Point at opaque and closure type definitions in type errors

src/librustc/infer/error_reporting/mod.rs

@@ -68,9 +68,12 @@ use rustc_hir as hir;
 use rustc_hir::def_id::DefId;
 use rustc_hir::Node;
 
-use errors::{struct_span_err, Applicability, DiagnosticBuilder, DiagnosticStyledString};
+use errors::{
+    pluralize, struct_span_err, Applicability, DiagnosticBuilder, DiagnosticStyledString,
+};
+use rustc_data_structures::fx::{FxHashMap, FxHashSet};
 use rustc_error_codes::*;
-use rustc_span::{Pos, Span};
+use rustc_span::{DesugaringKind, Pos, Span};
 use rustc_target::spec::abi;
 use std::{cmp, fmt};
 
@@ -1289,6 +1292,8 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
         mut values: Option<ValuePairs<'tcx>>,
         terr: &TypeError<'tcx>,
     ) {
+        let span = cause.span(self.tcx);
+
         // For some types of errors, expected-found does not make
         // sense, so just ignore the values we were given.
         match terr {
@@ -1298,6 +1303,100 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
             _ => {}
         }
 
+        struct OpaqueTypesVisitor<'tcx> {
+            types: FxHashMap<TyCategory, FxHashSet<Span>>,
+            expected: FxHashMap<TyCategory, FxHashSet<Span>>,
+            found: FxHashMap<TyCategory, FxHashSet<Span>>,
+            ignore_span: Span,
+            tcx: TyCtxt<'tcx>,
+        }
+
+        impl<'tcx> OpaqueTypesVisitor<'tcx> {
+            fn visit_expected_found(
+                tcx: TyCtxt<'tcx>,
+                expected: Ty<'tcx>,
+                found: Ty<'tcx>,
+                ignore_span: Span,
+            ) -> Self {
+                let mut types_visitor = OpaqueTypesVisitor {
+                    types: Default::default(),
+                    expected: Default::default(),
+                    found: Default::default(),
+                    ignore_span,
+                    tcx,
+                };
+                // The visitor puts all the relevant encountered types in `self.types`, but in
+                // here we want to visit two separate types with no relation to each other, so we
+                // move the results from `types` to `expected` or `found` as appropriate.
+                expected.visit_with(&mut types_visitor);
+                std::mem::swap(&mut types_visitor.expected, &mut types_visitor.types);
+                found.visit_with(&mut types_visitor);
+                std::mem::swap(&mut types_visitor.found, &mut types_visitor.types);
+                types_visitor
+            }
+
+            fn report(&self, err: &mut DiagnosticBuilder<'_>) {
+                self.add_labels_for_types(err, "expected", &self.expected);
+                self.add_labels_for_types(err, "found", &self.found);
+            }
+
+            fn add_labels_for_types(
+                &self,
+                err: &mut DiagnosticBuilder<'_>,
+                target: &str,
+                types: &FxHashMap<TyCategory, FxHashSet<Span>>,
+            ) {
+                for (key, values) in types.iter() {
+                    let count = values.len();
+                    let kind = key.descr();
+                    for sp in values {
+                        err.span_label(
+                            *sp,
+                            format!(
+                                "{}{}{} {}{}",
+                                if sp.is_desugaring(DesugaringKind::Async) {
+                                    "the `Output` of this `async fn`'s "
+                                } else if count == 1 {
+                                    "the "
+                                } else {
+                                    ""
+                                },
+                                if count > 1 { "one of the " } else { "" },
+                                target,
+                                kind,
+                                pluralize!(count),
+                            ),
+                        );
+                    }
+                }
+            }
+        }
+
+        impl<'tcx> ty::fold::TypeVisitor<'tcx> for OpaqueTypesVisitor<'tcx> {
+            fn visit_ty(&mut self, t: Ty<'tcx>) -> bool {
+                if let Some((kind, def_id)) = TyCategory::from_ty(t) {
+                    let span = self.tcx.def_span(def_id);
+                    // Avoid cluttering the output when the "found" and error span overlap:
+                    //
+                    // error[E0308]: mismatched types
+                    //   --> $DIR/issue-20862.rs:2:5
+                    //    |
+                    // LL |     |y| x + y
+                    //    |     ^^^^^^^^^
+                    //    |     |
+                    //    |     the found closure
+                    //    |     expected `()`, found closure
+                    //    |
+                    //    = note: expected unit type `()`
+                    //                 found closure `[closure@$DIR/issue-20862.rs:2:5: 2:14 x:_]`
+                    if !self.ignore_span.overlaps(span) {
+                        self.types.entry(kind).or_default().insert(span);
+                    }
+                }
+                t.super_visit_with(self)
+            }
+        }
+
         debug!("note_type_err(diag={:?})", diag);
         let (expected_found, exp_found, is_simple_error) = match values {
             None => (None, None, false),
@@ -1306,6 +1405,13 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
                     ValuePairs::Types(exp_found) => {
                         let is_simple_err =
                             exp_found.expected.is_simple_text() && exp_found.found.is_simple_text();
+                        OpaqueTypesVisitor::visit_expected_found(
+                            self.tcx,
+                            exp_found.expected,
+                            exp_found.found,
+                            span,
+                        )
+                        .report(diag);
 
                         (is_simple_err, Some(exp_found))
                     }
@@ -1323,8 +1429,6 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
             }
         };
 
-        let span = cause.span(self.tcx);
-
         // Ignore msg for object safe coercion
         // since E0038 message will be printed
         match terr {
@@ -1336,7 +1440,6 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
                 }
             }
         };
-
         if let Some((expected, found)) = expected_found {
             let expected_label = exp_found.map_or("type".into(), |ef| ef.expected.prefix_string());
             let found_label = exp_found.map_or("type".into(), |ef| ef.found.prefix_string());
@@ -1933,3 +2036,34 @@ impl<'tcx> ObligationCause<'tcx> {
         }
     }
 }
+
+/// This is a bare signal of what kind of type we're dealing with. `ty::TyKind` tracks
+/// extra information about each type, but we only care about the category.
+#[derive(Clone, Copy, PartialEq, Eq, Hash)]
+crate enum TyCategory {
+    Closure,
+    Opaque,
+    Generator,
+    Foreign,
+}
+
+impl TyCategory {
+    fn descr(&self) -> &'static str {
+        match self {
+            Self::Closure => "closure",
+            Self::Opaque => "opaque type",
+            Self::Generator => "generator",
+            Self::Foreign => "foreign type",
+        }
+    }
+
+    pub fn from_ty(ty: Ty<'_>) -> Option<(Self, DefId)> {
+        match ty.kind {
+            ty::Closure(def_id, _) => Some((Self::Closure, def_id)),
+            ty::Opaque(def_id, _) => Some((Self::Opaque, def_id)),
+            ty::Generator(def_id, ..) => Some((Self::Generator, def_id)),
+            ty::Foreign(def_id) => Some((Self::Foreign, def_id)),
+            _ => None,
+        }
+    }
+}

src/librustc/traits/error_reporting.rs

@@ -6,7 +6,7 @@ use super::{
     TraitNotObjectSafe,
 };
 
-use crate::infer::error_reporting::TypeAnnotationNeeded as ErrorCode;
+use crate::infer::error_reporting::{TyCategory, TypeAnnotationNeeded as ErrorCode};
 use crate::infer::type_variable::{TypeVariableOrigin, TypeVariableOriginKind};
 use crate::infer::{self, InferCtxt};
 use crate::mir::interpret::ErrorHandled;
@@ -446,7 +446,7 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
                 flags.push((sym::from_method, Some(method.to_string())));
             }
         }
-        if let Some(t) = self.get_parent_trait_ref(&obligation.cause.code) {
+        if let Some((t, _)) = self.get_parent_trait_ref(&obligation.cause.code) {
             flags.push((sym::parent_trait, Some(t)));
         }
 
@@ -665,13 +665,21 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
     }
 
     /// Gets the parent trait chain start
-    fn get_parent_trait_ref(&self, code: &ObligationCauseCode<'tcx>) -> Option<String> {
+    fn get_parent_trait_ref(
+        &self,
+        code: &ObligationCauseCode<'tcx>,
+    ) -> Option<(String, Option<Span>)> {
         match code {
             &ObligationCauseCode::BuiltinDerivedObligation(ref data) => {
                 let parent_trait_ref = self.resolve_vars_if_possible(&data.parent_trait_ref);
                 match self.get_parent_trait_ref(&data.parent_code) {
                     Some(t) => Some(t),
-                    None => Some(parent_trait_ref.skip_binder().self_ty().to_string()),
+                    None => {
+                        let ty = parent_trait_ref.skip_binder().self_ty();
+                        let span =
+                            TyCategory::from_ty(ty).map(|(_, def_id)| self.tcx.def_span(def_id));
+                        Some((ty.to_string(), span))
+                    }
                 }
             }
             _ => None,
@@ -719,9 +727,15 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
                             return;
                         }
                         let trait_ref = trait_predicate.to_poly_trait_ref();
-                        let (post_message, pre_message) = self
+                        let (post_message, pre_message, type_def) = self
                             .get_parent_trait_ref(&obligation.cause.code)
-                            .map(|t| (format!(" in `{}`", t), format!("within `{}`, ", t)))
+                            .map(|(t, s)| {
+                                (
+                                    format!(" in `{}`", t),
+                                    format!("within `{}`, ", t),
+                                    s.map(|s| (format!("within this `{}`", t), s)),
+                                )
+                            })
                             .unwrap_or_default();
 
                         let OnUnimplementedNote { message, label, note, enclosing_scope } =
@@ -795,6 +809,9 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
                         } else {
                             err.span_label(span, explanation);
                         }
+                        if let Some((msg, span)) = type_def {
+                            err.span_label(span, &msg);
+                        }
                         if let Some(ref s) = note {
                             // If it has a custom `#[rustc_on_unimplemented]` note, let's display it
                             err.note(s.as_str());

src/librustc_typeck/check/mod.rs

@@ -4743,14 +4743,13 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                         .join(", ");
                 }
                 Some(Node::Expr(hir::Expr {
-                    kind: ExprKind::Closure(_, _, body_id, closure_span, _),
+                    kind: ExprKind::Closure(_, _, body_id, _, _),
                     span: full_closure_span,
                     ..
                 })) => {
                     if *full_closure_span == expr.span {
                         return false;
                     }
-                    err.span_label(*closure_span, "closure defined here");
                     msg = "call this closure";
                     let body = hir.body(*body_id);
                     sugg_call = body

src/test/ui/async-await/dont-suggest-missing-await.stderr

@@ -1,6 +1,9 @@
 error[E0308]: mismatched types
   --> $DIR/dont-suggest-missing-await.rs:14:18
    |
+LL | async fn make_u32() -> u32 {
+   |                        --- the `Output` of this `async fn`'s found opaque type
+...
 LL |         take_u32(x)
    |                  ^ expected `u32`, found opaque type
    |

src/test/ui/async-await/issue-64130-3-other.stderr

@@ -3,6 +3,9 @@ error[E0277]: the trait bound `Foo: Qux` is not satisfied in `impl std::future::
    |
 LL | fn is_qux<T: Qux>(t: T) { }
    |    ------    --- required by this bound in `is_qux`
+LL | 
+LL | async fn bar() {
+   |                - within this `impl std::future::Future`
 ...
 LL |     is_qux(bar());
    |     ^^^^^^ within `impl std::future::Future`, the trait `Qux` is not implemented for `Foo`

src/test/ui/async-await/suggest-missing-await-closure.stderr

@@ -1,6 +1,9 @@
 error[E0308]: mismatched types
   --> $DIR/suggest-missing-await-closure.rs:16:18
    |
+LL | async fn make_u32() -> u32 {
+   |                        --- the `Output` of this `async fn`'s found opaque type
+...
 LL |         take_u32(x)
    |                  ^
    |                  |

src/test/ui/async-await/suggest-missing-await.stderr

@@ -1,6 +1,9 @@
 error[E0308]: mismatched types
   --> $DIR/suggest-missing-await.rs:13:14
    |
+LL | async fn make_u32() -> u32 {
+   |                        --- the `Output` of this `async fn`'s found opaque type
+...
 LL |     take_u32(x)
    |              ^
    |              |
@@ -13,6 +16,9 @@ LL |     take_u32(x)
 error[E0308]: mismatched types
   --> $DIR/suggest-missing-await.rs:23:5
    |
+LL | async fn dummy() {}
+   |                  - the `Output` of this `async fn`'s found opaque type
+...
 LL |     dummy()
    |     ^^^^^^^ expected `()`, found opaque type
    |

src/test/ui/closures/closure-reform-bad.stderr

@@ -1,6 +1,8 @@
 error[E0308]: mismatched types
   --> $DIR/closure-reform-bad.rs:11:15
    |
+LL |     let f = |s: &str| println!("{}{}", s, string);
+   |             ------------------------------------- the found closure
 LL |     call_bare(f)
    |               ^ expected fn pointer, found closure
    |

src/test/ui/extern/extern-types-distinct-types.stderr

@@ -1,6 +1,11 @@
 error[E0308]: mismatched types
   --> $DIR/extern-types-distinct-types.rs:9:5
    |
+LL |     type A;
+   |     ------- the found foreign type
+LL |     type B;
+   |     ------- the expected foreign type
+...
 LL |     r
    |     ^ expected extern type `B`, found extern type `A`
    |

src/test/ui/impl-trait/auto-trait-leak.stderr

@@ -77,6 +77,9 @@ LL | fn send<T: Send>(_: T) {}
 ...
 LL |     send(cycle2().clone());
    |     ^^^^ `std::rc::Rc<std::string::String>` cannot be sent between threads safely
+...
+LL | fn cycle2() -> impl Clone {
+   |                ---------- within this `impl std::clone::Clone`
    |
    = help: within `impl std::clone::Clone`, the trait `std::marker::Send` is not implemented for `std::rc::Rc<std::string::String>`
    = note: required because it appears within the type `impl std::clone::Clone`

src/test/ui/impl-trait/auto-trait-leak2.stderr

@@ -1,6 +1,9 @@
 error[E0277]: `std::rc::Rc<std::cell::Cell<i32>>` cannot be sent between threads safely
   --> $DIR/auto-trait-leak2.rs:13:5
    |
+LL | fn before() -> impl Fn(i32) {
+   |                ------------ within this `impl std::ops::Fn<(i32,)>`
+...
 LL | fn send<T: Send>(_: T) {}
    |    ----    ---- required by this bound in `send`
 ...
@@ -19,6 +22,9 @@ LL | fn send<T: Send>(_: T) {}
 ...
 LL |     send(after());
    |     ^^^^ `std::rc::Rc<std::cell::Cell<i32>>` cannot be sent between threads safely
+...
+LL | fn after() -> impl Fn(i32) {
+   |               ------------ within this `impl std::ops::Fn<(i32,)>`
    |
    = help: within `impl std::ops::Fn<(i32,)>`, the trait `std::marker::Send` is not implemented for `std::rc::Rc<std::cell::Cell<i32>>`
    = note: required because it appears within the type `[closure@$DIR/auto-trait-leak2.rs:24:5: 24:22 p:std::rc::Rc<std::cell::Cell<i32>>]`