Fix span for non-satisfied trivial trait bounds

compiler/rustc_infer/src/traits/util.rs

@@ -5,6 +5,7 @@ use crate::traits::{Obligation, ObligationCause, PredicateObligation};
 use rustc_data_structures::fx::{FxHashSet, FxIndexSet};
 use rustc_middle::ty::{self, ToPredicate, TyCtxt, WithConstness};
 use rustc_span::symbol::Ident;
+use rustc_span::Span;
 
 pub fn anonymize_predicate<'tcx>(
     tcx: TyCtxt<'tcx>,
@@ -97,6 +98,22 @@ pub fn elaborate_predicates<'tcx>(
     elaborate_obligations(tcx, obligations)
 }
 
+pub fn elaborate_predicates_with_span<'tcx>(
+    tcx: TyCtxt<'tcx>,
+    predicates: impl Iterator<Item = (ty::Predicate<'tcx>, Span)>,
+) -> Elaborator<'tcx> {
+    let obligations = predicates
+        .map(|(predicate, span)| {
+            predicate_obligation(
+                predicate,
+                ty::ParamEnv::empty(),
+                ObligationCause::dummy_with_span(span),
+            )
+        })
+        .collect();
+    elaborate_obligations(tcx, obligations)
+}
+
 pub fn elaborate_obligations<'tcx>(
     tcx: TyCtxt<'tcx>,
     mut obligations: Vec<PredicateObligation<'tcx>>,

compiler/rustc_trait_selection/src/traits/mod.rs

@@ -65,7 +65,8 @@ pub use self::specialize::{specialization_graph, translate_substs, OverlapError}
 pub use self::structural_match::search_for_structural_match_violation;
 pub use self::structural_match::NonStructuralMatchTy;
 pub use self::util::{
-    elaborate_obligations, elaborate_predicates, elaborate_trait_ref, elaborate_trait_refs,
+    elaborate_obligations, elaborate_predicates, elaborate_predicates_with_span,
+    elaborate_trait_ref, elaborate_trait_refs,
 };
 pub use self::util::{expand_trait_aliases, TraitAliasExpander};
 pub use self::util::{

compiler/rustc_typeck/src/check/wfcheck.rs

@@ -1641,19 +1641,38 @@ fn report_bivariance(tcx: TyCtxt<'_>, param: &rustc_hir::GenericParam<'_>) {
 
 /// Feature gates RFC 2056 -- trivial bounds, checking for global bounds that
 /// aren't true.
-fn check_false_global_bounds(fcx: &FnCtxt<'_, '_>, span: Span, id: hir::HirId) {
+fn check_false_global_bounds(fcx: &FnCtxt<'_, '_>, mut span: Span, id: hir::HirId) {
     let empty_env = ty::ParamEnv::empty();
 
     let def_id = fcx.tcx.hir().local_def_id(id);
-    let predicates = fcx.tcx.predicates_of(def_id).predicates.iter().map(|(p, _)| *p);
+    let predicates_with_span =
+        fcx.tcx.predicates_of(def_id).predicates.iter().map(|(p, span)| (*p, *span));
     // Check elaborated bounds.
-    let implied_obligations = traits::elaborate_predicates(fcx.tcx, predicates);
+    let implied_obligations = traits::elaborate_predicates_with_span(fcx.tcx, predicates_with_span);
 
     for obligation in implied_obligations {
         let pred = obligation.predicate;
         // Match the existing behavior.
         if pred.is_global(fcx.tcx) && !pred.has_late_bound_regions() {
             let pred = fcx.normalize_associated_types_in(span, pred);
+            let hir_node = fcx.tcx.hir().find(id);
+
+            // only use the span of the predicate clause (#90869)
+
+            if let Some(hir::Generics { where_clause, .. }) =
+                hir_node.and_then(|node| node.generics())
+            {
+                let obligation_span = obligation.cause.span(fcx.tcx);
+
+                span = where_clause
+                    .predicates
+                    .iter()
+                    // There seems to be no better way to find out which predicate we are in
+                    .find(|pred| pred.span().contains(obligation_span))
+                    .map(|pred| pred.span())
+                    .unwrap_or(obligation_span);
+            }
+
             let obligation = traits::Obligation::new(
                 traits::ObligationCause::new(span, id, traits::TrivialBound),
                 empty_env,

src/test/ui/const-generics/issues/issue-67185-2.rs

@@ -9,11 +9,10 @@ trait Bar {}
 impl Bar for [u16; 4] {}
 impl Bar for [[u16; 3]; 3] {}
 
-trait Foo  //~ ERROR the trait bound `[u16; 3]: Bar` is not satisfied [E0277]
-           //~^ ERROR the trait bound `[[u16; 3]; 2]: Bar` is not satisfied [E0277]
-    where
-        [<u8 as Baz>::Quaks; 2]: Bar,
-        <u8 as Baz>::Quaks: Bar,
+trait Foo
+where
+    [<u8 as Baz>::Quaks; 2]: Bar, //~ ERROR the trait bound `[[u16; 3]; 2]: Bar` is not satisfied [E0277]
+    <u8 as Baz>::Quaks: Bar,  //~ ERROR the trait bound `[u16; 3]: Bar` is not satisfied [E0277]
 {
 }
 

src/test/ui/const-generics/issues/issue-67185-2.stderr

@@ -1,14 +1,8 @@
 error[E0277]: the trait bound `[u16; 3]: Bar` is not satisfied
-  --> $DIR/issue-67185-2.rs:12:1
+  --> $DIR/issue-67185-2.rs:15:5
    |
-LL | / trait Foo
-LL | |
-LL | |     where
-LL | |         [<u8 as Baz>::Quaks; 2]: Bar,
-LL | |         <u8 as Baz>::Quaks: Bar,
-LL | | {
-LL | | }
-   | |_^ the trait `Bar` is not implemented for `[u16; 3]`
+LL |     <u8 as Baz>::Quaks: Bar,
+   |     ^^^^^^^^^^^^^^^^^^^^^^^ the trait `Bar` is not implemented for `[u16; 3]`
    |
    = help: the following implementations were found:
              <[[u16; 3]; 3] as Bar>
@@ -17,16 +11,10 @@ LL | | }
    = help: add `#![feature(trivial_bounds)]` to the crate attributes to enable
 
 error[E0277]: the trait bound `[[u16; 3]; 2]: Bar` is not satisfied
-  --> $DIR/issue-67185-2.rs:12:1
+  --> $DIR/issue-67185-2.rs:14:5
    |
-LL | / trait Foo
-LL | |
-LL | |     where
-LL | |         [<u8 as Baz>::Quaks; 2]: Bar,
-LL | |         <u8 as Baz>::Quaks: Bar,
-LL | | {
-LL | | }
-   | |_^ the trait `Bar` is not implemented for `[[u16; 3]; 2]`
+LL |     [<u8 as Baz>::Quaks; 2]: Bar,
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ the trait `Bar` is not implemented for `[[u16; 3]; 2]`
    |
    = help: the following implementations were found:
              <[[u16; 3]; 3] as Bar>
@@ -35,7 +23,7 @@ LL | | }
    = help: add `#![feature(trivial_bounds)]` to the crate attributes to enable
 
 error[E0277]: the trait bound `[u16; 3]: Bar` is not satisfied
-  --> $DIR/issue-67185-2.rs:22:6
+  --> $DIR/issue-67185-2.rs:21:6
    |
 LL | impl Foo for FooImpl {}
    |      ^^^ the trait `Bar` is not implemented for `[u16; 3]`
@@ -44,16 +32,16 @@ LL | impl Foo for FooImpl {}
              <[[u16; 3]; 3] as Bar>
              <[u16; 4] as Bar>
 note: required by a bound in `Foo`
-  --> $DIR/issue-67185-2.rs:16:29
+  --> $DIR/issue-67185-2.rs:15:25
    |
 LL | trait Foo
    |       --- required by a bound in this
 ...
-LL |         <u8 as Baz>::Quaks: Bar,
-   |                             ^^^ required by this bound in `Foo`
+LL |     <u8 as Baz>::Quaks: Bar,
+   |                         ^^^ required by this bound in `Foo`
 
 error[E0277]: the trait bound `[[u16; 3]; 2]: Bar` is not satisfied
-  --> $DIR/issue-67185-2.rs:22:6
+  --> $DIR/issue-67185-2.rs:21:6
    |
 LL | impl Foo for FooImpl {}
    |      ^^^ the trait `Bar` is not implemented for `[[u16; 3]; 2]`
@@ -62,16 +50,16 @@ LL | impl Foo for FooImpl {}
              <[[u16; 3]; 3] as Bar>
              <[u16; 4] as Bar>
 note: required by a bound in `Foo`
-  --> $DIR/issue-67185-2.rs:15:34
+  --> $DIR/issue-67185-2.rs:14:30
    |
 LL | trait Foo
    |       --- required by a bound in this
-...
-LL |         [<u8 as Baz>::Quaks; 2]: Bar,
-   |                                  ^^^ required by this bound in `Foo`
+LL | where
+LL |     [<u8 as Baz>::Quaks; 2]: Bar,
+   |                              ^^^ required by this bound in `Foo`
 
 error[E0277]: the trait bound `[[u16; 3]; 2]: Bar` is not satisfied
-  --> $DIR/issue-67185-2.rs:26:14
+  --> $DIR/issue-67185-2.rs:25:14
    |
 LL | fn f(_: impl Foo) {}
    |              ^^^ the trait `Bar` is not implemented for `[[u16; 3]; 2]`
@@ -80,16 +68,16 @@ LL | fn f(_: impl Foo) {}
              <[[u16; 3]; 3] as Bar>
              <[u16; 4] as Bar>
 note: required by a bound in `Foo`
-  --> $DIR/issue-67185-2.rs:15:34
+  --> $DIR/issue-67185-2.rs:14:30
    |
 LL | trait Foo
    |       --- required by a bound in this
-...
-LL |         [<u8 as Baz>::Quaks; 2]: Bar,
-   |                                  ^^^ required by this bound in `Foo`
+LL | where
+LL |     [<u8 as Baz>::Quaks; 2]: Bar,
+   |                              ^^^ required by this bound in `Foo`
 
 error[E0277]: the trait bound `[u16; 3]: Bar` is not satisfied
-  --> $DIR/issue-67185-2.rs:26:14
+  --> $DIR/issue-67185-2.rs:25:14
    |
 LL | fn f(_: impl Foo) {}
    |              ^^^ the trait `Bar` is not implemented for `[u16; 3]`
@@ -98,13 +86,13 @@ LL | fn f(_: impl Foo) {}
              <[[u16; 3]; 3] as Bar>
              <[u16; 4] as Bar>
 note: required by a bound in `Foo`
-  --> $DIR/issue-67185-2.rs:16:29
+  --> $DIR/issue-67185-2.rs:15:25
    |
 LL | trait Foo
    |       --- required by a bound in this
 ...
-LL |         <u8 as Baz>::Quaks: Bar,
-   |                             ^^^ required by this bound in `Foo`
+LL |     <u8 as Baz>::Quaks: Bar,
+   |                         ^^^ required by this bound in `Foo`
 
 error: aborting due to 6 previous errors
 

src/test/ui/cross/cross-fn-cache-hole.rs

@@ -12,8 +12,8 @@ trait Bar<X> { }
 
 // We don't always check where clauses for sanity, but in this case
 // wfcheck does report an error here:
-fn vacuous<A>() //~ ERROR the trait bound `i32: Bar<u32>` is not satisfied
-    where i32: Foo<u32, A>
+fn vacuous<A>()
+    where i32: Foo<u32, A> //~ ERROR the trait bound `i32: Bar<u32>` is not satisfied
 {
     // ... the original intention was to check that we don't use that
     // vacuous where clause (which could never be satisfied) to accept

src/test/ui/cross/cross-fn-cache-hole.stderr

@@ -1,14 +1,8 @@
 error[E0277]: the trait bound `i32: Bar<u32>` is not satisfied
-  --> $DIR/cross-fn-cache-hole.rs:15:1
+  --> $DIR/cross-fn-cache-hole.rs:16:11
    |
-LL | / fn vacuous<A>()
-LL | |     where i32: Foo<u32, A>
-LL | | {
-LL | |     // ... the original intention was to check that we don't use that
-...  |
-LL | |     require::<i32, u32>();
-LL | | }
-   | |_^ the trait `Bar<u32>` is not implemented for `i32`
+LL |     where i32: Foo<u32, A>
+   |           ^^^^^^^^^^^^^^^^ the trait `Bar<u32>` is not implemented for `i32`
    |
    = help: see issue #48214
    = help: add `#![feature(trivial_bounds)]` to the crate attributes to enable