Rollup of 9 pull requests

compiler/rustc_codegen_ssa/src/target_features.rs

@@ -442,7 +442,7 @@ fn asm_target_features(tcx: TyCtxt<'_>, did: DefId) -> &FxIndexSet<Symbol> {
 pub fn check_target_feature_trait_unsafe(tcx: TyCtxt<'_>, id: LocalDefId, attr_span: Span) {
     if let DefKind::AssocFn = tcx.def_kind(id) {
         let parent_id = tcx.local_parent(id);
-        if let DefKind::Impl { of_trait: true } = tcx.def_kind(parent_id) {
+        if let DefKind::Trait | DefKind::Impl { of_trait: true } = tcx.def_kind(parent_id) {
             tcx.sess
                 .struct_span_err(
                     attr_span,

compiler/rustc_hir_analysis/locales/en-US.ftl

@@ -42,6 +42,9 @@ hir_analysis_assoc_type_binding_not_allowed =
     associated type bindings are not allowed here
     .label = associated type not allowed here
 
+hir_analysis_parenthesized_fn_trait_expansion =
+    parenthesized trait syntax expands to `{$expanded_type}`
+
 hir_analysis_typeof_reserved_keyword_used =
     `typeof` is a reserved keyword but unimplemented
     .suggestion = consider replacing `typeof(...)` with an actual type

compiler/rustc_hir_analysis/src/astconv/errors.rs

@@ -1,10 +1,14 @@
 use crate::astconv::AstConv;
-use crate::errors::{ManualImplementation, MissingTypeParams};
+use crate::errors::{
+    AssocTypeBindingNotAllowed, ManualImplementation, MissingTypeParams,
+    ParenthesizedFnTraitExpansion,
+};
 use rustc_data_structures::fx::FxHashMap;
 use rustc_errors::{pluralize, struct_span_err, Applicability, Diagnostic, ErrorGuaranteed};
 use rustc_hir as hir;
 use rustc_hir::def_id::DefId;
 use rustc_infer::traits::FulfillmentError;
+use rustc_middle::ty::TyCtxt;
 use rustc_middle::ty::{self, Ty};
 use rustc_session::parse::feature_err;
 use rustc_span::edit_distance::find_best_match_for_name;
@@ -78,43 +82,10 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
             // Do not suggest the other syntax if we are in trait impl:
             // the desugaring would contain an associated type constraint.
             if !is_impl {
-                let args = trait_segment
-                    .args
-                    .as_ref()
-                    .and_then(|args| args.args.get(0))
-                    .and_then(|arg| match arg {
-                        hir::GenericArg::Type(ty) => match ty.kind {
-                            hir::TyKind::Tup(t) => t
-                                .iter()
-                                .map(|e| sess.source_map().span_to_snippet(e.span))
-                                .collect::<Result<Vec<_>, _>>()
-                                .map(|a| a.join(", ")),
-                            _ => sess.source_map().span_to_snippet(ty.span),
-                        }
-                        .map(|s| format!("({})", s))
-                        .ok(),
-                        _ => None,
-                    })
-                    .unwrap_or_else(|| "()".to_string());
-                let ret = trait_segment
-                    .args()
-                    .bindings
-                    .iter()
-                    .find_map(|b| match (b.ident.name == sym::Output, &b.kind) {
-                        (true, hir::TypeBindingKind::Equality { term }) => {
-                            let span = match term {
-                                hir::Term::Ty(ty) => ty.span,
-                                hir::Term::Const(c) => self.tcx().hir().span(c.hir_id),
-                            };
-                            sess.source_map().span_to_snippet(span).ok()
-                        }
-                        _ => None,
-                    })
-                    .unwrap_or_else(|| "()".to_string());
                 err.span_suggestion(
                     span,
                     "use parenthetical notation instead",
-                    format!("{}{} -> {}", trait_segment.ident, args, ret),
+                    fn_trait_to_string(self.tcx(), trait_segment, true),
                     Applicability::MaybeIncorrect,
                 );
             }
@@ -629,3 +600,69 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
         err.emit();
     }
 }
+
+/// Emits an error regarding forbidden type binding associations
+pub fn prohibit_assoc_ty_binding(
+    tcx: TyCtxt<'_>,
+    span: Span,
+    segment: Option<(&hir::PathSegment<'_>, Span)>,
+) {
+    tcx.sess.emit_err(AssocTypeBindingNotAllowed { span, fn_trait_expansion: if let Some((segment, span)) = segment && segment.args().parenthesized {
+        Some(ParenthesizedFnTraitExpansion { span, expanded_type: fn_trait_to_string(tcx, segment, false) })
+    } else {
+        None
+    }});
+}
+
+pub(crate) fn fn_trait_to_string(
+    tcx: TyCtxt<'_>,
+    trait_segment: &hir::PathSegment<'_>,
+    parenthesized: bool,
+) -> String {
+    let args = trait_segment
+        .args
+        .as_ref()
+        .and_then(|args| args.args.get(0))
+        .and_then(|arg| match arg {
+            hir::GenericArg::Type(ty) => match ty.kind {
+                hir::TyKind::Tup(t) => t
+                    .iter()
+                    .map(|e| tcx.sess.source_map().span_to_snippet(e.span))
+                    .collect::<Result<Vec<_>, _>>()
+                    .map(|a| a.join(", ")),
+                _ => tcx.sess.source_map().span_to_snippet(ty.span),
+            }
+            .map(|s| {
+                // `s.empty()` checks to see if the type is the unit tuple, if so we don't want a comma
+                if parenthesized || s.is_empty() { format!("({})", s) } else { format!("({},)", s) }
+            })
+            .ok(),
+            _ => None,
+        })
+        .unwrap_or_else(|| "()".to_string());
+
+    let ret = trait_segment
+        .args()
+        .bindings
+        .iter()
+        .find_map(|b| match (b.ident.name == sym::Output, &b.kind) {
+            (true, hir::TypeBindingKind::Equality { term }) => {
+                let span = match term {
+                    hir::Term::Ty(ty) => ty.span,
+                    hir::Term::Const(c) => tcx.hir().span(c.hir_id),
+                };
+
+                (span != tcx.hir().span(trait_segment.hir_id))
+                    .then_some(tcx.sess.source_map().span_to_snippet(span).ok())
+                    .flatten()
+            }
+            _ => None,
+        })
+        .unwrap_or_else(|| "()".to_string());
+
+    if parenthesized {
+        format!("{}{} -> {}", trait_segment.ident, args, ret)
+    } else {
+        format!("{}<{}, Output={}>", trait_segment.ident, args, ret)
+    }
+}

compiler/rustc_hir_analysis/src/astconv/generics.rs

@@ -1,9 +1,8 @@
 use super::IsMethodCall;
 use crate::astconv::{
-    CreateSubstsForGenericArgsCtxt, ExplicitLateBound, GenericArgCountMismatch,
-    GenericArgCountResult, GenericArgPosition,
+    errors::prohibit_assoc_ty_binding, CreateSubstsForGenericArgsCtxt, ExplicitLateBound,
+    GenericArgCountMismatch, GenericArgCountResult, GenericArgPosition,
 };
-use crate::errors::AssocTypeBindingNotAllowed;
 use crate::structured_errors::{GenericArgsInfo, StructuredDiagnostic, WrongNumberOfGenericArgs};
 use rustc_ast::ast::ParamKindOrd;
 use rustc_errors::{struct_span_err, Applicability, Diagnostic, ErrorGuaranteed, MultiSpan};
@@ -433,7 +432,7 @@ pub(crate) fn check_generic_arg_count(
         (gen_pos != GenericArgPosition::Type || infer_args) && !gen_args.has_lifetime_params();
 
     if gen_pos != GenericArgPosition::Type && let Some(b) = gen_args.bindings.first() {
-            prohibit_assoc_ty_binding(tcx, b.span);
+             prohibit_assoc_ty_binding(tcx, b.span, None);
         }
 
     let explicit_late_bound =
@@ -589,11 +588,6 @@ pub(crate) fn check_generic_arg_count(
     }
 }
 
-/// Emits an error regarding forbidden type binding associations
-pub fn prohibit_assoc_ty_binding(tcx: TyCtxt<'_>, span: Span) {
-    tcx.sess.emit_err(AssocTypeBindingNotAllowed { span });
-}
-
 /// Prohibits explicit lifetime arguments if late-bound lifetime parameters
 /// are present. This is used both for datatypes and function calls.
 pub(crate) fn prohibit_explicit_late_bound_lifetimes(

compiler/rustc_hir_analysis/src/astconv/mod.rs

@@ -5,9 +5,8 @@
 mod errors;
 pub mod generics;
 
-use crate::astconv::generics::{
-    check_generic_arg_count, create_substs_for_generic_args, prohibit_assoc_ty_binding,
-};
+use crate::astconv::errors::prohibit_assoc_ty_binding;
+use crate::astconv::generics::{check_generic_arg_count, create_substs_for_generic_args};
 use crate::bounds::Bounds;
 use crate::collect::HirPlaceholderCollector;
 use crate::errors::{
@@ -295,7 +294,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
             ty::BoundConstness::NotConst,
         );
         if let Some(b) = item_segment.args().bindings.first() {
-            prohibit_assoc_ty_binding(self.tcx(), b.span);
+            prohibit_assoc_ty_binding(self.tcx(), b.span, Some((item_segment, span)));
         }
 
         substs
@@ -631,7 +630,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
         );
 
         if let Some(b) = item_segment.args().bindings.first() {
-            prohibit_assoc_ty_binding(self.tcx(), b.span);
+            prohibit_assoc_ty_binding(self.tcx(), b.span, Some((item_segment, span)));
         }
 
         args
@@ -825,7 +824,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
             constness,
         );
         if let Some(b) = trait_segment.args().bindings.first() {
-            prohibit_assoc_ty_binding(self.tcx(), b.span);
+            prohibit_assoc_ty_binding(self.tcx(), b.span, Some((trait_segment, span)));
         }
         self.tcx().mk_trait_ref(trait_def_id, substs)
     }
@@ -2596,7 +2595,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
         for segment in segments {
             // Only emit the first error to avoid overloading the user with error messages.
             if let Some(b) = segment.args().bindings.first() {
-                prohibit_assoc_ty_binding(self.tcx(), b.span);
+                prohibit_assoc_ty_binding(self.tcx(), b.span, None);
                 return true;
             }
         }

compiler/rustc_hir_analysis/src/errors.rs

@@ -129,6 +129,18 @@ pub struct AssocTypeBindingNotAllowed {
     #[primary_span]
     #[label]
     pub span: Span,
+
+    #[subdiagnostic]
+    pub fn_trait_expansion: Option<ParenthesizedFnTraitExpansion>,
+}
+
+#[derive(Subdiagnostic)]
+#[help(hir_analysis_parenthesized_fn_trait_expansion)]
+pub struct ParenthesizedFnTraitExpansion {
+    #[primary_span]
+    pub span: Span,
+
+    pub expanded_type: String,
 }
 
 #[derive(Diagnostic)]

compiler/rustc_hir_typeck/src/op.rs

@@ -148,10 +148,11 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                         rhs_ty,
                         op,
                     );
-                    self.demand_suptype(expr.span, builtin_return_ty, return_ty);
+                    self.demand_eqtype(expr.span, builtin_return_ty, return_ty);
+                    builtin_return_ty
+                } else {
+                    return_ty
                 }
-
-                return_ty
             }
         }
     }

compiler/rustc_infer/src/infer/canonical/canonicalizer.rs

@@ -411,15 +411,28 @@ impl<'cx, 'tcx> TypeFolder<TyCtxt<'tcx>> for Canonicalizer<'cx, 'tcx> {
                 }
             }
 
-            ty::Infer(ty::IntVar(_)) => self.canonicalize_ty_var(
-                CanonicalVarInfo { kind: CanonicalVarKind::Ty(CanonicalTyVarKind::Int) },
-                t,
-            ),
-
-            ty::Infer(ty::FloatVar(_)) => self.canonicalize_ty_var(
-                CanonicalVarInfo { kind: CanonicalVarKind::Ty(CanonicalTyVarKind::Float) },
-                t,
-            ),
+            ty::Infer(ty::IntVar(vid)) => {
+                let nt = self.infcx.opportunistic_resolve_int_var(vid);
+                if nt != t {
+                    return self.fold_ty(nt);
+                } else {
+                    self.canonicalize_ty_var(
+                        CanonicalVarInfo { kind: CanonicalVarKind::Ty(CanonicalTyVarKind::Int) },
+                        t,
+                    )
+                }
+            }
+            ty::Infer(ty::FloatVar(vid)) => {
+                let nt = self.infcx.opportunistic_resolve_float_var(vid);
+                if nt != t {
+                    return self.fold_ty(nt);
+                } else {
+                    self.canonicalize_ty_var(
+                        CanonicalVarInfo { kind: CanonicalVarKind::Ty(CanonicalTyVarKind::Float) },
+                        t,
+                    )
+                }
+            }
 
             ty::Infer(ty::FreshTy(_) | ty::FreshIntTy(_) | ty::FreshFloatTy(_)) => {
                 bug!("encountered a fresh type during canonicalization")

compiler/rustc_infer/src/infer/combine.rs

@@ -34,7 +34,6 @@ use rustc_hir::def_id::DefId;
 use rustc_middle::infer::canonical::OriginalQueryValues;
 use rustc_middle::infer::unify_key::{ConstVarValue, ConstVariableValue};
 use rustc_middle::infer::unify_key::{ConstVariableOrigin, ConstVariableOriginKind};
-use rustc_middle::traits::query::NoSolution;
 use rustc_middle::traits::ObligationCause;
 use rustc_middle::ty::error::{ExpectedFound, TypeError};
 use rustc_middle::ty::relate::{self, Relate, RelateResult, TypeRelation};
@@ -119,20 +118,30 @@ impl<'tcx> InferCtxt<'tcx> {
                 self.unify_float_variable(!a_is_expected, v_id, v)
             }
 
-            // All other cases of inference are errors
-            (&ty::Infer(_), _) | (_, &ty::Infer(_)) => {
-                Err(TypeError::Sorts(ty::relate::expected_found(relation, a, b)))
+            // We don't expect `TyVar` or `Fresh*` vars at this point with lazy norm.
+            (
+                ty::Alias(AliasKind::Projection, _),
+                ty::Infer(ty::TyVar(_) | ty::FreshTy(_) | ty::FreshIntTy(_) | ty::FreshFloatTy(_)),
+            )
+            | (
+                ty::Infer(ty::TyVar(_) | ty::FreshTy(_) | ty::FreshIntTy(_) | ty::FreshFloatTy(_)),
+                ty::Alias(AliasKind::Projection, _),
+            ) if self.tcx.trait_solver_next() => {
+                bug!()
             }
 
-            (ty::Alias(AliasKind::Projection, _), _) if self.tcx.trait_solver_next() => {
+            (_, ty::Alias(AliasKind::Projection, _)) | (ty::Alias(AliasKind::Projection, _), _)
+                if self.tcx.trait_solver_next() =>
+            {
                 relation.register_type_equate_obligation(a, b);
-                Ok(b)
-            }
-            (_, ty::Alias(AliasKind::Projection, _)) if self.tcx.trait_solver_next() => {
-                relation.register_type_equate_obligation(b, a);
                 Ok(a)
             }
 
+            // All other cases of inference are errors
+            (&ty::Infer(_), _) | (_, &ty::Infer(_)) => {
+                Err(TypeError::Sorts(ty::relate::expected_found(relation, a, b)))
+            }
+
             _ => ty::relate::super_relate_tys(relation, a, b),
         }
     }
@@ -161,9 +170,9 @@ impl<'tcx> InferCtxt<'tcx> {
         //
         // This probe is probably not strictly necessary but it seems better to be safe and not accidentally find
         // ourselves with a check to find bugs being required for code to compile because it made inference progress.
-        self.probe(|_| {
+        let compatible_types = self.probe(|_| {
             if a.ty() == b.ty() {
-                return;
+                return Ok(());
             }
 
             // We don't have access to trait solving machinery in `rustc_infer` so the logic for determining if the
@@ -173,15 +182,24 @@ impl<'tcx> InferCtxt<'tcx> {
                 (relation.param_env(), a.ty(), b.ty()),
                 &mut OriginalQueryValues::default(),
             );
-
-            if let Err(NoSolution) = self.tcx.check_tys_might_be_eq(canonical) {
+            self.tcx.check_tys_might_be_eq(canonical).map_err(|_| {
                 self.tcx.sess.delay_span_bug(
                     DUMMY_SP,
                     &format!("cannot relate consts of different types (a={:?}, b={:?})", a, b,),
-                );
-            }
+                )
+            })
         });
 
+        // If the consts have differing types, just bail with a const error with
+        // the expected const's type. Specifically, we don't want const infer vars
+        // to do any type shapeshifting before and after resolution.
+        if let Err(guar) = compatible_types {
+            return Ok(self.tcx.const_error_with_guaranteed(
+                if relation.a_is_expected() { a.ty() } else { b.ty() },
+                guar,
+            ));
+        }
+
         match (a.kind(), b.kind()) {
             (
                 ty::ConstKind::Infer(InferConst::Var(a_vid)),