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Diffstat (limited to 'compiler/rustc_typeck/src/expr_use_visitor.rs')
| -rw-r--r-- | compiler/rustc_typeck/src/expr_use_visitor.rs | 914 |
1 files changed, 914 insertions, 0 deletions
diff --git a/compiler/rustc_typeck/src/expr_use_visitor.rs b/compiler/rustc_typeck/src/expr_use_visitor.rs new file mode 100644 index 000000000..74a5b6e42 --- /dev/null +++ b/compiler/rustc_typeck/src/expr_use_visitor.rs @@ -0,0 +1,914 @@ +//! A different sort of visitor for walking fn bodies. Unlike the +//! normal visitor, which just walks the entire body in one shot, the +//! `ExprUseVisitor` determines how expressions are being used. + +use std::slice::from_ref; + +use hir::def::DefKind; +use hir::Expr; +// Export these here so that Clippy can use them. +pub use rustc_middle::hir::place::{Place, PlaceBase, PlaceWithHirId, Projection}; + +use rustc_data_structures::fx::FxIndexMap; +use rustc_hir as hir; +use rustc_hir::def::Res; +use rustc_hir::def_id::LocalDefId; +use rustc_hir::PatKind; +use rustc_index::vec::Idx; +use rustc_infer::infer::InferCtxt; +use rustc_middle::hir::place::ProjectionKind; +use rustc_middle::mir::FakeReadCause; +use rustc_middle::ty::{self, adjustment, AdtKind, Ty, TyCtxt}; +use rustc_target::abi::VariantIdx; +use ty::BorrowKind::ImmBorrow; + +use crate::mem_categorization as mc; + +/// This trait defines the callbacks you can expect to receive when +/// employing the ExprUseVisitor. +pub trait Delegate<'tcx> { + /// The value found at `place` is moved, depending + /// on `mode`. Where `diag_expr_id` is the id used for diagnostics for `place`. + /// + /// Use of a `Copy` type in a ByValue context is considered a use + /// by `ImmBorrow` and `borrow` is called instead. This is because + /// a shared borrow is the "minimum access" that would be needed + /// to perform a copy. + /// + /// + /// The parameter `diag_expr_id` indicates the HIR id that ought to be used for + /// diagnostics. Around pattern matching such as `let pat = expr`, the diagnostic + /// id will be the id of the expression `expr` but the place itself will have + /// the id of the binding in the pattern `pat`. + fn consume(&mut self, place_with_id: &PlaceWithHirId<'tcx>, diag_expr_id: hir::HirId); + + /// The value found at `place` is being borrowed with kind `bk`. + /// `diag_expr_id` is the id used for diagnostics (see `consume` for more details). + fn borrow( + &mut self, + place_with_id: &PlaceWithHirId<'tcx>, + diag_expr_id: hir::HirId, + bk: ty::BorrowKind, + ); + + /// The value found at `place` is being copied. + /// `diag_expr_id` is the id used for diagnostics (see `consume` for more details). + fn copy(&mut self, place_with_id: &PlaceWithHirId<'tcx>, diag_expr_id: hir::HirId) { + // In most cases, copying data from `x` is equivalent to doing `*&x`, so by default + // we treat a copy of `x` as a borrow of `x`. + self.borrow(place_with_id, diag_expr_id, ty::BorrowKind::ImmBorrow) + } + + /// The path at `assignee_place` is being assigned to. + /// `diag_expr_id` is the id used for diagnostics (see `consume` for more details). + fn mutate(&mut self, assignee_place: &PlaceWithHirId<'tcx>, diag_expr_id: hir::HirId); + + /// The path at `binding_place` is a binding that is being initialized. + /// + /// This covers cases such as `let x = 42;` + fn bind(&mut self, binding_place: &PlaceWithHirId<'tcx>, diag_expr_id: hir::HirId) { + // Bindings can normally be treated as a regular assignment, so by default we + // forward this to the mutate callback. + self.mutate(binding_place, diag_expr_id) + } + + /// The `place` should be a fake read because of specified `cause`. + fn fake_read( + &mut self, + place_with_id: &PlaceWithHirId<'tcx>, + cause: FakeReadCause, + diag_expr_id: hir::HirId, + ); +} + +#[derive(Copy, Clone, PartialEq, Debug)] +enum ConsumeMode { + /// reference to x where x has a type that copies + Copy, + /// reference to x where x has a type that moves + Move, +} + +#[derive(Copy, Clone, PartialEq, Debug)] +pub enum MutateMode { + Init, + /// Example: `x = y` + JustWrite, + /// Example: `x += y` + WriteAndRead, +} + +/// The ExprUseVisitor type +/// +/// This is the code that actually walks the tree. +pub struct ExprUseVisitor<'a, 'tcx> { + mc: mc::MemCategorizationContext<'a, 'tcx>, + body_owner: LocalDefId, + delegate: &'a mut dyn Delegate<'tcx>, +} + +/// If the MC results in an error, it's because the type check +/// failed (or will fail, when the error is uncovered and reported +/// during writeback). In this case, we just ignore this part of the +/// code. +/// +/// Note that this macro appears similar to try!(), but, unlike try!(), +/// it does not propagate the error. +macro_rules! return_if_err { + ($inp: expr) => { + match $inp { + Ok(v) => v, + Err(()) => { + debug!("mc reported err"); + return; + } + } + }; +} + +impl<'a, 'tcx> ExprUseVisitor<'a, 'tcx> { + /// Creates the ExprUseVisitor, configuring it with the various options provided: + /// + /// - `delegate` -- who receives the callbacks + /// - `param_env` --- parameter environment for trait lookups (esp. pertaining to `Copy`) + /// - `typeck_results` --- typeck results for the code being analyzed + pub fn new( + delegate: &'a mut (dyn Delegate<'tcx> + 'a), + infcx: &'a InferCtxt<'a, 'tcx>, + body_owner: LocalDefId, + param_env: ty::ParamEnv<'tcx>, + typeck_results: &'a ty::TypeckResults<'tcx>, + ) -> Self { + ExprUseVisitor { + mc: mc::MemCategorizationContext::new(infcx, param_env, body_owner, typeck_results), + body_owner, + delegate, + } + } + + #[instrument(skip(self), level = "debug")] + pub fn consume_body(&mut self, body: &hir::Body<'_>) { + for param in body.params { + let param_ty = return_if_err!(self.mc.pat_ty_adjusted(param.pat)); + debug!("consume_body: param_ty = {:?}", param_ty); + + let param_place = self.mc.cat_rvalue(param.hir_id, param.pat.span, param_ty); + + self.walk_irrefutable_pat(¶m_place, param.pat); + } + + self.consume_expr(&body.value); + } + + fn tcx(&self) -> TyCtxt<'tcx> { + self.mc.tcx() + } + + fn delegate_consume(&mut self, place_with_id: &PlaceWithHirId<'tcx>, diag_expr_id: hir::HirId) { + delegate_consume(&self.mc, self.delegate, place_with_id, diag_expr_id) + } + + fn consume_exprs(&mut self, exprs: &[hir::Expr<'_>]) { + for expr in exprs { + self.consume_expr(expr); + } + } + + pub fn consume_expr(&mut self, expr: &hir::Expr<'_>) { + debug!("consume_expr(expr={:?})", expr); + + let place_with_id = return_if_err!(self.mc.cat_expr(expr)); + self.delegate_consume(&place_with_id, place_with_id.hir_id); + self.walk_expr(expr); + } + + fn mutate_expr(&mut self, expr: &hir::Expr<'_>) { + let place_with_id = return_if_err!(self.mc.cat_expr(expr)); + self.delegate.mutate(&place_with_id, place_with_id.hir_id); + self.walk_expr(expr); + } + + fn borrow_expr(&mut self, expr: &hir::Expr<'_>, bk: ty::BorrowKind) { + debug!("borrow_expr(expr={:?}, bk={:?})", expr, bk); + + let place_with_id = return_if_err!(self.mc.cat_expr(expr)); + self.delegate.borrow(&place_with_id, place_with_id.hir_id, bk); + + self.walk_expr(expr) + } + + fn select_from_expr(&mut self, expr: &hir::Expr<'_>) { + self.walk_expr(expr) + } + + pub fn walk_expr(&mut self, expr: &hir::Expr<'_>) { + debug!("walk_expr(expr={:?})", expr); + + self.walk_adjustment(expr); + + match expr.kind { + hir::ExprKind::Path(_) => {} + + hir::ExprKind::Type(subexpr, _) => self.walk_expr(subexpr), + + hir::ExprKind::Unary(hir::UnOp::Deref, base) => { + // *base + self.select_from_expr(base); + } + + hir::ExprKind::Field(base, _) => { + // base.f + self.select_from_expr(base); + } + + hir::ExprKind::Index(lhs, rhs) => { + // lhs[rhs] + self.select_from_expr(lhs); + self.consume_expr(rhs); + } + + hir::ExprKind::Call(callee, args) => { + // callee(args) + self.consume_expr(callee); + self.consume_exprs(args); + } + + hir::ExprKind::MethodCall(.., args, _) => { + // callee.m(args) + self.consume_exprs(args); + } + + hir::ExprKind::Struct(_, fields, ref opt_with) => { + self.walk_struct_expr(fields, opt_with); + } + + hir::ExprKind::Tup(exprs) => { + self.consume_exprs(exprs); + } + + hir::ExprKind::If(ref cond_expr, ref then_expr, ref opt_else_expr) => { + self.consume_expr(cond_expr); + self.consume_expr(then_expr); + if let Some(ref else_expr) = *opt_else_expr { + self.consume_expr(else_expr); + } + } + + hir::ExprKind::Let(hir::Let { pat, init, .. }) => { + self.walk_local(init, pat, None, |t| t.borrow_expr(init, ty::ImmBorrow)) + } + + hir::ExprKind::Match(ref discr, arms, _) => { + let discr_place = return_if_err!(self.mc.cat_expr(discr)); + self.maybe_read_scrutinee( + discr, + discr_place.clone(), + arms.iter().map(|arm| arm.pat), + ); + + // treatment of the discriminant is handled while walking the arms. + for arm in arms { + self.walk_arm(&discr_place, arm); + } + } + + hir::ExprKind::Array(exprs) => { + self.consume_exprs(exprs); + } + + hir::ExprKind::AddrOf(_, m, ref base) => { + // &base + // make sure that the thing we are pointing out stays valid + // for the lifetime `scope_r` of the resulting ptr: + let bk = ty::BorrowKind::from_mutbl(m); + self.borrow_expr(base, bk); + } + + hir::ExprKind::InlineAsm(asm) => { + for (op, _op_sp) in asm.operands { + match op { + hir::InlineAsmOperand::In { expr, .. } => self.consume_expr(expr), + hir::InlineAsmOperand::Out { expr: Some(expr), .. } + | hir::InlineAsmOperand::InOut { expr, .. } => { + self.mutate_expr(expr); + } + hir::InlineAsmOperand::SplitInOut { in_expr, out_expr, .. } => { + self.consume_expr(in_expr); + if let Some(out_expr) = out_expr { + self.mutate_expr(out_expr); + } + } + hir::InlineAsmOperand::Out { expr: None, .. } + | hir::InlineAsmOperand::Const { .. } + | hir::InlineAsmOperand::SymFn { .. } + | hir::InlineAsmOperand::SymStatic { .. } => {} + } + } + } + + hir::ExprKind::Continue(..) + | hir::ExprKind::Lit(..) + | hir::ExprKind::ConstBlock(..) + | hir::ExprKind::Err => {} + + hir::ExprKind::Loop(blk, ..) => { + self.walk_block(blk); + } + + hir::ExprKind::Unary(_, lhs) => { + self.consume_expr(lhs); + } + + hir::ExprKind::Binary(_, lhs, rhs) => { + self.consume_expr(lhs); + self.consume_expr(rhs); + } + + hir::ExprKind::Block(blk, _) => { + self.walk_block(blk); + } + + hir::ExprKind::Break(_, ref opt_expr) | hir::ExprKind::Ret(ref opt_expr) => { + if let Some(expr) = *opt_expr { + self.consume_expr(expr); + } + } + + hir::ExprKind::Assign(lhs, rhs, _) => { + self.mutate_expr(lhs); + self.consume_expr(rhs); + } + + hir::ExprKind::Cast(base, _) => { + self.consume_expr(base); + } + + hir::ExprKind::DropTemps(expr) => { + self.consume_expr(expr); + } + + hir::ExprKind::AssignOp(_, lhs, rhs) => { + if self.mc.typeck_results.is_method_call(expr) { + self.consume_expr(lhs); + } else { + self.mutate_expr(lhs); + } + self.consume_expr(rhs); + } + + hir::ExprKind::Repeat(base, _) => { + self.consume_expr(base); + } + + hir::ExprKind::Closure { .. } => { + self.walk_captures(expr); + } + + hir::ExprKind::Box(ref base) => { + self.consume_expr(base); + } + + hir::ExprKind::Yield(value, _) => { + self.consume_expr(value); + } + } + } + + fn walk_stmt(&mut self, stmt: &hir::Stmt<'_>) { + match stmt.kind { + hir::StmtKind::Local(hir::Local { pat, init: Some(expr), els, .. }) => { + self.walk_local(expr, pat, *els, |_| {}) + } + + hir::StmtKind::Local(_) => {} + + hir::StmtKind::Item(_) => { + // We don't visit nested items in this visitor, + // only the fn body we were given. + } + + hir::StmtKind::Expr(ref expr) | hir::StmtKind::Semi(ref expr) => { + self.consume_expr(expr); + } + } + } + + fn maybe_read_scrutinee<'t>( + &mut self, + discr: &Expr<'_>, + discr_place: PlaceWithHirId<'tcx>, + pats: impl Iterator<Item = &'t hir::Pat<'t>>, + ) { + // Matching should not always be considered a use of the place, hence + // discr does not necessarily need to be borrowed. + // We only want to borrow discr if the pattern contain something other + // than wildcards. + let ExprUseVisitor { ref mc, body_owner: _, delegate: _ } = *self; + let mut needs_to_be_read = false; + for pat in pats { + return_if_err!(mc.cat_pattern(discr_place.clone(), pat, |place, pat| { + match &pat.kind { + PatKind::Binding(.., opt_sub_pat) => { + // If the opt_sub_pat is None, than the binding does not count as + // a wildcard for the purpose of borrowing discr. + if opt_sub_pat.is_none() { + needs_to_be_read = true; + } + } + PatKind::Path(qpath) => { + // A `Path` pattern is just a name like `Foo`. This is either a + // named constant or else it refers to an ADT variant + + let res = self.mc.typeck_results.qpath_res(qpath, pat.hir_id); + match res { + Res::Def(DefKind::Const, _) | Res::Def(DefKind::AssocConst, _) => { + // Named constants have to be equated with the value + // being matched, so that's a read of the value being matched. + // + // FIXME: We don't actually reads for ZSTs. + needs_to_be_read = true; + } + _ => { + // Otherwise, this is a struct/enum variant, and so it's + // only a read if we need to read the discriminant. + needs_to_be_read |= is_multivariant_adt(place.place.ty()); + } + } + } + PatKind::TupleStruct(..) | PatKind::Struct(..) | PatKind::Tuple(..) => { + // For `Foo(..)`, `Foo { ... }` and `(...)` patterns, check if we are matching + // against a multivariant enum or struct. In that case, we have to read + // the discriminant. Otherwise this kind of pattern doesn't actually + // read anything (we'll get invoked for the `...`, which may indeed + // perform some reads). + + let place_ty = place.place.ty(); + needs_to_be_read |= is_multivariant_adt(place_ty); + } + PatKind::Lit(_) | PatKind::Range(..) => { + // If the PatKind is a Lit or a Range then we want + // to borrow discr. + needs_to_be_read = true; + } + PatKind::Or(_) + | PatKind::Box(_) + | PatKind::Slice(..) + | PatKind::Ref(..) + | PatKind::Wild => { + // If the PatKind is Or, Box, Slice or Ref, the decision is made later + // as these patterns contains subpatterns + // If the PatKind is Wild, the decision is made based on the other patterns being + // examined + } + } + })); + } + + if needs_to_be_read { + self.borrow_expr(discr, ty::ImmBorrow); + } else { + let closure_def_id = match discr_place.place.base { + PlaceBase::Upvar(upvar_id) => Some(upvar_id.closure_expr_id), + _ => None, + }; + + self.delegate.fake_read( + &discr_place, + FakeReadCause::ForMatchedPlace(closure_def_id), + discr_place.hir_id, + ); + + // We always want to walk the discriminant. We want to make sure, for instance, + // that the discriminant has been initialized. + self.walk_expr(discr); + } + } + + fn walk_local<F>( + &mut self, + expr: &hir::Expr<'_>, + pat: &hir::Pat<'_>, + els: Option<&hir::Block<'_>>, + mut f: F, + ) where + F: FnMut(&mut Self), + { + self.walk_expr(expr); + let expr_place = return_if_err!(self.mc.cat_expr(expr)); + f(self); + if let Some(els) = els { + // borrowing because we need to test the descriminant + self.maybe_read_scrutinee(expr, expr_place.clone(), from_ref(pat).iter()); + self.walk_block(els) + } + self.walk_irrefutable_pat(&expr_place, &pat); + } + + /// Indicates that the value of `blk` will be consumed, meaning either copied or moved + /// depending on its type. + fn walk_block(&mut self, blk: &hir::Block<'_>) { + debug!("walk_block(blk.hir_id={})", blk.hir_id); + + for stmt in blk.stmts { + self.walk_stmt(stmt); + } + + if let Some(ref tail_expr) = blk.expr { + self.consume_expr(tail_expr); + } + } + + fn walk_struct_expr<'hir>( + &mut self, + fields: &[hir::ExprField<'_>], + opt_with: &Option<&'hir hir::Expr<'_>>, + ) { + // Consume the expressions supplying values for each field. + for field in fields { + self.consume_expr(field.expr); + } + + let with_expr = match *opt_with { + Some(w) => &*w, + None => { + return; + } + }; + + let with_place = return_if_err!(self.mc.cat_expr(with_expr)); + + // Select just those fields of the `with` + // expression that will actually be used + match with_place.place.ty().kind() { + ty::Adt(adt, substs) if adt.is_struct() => { + // Consume those fields of the with expression that are needed. + for (f_index, with_field) in adt.non_enum_variant().fields.iter().enumerate() { + let is_mentioned = fields.iter().any(|f| { + self.tcx().field_index(f.hir_id, self.mc.typeck_results) == f_index + }); + if !is_mentioned { + let field_place = self.mc.cat_projection( + &*with_expr, + with_place.clone(), + with_field.ty(self.tcx(), substs), + ProjectionKind::Field(f_index as u32, VariantIdx::new(0)), + ); + self.delegate_consume(&field_place, field_place.hir_id); + } + } + } + _ => { + // the base expression should always evaluate to a + // struct; however, when EUV is run during typeck, it + // may not. This will generate an error earlier in typeck, + // so we can just ignore it. + if !self.tcx().sess.has_errors().is_some() { + span_bug!(with_expr.span, "with expression doesn't evaluate to a struct"); + } + } + } + + // walk the with expression so that complex expressions + // are properly handled. + self.walk_expr(with_expr); + } + + /// Invoke the appropriate delegate calls for anything that gets + /// consumed or borrowed as part of the automatic adjustment + /// process. + fn walk_adjustment(&mut self, expr: &hir::Expr<'_>) { + let adjustments = self.mc.typeck_results.expr_adjustments(expr); + let mut place_with_id = return_if_err!(self.mc.cat_expr_unadjusted(expr)); + for adjustment in adjustments { + debug!("walk_adjustment expr={:?} adj={:?}", expr, adjustment); + match adjustment.kind { + adjustment::Adjust::NeverToAny | adjustment::Adjust::Pointer(_) => { + // Creating a closure/fn-pointer or unsizing consumes + // the input and stores it into the resulting rvalue. + self.delegate_consume(&place_with_id, place_with_id.hir_id); + } + + adjustment::Adjust::Deref(None) => {} + + // Autoderefs for overloaded Deref calls in fact reference + // their receiver. That is, if we have `(*x)` where `x` + // is of type `Rc<T>`, then this in fact is equivalent to + // `x.deref()`. Since `deref()` is declared with `&self`, + // this is an autoref of `x`. + adjustment::Adjust::Deref(Some(ref deref)) => { + let bk = ty::BorrowKind::from_mutbl(deref.mutbl); + self.delegate.borrow(&place_with_id, place_with_id.hir_id, bk); + } + + adjustment::Adjust::Borrow(ref autoref) => { + self.walk_autoref(expr, &place_with_id, autoref); + } + } + place_with_id = + return_if_err!(self.mc.cat_expr_adjusted(expr, place_with_id, adjustment)); + } + } + + /// Walks the autoref `autoref` applied to the autoderef'd + /// `expr`. `base_place` is the mem-categorized form of `expr` + /// after all relevant autoderefs have occurred. + fn walk_autoref( + &mut self, + expr: &hir::Expr<'_>, + base_place: &PlaceWithHirId<'tcx>, + autoref: &adjustment::AutoBorrow<'tcx>, + ) { + debug!( + "walk_autoref(expr.hir_id={} base_place={:?} autoref={:?})", + expr.hir_id, base_place, autoref + ); + + match *autoref { + adjustment::AutoBorrow::Ref(_, m) => { + self.delegate.borrow( + base_place, + base_place.hir_id, + ty::BorrowKind::from_mutbl(m.into()), + ); + } + + adjustment::AutoBorrow::RawPtr(m) => { + debug!("walk_autoref: expr.hir_id={} base_place={:?}", expr.hir_id, base_place); + + self.delegate.borrow(base_place, base_place.hir_id, ty::BorrowKind::from_mutbl(m)); + } + } + } + + fn walk_arm(&mut self, discr_place: &PlaceWithHirId<'tcx>, arm: &hir::Arm<'_>) { + let closure_def_id = match discr_place.place.base { + PlaceBase::Upvar(upvar_id) => Some(upvar_id.closure_expr_id), + _ => None, + }; + + self.delegate.fake_read( + discr_place, + FakeReadCause::ForMatchedPlace(closure_def_id), + discr_place.hir_id, + ); + self.walk_pat(discr_place, arm.pat, arm.guard.is_some()); + + if let Some(hir::Guard::If(e)) = arm.guard { + self.consume_expr(e) + } else if let Some(hir::Guard::IfLet(ref l)) = arm.guard { + self.consume_expr(l.init) + } + + self.consume_expr(arm.body); + } + + /// Walks a pat that occurs in isolation (i.e., top-level of fn argument or + /// let binding, and *not* a match arm or nested pat.) + fn walk_irrefutable_pat(&mut self, discr_place: &PlaceWithHirId<'tcx>, pat: &hir::Pat<'_>) { + let closure_def_id = match discr_place.place.base { + PlaceBase::Upvar(upvar_id) => Some(upvar_id.closure_expr_id), + _ => None, + }; + + self.delegate.fake_read( + discr_place, + FakeReadCause::ForLet(closure_def_id), + discr_place.hir_id, + ); + self.walk_pat(discr_place, pat, false); + } + + /// The core driver for walking a pattern + fn walk_pat( + &mut self, + discr_place: &PlaceWithHirId<'tcx>, + pat: &hir::Pat<'_>, + has_guard: bool, + ) { + debug!("walk_pat(discr_place={:?}, pat={:?}, has_guard={:?})", discr_place, pat, has_guard); + + let tcx = self.tcx(); + let ExprUseVisitor { ref mc, body_owner: _, ref mut delegate } = *self; + return_if_err!(mc.cat_pattern(discr_place.clone(), pat, |place, pat| { + if let PatKind::Binding(_, canonical_id, ..) = pat.kind { + debug!("walk_pat: binding place={:?} pat={:?}", place, pat); + if let Some(bm) = + mc.typeck_results.extract_binding_mode(tcx.sess, pat.hir_id, pat.span) + { + debug!("walk_pat: pat.hir_id={:?} bm={:?}", pat.hir_id, bm); + + // pat_ty: the type of the binding being produced. + let pat_ty = return_if_err!(mc.node_ty(pat.hir_id)); + debug!("walk_pat: pat_ty={:?}", pat_ty); + + let def = Res::Local(canonical_id); + if let Ok(ref binding_place) = mc.cat_res(pat.hir_id, pat.span, pat_ty, def) { + delegate.bind(binding_place, binding_place.hir_id); + } + + // Subtle: MIR desugaring introduces immutable borrows for each pattern + // binding when lowering pattern guards to ensure that the guard does not + // modify the scrutinee. + if has_guard { + delegate.borrow(place, discr_place.hir_id, ImmBorrow); + } + + // It is also a borrow or copy/move of the value being matched. + // In a cases of pattern like `let pat = upvar`, don't use the span + // of the pattern, as this just looks confusing, instead use the span + // of the discriminant. + match bm { + ty::BindByReference(m) => { + let bk = ty::BorrowKind::from_mutbl(m); + delegate.borrow(place, discr_place.hir_id, bk); + } + ty::BindByValue(..) => { + debug!("walk_pat binding consuming pat"); + delegate_consume(mc, *delegate, place, discr_place.hir_id); + } + } + } + } + })); + } + + /// Handle the case where the current body contains a closure. + /// + /// When the current body being handled is a closure, then we must make sure that + /// - The parent closure only captures Places from the nested closure that are not local to it. + /// + /// In the following example the closures `c` only captures `p.x` even though `incr` + /// is a capture of the nested closure + /// + /// ``` + /// struct P { x: i32 } + /// let mut p = P { x: 4 }; + /// let c = || { + /// let incr = 10; + /// let nested = || p.x += incr; + /// }; + /// ``` + /// + /// - When reporting the Place back to the Delegate, ensure that the UpvarId uses the enclosing + /// closure as the DefId. + fn walk_captures(&mut self, closure_expr: &hir::Expr<'_>) { + fn upvar_is_local_variable<'tcx>( + upvars: Option<&'tcx FxIndexMap<hir::HirId, hir::Upvar>>, + upvar_id: hir::HirId, + body_owner_is_closure: bool, + ) -> bool { + upvars.map(|upvars| !upvars.contains_key(&upvar_id)).unwrap_or(body_owner_is_closure) + } + + debug!("walk_captures({:?})", closure_expr); + + let tcx = self.tcx(); + let closure_def_id = tcx.hir().local_def_id(closure_expr.hir_id); + let upvars = tcx.upvars_mentioned(self.body_owner); + + // For purposes of this function, generator and closures are equivalent. + let body_owner_is_closure = + matches!(tcx.hir().body_owner_kind(self.body_owner), hir::BodyOwnerKind::Closure,); + + // If we have a nested closure, we want to include the fake reads present in the nested closure. + if let Some(fake_reads) = self.mc.typeck_results.closure_fake_reads.get(&closure_def_id) { + for (fake_read, cause, hir_id) in fake_reads.iter() { + match fake_read.base { + PlaceBase::Upvar(upvar_id) => { + if upvar_is_local_variable( + upvars, + upvar_id.var_path.hir_id, + body_owner_is_closure, + ) { + // The nested closure might be fake reading the current (enclosing) closure's local variables. + // The only places we want to fake read before creating the parent closure are the ones that + // are not local to it/ defined by it. + // + // ```rust,ignore(cannot-test-this-because-pseudo-code) + // let v1 = (0, 1); + // let c = || { // fake reads: v1 + // let v2 = (0, 1); + // let e = || { // fake reads: v1, v2 + // let (_, t1) = v1; + // let (_, t2) = v2; + // } + // } + // ``` + // This check is performed when visiting the body of the outermost closure (`c`) and ensures + // that we don't add a fake read of v2 in c. + continue; + } + } + _ => { + bug!( + "Do not know how to get HirId out of Rvalue and StaticItem {:?}", + fake_read.base + ); + } + }; + self.delegate.fake_read( + &PlaceWithHirId { place: fake_read.clone(), hir_id: *hir_id }, + *cause, + *hir_id, + ); + } + } + + if let Some(min_captures) = self.mc.typeck_results.closure_min_captures.get(&closure_def_id) + { + for (var_hir_id, min_list) in min_captures.iter() { + if upvars.map_or(body_owner_is_closure, |upvars| !upvars.contains_key(var_hir_id)) { + // The nested closure might be capturing the current (enclosing) closure's local variables. + // We check if the root variable is ever mentioned within the enclosing closure, if not + // then for the current body (if it's a closure) these aren't captures, we will ignore them. + continue; + } + for captured_place in min_list { + let place = &captured_place.place; + let capture_info = captured_place.info; + + let place_base = if body_owner_is_closure { + // Mark the place to be captured by the enclosing closure + PlaceBase::Upvar(ty::UpvarId::new(*var_hir_id, self.body_owner)) + } else { + // If the body owner isn't a closure then the variable must + // be a local variable + PlaceBase::Local(*var_hir_id) + }; + let place_with_id = PlaceWithHirId::new( + capture_info.path_expr_id.unwrap_or( + capture_info.capture_kind_expr_id.unwrap_or(closure_expr.hir_id), + ), + place.base_ty, + place_base, + place.projections.clone(), + ); + + match capture_info.capture_kind { + ty::UpvarCapture::ByValue => { + self.delegate_consume(&place_with_id, place_with_id.hir_id); + } + ty::UpvarCapture::ByRef(upvar_borrow) => { + self.delegate.borrow( + &place_with_id, + place_with_id.hir_id, + upvar_borrow, + ); + } + } + } + } + } + } +} + +fn copy_or_move<'a, 'tcx>( + mc: &mc::MemCategorizationContext<'a, 'tcx>, + place_with_id: &PlaceWithHirId<'tcx>, +) -> ConsumeMode { + if !mc.type_is_copy_modulo_regions( + place_with_id.place.ty(), + mc.tcx().hir().span(place_with_id.hir_id), + ) { + ConsumeMode::Move + } else { + ConsumeMode::Copy + } +} + +// - If a place is used in a `ByValue` context then move it if it's not a `Copy` type. +// - If the place that is a `Copy` type consider it an `ImmBorrow`. +fn delegate_consume<'a, 'tcx>( + mc: &mc::MemCategorizationContext<'a, 'tcx>, + delegate: &mut (dyn Delegate<'tcx> + 'a), + place_with_id: &PlaceWithHirId<'tcx>, + diag_expr_id: hir::HirId, +) { + debug!("delegate_consume(place_with_id={:?})", place_with_id); + + let mode = copy_or_move(mc, place_with_id); + + match mode { + ConsumeMode::Move => delegate.consume(place_with_id, diag_expr_id), + ConsumeMode::Copy => delegate.copy(place_with_id, diag_expr_id), + } +} + +fn is_multivariant_adt(ty: Ty<'_>) -> bool { + if let ty::Adt(def, _) = ty.kind() { + // Note that if a non-exhaustive SingleVariant is defined in another crate, we need + // to assume that more cases will be added to the variant in the future. This mean + // that we should handle non-exhaustive SingleVariant the same way we would handle + // a MultiVariant. + // If the variant is not local it must be defined in another crate. + let is_non_exhaustive = match def.adt_kind() { + AdtKind::Struct | AdtKind::Union => { + def.non_enum_variant().is_field_list_non_exhaustive() + } + AdtKind::Enum => def.is_variant_list_non_exhaustive(), + }; + def.variants().len() > 1 || (!def.did().is_local() && is_non_exhaustive) + } else { + false + } +} |