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+/*!
+
+# typeck: check phase
+
+Within the check phase of type check, we check each item one at a time
+(bodies of function expressions are checked as part of the containing
+function). Inference is used to supply types wherever they are unknown.
+
+By far the most complex case is checking the body of a function. This
+can be broken down into several distinct phases:
+
+- gather: creates type variables to represent the type of each local
+ variable and pattern binding.
+
+- main: the main pass does the lion's share of the work: it
+ determines the types of all expressions, resolves
+ methods, checks for most invalid conditions, and so forth. In
+ some cases, where a type is unknown, it may create a type or region
+ variable and use that as the type of an expression.
+
+ In the process of checking, various constraints will be placed on
+ these type variables through the subtyping relationships requested
+ through the `demand` module. The `infer` module is in charge
+ of resolving those constraints.
+
+- regionck: after main is complete, the regionck pass goes over all
+ types looking for regions and making sure that they did not escape
+ into places where they are not in scope. This may also influence the
+ final assignments of the various region variables if there is some
+ flexibility.
+
+- writeback: writes the final types within a function body, replacing
+ type variables with their final inferred types. These final types
+ are written into the `tcx.node_types` table, which should *never* contain
+ any reference to a type variable.
+
+## Intermediate types
+
+While type checking a function, the intermediate types for the
+expressions, blocks, and so forth contained within the function are
+stored in `fcx.node_types` and `fcx.node_substs`. These types
+may contain unresolved type variables. After type checking is
+complete, the functions in the writeback module are used to take the
+types from this table, resolve them, and then write them into their
+permanent home in the type context `tcx`.
+
+This means that during inferencing you should use `fcx.write_ty()`
+and `fcx.expr_ty()` / `fcx.node_ty()` to write/obtain the types of
+nodes within the function.
+
+The types of top-level items, which never contain unbound type
+variables, are stored directly into the `tcx` typeck_results.
+
+N.B., a type variable is not the same thing as a type parameter. A
+type variable is an instance of a type parameter. That is,
+given a generic function `fn foo<T>(t: T)`, while checking the
+function `foo`, the type `ty_param(0)` refers to the type `T`, which
+is treated in abstract. However, when `foo()` is called, `T` will be
+substituted for a fresh type variable `N`. This variable will
+eventually be resolved to some concrete type (which might itself be
+a type parameter).
+
+*/
+
+mod check;
+mod compare_method;
+pub mod dropck;
+pub mod intrinsic;
+pub mod intrinsicck;
+mod region;
+pub mod wfcheck;
+
+pub use check::check_abi;
+
+use check::check_mod_item_types;
+use rustc_data_structures::fx::{FxHashMap, FxHashSet};
+use rustc_errors::{pluralize, struct_span_err, Applicability, Diagnostic, DiagnosticBuilder};
+use rustc_hir as hir;
+use rustc_hir::def_id::{DefId, LocalDefId};
+use rustc_hir::intravisit::Visitor;
+use rustc_index::bit_set::BitSet;
+use rustc_middle::ty::query::Providers;
+use rustc_middle::ty::{self, Ty, TyCtxt};
+use rustc_middle::ty::{InternalSubsts, SubstsRef};
+use rustc_session::parse::feature_err;
+use rustc_span::source_map::DUMMY_SP;
+use rustc_span::symbol::{kw, Ident};
+use rustc_span::{self, BytePos, Span, Symbol};
+use rustc_target::abi::VariantIdx;
+use rustc_target::spec::abi::Abi;
+use rustc_trait_selection::traits::error_reporting::suggestions::ReturnsVisitor;
+use std::num::NonZeroU32;
+
+use crate::require_c_abi_if_c_variadic;
+use crate::util::common::indenter;
+
+use self::compare_method::collect_trait_impl_trait_tys;
+use self::region::region_scope_tree;
+
+pub fn provide(providers: &mut Providers) {
+ wfcheck::provide(providers);
+ *providers = Providers {
+ adt_destructor,
+ check_mod_item_types,
+ region_scope_tree,
+ collect_trait_impl_trait_tys,
+ compare_assoc_const_impl_item_with_trait_item: compare_method::raw_compare_const_impl,
+ ..*providers
+ };
+}
+
+fn adt_destructor(tcx: TyCtxt<'_>, def_id: DefId) -> Option<ty::Destructor> {
+ tcx.calculate_dtor(def_id, dropck::check_drop_impl)
+}
+
+/// Given a `DefId` for an opaque type in return position, find its parent item's return
+/// expressions.
+fn get_owner_return_paths<'tcx>(
+ tcx: TyCtxt<'tcx>,
+ def_id: LocalDefId,
+) -> Option<(LocalDefId, ReturnsVisitor<'tcx>)> {
+ let hir_id = tcx.hir().local_def_id_to_hir_id(def_id);
+ let parent_id = tcx.hir().get_parent_item(hir_id).def_id;
+ tcx.hir().find_by_def_id(parent_id).and_then(|node| node.body_id()).map(|body_id| {
+ let body = tcx.hir().body(body_id);
+ let mut visitor = ReturnsVisitor::default();
+ visitor.visit_body(body);
+ (parent_id, visitor)
+ })
+}
+
+/// Forbid defining intrinsics in Rust code,
+/// as they must always be defined by the compiler.
+// FIXME: Move this to a more appropriate place.
+pub fn fn_maybe_err(tcx: TyCtxt<'_>, sp: Span, abi: Abi) {
+ if let Abi::RustIntrinsic | Abi::PlatformIntrinsic = abi {
+ tcx.sess.span_err(sp, "intrinsic must be in `extern \"rust-intrinsic\" { ... }` block");
+ }
+}
+
+fn maybe_check_static_with_link_section(tcx: TyCtxt<'_>, id: LocalDefId) {
+ // Only restricted on wasm target for now
+ if !tcx.sess.target.is_like_wasm {
+ return;
+ }
+
+ // If `#[link_section]` is missing, then nothing to verify
+ let attrs = tcx.codegen_fn_attrs(id);
+ if attrs.link_section.is_none() {
+ return;
+ }
+
+ // For the wasm32 target statics with `#[link_section]` are placed into custom
+ // sections of the final output file, but this isn't link custom sections of
+ // other executable formats. Namely we can only embed a list of bytes,
+ // nothing with provenance (pointers to anything else). If any provenance
+ // show up, reject it here.
+ // `#[link_section]` may contain arbitrary, or even undefined bytes, but it is
+ // the consumer's responsibility to ensure all bytes that have been read
+ // have defined values.
+ if let Ok(alloc) = tcx.eval_static_initializer(id.to_def_id())
+ && alloc.inner().provenance().len() != 0
+ {
+ let msg = "statics with a custom `#[link_section]` must be a \
+ simple list of bytes on the wasm target with no \
+ extra levels of indirection such as references";
+ tcx.sess.span_err(tcx.def_span(id), msg);
+ }
+}
+
+fn report_forbidden_specialization(
+ tcx: TyCtxt<'_>,
+ impl_item: &hir::ImplItemRef,
+ parent_impl: DefId,
+) {
+ let mut err = struct_span_err!(
+ tcx.sess,
+ impl_item.span,
+ E0520,
+ "`{}` specializes an item from a parent `impl`, but \
+ that item is not marked `default`",
+ impl_item.ident
+ );
+ err.span_label(impl_item.span, format!("cannot specialize default item `{}`", impl_item.ident));
+
+ match tcx.span_of_impl(parent_impl) {
+ Ok(span) => {
+ err.span_label(span, "parent `impl` is here");
+ err.note(&format!(
+ "to specialize, `{}` in the parent `impl` must be marked `default`",
+ impl_item.ident
+ ));
+ }
+ Err(cname) => {
+ err.note(&format!("parent implementation is in crate `{cname}`"));
+ }
+ }
+
+ err.emit();
+}
+
+fn missing_items_err(
+ tcx: TyCtxt<'_>,
+ impl_span: Span,
+ missing_items: &[&ty::AssocItem],
+ full_impl_span: Span,
+) {
+ let missing_items_msg = missing_items
+ .iter()
+ .map(|trait_item| trait_item.name.to_string())
+ .collect::<Vec<_>>()
+ .join("`, `");
+
+ let mut err = struct_span_err!(
+ tcx.sess,
+ impl_span,
+ E0046,
+ "not all trait items implemented, missing: `{missing_items_msg}`",
+ );
+ err.span_label(impl_span, format!("missing `{missing_items_msg}` in implementation"));
+
+ // `Span` before impl block closing brace.
+ let hi = full_impl_span.hi() - BytePos(1);
+ // Point at the place right before the closing brace of the relevant `impl` to suggest
+ // adding the associated item at the end of its body.
+ let sugg_sp = full_impl_span.with_lo(hi).with_hi(hi);
+ // Obtain the level of indentation ending in `sugg_sp`.
+ let padding =
+ tcx.sess.source_map().indentation_before(sugg_sp).unwrap_or_else(|| String::new());
+
+ for trait_item in missing_items {
+ let snippet = suggestion_signature(trait_item, tcx);
+ let code = format!("{}{}\n{}", padding, snippet, padding);
+ let msg = format!("implement the missing item: `{snippet}`");
+ let appl = Applicability::HasPlaceholders;
+ if let Some(span) = tcx.hir().span_if_local(trait_item.def_id) {
+ err.span_label(span, format!("`{}` from trait", trait_item.name));
+ err.tool_only_span_suggestion(sugg_sp, &msg, code, appl);
+ } else {
+ err.span_suggestion_hidden(sugg_sp, &msg, code, appl);
+ }
+ }
+ err.emit();
+}
+
+fn missing_items_must_implement_one_of_err(
+ tcx: TyCtxt<'_>,
+ impl_span: Span,
+ missing_items: &[Ident],
+ annotation_span: Option<Span>,
+) {
+ let missing_items_msg =
+ missing_items.iter().map(Ident::to_string).collect::<Vec<_>>().join("`, `");
+
+ let mut err = struct_span_err!(
+ tcx.sess,
+ impl_span,
+ E0046,
+ "not all trait items implemented, missing one of: `{missing_items_msg}`",
+ );
+ err.span_label(impl_span, format!("missing one of `{missing_items_msg}` in implementation"));
+
+ if let Some(annotation_span) = annotation_span {
+ err.span_note(annotation_span, "required because of this annotation");
+ }
+
+ err.emit();
+}
+
+fn default_body_is_unstable(
+ tcx: TyCtxt<'_>,
+ impl_span: Span,
+ item_did: DefId,
+ feature: Symbol,
+ reason: Option<Symbol>,
+ issue: Option<NonZeroU32>,
+) {
+ let missing_item_name = &tcx.associated_item(item_did).name;
+ let use_of_unstable_library_feature_note = match reason {
+ Some(r) => format!("use of unstable library feature '{feature}': {r}"),
+ None => format!("use of unstable library feature '{feature}'"),
+ };
+
+ let mut err = struct_span_err!(
+ tcx.sess,
+ impl_span,
+ E0046,
+ "not all trait items implemented, missing: `{missing_item_name}`",
+ );
+ err.note(format!("default implementation of `{missing_item_name}` is unstable"));
+ err.note(use_of_unstable_library_feature_note);
+ rustc_session::parse::add_feature_diagnostics_for_issue(
+ &mut err,
+ &tcx.sess.parse_sess,
+ feature,
+ rustc_feature::GateIssue::Library(issue),
+ );
+ err.emit();
+}
+
+/// Re-sugar `ty::GenericPredicates` in a way suitable to be used in structured suggestions.
+fn bounds_from_generic_predicates<'tcx>(
+ tcx: TyCtxt<'tcx>,
+ predicates: ty::GenericPredicates<'tcx>,
+) -> (String, String) {
+ let mut types: FxHashMap<Ty<'tcx>, Vec<DefId>> = FxHashMap::default();
+ let mut projections = vec![];
+ for (predicate, _) in predicates.predicates {
+ debug!("predicate {:?}", predicate);
+ let bound_predicate = predicate.kind();
+ match bound_predicate.skip_binder() {
+ ty::PredicateKind::Trait(trait_predicate) => {
+ let entry = types.entry(trait_predicate.self_ty()).or_default();
+ let def_id = trait_predicate.def_id();
+ if Some(def_id) != tcx.lang_items().sized_trait() {
+ // Type params are `Sized` by default, do not add that restriction to the list
+ // if it is a positive requirement.
+ entry.push(trait_predicate.def_id());
+ }
+ }
+ ty::PredicateKind::Projection(projection_pred) => {
+ projections.push(bound_predicate.rebind(projection_pred));
+ }
+ _ => {}
+ }
+ }
+ let generics = if types.is_empty() {
+ "".to_string()
+ } else {
+ format!(
+ "<{}>",
+ types
+ .keys()
+ .filter_map(|t| match t.kind() {
+ ty::Param(_) => Some(t.to_string()),
+ // Avoid suggesting the following:
+ // fn foo<T, <T as Trait>::Bar>(_: T) where T: Trait, <T as Trait>::Bar: Other {}
+ _ => None,
+ })
+ .collect::<Vec<_>>()
+ .join(", ")
+ )
+ };
+ let mut where_clauses = vec![];
+ for (ty, bounds) in types {
+ where_clauses
+ .extend(bounds.into_iter().map(|bound| format!("{}: {}", ty, tcx.def_path_str(bound))));
+ }
+ for projection in &projections {
+ let p = projection.skip_binder();
+ // FIXME: this is not currently supported syntax, we should be looking at the `types` and
+ // insert the associated types where they correspond, but for now let's be "lazy" and
+ // propose this instead of the following valid resugaring:
+ // `T: Trait, Trait::Assoc = K` → `T: Trait<Assoc = K>`
+ where_clauses.push(format!(
+ "{} = {}",
+ tcx.def_path_str(p.projection_ty.item_def_id),
+ p.term,
+ ));
+ }
+ let where_clauses = if where_clauses.is_empty() {
+ String::new()
+ } else {
+ format!(" where {}", where_clauses.join(", "))
+ };
+ (generics, where_clauses)
+}
+
+/// Return placeholder code for the given function.
+fn fn_sig_suggestion<'tcx>(
+ tcx: TyCtxt<'tcx>,
+ sig: ty::FnSig<'tcx>,
+ ident: Ident,
+ predicates: ty::GenericPredicates<'tcx>,
+ assoc: &ty::AssocItem,
+) -> String {
+ let args = sig
+ .inputs()
+ .iter()
+ .enumerate()
+ .map(|(i, ty)| {
+ Some(match ty.kind() {
+ ty::Param(_) if assoc.fn_has_self_parameter && i == 0 => "self".to_string(),
+ ty::Ref(reg, ref_ty, mutability) if i == 0 => {
+ let reg = format!("{reg} ");
+ let reg = match &reg[..] {
+ "'_ " | " " => "",
+ reg => reg,
+ };
+ if assoc.fn_has_self_parameter {
+ match ref_ty.kind() {
+ ty::Param(param) if param.name == kw::SelfUpper => {
+ format!("&{}{}self", reg, mutability.prefix_str())
+ }
+
+ _ => format!("self: {ty}"),
+ }
+ } else {
+ format!("_: {ty}")
+ }
+ }
+ _ => {
+ if assoc.fn_has_self_parameter && i == 0 {
+ format!("self: {ty}")
+ } else {
+ format!("_: {ty}")
+ }
+ }
+ })
+ })
+ .chain(std::iter::once(if sig.c_variadic { Some("...".to_string()) } else { None }))
+ .flatten()
+ .collect::<Vec<String>>()
+ .join(", ");
+ let output = sig.output();
+ let output = if !output.is_unit() { format!(" -> {output}") } else { String::new() };
+
+ let unsafety = sig.unsafety.prefix_str();
+ let (generics, where_clauses) = bounds_from_generic_predicates(tcx, predicates);
+
+ // FIXME: this is not entirely correct, as the lifetimes from borrowed params will
+ // not be present in the `fn` definition, not will we account for renamed
+ // lifetimes between the `impl` and the `trait`, but this should be good enough to
+ // fill in a significant portion of the missing code, and other subsequent
+ // suggestions can help the user fix the code.
+ format!("{unsafety}fn {ident}{generics}({args}){output}{where_clauses} {{ todo!() }}")
+}
+
+pub fn ty_kind_suggestion(ty: Ty<'_>) -> Option<&'static str> {
+ Some(match ty.kind() {
+ ty::Bool => "true",
+ ty::Char => "'a'",
+ ty::Int(_) | ty::Uint(_) => "42",
+ ty::Float(_) => "3.14159",
+ ty::Error(_) | ty::Never => return None,
+ _ => "value",
+ })
+}
+
+/// Return placeholder code for the given associated item.
+/// Similar to `ty::AssocItem::suggestion`, but appropriate for use as the code snippet of a
+/// structured suggestion.
+fn suggestion_signature(assoc: &ty::AssocItem, tcx: TyCtxt<'_>) -> String {
+ match assoc.kind {
+ ty::AssocKind::Fn => {
+ // We skip the binder here because the binder would deanonymize all
+ // late-bound regions, and we don't want method signatures to show up
+ // `as for<'r> fn(&'r MyType)`. Pretty-printing handles late-bound
+ // regions just fine, showing `fn(&MyType)`.
+ fn_sig_suggestion(
+ tcx,
+ tcx.fn_sig(assoc.def_id).skip_binder(),
+ assoc.ident(tcx),
+ tcx.predicates_of(assoc.def_id),
+ assoc,
+ )
+ }
+ ty::AssocKind::Type => format!("type {} = Type;", assoc.name),
+ ty::AssocKind::Const => {
+ let ty = tcx.type_of(assoc.def_id);
+ let val = ty_kind_suggestion(ty).unwrap_or("value");
+ format!("const {}: {} = {};", assoc.name, ty, val)
+ }
+ }
+}
+
+/// Emit an error when encountering two or more variants in a transparent enum.
+fn bad_variant_count<'tcx>(tcx: TyCtxt<'tcx>, adt: ty::AdtDef<'tcx>, sp: Span, did: DefId) {
+ let variant_spans: Vec<_> = adt
+ .variants()
+ .iter()
+ .map(|variant| tcx.hir().span_if_local(variant.def_id).unwrap())
+ .collect();
+ let msg = format!("needs exactly one variant, but has {}", adt.variants().len(),);
+ let mut err = struct_span_err!(tcx.sess, sp, E0731, "transparent enum {msg}");
+ err.span_label(sp, &msg);
+ if let [start @ .., end] = &*variant_spans {
+ for variant_span in start {
+ err.span_label(*variant_span, "");
+ }
+ err.span_label(*end, &format!("too many variants in `{}`", tcx.def_path_str(did)));
+ }
+ err.emit();
+}
+
+/// Emit an error when encountering two or more non-zero-sized fields in a transparent
+/// enum.
+fn bad_non_zero_sized_fields<'tcx>(
+ tcx: TyCtxt<'tcx>,
+ adt: ty::AdtDef<'tcx>,
+ field_count: usize,
+ field_spans: impl Iterator<Item = Span>,
+ sp: Span,
+) {
+ let msg = format!("needs at most one non-zero-sized field, but has {field_count}");
+ let mut err = struct_span_err!(
+ tcx.sess,
+ sp,
+ E0690,
+ "{}transparent {} {}",
+ if adt.is_enum() { "the variant of a " } else { "" },
+ adt.descr(),
+ msg,
+ );
+ err.span_label(sp, &msg);
+ for sp in field_spans {
+ err.span_label(sp, "this field is non-zero-sized");
+ }
+ err.emit();
+}
+
+// FIXME: Consider moving this method to a more fitting place.
+pub fn potentially_plural_count(count: usize, word: &str) -> String {
+ format!("{} {}{}", count, word, pluralize!(count))
+}