Manually register some bounds for a better span

Author: compiler-errors

compiler/rustc_hir_analysis/src/check/check.rs

@@ -8,7 +8,7 @@ use rustc_errors::codes::*;
 use rustc_hir::def::{CtorKind, DefKind};
 use rustc_hir::{Node, intravisit};
 use rustc_infer::infer::{RegionVariableOrigin, TyCtxtInferExt};
-use rustc_infer::traits::Obligation;
+use rustc_infer::traits::{Obligation, ObligationCauseCode};
 use rustc_lint_defs::builtin::{
     REPR_TRANSPARENT_EXTERNAL_PRIVATE_FIELDS, UNSUPPORTED_FN_PTR_CALLING_CONVENTIONS,
 };
@@ -305,8 +305,32 @@ fn check_opaque_meets_bounds<'tcx>(
         _ => re,
     });
 
-    let misc_cause = traits::ObligationCause::misc(span, def_id);
+    // HACK: We eagerly instantiate some bounds to report better errors for them...
+    // This isn't necessary for correctness, since we register these bounds when
+    // equating the opaque below, but we should clean this up in the new solver.
+    for (predicate, pred_span) in
+        tcx.explicit_item_bounds(def_id).iter_instantiated_copied(tcx, args)
+    {
+        let predicate = predicate.fold_with(&mut BottomUpFolder {
+            tcx,
+            ty_op: |ty| if ty == opaque_ty { hidden_ty } else { ty },
+            lt_op: |lt| lt,
+            ct_op: |ct| ct,
+        });
+
+        ocx.register_obligation(Obligation::new(
+            tcx,
+            ObligationCause::new(
+                span,
+                def_id,
+                ObligationCauseCode::WhereClause(def_id.to_def_id(), pred_span),
+            ),
+            param_env,
+            predicate,
+        ));
+    }
 
+    let misc_cause = ObligationCause::misc(span, def_id);
     // FIXME: We should just register the item bounds here, rather than equating.
     match ocx.eq(&misc_cause, param_env, opaque_ty, hidden_ty) {
         Ok(()) => {}

tests/ui/async-await/issue-70935-complex-spans.stderr

@@ -35,6 +35,11 @@ note: required because it's used within this `async` block
    |
 LL |     async move {
    |     ^^^^^^^^^^
+note: required by a bound in `foo::{opaque#0}`
+  --> $DIR/issue-70935-complex-spans.rs:15:37
+   |
+LL | fn foo(x: NotSync) -> impl Future + Send {
+   |                                     ^^^^ required by this bound in `foo::{opaque#0}`
 
 error[E0277]: `*mut ()` cannot be shared between threads safely
   --> $DIR/issue-70935-complex-spans.rs:15:23

tests/ui/type-alias-impl-trait/bounds-are-checked-2.stderr

@@ -4,6 +4,11 @@ error[E0277]: the trait bound `T: Clone` is not satisfied
 LL |         t
    |         ^ the trait `Clone` is not implemented for `T`
    |
+note: required by a bound in `X::{opaque#0}`
+  --> $DIR/bounds-are-checked-2.rs:7:26
+   |
+LL |     pub type X<T> = impl Clone;
+   |                          ^^^^^ required by this bound in `X::{opaque#0}`
 help: consider restricting type parameter `T`
    |
 LL |     pub type X<T: std::clone::Clone> = impl Clone;

tests/ui/type-alias-impl-trait/generic_duplicate_param_use2.stderr

@@ -4,6 +4,11 @@ error[E0277]: `T` doesn't implement `Debug`
 LL |     t
    |     ^ `T` cannot be formatted using `{:?}` because it doesn't implement `Debug`
    |
+note: required by a bound in `Two::{opaque#0}`
+  --> $DIR/generic_duplicate_param_use2.rs:8:23
+   |
+LL | type Two<T, U> = impl Debug;
+   |                       ^^^^^ required by this bound in `Two::{opaque#0}`
 help: consider restricting type parameter `T`
    |
 LL | type Two<T: std::fmt::Debug, U> = impl Debug;

tests/ui/type-alias-impl-trait/generic_duplicate_param_use4.stderr

@@ -4,6 +4,11 @@ error[E0277]: `U` doesn't implement `Debug`
 LL |     u
    |     ^ `U` cannot be formatted using `{:?}` because it doesn't implement `Debug`
    |
+note: required by a bound in `Two::{opaque#0}`
+  --> $DIR/generic_duplicate_param_use4.rs:8:23
+   |
+LL | type Two<T, U> = impl Debug;
+   |                       ^^^^^ required by this bound in `Two::{opaque#0}`
 help: consider restricting type parameter `U`
    |
 LL | type Two<T, U: std::fmt::Debug> = impl Debug;

tests/ui/type-alias-impl-trait/hidden_type_mismatch.stderr

@@ -21,6 +21,11 @@ LL |     impl<T: Proj<Assoc = i32> + Copy> Copy for Bar<T> {}
    |                  -----------          ^^^^     ^^^^^^
    |                  |
    |                  unsatisfied trait bound introduced here
+note: required by a bound in `Tait::{opaque#0}`
+  --> $DIR/hidden_type_mismatch.rs:36:26
+   |
+LL |     pub type Tait = impl Copy + From<Bar<()>> + Into<Bar<()>>;
+   |                          ^^^^ required by this bound in `Tait::{opaque#0}`
 
 error: aborting due to 1 previous error
 

tests/ui/type-alias-impl-trait/implied_lifetime_wf_check4_static.stderr

@@ -5,8 +5,13 @@ LL |         s
    |         ^
    |         |
    |         the parameter type `A` must be valid for the static lifetime...
-   |         ...so that the type `A` will meet its required lifetime bounds
+   |         ...so that the type `A` will meet its required lifetime bounds...
    |
+note: ...that is required by this bound
+  --> $DIR/implied_lifetime_wf_check4_static.rs:4:35
+   |
+LL |     pub type Ty<A> = impl Sized + 'static;
+   |                                   ^^^^^^^
 help: consider adding an explicit lifetime bound
    |
 LL |     pub type Ty<A: 'static> = impl Sized + 'static;

tests/ui/type-alias-impl-trait/issue-52843.stderr

@@ -4,6 +4,11 @@ error[E0277]: the trait bound `T: Default` is not satisfied
 LL |     t
    |     ^ the trait `Default` is not implemented for `T`
    |
+note: required by a bound in `Foo::{opaque#0}`
+  --> $DIR/issue-52843.rs:3:20
+   |
+LL | type Foo<T> = impl Default;
+   |                    ^^^^^^^ required by this bound in `Foo::{opaque#0}`
 help: consider restricting type parameter `T`
    |
 LL | type Foo<T: std::default::Default> = impl Default;

tests/ui/type-alias-impl-trait/issue-90400-2.stderr

@@ -4,11 +4,18 @@ error[E0277]: the trait bound `B: Bar` is not satisfied
 LL |         MyBaz(bar)
    |         ^^^^^^^^^^ the trait `Bar` is not implemented for `B`
    |
-note: required by a bound in `MyBaz`
-  --> $DIR/issue-90400-2.rs:29:17
+note: required for `MyBaz<B>` to implement `Baz`
+  --> $DIR/issue-90400-2.rs:30:14
    |
-LL | struct MyBaz<B: Bar>(B);
-   |                 ^^^ required by this bound in `MyBaz`
+LL | impl<B: Bar> Baz for MyBaz<B> {
+   |         ---  ^^^     ^^^^^^^^
+   |         |
+   |         unsatisfied trait bound introduced here
+note: required by a bound in `<MyFoo as Foo>::FooFn::{opaque#0}`
+  --> $DIR/issue-90400-2.rs:22:26
+   |
+LL |     type FooFn<B> = impl Baz;
+   |                          ^^^ required by this bound in `<MyFoo as Foo>::FooFn::{opaque#0}`
 help: consider restricting type parameter `B`
    |
 LL |     type FooFn<B: Bar> = impl Baz;

tests/ui/type-alias-impl-trait/underconstrained_generic.stderr

@@ -11,6 +11,11 @@ LL | impl<X: Trait> ProofForConversion<X> for () {
    |         -----  ^^^^^^^^^^^^^^^^^^^^^     ^^
    |         |
    |         unsatisfied trait bound introduced here
+note: required by a bound in `Converter::{opaque#0}`
+  --> $DIR/underconstrained_generic.rs:19:26
+   |
+LL | type Converter<T> = impl ProofForConversion<T>;
+   |                          ^^^^^^^^^^^^^^^^^^^^^ required by this bound in `Converter::{opaque#0}`
 help: consider restricting type parameter `T`
    |
 LL | type Converter<T: Trait> = impl ProofForConversion<T>;

tests/ui/type-alias-impl-trait/wf-in-associated-type.fail.stderr

@@ -5,8 +5,13 @@ LL |     impl<'a, T> Trait<'a, T> for () {
    |          -- the parameter type `T` must be valid for the lifetime `'a` as defined here...
 ...
 LL |             req
-   |             ^^^ ...so that the type `&'a T` will meet its required lifetime bounds
+   |             ^^^ ...so that the type `&'a T` will meet its required lifetime bounds...
    |
+note: ...that is required by this bound
+  --> $DIR/wf-in-associated-type.rs:38:36
+   |
+LL |         type Opaque = impl Sized + 'a;
+   |                                    ^^
 help: consider adding an explicit lifetime bound
    |
 LL |     impl<'a, T: 'a> Trait<'a, T> for () {