Rollup of 8 pull requests

compiler/rustc_const_eval/src/interpret/step.rs

@@ -197,12 +197,17 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
             }
 
             Aggregate(ref kind, ref operands) => {
+                // active_field_index is for union initialization.
                 let (dest, active_field_index) = match **kind {
                     mir::AggregateKind::Adt(adt_def, variant_index, _, _, active_field_index) => {
                         self.write_discriminant(variant_index, &dest)?;
                         if adt_def.is_enum() {
-                            (self.place_downcast(&dest, variant_index)?, active_field_index)
+                            assert!(active_field_index.is_none());
+                            (self.place_downcast(&dest, variant_index)?, None)
                         } else {
+                            if active_field_index.is_some() {
+                                assert_eq!(operands.len(), 1);
+                            }
                             (dest, active_field_index)
                         }
                     }
@@ -211,12 +216,9 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
 
                 for (i, operand) in operands.iter().enumerate() {
                     let op = self.eval_operand(operand, None)?;
-                    // Ignore zero-sized fields.
-                    if !op.layout.is_zst() {
-                        let field_index = active_field_index.unwrap_or(i);
-                        let field_dest = self.place_field(&dest, field_index)?;
-                        self.copy_op(&op, &field_dest)?;
-                    }
+                    let field_index = active_field_index.unwrap_or(i);
+                    let field_dest = self.place_field(&dest, field_index)?;
+                    self.copy_op(&op, &field_dest)?;
                 }
             }
 
@@ -253,7 +255,6 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
             }
 
             Len(place) => {
-                // FIXME(CTFE): don't allow computing the length of arrays in const eval
                 let src = self.eval_place(place)?;
                 let mplace = self.force_allocation(&src)?;
                 let len = mplace.len(self)?;

compiler/rustc_hir/src/lang_items.rs

@@ -300,7 +300,7 @@ language_item_table! {
     Oom,                     sym::oom,                 oom,                        Target::Fn,             GenericRequirement::None;
     AllocLayout,             sym::alloc_layout,        alloc_layout,               Target::Struct,         GenericRequirement::None;
 
-    Start,                   sym::start,               start_fn,                   Target::Fn,             GenericRequirement::None;
+    Start,                   sym::start,               start_fn,                   Target::Fn,             GenericRequirement::Exact(1);
 
     EhPersonality,           sym::eh_personality,      eh_personality,             Target::Fn,             GenericRequirement::None;
     EhCatchTypeinfo,         sym::eh_catch_typeinfo,   eh_catch_typeinfo,          Target::Static,         GenericRequirement::None;

compiler/rustc_mir_build/src/thir/pattern/check_match.rs

@@ -39,6 +39,13 @@ fn create_e0004(sess: &Session, sp: Span, error_message: String) -> DiagnosticBu
     struct_span_err!(sess, sp, E0004, "{}", &error_message)
 }
 
+#[derive(PartialEq)]
+enum RefutableFlag {
+    Irrefutable,
+    Refutable,
+}
+use RefutableFlag::*;
+
 struct MatchVisitor<'a, 'p, 'tcx> {
     tcx: TyCtxt<'tcx>,
     typeck_results: &'a ty::TypeckResults<'tcx>,
@@ -73,13 +80,13 @@ impl<'tcx> Visitor<'tcx> for MatchVisitor<'_, '_, 'tcx> {
             hir::LocalSource::AssignDesugar(_) => ("destructuring assignment binding", None),
         };
         self.check_irrefutable(&loc.pat, msg, sp);
-        self.check_patterns(&loc.pat);
+        self.check_patterns(&loc.pat, Irrefutable);
     }
 
     fn visit_param(&mut self, param: &'tcx hir::Param<'tcx>) {
         intravisit::walk_param(self, param);
         self.check_irrefutable(&param.pat, "function argument", None);
-        self.check_patterns(&param.pat);
+        self.check_patterns(&param.pat, Irrefutable);
     }
 }
 
@@ -113,9 +120,9 @@ impl PatCtxt<'_, '_> {
 }
 
 impl<'p, 'tcx> MatchVisitor<'_, 'p, 'tcx> {
-    fn check_patterns(&self, pat: &Pat<'_>) {
+    fn check_patterns(&self, pat: &Pat<'_>, rf: RefutableFlag) {
         pat.walk_always(|pat| check_borrow_conflicts_in_at_patterns(self, pat));
-        check_for_bindings_named_same_as_variants(self, pat);
+        check_for_bindings_named_same_as_variants(self, pat, rf);
     }
 
     fn lower_pattern(
@@ -145,7 +152,7 @@ impl<'p, 'tcx> MatchVisitor<'_, 'p, 'tcx> {
     }
 
     fn check_let(&mut self, pat: &'tcx hir::Pat<'tcx>, expr: &hir::Expr<'_>, span: Span) {
-        self.check_patterns(pat);
+        self.check_patterns(pat, Refutable);
         let mut cx = self.new_cx(expr.hir_id);
         let tpat = self.lower_pattern(&mut cx, pat, &mut false);
         check_let_reachability(&mut cx, pat.hir_id, tpat, span);
@@ -161,9 +168,9 @@ impl<'p, 'tcx> MatchVisitor<'_, 'p, 'tcx> {
 
         for arm in arms {
             // Check the arm for some things unrelated to exhaustiveness.
-            self.check_patterns(&arm.pat);
+            self.check_patterns(&arm.pat, Refutable);
             if let Some(hir::Guard::IfLet(ref pat, _)) = arm.guard {
-                self.check_patterns(pat);
+                self.check_patterns(pat, Refutable);
                 let tpat = self.lower_pattern(&mut cx, pat, &mut false);
                 check_let_reachability(&mut cx, pat.hir_id, tpat, tpat.span());
             }
@@ -297,7 +304,11 @@ fn const_not_var(
     }
 }
 
-fn check_for_bindings_named_same_as_variants(cx: &MatchVisitor<'_, '_, '_>, pat: &Pat<'_>) {
+fn check_for_bindings_named_same_as_variants(
+    cx: &MatchVisitor<'_, '_, '_>,
+    pat: &Pat<'_>,
+    rf: RefutableFlag,
+) {
     pat.walk_always(|p| {
         if let hir::PatKind::Binding(_, _, ident, None) = p.kind {
             if let Some(ty::BindByValue(hir::Mutability::Not)) =
@@ -310,25 +321,31 @@ fn check_for_bindings_named_same_as_variants(cx: &MatchVisitor<'_, '_, '_>, pat:
                             variant.ident == ident && variant.ctor_kind == CtorKind::Const
                         })
                     {
+                        let variant_count = edef.variants.len();
                         cx.tcx.struct_span_lint_hir(
                             BINDINGS_WITH_VARIANT_NAME,
                             p.hir_id,
                             p.span,
                             |lint| {
                                 let ty_path = cx.tcx.def_path_str(edef.did);
-                                lint.build(&format!(
+                                let mut err = lint.build(&format!(
                                     "pattern binding `{}` is named the same as one \
-                                                of the variants of the type `{}`",
+                                                    of the variants of the type `{}`",
                                     ident, ty_path
-                                ))
-                                .code(error_code!(E0170))
-                                .span_suggestion(
-                                    p.span,
-                                    "to match on the variant, qualify the path",
-                                    format!("{}::{}", ty_path, ident),
-                                    Applicability::MachineApplicable,
-                                )
-                                .emit();
+                                ));
+                                err.code(error_code!(E0170));
+                                // If this is an irrefutable pattern, and there's > 1 variant,
+                                // then we can't actually match on this. Applying the below
+                                // suggestion would produce code that breaks on `check_irrefutable`.
+                                if rf == Refutable || variant_count == 1 {
+                                    err.span_suggestion(
+                                        p.span,
+                                        "to match on the variant, qualify the path",
+                                        format!("{}::{}", ty_path, ident),
+                                        Applicability::MachineApplicable,
+                                    );
+                                }
+                                err.emit();
                             },
                         )
                     }

compiler/rustc_resolve/src/diagnostics.rs

@@ -198,7 +198,7 @@ impl<'a> Resolver<'a> {
                 err.span_label(first_use_span, format!("first use of `{}`", name));
                 err
             }
-            ResolutionError::MethodNotMemberOfTrait(method, trait_) => {
+            ResolutionError::MethodNotMemberOfTrait(method, trait_, candidate) => {
                 let mut err = struct_span_err!(
                     self.session,
                     span,
@@ -208,9 +208,17 @@ impl<'a> Resolver<'a> {
                     trait_
                 );
                 err.span_label(span, format!("not a member of trait `{}`", trait_));
+                if let Some(candidate) = candidate {
+                    err.span_suggestion(
+                        method.span,
+                        "there is an associated function with a similar name",
+                        candidate.to_ident_string(),
+                        Applicability::MaybeIncorrect,
+                    );
+                }
                 err
             }
-            ResolutionError::TypeNotMemberOfTrait(type_, trait_) => {
+            ResolutionError::TypeNotMemberOfTrait(type_, trait_, candidate) => {
                 let mut err = struct_span_err!(
                     self.session,
                     span,
@@ -220,9 +228,17 @@ impl<'a> Resolver<'a> {
                     trait_
                 );
                 err.span_label(span, format!("not a member of trait `{}`", trait_));
+                if let Some(candidate) = candidate {
+                    err.span_suggestion(
+                        type_.span,
+                        "there is an associated type with a similar name",
+                        candidate.to_ident_string(),
+                        Applicability::MaybeIncorrect,
+                    );
+                }
                 err
             }
-            ResolutionError::ConstNotMemberOfTrait(const_, trait_) => {
+            ResolutionError::ConstNotMemberOfTrait(const_, trait_, candidate) => {
                 let mut err = struct_span_err!(
                     self.session,
                     span,
@@ -232,6 +248,14 @@ impl<'a> Resolver<'a> {
                     trait_
                 );
                 err.span_label(span, format!("not a member of trait `{}`", trait_));
+                if let Some(candidate) = candidate {
+                    err.span_suggestion(
+                        const_.span,
+                        "there is an associated constant with a similar name",
+                        candidate.to_ident_string(),
+                        Applicability::MaybeIncorrect,
+                    );
+                }
                 err
             }
             ResolutionError::VariableNotBoundInPattern(binding_error) => {

compiler/rustc_resolve/src/late.rs

@@ -1309,14 +1309,15 @@ impl<'a: 'ast, 'b, 'ast> LateResolutionVisitor<'a, 'b, 'ast> {
                                     use crate::ResolutionError::*;
                                     match &item.kind {
                                         AssocItemKind::Const(_default, _ty, _expr) => {
-                                            debug!("resolve_implementation AssocItemKind::Const",);
+                                            debug!("resolve_implementation AssocItemKind::Const");
                                             // If this is a trait impl, ensure the const
                                             // exists in trait
                                             this.check_trait_item(
                                                 item.ident,
+                                                &item.kind,
                                                 ValueNS,
                                                 item.span,
-                                                |n, s| ConstNotMemberOfTrait(n, s),
+                                                |i, s, c| ConstNotMemberOfTrait(i, s, c),
                                             );
 
                                             // We allow arbitrary const expressions inside of associated consts,
@@ -1338,6 +1339,7 @@ impl<'a: 'ast, 'b, 'ast> LateResolutionVisitor<'a, 'b, 'ast> {
                                             );
                                         }
                                         AssocItemKind::Fn(box FnKind(.., generics, _)) => {
+                                            debug!("resolve_implementation AssocItemKind::Fn");
                                             // We also need a new scope for the impl item type parameters.
                                             this.with_generic_param_rib(
                                                 generics,
@@ -1347,9 +1349,10 @@ impl<'a: 'ast, 'b, 'ast> LateResolutionVisitor<'a, 'b, 'ast> {
                                                     // exists in trait
                                                     this.check_trait_item(
                                                         item.ident,
+                                                        &item.kind,
                                                         ValueNS,
                                                         item.span,
-                                                        |n, s| MethodNotMemberOfTrait(n, s),
+                                                        |i, s, c| MethodNotMemberOfTrait(i, s, c),
                                                     );
 
                                                     visit::walk_assoc_item(
@@ -1366,6 +1369,7 @@ impl<'a: 'ast, 'b, 'ast> LateResolutionVisitor<'a, 'b, 'ast> {
                                             _,
                                             _,
                                         )) => {
+                                            debug!("resolve_implementation AssocItemKind::TyAlias");
                                             // We also need a new scope for the impl item type parameters.
                                             this.with_generic_param_rib(
                                                 generics,
@@ -1375,9 +1379,10 @@ impl<'a: 'ast, 'b, 'ast> LateResolutionVisitor<'a, 'b, 'ast> {
                                                     // exists in trait
                                                     this.check_trait_item(
                                                         item.ident,
+                                                        &item.kind,
                                                         TypeNS,
                                                         item.span,
-                                                        |n, s| TypeNotMemberOfTrait(n, s),
+                                                        |i, s, c| TypeNotMemberOfTrait(i, s, c),
                                                     );
 
                                                     visit::walk_assoc_item(
@@ -1401,9 +1406,15 @@ impl<'a: 'ast, 'b, 'ast> LateResolutionVisitor<'a, 'b, 'ast> {
         });
     }
 
-    fn check_trait_item<F>(&mut self, ident: Ident, ns: Namespace, span: Span, err: F)
-    where
-        F: FnOnce(Symbol, &str) -> ResolutionError<'_>,
+    fn check_trait_item<F>(
+        &mut self,
+        ident: Ident,
+        kind: &AssocItemKind,
+        ns: Namespace,
+        span: Span,
+        err: F,
+    ) where
+        F: FnOnce(Ident, &str, Option<Symbol>) -> ResolutionError<'_>,
     {
         // If there is a TraitRef in scope for an impl, then the method must be in the
         // trait.
@@ -1420,8 +1431,9 @@ impl<'a: 'ast, 'b, 'ast> LateResolutionVisitor<'a, 'b, 'ast> {
                 )
                 .is_err()
             {
+                let candidate = self.find_similarly_named_assoc_item(ident.name, kind);
                 let path = &self.current_trait_ref.as_ref().unwrap().1.path;
-                self.report_error(span, err(ident.name, &path_names_to_string(path)));
+                self.report_error(span, err(ident, &path_names_to_string(path), candidate));
             }
         }
     }

compiler/rustc_resolve/src/late/diagnostics.rs

@@ -7,8 +7,8 @@ use crate::{PathResult, PathSource, Segment};
 
 use rustc_ast::visit::FnKind;
 use rustc_ast::{
-    self as ast, Expr, ExprKind, GenericParam, GenericParamKind, Item, ItemKind, NodeId, Path, Ty,
-    TyKind,
+    self as ast, AssocItemKind, Expr, ExprKind, GenericParam, GenericParamKind, Item, ItemKind,
+    NodeId, Path, Ty, TyKind,
 };
 use rustc_ast_pretty::pprust::path_segment_to_string;
 use rustc_data_structures::fx::FxHashSet;
@@ -1150,6 +1150,40 @@ impl<'a: 'ast, 'ast> LateResolutionVisitor<'a, '_, 'ast> {
         true
     }
 
+    /// Given the target `ident` and `kind`, search for the similarly named associated item
+    /// in `self.current_trait_ref`.
+    crate fn find_similarly_named_assoc_item(
+        &mut self,
+        ident: Symbol,
+        kind: &AssocItemKind,
+    ) -> Option<Symbol> {
+        let module = if let Some((module, _)) = self.current_trait_ref {
+            module
+        } else {
+            return None;
+        };
+        if ident == kw::Underscore {
+            // We do nothing for `_`.
+            return None;
+        }
+
+        let resolutions = self.r.resolutions(module);
+        let targets = resolutions
+            .borrow()
+            .iter()
+            .filter_map(|(key, res)| res.borrow().binding.map(|binding| (key, binding.res())))
+            .filter(|(_, res)| match (kind, res) {
+                (AssocItemKind::Const(..), Res::Def(DefKind::AssocConst, _)) => true,
+                (AssocItemKind::Fn(_), Res::Def(DefKind::AssocFn, _)) => true,
+                (AssocItemKind::TyAlias(..), Res::Def(DefKind::AssocTy, _)) => true,
+                _ => false,
+            })
+            .map(|(key, _)| key.ident.name)
+            .collect::<Vec<_>>();
+
+        find_best_match_for_name(&targets, ident, None)
+    }
+
     fn lookup_assoc_candidate<FilterFn>(
         &mut self,
         ident: Ident,

compiler/rustc_resolve/src/lib.rs

@@ -206,11 +206,11 @@ enum ResolutionError<'a> {
     /// parameter list.
     NameAlreadyUsedInParameterList(Symbol, Span),
     /// Error E0407: method is not a member of trait.
-    MethodNotMemberOfTrait(Symbol, &'a str),
+    MethodNotMemberOfTrait(Ident, &'a str, Option<Symbol>),
     /// Error E0437: type is not a member of trait.
-    TypeNotMemberOfTrait(Symbol, &'a str),
+    TypeNotMemberOfTrait(Ident, &'a str, Option<Symbol>),
     /// Error E0438: const is not a member of trait.
-    ConstNotMemberOfTrait(Symbol, &'a str),
+    ConstNotMemberOfTrait(Ident, &'a str, Option<Symbol>),
     /// Error E0408: variable `{}` is not bound in all patterns.
     VariableNotBoundInPattern(&'a BindingError),
     /// Error E0409: variable `{}` is bound in inconsistent ways within the same match arm.

compiler/rustc_typeck/src/check/callee.rs

@@ -356,6 +356,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                     }
                 }
 
+                let callee_ty = self.resolve_vars_if_possible(callee_ty);
                 let mut err = type_error_struct!(
                     self.tcx.sess,
                     callee_expr.span,