .. });
+                if is_closure != check_closures {
+                    continue;
+                }
+
+                while skip_indices.peek().map_or(false, |i| *i < idx as u32) {
+                    skip_indices.next();
+                }
+                if skip_indices.peek().copied() == Some(idx as u32) {
+                    continue;
+                }
+
+                // the difference between param_ty and expected here is that
+                // expected is the parameter when the expected *return* type is
+                // taken into account. So in `let _: &[i32] = identity(&[1, 2])`
+                // the expected type is already `&[i32]`, whereas param_ty is
+                // still an unbound type variable. We don't always want to force
+                // the parameter to coerce to the expected type (for example in
+                // `coerce_unsize_expected_type_4`).
+                let param_ty = self.normalize_associated_types_in(param_ty);
+                let expected = Expectation::rvalue_hint(&mut self.table, expected_ty);
+                // infer with the expected type we have...
+                let ty = self.infer_expr_inner(arg, &expected);
+
+                // then coerce to either the expected type or just the formal parameter type
+                let coercion_target = if let Some(ty) = expected.only_has_type(&mut self.table) {
+                    // if we are coercing to the expectation, unify with the
+                    // formal parameter type to connect everything
+                    self.unify(&ty, &param_ty);
+                    ty
+                } else {
+                    param_ty
+                };
+                if !coercion_target.is_unknown() {
+                    if self.coerce(Some(arg), &ty, &coercion_target).is_err() {
+                        self.result.type_mismatches.insert(
+                            arg.into(),
+                            TypeMismatch { expected: coercion_target, actual: ty.clone() },
+                        );
+                    }
+                }
+            }
+        }
+    }
+
+    fn substs_for_method_call(
+        &mut self,
+        def_generics: Generics,
+        generic_args: Option<&GenericArgs>,
+    ) -> Substitution {
+        let (parent_params, self_params, type_params, const_params, impl_trait_params) =
+            def_generics.provenance_split();
+        assert_eq!(self_params, 0); // method shouldn't have another Self param
+        let total_len = parent_params + type_params + const_params + impl_trait_params;
+        let mut substs = Vec::with_capacity(total_len);
+        // Parent arguments are unknown
+        for (id, param) in def_generics.iter_parent() {
+            match param {
+                TypeOrConstParamData::TypeParamData(_) => {
+                    substs.push(GenericArgData::Ty(self.table.new_type_var()).intern(Interner));
+                }
+                TypeOrConstParamData::ConstParamData(_) => {
+                    let ty = self.db.const_param_ty(ConstParamId::from_unchecked(id));
+                    substs
+                        .push(GenericArgData::Const(self.table.new_const_var(ty)).intern(Interner));
+                }
+            }
+        }
+        // handle provided arguments
+        if let Some(generic_args) = generic_args {
+            // if args are provided, it should be all of them, but we can't rely on that
+            for (arg, kind_id) in generic_args
+                .args
+                .iter()
+                .filter(|arg| !matches!(arg, GenericArg::Lifetime(_)))
+                .take(type_params + const_params)
+                .zip(def_generics.iter_id().skip(parent_params))
+            {
+                if let Some(g) = generic_arg_to_chalk(
+                    self.db,
+                    kind_id,
+                    arg,
+                    self,
+                    |this, type_ref| this.make_ty(type_ref),
+                    |this, c, ty| {
+                        const_or_path_to_chalk(
+                            this.db,
+                            &this.resolver,
+                            ty,
+                            c,
+                            ParamLoweringMode::Placeholder,
+                            || generics(this.db.upcast(), (&this.resolver).generic_def().unwrap()),
+                            DebruijnIndex::INNERMOST,
+                        )
+                    },
+                ) {
+                    substs.push(g);
+                }
+            }
+        };
+        for (id, data) in def_generics.iter().skip(substs.len()) {
+            match data {
+                TypeOrConstParamData::TypeParamData(_) => {
+                    substs.push(GenericArgData::Ty(self.table.new_type_var()).intern(Interner))
+                }
+                TypeOrConstParamData::ConstParamData(_) => {
+                    substs.push(
+                        GenericArgData::Const(self.table.new_const_var(
+                            self.db.const_param_ty(ConstParamId::from_unchecked(id)),
+                        ))
+                        .intern(Interner),
+                    )
+                }
+            }
+        }
+        assert_eq!(substs.len(), total_len);
+        Substitution::from_iter(Interner, substs)
+    }
+
+    fn register_obligations_for_call(&mut self, callable_ty: &Ty) {
+        let callable_ty = self.resolve_ty_shallow(callable_ty);
+        if let TyKind::FnDef(fn_def, parameters) = callable_ty.kind(Interner) {
+            let def: CallableDefId = from_chalk(self.db, *fn_def);
+            let generic_predicates = self.db.generic_predicates(def.into());
+            for predicate in generic_predicates.iter() {
+                let (predicate, binders) = predicate
+                    .clone()
+                    .substitute(Interner, parameters)
+                    .into_value_and_skipped_binders();
+                always!(binders.len(Interner) == 0); // quantified where clauses not yet handled
+                self.push_obligation(predicate.cast(Interner));
+            }
+            // add obligation for trait implementation, if this is a trait method
+            match def {
+                CallableDefId::FunctionId(f) => {
+                    if let ItemContainerId::TraitId(trait_) = f.lookup(self.db.upcast()).container {
+                        // construct a TraitRef
+                        let substs = crate::subst_prefix(
+                            &*parameters,
+                            generics(self.db.upcast(), trait_.into()).len(),
+                        );
+                        self.push_obligation(
+                            TraitRef { trait_id: to_chalk_trait_id(trait_), substitution: substs }
+                                .cast(Interner),
+                        );
+                    }
+                }
+                CallableDefId::StructId(_) | CallableDefId::EnumVariantId(_) => {}
+            }
+        }
+    }
+
+    /// Returns the argument indices to skip.
+    fn check_legacy_const_generics(&mut self, callee: Ty, args: &[ExprId]) -> Box<[u32]> {
+        let (func, subst) = match callee.kind(Interner) {
+            TyKind::FnDef(fn_id, subst) => {
+                let callable = CallableDefId::from_chalk(self.db, *fn_id);
+                let func = match callable {
+                    CallableDefId::FunctionId(f) => f,
+                    _ => return Default::default(),
+                };
+                (func, subst)
+            }
+            _ => return Default::default(),
+        };
+
+        let data = self.db.function_data(func);
+        if data.legacy_const_generics_indices.is_empty() {
+            return Default::default();
+        }
+
+        // only use legacy const generics if the param count matches with them
+        if data.params.len() + data.legacy_const_generics_indices.len() != args.len() {
+            if args.len() <= data.params.len() {
+                return Default::default();
+            } else {
+                // there are more parameters than there should be without legacy
+                // const params; use them
+                let mut indices = data.legacy_const_generics_indices.clone();
+                indices.sort();
+                return indices;
+            }
+        }
+
+        // check legacy const parameters
+        for (subst_idx, arg_idx) in data.legacy_const_generics_indices.iter().copied().enumerate() {
+            let arg = match subst.at(Interner, subst_idx).constant(Interner) {
+                Some(c) => c,
+                None => continue, // not a const parameter?
+            };
+            if arg_idx >= args.len() as u32 {
+                continue;
+            }
+            let _ty = arg.data(Interner).ty.clone();
+            let expected = Expectation::none(); // FIXME use actual const ty, when that is lowered correctly
+            self.infer_expr(args[arg_idx as usize], &expected);
+            // FIXME: evaluate and unify with the const
+        }
+        let mut indices = data.legacy_const_generics_indices.clone();
+        indices.sort();
+        indices
+    }
+
+    fn builtin_binary_op_return_ty(&mut self, op: BinaryOp, lhs_ty: Ty, rhs_ty: Ty) -> Option<Ty> {
+        let lhs_ty = self.resolve_ty_shallow(&lhs_ty);
+        let rhs_ty = self.resolve_ty_shallow(&rhs_ty);
+        match op {
+            BinaryOp::LogicOp(_) | BinaryOp::CmpOp(_) => {
+                Some(TyKind::Scalar(Scalar::Bool).intern(Interner))
+            }
+            BinaryOp::Assignment { .. } => Some(TyBuilder::unit()),
+            BinaryOp::ArithOp(ArithOp::Shl | ArithOp::Shr) => {
+                // all integer combinations are valid here
+                if matches!(
+                    lhs_ty.kind(Interner),
+                    TyKind::Scalar(Scalar::Int(_) | Scalar::Uint(_))
+                        | TyKind::InferenceVar(_, TyVariableKind::Integer)
+                ) && matches!(
+                    rhs_ty.kind(Interner),
+                    TyKind::Scalar(Scalar::Int(_) | Scalar::Uint(_))
+                        | TyKind::InferenceVar(_, TyVariableKind::Integer)
+                ) {
+                    Some(lhs_ty)
+                } else {
+                    None
+                }
+            }
+            BinaryOp::ArithOp(_) => match (lhs_ty.kind(Interner), rhs_ty.kind(Interner)) {
+                // (int, int) | (uint, uint) | (float, float)
+                (TyKind::Scalar(Scalar::Int(_)), TyKind::Scalar(Scalar::Int(_)))
+                | (TyKind::Scalar(Scalar::Uint(_)), TyKind::Scalar(Scalar::Uint(_)))
+                | (TyKind::Scalar(Scalar::Float(_)), TyKind::Scalar(Scalar::Float(_))) => {
+                    Some(rhs_ty)
+                }
+                // ({int}, int) | ({int}, uint)
+                (
+                    TyKind::InferenceVar(_, TyVariableKind::Integer),
+                    TyKind::Scalar(Scalar::Int(_) | Scalar::Uint(_)),
+                ) => Some(rhs_ty),
+                // (int, {int}) | (uint, {int})
+                (
+                    TyKind::Scalar(Scalar::Int(_) | Scalar::Uint(_)),
+                    TyKind::InferenceVar(_, TyVariableKind::Integer),
+                ) => Some(lhs_ty),
+                // ({float} | float)
+                (
+                    TyKind::InferenceVar(_, TyVariableKind::Float),
+                    TyKind::Scalar(Scalar::Float(_)),
+                ) => Some(rhs_ty),
+                // (float, {float})
+                (
+                    TyKind::Scalar(Scalar::Float(_)),
+                    TyKind::InferenceVar(_, TyVariableKind::Float),
+                ) => Some(lhs_ty),
+                // ({int}, {int}) | ({float}, {float})
+                (
+                    TyKind::InferenceVar(_, TyVariableKind::Integer),
+                    TyKind::InferenceVar(_, TyVariableKind::Integer),
+                )
+                | (
+                    TyKind::InferenceVar(_, TyVariableKind::Float),
+                    TyKind::InferenceVar(_, TyVariableKind::Float),
+                ) => Some(rhs_ty),
+                _ => None,
+            },
+        }
+    }
+
+    fn builtin_binary_op_rhs_expectation(&mut self, op: BinaryOp, lhs_ty: Ty) -> Option<Ty> {
+        Some(match op {
+            BinaryOp::LogicOp(..) => TyKind::Scalar(Scalar::Bool).intern(Interner),
+            BinaryOp::Assignment { op: None } => lhs_ty,
+            BinaryOp::CmpOp(CmpOp::Eq { .. }) => match self
+                .resolve_ty_shallow(&lhs_ty)
+                .kind(Interner)
+            {
+                TyKind::Scalar(_) | TyKind::Str => lhs_ty,
+                TyKind::InferenceVar(_, TyVariableKind::Integer | TyVariableKind::Float) => lhs_ty,
+                _ => return None,
+            },
+            BinaryOp::ArithOp(ArithOp::Shl | ArithOp::Shr) => return None,
+            BinaryOp::CmpOp(CmpOp::Ord { .. })
+            | BinaryOp::Assignment { op: Some(_) }
+            | BinaryOp::ArithOp(_) => match self.resolve_ty_shallow(&lhs_ty).kind(Interner) {
+                TyKind::Scalar(Scalar::Int(_) | Scalar::Uint(_) | Scalar::Float(_)) => lhs_ty,
+                TyKind::InferenceVar(_, TyVariableKind::Integer | TyVariableKind::Float) => lhs_ty,
+                _ => return None,
+            },
+        })
+    }
+
+    fn resolve_binop_method(&self, op: BinaryOp) -> Option<FunctionId> {
+        let (name, lang_item) = match op {
+            BinaryOp::LogicOp(_) => return None,
+            BinaryOp::ArithOp(aop) => match aop {
+                ArithOp::Add => (name!(add), name!(add)),
+                ArithOp::Mul => (name!(mul), name!(mul)),
+                ArithOp::Sub => (name!(sub), name!(sub)),
+                ArithOp::Div => (name!(div), name!(div)),
+                ArithOp::Rem => (name!(rem), name!(rem)),
+                ArithOp::Shl => (name!(shl), name!(shl)),
+                ArithOp::Shr => (name!(shr), name!(shr)),
+                ArithOp::BitXor => (name!(bitxor), name!(bitxor)),
+                ArithOp::BitOr => (name!(bitor), name!(bitor)),
+                ArithOp::BitAnd => (name!(bitand), name!(bitand)),
+            },
+            BinaryOp::Assignment { op: Some(aop) } => match aop {
+                ArithOp::Add => (name!(add_assign), name!(add_assign)),
+                ArithOp::Mul => (name!(mul_assign), name!(mul_assign)),
+                ArithOp::Sub => (name!(sub_assign), name!(sub_assign)),
+                ArithOp::Div => (name!(div_assign), name!(div_assign)),
+                ArithOp::Rem => (name!(rem_assign), name!(rem_assign)),
+                ArithOp::Shl => (name!(shl_assign), name!(shl_assign)),
+                ArithOp::Shr => (name!(shr_assign), name!(shr_assign)),
+                ArithOp::BitXor => (name!(bitxor_assign), name!(bitxor_assign)),
+                ArithOp::BitOr => (name!(bitor_assign), name!(bitor_assign)),
+                ArithOp::BitAnd => (name!(bitand_assign), name!(bitand_assign)),
+            },
+            BinaryOp::CmpOp(cop) => match cop {
+                CmpOp::Eq { negated: false } => (name!(eq), name!(eq)),
+                CmpOp::Eq { negated: true } => (name!(ne), name!(eq)),
+                CmpOp::Ord { ordering: Ordering::Less, strict: false } => {
+                    (name!(le), name!(partial_ord))
+                }
+                CmpOp::Ord { ordering: Ordering::Less, strict: true } => {
+                    (name!(lt), name!(partial_ord))
+                }
+                CmpOp::Ord { ordering: Ordering::Greater, strict: false } => {
+                    (name!(ge), name!(partial_ord))
+                }
+                CmpOp::Ord { ordering: Ordering::Greater, strict: true } => {
+                    (name!(gt), name!(partial_ord))
+                }
+            },
+            BinaryOp::Assignment { op: None } => return None,
+        };
+
+        let trait_ = self.resolve_lang_item(lang_item)?.as_trait()?;
+
+        self.db.trait_data(trait_).method_by_name(&name)
+    }
+}
diff --git a/src/tools/rust-analyzer/crates/hir-ty/src/infer/pat.rs b/src/tools/rust-analyzer/crates/hir-ty/src/infer/pat.rs
new file mode 100644
index 000000000..5e7320a5d
--- /dev/null
+++ b/src/tools/rust-analyzer/crates/hir-ty/src/infer/pat.rs
@@ -0,0 +1,354 @@
+//! Type inference for patterns.
+
+use std::iter::repeat_with;
+
+use chalk_ir::Mutability;
+use hir_def::{
+    expr::{BindingAnnotation, Expr, Literal, Pat, PatId},
+    path::Path,
+    type_ref::ConstScalar,
+};
+use hir_expand::name::Name;
+
+use crate::{
+    consteval::intern_const_scalar,
+    infer::{BindingMode, Expectation, InferenceContext, TypeMismatch},
+    lower::lower_to_chalk_mutability,
+    static_lifetime, ConcreteConst, ConstValue, Interner, Substitution, Ty, TyBuilder, TyExt,
+    TyKind,
+};
+
+use super::PatLike;
+
+impl<'a> InferenceContext<'a> {
+    /// Infers type for tuple struct pattern or its corresponding assignee expression.
+    ///
+    /// Ellipses found in the original pattern or expression must be filtered out.
+    pub(super) fn infer_tuple_struct_pat_like<T: PatLike>(
+        &mut self,
+        path: Option<&Path>,
+        expected: &Ty,
+        default_bm: T::BindingMode,
+        id: T,
+        ellipsis: Option<usize>,
+        subs: &[T],
+    ) -> Ty {
+        let (ty, def) = self.resolve_variant(path, true);
+        let var_data = def.map(|it| it.variant_data(self.db.upcast()));
+        if let Some(variant) = def {
+            self.write_variant_resolution(id.into(), variant);
+        }
+        self.unify(&ty, expected);
+
+        let substs =
+            ty.as_adt().map(|(_, s)| s.clone()).unwrap_or_else(|| Substitution::empty(Interner));
+
+        let field_tys = def.map(|it| self.db.field_types(it)).unwrap_or_default();
+        let (pre, post) = match ellipsis {
+            Some(idx) => subs.split_at(idx),
+            None => (subs, &[][..]),
+        };
+        let post_idx_offset = field_tys.iter().count().saturating_sub(post.len());
+
+        let pre_iter = pre.iter().enumerate();
+        let post_iter = (post_idx_offset..).zip(post.iter());
+        for (i, &subpat) in pre_iter.chain(post_iter) {
+            let expected_ty = var_data
+                .as_ref()
+                .and_then(|d| d.field(&Name::new_tuple_field(i)))
+                .map_or(self.err_ty(), |field| {
+                    field_tys[field].clone().substitute(Interner, &substs)
+                });
+            let expected_ty = self.normalize_associated_types_in(expected_ty);
+            T::infer(self, subpat, &expected_ty, default_bm);
+        }
+
+        ty
+    }
+
+    /// Infers type for record pattern or its corresponding assignee expression.
+    pub(super) fn infer_record_pat_like<T: PatLike>(
+        &mut self,
+        path: Option<&Path>,
+        expected: &Ty,
+        default_bm: T::BindingMode,
+        id: T,
+        subs: impl Iterator<Item = (Name, T)>,
+    ) -> Ty {
+        let (ty, def) = self.resolve_variant(path, false);
+        if let Some(variant) = def {
+            self.write_variant_resolution(id.into(), variant);
+        }
+
+        self.unify(&ty, expected);
+
+        let substs =
+            ty.as_adt().map(|(_, s)| s.clone()).unwrap_or_else(|| Substitution::empty(Interner));
+
+        let field_tys = def.map(|it| self.db.field_types(it)).unwrap_or_default();
+        let var_data = def.map(|it| it.variant_data(self.db.upcast()));
+
+        for (name, inner) in subs {
+            let expected_ty = var_data
+                .as_ref()
+                .and_then(|it| it.field(&name))
+                .map_or(self.err_ty(), |f| field_tys[f].clone().substitute(Interner, &substs));
+            let expected_ty = self.normalize_associated_types_in(expected_ty);
+
+            T::infer(self, inner, &expected_ty, default_bm);
+        }
+
+        ty
+    }
+
+    /// Infers type for tuple pattern or its corresponding assignee expression.
+    ///
+    /// Ellipses found in the original pattern or expression must be filtered out.
+    pub(super) fn infer_tuple_pat_like<T: PatLike>(
+        &mut self,
+        expected: &Ty,
+        default_bm: T::BindingMode,
+        ellipsis: Option<usize>,
+        subs: &[T],
+    ) -> Ty {
+        let expectations = match expected.as_tuple() {
+            Some(parameters) => &*parameters.as_slice(Interner),
+            _ => &[],
+        };
+
+        let ((pre, post), n_uncovered_patterns) = match ellipsis {
+            Some(idx) => (subs.split_at(idx), expectations.len().saturating_sub(subs.len())),
+            None => ((&subs[..], &[][..]), 0),
+        };
+        let mut expectations_iter = expectations
+            .iter()
+            .cloned()
+            .map(|a| a.assert_ty_ref(Interner).clone())
+            .chain(repeat_with(|| self.table.new_type_var()));
+
+        let mut inner_tys = Vec::with_capacity(n_uncovered_patterns + subs.len());
+
+        inner_tys.extend(expectations_iter.by_ref().take(n_uncovered_patterns + subs.len()));
+
+        // Process pre
+        for (ty, pat) in inner_tys.iter_mut().zip(pre) {
+            *ty = T::infer(self, *pat, ty, default_bm);
+        }
+
+        // Process post
+        for (ty, pat) in inner_tys.iter_mut().skip(pre.len() + n_uncovered_patterns).zip(post) {
+            *ty = T::infer(self, *pat, ty, default_bm);
+        }
+
+        TyKind::Tuple(inner_tys.len(), Substitution::from_iter(Interner, inner_tys))
+            .intern(Interner)
+    }
+
+    pub(super) fn infer_pat(
+        &mut self,
+        pat: PatId,
+        expected: &Ty,
+        mut default_bm: BindingMode,
+    ) -> Ty {
+        let mut expected = self.resolve_ty_shallow(expected);
+
+        if is_non_ref_pat(&self.body, pat) {
+            let mut pat_adjustments = Vec::new();
+            while let Some((inner, _lifetime, mutability)) = expected.as_reference() {
+                pat_adjustments.push(expected.clone());
+                expected = self.resolve_ty_shallow(inner);
+                default_bm = match default_bm {
+                    BindingMode::Move => BindingMode::Ref(mutability),
+                    BindingMode::Ref(Mutability::Not) => BindingMode::Ref(Mutability::Not),
+                    BindingMode::Ref(Mutability::Mut) => BindingMode::Ref(mutability),
+                }
+            }
+
+            if !pat_adjustments.is_empty() {
+                pat_adjustments.shrink_to_fit();
+                self.result.pat_adjustments.insert(pat, pat_adjustments);
+            }
+        } else if let Pat::Ref { .. } = &self.body[pat] {
+            cov_mark::hit!(match_ergonomics_ref);
+            // When you encounter a `&pat` pattern, reset to Move.
+            // This is so that `w` is by value: `let (_, &w) = &(1, &2);`
+            default_bm = BindingMode::Move;
+        }
+
+        // Lose mutability.
+        let default_bm = default_bm;
+        let expected = expected;
+
+        let ty = match &self.body[pat] {
+            Pat::Tuple { args, ellipsis } => {
+                self.infer_tuple_pat_like(&expected, default_bm, *ellipsis, args)
+            }
+            Pat::Or(pats) => {
+                if let Some((first_pat, rest)) = pats.split_first() {
+                    let ty = self.infer_pat(*first_pat, &expected, default_bm);
+                    for pat in rest {
+                        self.infer_pat(*pat, &expected, default_bm);
+                    }
+                    ty
+                } else {
+                    self.err_ty()
+                }
+            }
+            Pat::Ref { pat, mutability } => {
+                let mutability = lower_to_chalk_mutability(*mutability);
+                let expectation = match expected.as_reference() {
+                    Some((inner_ty, _lifetime, exp_mut)) => {
+                        if mutability != exp_mut {
+                            // FIXME: emit type error?
+                        }
+                        inner_ty.clone()
+                    }
+                    _ => self.result.standard_types.unknown.clone(),
+                };
+                let subty = self.infer_pat(*pat, &expectation, default_bm);
+                TyKind::Ref(mutability, static_lifetime(), subty).intern(Interner)
+            }
+            Pat::TupleStruct { path: p, args: subpats, ellipsis } => self
+                .infer_tuple_struct_pat_like(
+                    p.as_deref(),
+                    &expected,
+                    default_bm,
+                    pat,
+                    *ellipsis,
+                    subpats,
+                ),
+            Pat::Record { path: p, args: fields, ellipsis: _ } => {
+                let subs = fields.iter().map(|f| (f.name.clone(), f.pat));
+                self.infer_record_pat_like(p.as_deref(), &expected, default_bm, pat.into(), subs)
+            }
+            Pat::Path(path) => {
+                // FIXME use correct resolver for the surrounding expression
+                let resolver = self.resolver.clone();
+                self.infer_path(&resolver, path, pat.into()).unwrap_or_else(|| self.err_ty())
+            }
+            Pat::Bind { mode, name: _, subpat } => {
+                let mode = if mode == &BindingAnnotation::Unannotated {
+                    default_bm
+                } else {
+                    BindingMode::convert(*mode)
+                };
+                self.result.pat_binding_modes.insert(pat, mode);
+
+                let inner_ty = match subpat {
+                    Some(subpat) => self.infer_pat(*subpat, &expected, default_bm),
+                    None => expected,
+                };
+                let inner_ty = self.insert_type_vars_shallow(inner_ty);
+
+                let bound_ty = match mode {
+                    BindingMode::Ref(mutability) => {
+                        TyKind::Ref(mutability, static_lifetime(), inner_ty.clone())
+                            .intern(Interner)
+                    }
+                    BindingMode::Move => inner_ty.clone(),
+                };
+                self.write_pat_ty(pat, bound_ty);
+                return inner_ty;
+            }
+            Pat::Slice { prefix, slice, suffix } => {
+                let elem_ty = match expected.kind(Interner) {
+                    TyKind::Array(st, _) | TyKind::Slice(st) => st.clone(),
+                    _ => self.err_ty(),
+                };
+
+                for &pat_id in prefix.iter().chain(suffix.iter()) {
+                    self.infer_pat(pat_id, &elem_ty, default_bm);
+                }
+
+                if let &Some(slice_pat_id) = slice {
+                    let rest_pat_ty = match expected.kind(Interner) {
+                        TyKind::Array(_, length) => {
+                            let len = match length.data(Interner).value {
+                                ConstValue::Concrete(ConcreteConst {
+                                    interned: ConstScalar::UInt(len),
+                                }) => len.checked_sub((prefix.len() + suffix.len()) as u128),
+                                _ => None,
+                            };
+                            TyKind::Array(
+                                elem_ty.clone(),
+                                intern_const_scalar(
+                                    len.map_or(ConstScalar::Unknown, |len| ConstScalar::UInt(len)),
+                                    TyBuilder::usize(),
+                                ),
+                            )
+                        }
+                        _ => TyKind::Slice(elem_ty.clone()),
+                    }
+                    .intern(Interner);
+                    self.infer_pat(slice_pat_id, &rest_pat_ty, default_bm);
+                }
+
+                match expected.kind(Interner) {
+                    TyKind::Array(_, const_) => TyKind::Array(elem_ty, const_.clone()),
+                    _ => TyKind::Slice(elem_ty),
+                }
+                .intern(Interner)
+            }
+            Pat::Wild => expected.clone(),
+            Pat::Range { start, end } => {
+                let start_ty = self.infer_expr(*start, &Expectation::has_type(expected.clone()));
+                self.infer_expr(*end, &Expectation::has_type(start_ty))
+            }
+            Pat::Lit(expr) => self.infer_expr(*expr, &Expectation::has_type(expected.clone())),
+            Pat::Box { inner } => match self.resolve_boxed_box() {
+                Some(box_adt) => {
+                    let (inner_ty, alloc_ty) = match expected.as_adt() {
+                        Some((adt, subst)) if adt == box_adt => (
+                            subst.at(Interner, 0).assert_ty_ref(Interner).clone(),
+                            subst.as_slice(Interner).get(1).and_then(|a| a.ty(Interner).cloned()),
+                        ),
+                        _ => (self.result.standard_types.unknown.clone(), None),
+                    };
+
+                    let inner_ty = self.infer_pat(*inner, &inner_ty, default_bm);
+                    let mut b = TyBuilder::adt(self.db, box_adt).push(inner_ty);
+
+                    if let Some(alloc_ty) = alloc_ty {
+                        b = b.push(alloc_ty);
+                    }
+                    b.fill_with_defaults(self.db, || self.table.new_type_var()).build()
+                }
+                None => self.err_ty(),
+            },
+            Pat::ConstBlock(expr) => {
+                self.infer_expr(*expr, &Expectation::has_type(expected.clone()))
+            }
+            Pat::Missing => self.err_ty(),
+        };
+        // use a new type variable if we got error type here
+        let ty = self.insert_type_vars_shallow(ty);
+        if !self.unify(&ty, &expected) {
+            self.result
+                .type_mismatches
+                .insert(pat.into(), TypeMismatch { expected, actual: ty.clone() });
+        }
+        self.write_pat_ty(pat, ty.clone());
+        ty
+    }
+}
+
+fn is_non_ref_pat(body: &hir_def::body::Body, pat: PatId) -> bool {
+    match &body[pat] {
+        Pat::Tuple { .. }
+        | Pat::TupleStruct { .. }
+        | Pat::Record { .. }
+        | Pat::Range { .. }
+        | Pat::Slice { .. } => true,
+        Pat::Or(pats) => pats.iter().all(|p| is_non_ref_pat(body, *p)),
+        // FIXME: ConstBlock/Path/Lit might actually evaluate to ref, but inference is unimplemented.
+        Pat::Path(..) => true,
+        Pat::ConstBlock(..) => true,
+        Pat::Lit(expr) => !matches!(body[*expr], Expr::Literal(Literal::String(..))),
+        Pat::Bind {
+            mode: BindingAnnotation::Mutable | BindingAnnotation::Unannotated,
+            subpat: Some(subpat),
+            ..
+        } => is_non_ref_pat(body, *subpat),
+        Pat::Wild | Pat::Bind { .. } | Pat::Ref { .. } | Pat::Box { .. } | Pat::Missing => false,
+    }
+}
diff --git a/src/tools/rust-analyzer/crates/hir-ty/src/infer/path.rs b/src/tools/rust-analyzer/crates/hir-ty/src/infer/path.rs
new file mode 100644
index 000000000..f580e09e9
--- /dev/null
+++ b/src/tools/rust-analyzer/crates/hir-ty/src/infer/path.rs
@@ -0,0 +1,295 @@
+//! Path expression resolution.
+
+use chalk_ir::cast::Cast;
+use hir_def::{
+    path::{Path, PathSegment},
+    resolver::{ResolveValueResult, Resolver, TypeNs, ValueNs},
+    AdtId, AssocItemId, EnumVariantId, ItemContainerId, Lookup,
+};
+use hir_expand::name::Name;
+
+use crate::{
+    builder::ParamKind,
+    consteval,
+    method_resolution::{self, VisibleFromModule},
+    GenericArgData, Interner, Substitution, TraitRefExt, Ty, TyBuilder, TyExt, TyKind,
+    ValueTyDefId,
+};
+
+use super::{ExprOrPatId, InferenceContext, TraitRef};
+
+impl<'a> InferenceContext<'a> {
+    pub(super) fn infer_path(
+        &mut self,
+        resolver: &Resolver,
+        path: &Path,
+        id: ExprOrPatId,
+    ) -> Option<Ty> {
+        let ty = self.resolve_value_path(resolver, path, id)?;
+        let ty = self.insert_type_vars(ty);
+        let ty = self.normalize_associated_types_in(ty);
+        Some(ty)
+    }
+
+    fn resolve_value_path(
+        &mut self,
+        resolver: &Resolver,
+        path: &Path,
+        id: ExprOrPatId,
+    ) -> Option<Ty> {
+        let (value, self_subst) = if let Some(type_ref) = path.type_anchor() {
+            if path.segments().is_empty() {
+                // This can't actually happen syntax-wise
+                return None;
+            }
+            let ty = self.make_ty(type_ref);
+            let remaining_segments_for_ty = path.segments().take(path.segments().len() - 1);
+            let ctx = crate::lower::TyLoweringContext::new(self.db, resolver);
+            let (ty, _) = ctx.lower_ty_relative_path(ty, None, remaining_segments_for_ty);
+            self.resolve_ty_assoc_item(
+                ty,
+                path.segments().last().expect("path had at least one segment").name,
+                id,
+            )?
+        } else {
+            let value_or_partial =
+                resolver.resolve_path_in_value_ns(self.db.upcast(), path.mod_path())?;
+
+            match value_or_partial {
+                ResolveValueResult::ValueNs(it) => (it, None),
+                ResolveValueResult::Partial(def, remaining_index) => {
+                    self.resolve_assoc_item(def, path, remaining_index, id)?
+                }
+            }
+        };
+
+        let typable: ValueTyDefId = match value {
+            ValueNs::LocalBinding(pat) => {
+                let ty = self.result.type_of_pat.get(pat)?.clone();
+                return Some(ty);
+            }
+            ValueNs::FunctionId(it) => it.into(),
+            ValueNs::ConstId(it) => it.into(),
+            ValueNs::StaticId(it) => it.into(),
+            ValueNs::StructId(it) => {
+                self.write_variant_resolution(id, it.into());
+
+                it.into()
+            }
+            ValueNs::EnumVariantId(it) => {
+                self.write_variant_resolution(id, it.into());
+
+                it.into()
+            }
+            ValueNs::ImplSelf(impl_id) => {
+                let generics = crate::utils::generics(self.db.upcast(), impl_id.into());
+                let substs = generics.placeholder_subst(self.db);
+                let ty = self.db.impl_self_ty(impl_id).substitute(Interner, &substs);
+                if let Some((AdtId::StructId(struct_id), substs)) = ty.as_adt() {
+                    let ty = self.db.value_ty(struct_id.into()).substitute(Interner, &substs);
+                    return Some(ty);
+                } else {
+                    // FIXME: diagnostic, invalid Self reference
+                    return None;
+                }
+            }
+            ValueNs::GenericParam(it) => return Some(self.db.const_param_ty(it)),
+        };
+
+        let parent_substs = self_subst.unwrap_or_else(|| Substitution::empty(Interner));
+        let ctx = crate::lower::TyLoweringContext::new(self.db, &self.resolver);
+        let substs = ctx.substs_from_path(path, typable, true);
+        let mut it = substs.as_slice(Interner)[parent_substs.len(Interner)..].iter().cloned();
+        let ty = TyBuilder::value_ty(self.db, typable)
+            .use_parent_substs(&parent_substs)
+            .fill(|x| {
+                it.next().unwrap_or_else(|| match x {
+                    ParamKind::Type => {
+                        GenericArgData::Ty(TyKind::Error.intern(Interner)).intern(Interner)
+                    }
+                    ParamKind::Const(ty) => consteval::unknown_const_as_generic(ty.clone()),
+                })
+            })
+            .build();
+        Some(ty)
+    }
+
+    fn resolve_assoc_item(
+        &mut self,
+        def: TypeNs,
+        path: &Path,
+        remaining_index: usize,
+        id: ExprOrPatId,
+    ) -> Option<(ValueNs, Option<Substitution>)> {
+        assert!(remaining_index < path.segments().len());
+        // there may be more intermediate segments between the resolved one and
+        // the end. Only the last segment needs to be resolved to a value; from
+        // the segments before that, we need to get either a type or a trait ref.
+
+        let resolved_segment = path.segments().get(remaining_index - 1).unwrap();
+        let remaining_segments = path.segments().skip(remaining_index);
+        let is_before_last = remaining_segments.len() == 1;
+
+        match (def, is_before_last) {
+            (TypeNs::TraitId(trait_), true) => {
+                let segment =
+                    remaining_segments.last().expect("there should be at least one segment here");
+                let ctx = crate::lower::TyLoweringContext::new(self.db, &self.resolver);
+                let trait_ref =
+                    ctx.lower_trait_ref_from_resolved_path(trait_, resolved_segment, None);
+                self.resolve_trait_assoc_item(trait_ref, segment, id)
+            }
+            (def, _) => {
+                // Either we already have a type (e.g. `Vec::new`), or we have a
+                // trait but it's not the last segment, so the next segment
+                // should resolve to an associated type of that trait (e.g. `<T
+                // as Iterator>::Item::default`)
+                let remaining_segments_for_ty =
+                    remaining_segments.take(remaining_segments.len() - 1);
+                let ctx = crate::lower::TyLoweringContext::new(self.db, &self.resolver);
+                let (ty, _) = ctx.lower_partly_resolved_path(
+                    def,
+                    resolved_segment,
+                    remaining_segments_for_ty,
+                    true,
+                );
+                if let TyKind::Error = ty.kind(Interner) {
+                    return None;
+                }
+
+                let ty = self.insert_type_vars(ty);
+                let ty = self.normalize_associated_types_in(ty);
+
+                let segment =
+                    remaining_segments.last().expect("there should be at least one segment here");
+
+                self.resolve_ty_assoc_item(ty, segment.name, id)
+            }
+        }
+    }
+
+    fn resolve_trait_assoc_item(
+        &mut self,
+        trait_ref: TraitRef,
+        segment: PathSegment<'_>,
+        id: ExprOrPatId,
+    ) -> Option<(ValueNs, Option<Substitution>)> {
+        let trait_ = trait_ref.hir_trait_id();
+        let item =
+            self.db.trait_data(trait_).items.iter().map(|(_name, id)| (*id)).find_map(|item| {
+                match item {
+                    AssocItemId::FunctionId(func) => {
+                        if segment.name == &self.db.function_data(func).name {
+                            Some(AssocItemId::FunctionId(func))
+                        } else {
+                            None
+                        }
+                    }
+
+                    AssocItemId::ConstId(konst) => {
+                        if self
+                            .db
+                            .const_data(konst)
+                            .name
+                            .as_ref()
+                            .map_or(false, |n| n == segment.name)
+                        {
+                            Some(AssocItemId::ConstId(konst))
+                        } else {
+                            None
+                        }
+                    }
+                    AssocItemId::TypeAliasId(_) => None,
+                }
+            })?;
+        let def = match item {
+            AssocItemId::FunctionId(f) => ValueNs::FunctionId(f),
+            AssocItemId::ConstId(c) => ValueNs::ConstId(c),
+            AssocItemId::TypeAliasId(_) => unreachable!(),
+        };
+
+        self.write_assoc_resolution(id, item);
+        Some((def, Some(trait_ref.substitution)))
+    }
+
+    fn resolve_ty_assoc_item(
+        &mut self,
+        ty: Ty,
+        name: &Name,
+        id: ExprOrPatId,
+    ) -> Option<(ValueNs, Option<Substitution>)> {
+        if let TyKind::Error = ty.kind(Interner) {
+            return None;
+        }
+
+        if let Some(result) = self.resolve_enum_variant_on_ty(&ty, name, id) {
+            return Some(result);
+        }
+
+        let canonical_ty = self.canonicalize(ty.clone());
+        let traits_in_scope = self.resolver.traits_in_scope(self.db.upcast());
+
+        method_resolution::iterate_method_candidates(
+            &canonical_ty.value,
+            self.db,
+            self.table.trait_env.clone(),
+            &traits_in_scope,
+            VisibleFromModule::Filter(self.resolver.module()),
+            Some(name),
+            method_resolution::LookupMode::Path,
+            move |_ty, item| {
+                let (def, container) = match item {
+                    AssocItemId::FunctionId(f) => {
+                        (ValueNs::FunctionId(f), f.lookup(self.db.upcast()).container)
+                    }
+                    AssocItemId::ConstId(c) => {
+                        (ValueNs::ConstId(c), c.lookup(self.db.upcast()).container)
+                    }
+                    AssocItemId::TypeAliasId(_) => unreachable!(),
+                };
+                let substs = match container {
+                    ItemContainerId::ImplId(impl_id) => {
+                        let impl_substs = TyBuilder::subst_for_def(self.db, impl_id)
+                            .fill_with_inference_vars(&mut self.table)
+                            .build();
+                        let impl_self_ty =
+                            self.db.impl_self_ty(impl_id).substitute(Interner, &impl_substs);
+                        self.unify(&impl_self_ty, &ty);
+                        Some(impl_substs)
+                    }
+                    ItemContainerId::TraitId(trait_) => {
+                        // we're picking this method
+                        let trait_ref = TyBuilder::trait_ref(self.db, trait_)
+                            .push(ty.clone())
+                            .fill_with_inference_vars(&mut self.table)
+                            .build();
+                        self.push_obligation(trait_ref.clone().cast(Interner));
+                        Some(trait_ref.substitution)
+                    }
+                    ItemContainerId::ModuleId(_) | ItemContainerId::ExternBlockId(_) => None,
+                };
+
+                self.write_assoc_resolution(id, item);
+                Some((def, substs))
+            },
+        )
+    }
+
+    fn resolve_enum_variant_on_ty(
+        &mut self,
+        ty: &Ty,
+        name: &Name,
+        id: ExprOrPatId,
+    ) -> Option<(ValueNs, Option<Substitution>)> {
+        let ty = self.resolve_ty_shallow(ty);
+        let (enum_id, subst) = match ty.as_adt() {
+            Some((AdtId::EnumId(e), subst)) => (e, subst),
+            _ => return None,
+        };
+        let enum_data = self.db.enum_data(enum_id);
+        let local_id = enum_data.variant(name)?;
+        let variant = EnumVariantId { parent: enum_id, local_id };
+        self.write_variant_resolution(id, variant.into());
+        Some((ValueNs::EnumVariantId(variant), Some(subst.clone())))
+    }
+}
diff --git a/src/tools/rust-analyzer/crates/hir-ty/src/infer/unify.rs b/src/tools/rust-analyzer/crates/hir-ty/src/infer/unify.rs
new file mode 100644
index 000000000..e77b55670
--- /dev/null
+++ b/src/tools/rust-analyzer/crates/hir-ty/src/infer/unify.rs
@@ -0,0 +1,738 @@
+//! Unification and canonicalization logic.
+
+use std::{fmt, mem, sync::Arc};
+
+use chalk_ir::{
+    cast::Cast, fold::TypeFoldable, interner::HasInterner, zip::Zip, CanonicalVarKind, FloatTy,
+    IntTy, NoSolution, TyVariableKind, UniverseIndex,
+};
+use chalk_solve::infer::ParameterEnaVariableExt;
+use ena::unify::UnifyKey;
+use hir_expand::name;
+use stdx::never;
+
+use super::{InferOk, InferResult, InferenceContext, TypeError};
+use crate::{
+    db::HirDatabase, fold_tys, static_lifetime, traits::FnTrait, AliasEq, AliasTy, BoundVar,
+    Canonical, Const, DebruijnIndex, GenericArg, GenericArgData, Goal, Guidance, InEnvironment,
+    InferenceVar, Interner, Lifetime, ParamKind, ProjectionTy, ProjectionTyExt, Scalar, Solution,
+    Substitution, TraitEnvironment, Ty, TyBuilder, TyExt, TyKind, VariableKind,
+};
+
+impl<'a> InferenceContext<'a> {
+    pub(super) fn canonicalize<T: TypeFoldable<Interner> + HasInterner<Interner = Interner>>(
+        &mut self,
+        t: T,
+    ) -> Canonicalized<T>
+    where
+        T: HasInterner<Interner = Interner>,
+    {
+        self.table.canonicalize(t)
+    }
+}
+
+#[derive(Debug, Clone)]
+pub(crate) struct Canonicalized<T>
+where
+    T: HasInterner<Interner = Interner>,
+{
+    pub(crate) value: Canonical<T>,
+    free_vars: Vec<GenericArg>,
+}
+
+impl<T: HasInterner<Interner = Interner>> Canonicalized<T> {
+    pub(super) fn apply_solution(
+        &self,
+        ctx: &mut InferenceTable<'_>,
+        solution: Canonical<Substitution>,
+    ) {
+        // the solution may contain new variables, which we need to convert to new inference vars
+        let new_vars = Substitution::from_iter(
+            Interner,
+            solution.binders.iter(Interner).map(|k| match &k.kind {
+                VariableKind::Ty(TyVariableKind::General) => ctx.new_type_var().cast(Interner),
+                VariableKind::Ty(TyVariableKind::Integer) => ctx.new_integer_var().cast(Interner),
+                VariableKind::Ty(TyVariableKind::Float) => ctx.new_float_var().cast(Interner),
+                // Chalk can sometimes return new lifetime variables. We just use the static lifetime everywhere
+                VariableKind::Lifetime => static_lifetime().cast(Interner),
+                VariableKind::Const(ty) => ctx.new_const_var(ty.clone()).cast(Interner),
+            }),
+        );
+        for (i, v) in solution.value.iter(Interner).enumerate() {
+            let var = self.free_vars[i].clone();
+            if let Some(ty) = v.ty(Interner) {
+                // eagerly replace projections in the type; we may be getting types
+                // e.g. from where clauses where this hasn't happened yet
+                let ty = ctx.normalize_associated_types_in(new_vars.apply(ty.clone(), Interner));
+                ctx.unify(var.assert_ty_ref(Interner), &ty);
+            } else {
+                let _ = ctx.try_unify(&var, &new_vars.apply(v.clone(), Interner));
+            }
+        }
+    }
+}
+
+pub fn could_unify(
+    db: &dyn HirDatabase,
+    env: Arc<TraitEnvironment>,
+    tys: &Canonical<(Ty, Ty)>,
+) -> bool {
+    unify(db, env, tys).is_some()
+}
+
+pub(crate) fn unify(
+    db: &dyn HirDatabase,
+    env: Arc<TraitEnvironment>,
+    tys: &Canonical<(Ty, Ty)>,
+) -> Option<Substitution> {
+    let mut table = InferenceTable::new(db, env);
+    let vars = Substitution::from_iter(
+        Interner,
+        tys.binders.iter(Interner).map(|x| match &x.kind {
+            chalk_ir::VariableKind::Ty(_) => {
+                GenericArgData::Ty(table.new_type_var()).intern(Interner)
+            }
+            chalk_ir::VariableKind::Lifetime => {
+                GenericArgData::Ty(table.new_type_var()).intern(Interner)
+            } // FIXME: maybe wrong?
+            chalk_ir::VariableKind::Const(ty) => {
+                GenericArgData::Const(table.new_const_var(ty.clone())).intern(Interner)
+            }
+        }),
+    );
+    let ty1_with_vars = vars.apply(tys.value.0.clone(), Interner);
+    let ty2_with_vars = vars.apply(tys.value.1.clone(), Interner);
+    if !table.unify(&ty1_with_vars, &ty2_with_vars) {
+        return None;
+    }
+    // default any type vars that weren't unified back to their original bound vars
+    // (kind of hacky)
+    let find_var = |iv| {
+        vars.iter(Interner).position(|v| match v.interned() {
+            chalk_ir::GenericArgData::Ty(ty) => ty.inference_var(Interner),
+            chalk_ir::GenericArgData::Lifetime(lt) => lt.inference_var(Interner),
+            chalk_ir::GenericArgData::Const(c) => c.inference_var(Interner),
+        } == Some(iv))
+    };
+    let fallback = |iv, kind, default, binder| match kind {
+        chalk_ir::VariableKind::Ty(_ty_kind) => find_var(iv)
+            .map_or(default, |i| BoundVar::new(binder, i).to_ty(Interner).cast(Interner)),
+        chalk_ir::VariableKind::Lifetime => find_var(iv)
+            .map_or(default, |i| BoundVar::new(binder, i).to_lifetime(Interner).cast(Interner)),
+        chalk_ir::VariableKind::Const(ty) => find_var(iv)
+            .map_or(default, |i| BoundVar::new(binder, i).to_const(Interner, ty).cast(Interner)),
+    };
+    Some(Substitution::from_iter(
+        Interner,
+        vars.iter(Interner).map(|v| table.resolve_with_fallback(v.clone(), &fallback)),
+    ))
+}
+
+#[derive(Copy, Clone, Debug)]
+pub(crate) struct TypeVariableData {
+    diverging: bool,
+}
+
+type ChalkInferenceTable = chalk_solve::infer::InferenceTable<Interner>;
+
+#[derive(Clone)]
+pub(crate) struct InferenceTable<'a> {
+    pub(crate) db: &'a dyn HirDatabase,
+    pub(crate) trait_env: Arc<TraitEnvironment>,
+    var_unification_table: ChalkInferenceTable,
+    type_variable_table: Vec<TypeVariableData>,
+    pending_obligations: Vec<Canonicalized<InEnvironment<Goal>>>,
+}
+
+pub(crate) struct InferenceTableSnapshot {
+    var_table_snapshot: chalk_solve::infer::InferenceSnapshot<Interner>,
+    pending_obligations: Vec<Canonicalized<InEnvironment<Goal>>>,
+    type_variable_table_snapshot: Vec<TypeVariableData>,
+}
+
+impl<'a> InferenceTable<'a> {
+    pub(crate) fn new(db: &'a dyn HirDatabase, trait_env: Arc<TraitEnvironment>) -> Self {
+        InferenceTable {
+            db,
+            trait_env,
+            var_unification_table: ChalkInferenceTable::new(),
+            type_variable_table: Vec::new(),
+            pending_obligations: Vec::new(),
+        }
+    }
+
+    /// Chalk doesn't know about the `diverging` flag, so when it unifies two
+    /// type variables of which one is diverging, the chosen root might not be
+    /// diverging and we have no way of marking it as such at that time. This
+    /// function goes through all type variables and make sure their root is
+    /// marked as diverging if necessary, so that resolving them gives the right
+    /// result.
+    pub(super) fn propagate_diverging_flag(&mut self) {
+        for i in 0..self.type_variable_table.len() {
+            if !self.type_variable_table[i].diverging {
+                continue;
+            }
+            let v = InferenceVar::from(i as u32);
+            let root = self.var_unification_table.inference_var_root(v);
+            if let Some(data) = self.type_variable_table.get_mut(root.index() as usize) {
+                data.diverging = true;
+            }
+        }
+    }
+
+    pub(super) fn set_diverging(&mut self, iv: InferenceVar, diverging: bool) {
+        self.type_variable_table[iv.index() as usize].diverging = diverging;
+    }
+
+    fn fallback_value(&self, iv: InferenceVar, kind: TyVariableKind) -> Ty {
+        match kind {
+            _ if self
+                .type_variable_table
+                .get(iv.index() as usize)
+                .map_or(false, |data| data.diverging) =>
+            {
+                TyKind::Never
+            }
+            TyVariableKind::General => TyKind::Error,
+            TyVariableKind::Integer => TyKind::Scalar(Scalar::Int(IntTy::I32)),
+            TyVariableKind::Float => TyKind::Scalar(Scalar::Float(FloatTy::F64)),
+        }
+        .intern(Interner)
+    }
+
+    pub(crate) fn canonicalize<T: TypeFoldable<Interner> + HasInterner<Interner = Interner>>(
+        &mut self,
+        t: T,
+    ) -> Canonicalized<T>
+    where
+        T: HasInterner<Interner = Interner>,
+    {
+        // try to resolve obligations before canonicalizing, since this might
+        // result in new knowledge about variables
+        self.resolve_obligations_as_possible();
+        let result = self.var_unification_table.canonicalize(Interner, t);
+        let free_vars = result
+            .free_vars
+            .into_iter()
+            .map(|free_var| free_var.to_generic_arg(Interner))
+            .collect();
+        Canonicalized { value: result.quantified, free_vars }
+    }
+
+    /// Recurses through the given type, normalizing associated types mentioned
+    /// in it by replacing them by type variables and registering obligations to
+    /// resolve later. This should be done once for every type we get from some
+    /// type annotation (e.g. from a let type annotation, field type or function
+    /// call). `make_ty` handles this already, but e.g. for field types we need
+    /// to do it as well.
+    pub(crate) fn normalize_associated_types_in(&mut self, ty: Ty) -> Ty {
+        fold_tys(
+            ty,
+            |ty, _| match ty.kind(Interner) {
+                TyKind::Alias(AliasTy::Projection(proj_ty)) => {
+                    self.normalize_projection_ty(proj_ty.clone())
+                }
+                _ => ty,
+            },
+            DebruijnIndex::INNERMOST,
+        )
+    }
+
+    pub(crate) fn normalize_projection_ty(&mut self, proj_ty: ProjectionTy) -> Ty {
+        let var = self.new_type_var();
+        let alias_eq = AliasEq { alias: AliasTy::Projection(proj_ty), ty: var.clone() };
+        let obligation = alias_eq.cast(Interner);
+        self.register_obligation(obligation);
+        var
+    }
+
+    fn extend_type_variable_table(&mut self, to_index: usize) {
+        self.type_variable_table.extend(
+            (0..1 + to_index - self.type_variable_table.len())
+                .map(|_| TypeVariableData { diverging: false }),
+        );
+    }
+
+    fn new_var(&mut self, kind: TyVariableKind, diverging: bool) -> Ty {
+        let var = self.var_unification_table.new_variable(UniverseIndex::ROOT);
+        // Chalk might have created some type variables for its own purposes that we don't know about...
+        self.extend_type_variable_table(var.index() as usize);
+        assert_eq!(var.index() as usize, self.type_variable_table.len() - 1);
+        self.type_variable_table[var.index() as usize].diverging = diverging;
+        var.to_ty_with_kind(Interner, kind)
+    }
+
+    pub(crate) fn new_type_var(&mut self) -> Ty {
+        self.new_var(TyVariableKind::General, false)
+    }
+
+    pub(crate) fn new_integer_var(&mut self) -> Ty {
+        self.new_var(TyVariableKind::Integer, false)
+    }
+
+    pub(crate) fn new_float_var(&mut self) -> Ty {
+        self.new_var(TyVariableKind::Float, false)
+    }
+
+    pub(crate) fn new_maybe_never_var(&mut self) -> Ty {
+        self.new_var(TyVariableKind::General, true)
+    }
+
+    pub(crate) fn new_const_var(&mut self, ty: Ty) -> Const {
+        let var = self.var_unification_table.new_variable(UniverseIndex::ROOT);
+        var.to_const(Interner, ty)
+    }
+
+    pub(crate) fn new_lifetime_var(&mut self) -> Lifetime {
+        let var = self.var_unification_table.new_variable(UniverseIndex::ROOT);
+        var.to_lifetime(Interner)
+    }
+
+    pub(crate) fn resolve_with_fallback<T>(
+        &mut self,
+        t: T,
+        fallback: &dyn Fn(InferenceVar, VariableKind, GenericArg, DebruijnIndex) -> GenericArg,
+    ) -> T
+    where
+        T: HasInterner<Interner = Interner> + TypeFoldable<Interner>,
+    {
+        self.resolve_with_fallback_inner(&mut Vec::new(), t, &fallback)
+    }
+
+    pub(crate) fn fresh_subst(&mut self, binders: &[CanonicalVarKind<Interner>]) -> Substitution {
+        Substitution::from_iter(
+            Interner,
+            binders.iter().map(|kind| {
+                let param_infer_var =
+                    kind.map_ref(|&ui| self.var_unification_table.new_variable(ui));
+                param_infer_var.to_generic_arg(Interner)
+            }),
+        )
+    }
+
+    pub(crate) fn instantiate_canonical<T>(&mut self, canonical: Canonical<T>) -> T
+    where
+        T: HasInterner<Interner = Interner> + TypeFoldable<Interner> + std::fmt::Debug,
+    {
+        let subst = self.fresh_subst(canonical.binders.as_slice(Interner));
+        subst.apply(canonical.value, Interner)
+    }
+
+    fn resolve_with_fallback_inner<T>(
+        &mut self,
+        var_stack: &mut Vec<InferenceVar>,
+        t: T,
+        fallback: &dyn Fn(InferenceVar, VariableKind, GenericArg, DebruijnIndex) -> GenericArg,
+    ) -> T
+    where
+        T: HasInterner<Interner = Interner> + TypeFoldable<Interner>,
+    {
+        t.fold_with(
+            &mut resolve::Resolver { table: self, var_stack, fallback },
+            DebruijnIndex::INNERMOST,
+        )
+        .expect("fold failed unexpectedly")
+    }
+
+    pub(crate) fn resolve_completely<T>(&mut self, t: T) -> T
+    where
+        T: HasInterner<Interner = Interner> + TypeFoldable<Interner>,
+    {
+        self.resolve_with_fallback(t, &|_, _, d, _| d)
+    }
+
+    /// Unify two types and register new trait goals that arise from that.
+    pub(crate) fn unify(&mut self, ty1: &Ty, ty2: &Ty) -> bool {
+        let result = match self.try_unify(ty1, ty2) {
+            Ok(r) => r,
+            Err(_) => return false,
+        };
+        self.register_infer_ok(result);
+        true
+    }
+
+    /// Unify two types and return new trait goals arising from it, so the
+    /// caller needs to deal with them.
+    pub(crate) fn try_unify<T: Zip<Interner>>(&mut self, t1: &T, t2: &T) -> InferResult<()> {
+        match self.var_unification_table.relate(
+            Interner,
+            &self.db,
+            &self.trait_env.env,
+            chalk_ir::Variance::Invariant,
+            t1,
+            t2,
+        ) {
+            Ok(result) => Ok(InferOk { goals: result.goals, value: () }),
+            Err(chalk_ir::NoSolution) => Err(TypeError),
+        }
+    }
+
+    /// If `ty` is a type variable with known type, returns that type;
+    /// otherwise, return ty.
+    pub(crate) fn resolve_ty_shallow(&mut self, ty: &Ty) -> Ty {
+        self.resolve_obligations_as_possible();
+        self.var_unification_table.normalize_ty_shallow(Interner, ty).unwrap_or_else(|| ty.clone())
+    }
+
+    pub(crate) fn snapshot(&mut self) -> InferenceTableSnapshot {
+        let var_table_snapshot = self.var_unification_table.snapshot();
+        let type_variable_table_snapshot = self.type_variable_table.clone();
+        let pending_obligations = self.pending_obligations.clone();
+        InferenceTableSnapshot {
+            var_table_snapshot,
+            pending_obligations,
+            type_variable_table_snapshot,
+        }
+    }
+
+    pub(crate) fn rollback_to(&mut self, snapshot: InferenceTableSnapshot) {
+        self.var_unification_table.rollback_to(snapshot.var_table_snapshot);
+        self.type_variable_table = snapshot.type_variable_table_snapshot;
+        self.pending_obligations = snapshot.pending_obligations;
+    }
+
+    pub(crate) fn run_in_snapshot<T>(&mut self, f: impl FnOnce(&mut InferenceTable<'_>) -> T) -> T {
+        let snapshot = self.snapshot();
+        let result = f(self);
+        self.rollback_to(snapshot);
+        result
+    }
+
+    /// Checks an obligation without registering it. Useful mostly to check
+    /// whether a trait *might* be implemented before deciding to 'lock in' the
+    /// choice (during e.g. method resolution or deref).
+    pub(crate) fn try_obligation(&mut self, goal: Goal) -> Option<Solution> {
+        let in_env = InEnvironment::new(&self.trait_env.env, goal);
+        let canonicalized = self.canonicalize(in_env);
+        let solution = self.db.trait_solve(self.trait_env.krate, canonicalized.value);
+        solution
+    }
+
+    pub(crate) fn register_obligation(&mut self, goal: Goal) {
+        let in_env = InEnvironment::new(&self.trait_env.env, goal);
+        self.register_obligation_in_env(in_env)
+    }
+
+    fn register_obligation_in_env(&mut self, goal: InEnvironment<Goal>) {
+        let canonicalized = self.canonicalize(goal);
+        if !self.try_resolve_obligation(&canonicalized) {
+            self.pending_obligations.push(canonicalized);
+        }
+    }
+
+    pub(crate) fn register_infer_ok<T>(&mut self, infer_ok: InferOk<T>) {
+        infer_ok.goals.into_iter().for_each(|goal| self.register_obligation_in_env(goal));
+    }
+
+    pub(crate) fn resolve_obligations_as_possible(&mut self) {
+        let _span = profile::span("resolve_obligations_as_possible");
+        let mut changed = true;
+        let mut obligations = Vec::new();
+        while changed {
+            changed = false;
+            mem::swap(&mut self.pending_obligations, &mut obligations);
+            for canonicalized in obligations.drain(..) {
+                if !self.check_changed(&canonicalized) {
+                    self.pending_obligations.push(canonicalized);
+                    continue;
+                }
+                changed = true;
+                let uncanonical = chalk_ir::Substitute::apply(
+                    &canonicalized.free_vars,
+                    canonicalized.value.value,
+                    Interner,
+                );
+                self.register_obligation_in_env(uncanonical);
+            }
+        }
+    }
+
+    pub(crate) fn fudge_inference<T: TypeFoldable<Interner>>(
+        &mut self,
+        f: impl FnOnce(&mut Self) -> T,
+    ) -> T {
+        use chalk_ir::fold::TypeFolder;
+        struct VarFudger<'a, 'b> {
+            table: &'a mut InferenceTable<'b>,
+            highest_known_var: InferenceVar,
+        }
+        impl<'a, 'b> TypeFolder<Interner> for VarFudger<'a, 'b> {
+            type Error = NoSolution;
+
+            fn as_dyn(&mut self) -> &mut dyn TypeFolder<Interner, Error = Self::Error> {
+                self
+            }
+
+            fn interner(&self) -> Interner {
+                Interner
+            }
+
+            fn fold_inference_ty(
+                &mut self,
+                var: chalk_ir::InferenceVar,
+                kind: TyVariableKind,
+                _outer_binder: chalk_ir::DebruijnIndex,
+            ) -> chalk_ir::Fallible<chalk_ir::Ty<Interner>> {
+                Ok(if var < self.highest_known_var {
+                    var.to_ty(Interner, kind)
+                } else {
+                    self.table.new_type_var()
+                })
+            }
+
+            fn fold_inference_lifetime(
+                &mut self,
+                var: chalk_ir::InferenceVar,
+                _outer_binder: chalk_ir::DebruijnIndex,
+            ) -> chalk_ir::Fallible<chalk_ir::Lifetime<Interner>> {
+                Ok(if var < self.highest_known_var {
+                    var.to_lifetime(Interner)
+                } else {
+                    self.table.new_lifetime_var()
+                })
+            }
+
+            fn fold_inference_const(
+                &mut self,
+                ty: chalk_ir::Ty<Interner>,
+                var: chalk_ir::InferenceVar,
+                _outer_binder: chalk_ir::DebruijnIndex,
+            ) -> chalk_ir::Fallible<chalk_ir::Const<Interner>> {
+                Ok(if var < self.highest_known_var {
+                    var.to_const(Interner, ty)
+                } else {
+                    self.table.new_const_var(ty)
+                })
+            }
+        }
+
+        let snapshot = self.snapshot();
+        let highest_known_var = self.new_type_var().inference_var(Interner).expect("inference_var");
+        let result = f(self);
+        self.rollback_to(snapshot);
+        result
+            .fold_with(&mut VarFudger { table: self, highest_known_var }, DebruijnIndex::INNERMOST)
+            .expect("fold_with with VarFudger")
+    }
+
+    /// This checks whether any of the free variables in the `canonicalized`
+    /// have changed (either been unified with another variable, or with a
+    /// value). If this is not the case, we don't need to try to solve the goal
+    /// again -- it'll give the same result as last time.
+    fn check_changed(&mut self, canonicalized: &Canonicalized<InEnvironment<Goal>>) -> bool {
+        canonicalized.free_vars.iter().any(|var| {
+            let iv = match var.data(Interner) {
+                chalk_ir::GenericArgData::Ty(ty) => ty.inference_var(Interner),
+                chalk_ir::GenericArgData::Lifetime(lt) => lt.inference_var(Interner),
+                chalk_ir::GenericArgData::Const(c) => c.inference_var(Interner),
+            }
+            .expect("free var is not inference var");
+            if self.var_unification_table.probe_var(iv).is_some() {
+                return true;
+            }
+            let root = self.var_unification_table.inference_var_root(iv);
+            iv != root
+        })
+    }
+
+    fn try_resolve_obligation(
+        &mut self,
+        canonicalized: &Canonicalized<InEnvironment<Goal>>,
+    ) -> bool {
+        let solution = self.db.trait_solve(self.trait_env.krate, canonicalized.value.clone());
+
+        match solution {
+            Some(Solution::Unique(canonical_subst)) => {
+                canonicalized.apply_solution(
+                    self,
+                    Canonical {
+                        binders: canonical_subst.binders,
+                        // FIXME: handle constraints
+                        value: canonical_subst.value.subst,
+                    },
+                );
+                true
+            }
+            Some(Solution::Ambig(Guidance::Definite(substs))) => {
+                canonicalized.apply_solution(self, substs);
+                false
+            }
+            Some(_) => {
+                // FIXME use this when trying to resolve everything at the end
+                false
+            }
+            None => {
+                // FIXME obligation cannot be fulfilled => diagnostic
+                true
+            }
+        }
+    }
+
+    pub(crate) fn callable_sig(&mut self, ty: &Ty, num_args: usize) -> Option<(Vec<Ty>, Ty)> {
+        match ty.callable_sig(self.db) {
+            Some(sig) => Some((sig.params().to_vec(), sig.ret().clone())),
+            None => self.callable_sig_from_fn_trait(ty, num_args),
+        }
+    }
+
+    fn callable_sig_from_fn_trait(&mut self, ty: &Ty, num_args: usize) -> Option<(Vec<Ty>, Ty)> {
+        let krate = self.trait_env.krate;
+        let fn_once_trait = FnTrait::FnOnce.get_id(self.db, krate)?;
+        let output_assoc_type =
+            self.db.trait_data(fn_once_trait).associated_type_by_name(&name![Output])?;
+
+        let mut arg_tys = vec![];
+        let arg_ty = TyBuilder::tuple(num_args)
+            .fill(|x| {
+                let arg = match x {
+                    ParamKind::Type => self.new_type_var(),
+                    ParamKind::Const(ty) => {
+                        never!("Tuple with const parameter");
+                        return GenericArgData::Const(self.new_const_var(ty.clone()))
+                            .intern(Interner);
+                    }
+                };
+                arg_tys.push(arg.clone());
+                GenericArgData::Ty(arg).intern(Interner)
+            })
+            .build();
+
+        let projection = {
+            let b = TyBuilder::assoc_type_projection(self.db, output_assoc_type);
+            if b.remaining() != 2 {
+                return None;
+            }
+            b.push(ty.clone()).push(arg_ty).build()
+        };
+
+        let trait_env = self.trait_env.env.clone();
+        let obligation = InEnvironment {
+            goal: projection.trait_ref(self.db).cast(Interner),
+            environment: trait_env,
+        };
+        let canonical = self.canonicalize(obligation.clone());
+        if self.db.trait_solve(krate, canonical.value.cast(Interner)).is_some() {
+            self.register_obligation(obligation.goal);
+            let return_ty = self.normalize_projection_ty(projection);
+            Some((arg_tys, return_ty))
+        } else {
+            None
+        }
+    }
+}
+
+impl<'a> fmt::Debug for InferenceTable<'a> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("InferenceTable").field("num_vars", &self.type_variable_table.len()).finish()
+    }
+}
+
+mod resolve {
+    use super::InferenceTable;
+    use crate::{
+        ConcreteConst, Const, ConstData, ConstValue, DebruijnIndex, GenericArg, InferenceVar,
+        Interner, Lifetime, Ty, TyVariableKind, VariableKind,
+    };
+    use chalk_ir::{
+        cast::Cast,
+        fold::{TypeFoldable, TypeFolder},
+        Fallible, NoSolution,
+    };
+    use hir_def::type_ref::ConstScalar;
+
+    pub(super) struct Resolver<'a, 'b, F> {
+        pub(super) table: &'a mut InferenceTable<'b>,
+        pub(super) var_stack: &'a mut Vec<InferenceVar>,
+        pub(super) fallback: F,
+    }
+    impl<'a, 'b, 'i, F> TypeFolder<Interner> for Resolver<'a, 'b, F>
+    where
+        F: Fn(InferenceVar, VariableKind, GenericArg, DebruijnIndex) -> GenericArg + 'i,
+    {
+        type Error = NoSolution;
+
+        fn as_dyn(&mut self) -> &mut dyn TypeFolder<Interner, Error = Self::Error> {
+            self
+        }
+
+        fn interner(&self) -> Interner {
+            Interner
+        }
+
+        fn fold_inference_ty(
+            &mut self,
+            var: InferenceVar,
+            kind: TyVariableKind,
+            outer_binder: DebruijnIndex,
+        ) -> Fallible<Ty> {
+            let var = self.table.var_unification_table.inference_var_root(var);
+            if self.var_stack.contains(&var) {
+                // recursive type
+                let default = self.table.fallback_value(var, kind).cast(Interner);
+                return Ok((self.fallback)(var, VariableKind::Ty(kind), default, outer_binder)
+                    .assert_ty_ref(Interner)
+                    .clone());
+            }
+            let result = if let Some(known_ty) = self.table.var_unification_table.probe_var(var) {
+                // known_ty may contain other variables that are known by now
+                self.var_stack.push(var);
+                let result =
+                    known_ty.fold_with(self, outer_binder).expect("fold failed unexpectedly");
+                self.var_stack.pop();
+                result.assert_ty_ref(Interner).clone()
+            } else {
+                let default = self.table.fallback_value(var, kind).cast(Interner);
+                (self.fallback)(var, VariableKind::Ty(kind), default, outer_binder)
+                    .assert_ty_ref(Interner)
+                    .clone()
+            };
+            Ok(result)
+        }
+
+        fn fold_inference_const(
+            &mut self,
+            ty: Ty,
+            var: InferenceVar,
+            outer_binder: DebruijnIndex,
+        ) -> Fallible<Const> {
+            let var = self.table.var_unification_table.inference_var_root(var);
+            let default = ConstData {
+                ty: ty.clone(),
+                value: ConstValue::Concrete(ConcreteConst { interned: ConstScalar::Unknown }),
+            }
+            .intern(Interner)
+            .cast(Interner);
+            if self.var_stack.contains(&var) {
+                // recursive
+                return Ok((self.fallback)(var, VariableKind::Const(ty), default, outer_binder)
+                    .assert_const_ref(Interner)
+                    .clone());
+            }
+            let result = if let Some(known_ty) = self.table.var_unification_table.probe_var(var) {
+                // known_ty may contain other variables that are known by now
+                self.var_stack.push(var);
+                let result =
+                    known_ty.fold_with(self, outer_binder).expect("fold failed unexpectedly");
+                self.var_stack.pop();
+                result.assert_const_ref(Interner).clone()
+            } else {
+                (self.fallback)(var, VariableKind::Const(ty), default, outer_binder)
+                    .assert_const_ref(Interner)
+                    .clone()
+            };
+            Ok(result)
+        }
+
+        fn fold_inference_lifetime(
+            &mut self,
+            _var: InferenceVar,
+            _outer_binder: DebruijnIndex,
+        ) -> Fallible<Lifetime> {
+            // fall back all lifetimes to 'static -- currently we don't deal
+            // with any lifetimes, but we can sometimes get some lifetime
+            // variables through Chalk's unification, and this at least makes
+            // sure we don't leak them outside of inference
+            Ok(crate::static_lifetime())
+        }
+    }
+}