Make sure to ignore elided lifetimes when pointing at args for fulfillment errors

Author: compiler-errors

compiler/rustc_hir_typeck/src/fn_ctxt/adjust_fulfillment_errors.rs

@@ -316,12 +316,24 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             .tcx
             .generics_of(def_id)
             .own_args(ty::GenericArgs::identity_for_item(self.tcx, def_id));
-        let Some((index, _)) =
-            own_args.iter().enumerate().find(|(_, arg)| **arg == param_to_point_at)
-        else {
+        let Some(mut index) = own_args.iter().position(|arg| *arg == param_to_point_at) else {
             return false;
         };
-        let Some(arg) = segment.args().args.get(index) else {
+        // SUBTLE: We may or may not turbofish lifetime arguments, which will
+        // otherwise be elided. if our "own args" starts with a lifetime, but
+        // the args list does not, then we should chop off all of the lifetimes,
+        // since they're all elided.
+        let segment_args = segment.args().args;
+        if matches!(own_args[0].unpack(), ty::GenericArgKind::Lifetime(_))
+            && segment_args.first().is_some_and(|arg| arg.is_ty_or_const())
+            && let Some(offset) = own_args.iter().position(|arg| {
+                matches!(arg.unpack(), ty::GenericArgKind::Type(_) | ty::GenericArgKind::Const(_))
+            })
+            && let Some(new_index) = index.checked_sub(offset)
+        {
+            index = new_index;
+        }
+        let Some(arg) = segment_args.get(index) else {
             return false;
         };
         error.obligation.cause.span = arg

tests/ui/associated-types/hr-associated-type-bound-param-3.stderr

@@ -15,10 +15,10 @@ LL |     for<'b> <T as X<'b, T>>::U: Clone,
    |                                 ^^^^^ required by this bound in `X`
 
 error[E0277]: the trait bound `str: Clone` is not satisfied
-  --> $DIR/hr-associated-type-bound-param-3.rs:18:5
+  --> $DIR/hr-associated-type-bound-param-3.rs:18:18
    |
 LL |     <(i32,) as X<(i32,)>>::f("abc");
-   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ the trait `Clone` is not implemented for `str`
+   |                  ^^^^^^ the trait `Clone` is not implemented for `str`
    |
    = help: the trait `Clone` is implemented for `String`
 note: required by a bound in `X::f`

tests/ui/associated-types/hr-associated-type-bound-param-4.stderr

@@ -15,10 +15,10 @@ LL |     for<'b> <(T,) as X<'b, T>>::U: Clone,
    |                                    ^^^^^ required by this bound in `X`
 
 error[E0277]: the trait bound `str: Clone` is not satisfied
-  --> $DIR/hr-associated-type-bound-param-4.rs:18:5
+  --> $DIR/hr-associated-type-bound-param-4.rs:18:18
    |
 LL |     <(i32,) as X<i32>>::f("abc");
-   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ the trait `Clone` is not implemented for `str`
+   |                  ^^^ the trait `Clone` is not implemented for `str`
    |
    = help: the trait `Clone` is implemented for `String`
 note: required by a bound in `X::f`

tests/ui/associated-types/hr-associated-type-bound-param-5.stderr

@@ -31,10 +31,10 @@ LL |     for<'b> <T::Next as X<'b, T::Next>>::U: Clone,
    |                                             ^^^^^ required by this bound in `X`
 
 error[E0277]: the trait bound `str: Clone` is not satisfied
-  --> $DIR/hr-associated-type-bound-param-5.rs:36:5
+  --> $DIR/hr-associated-type-bound-param-5.rs:36:15
    |
 LL |     <i32 as X<Box<i32>>>::f("abc");
-   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ the trait `Clone` is not implemented for `str`
+   |               ^^^^^^^^ the trait `Clone` is not implemented for `str`
    |
    = help: the trait `Clone` is implemented for `String`
 note: required by a bound in `X::f`

tests/ui/associated-types/hr-associated-type-bound-param-6.rs

@@ -17,5 +17,6 @@ impl<S, T> X<'_, T> for (S,) {
 pub fn main() {
     <(i32,) as X<i32>>::f("abc");
     //~^ ERROR the trait bound `for<'b> i32: X<'b, i32>` is not satisfied
+    //~| ERROR the trait bound `for<'b> i32: X<'b, i32>` is not satisfied
     //~| ERROR the trait bound `i32: X<'_, i32>` is not satisfied
 }

tests/ui/associated-types/hr-associated-type-bound-param-6.stderr

@@ -17,6 +17,22 @@ LL |     <(i32,) as X<i32>>::f("abc");
    |
    = help: the trait `X<'_, T>` is implemented for `(S,)`
 
+error[E0277]: the trait bound `for<'b> i32: X<'b, i32>` is not satisfied
+  --> $DIR/hr-associated-type-bound-param-6.rs:18:18
+   |
+LL |     <(i32,) as X<i32>>::f("abc");
+   |                  ^^^ the trait `for<'b> X<'b, i32>` is not implemented for `i32`
+   |
+   = help: the trait `X<'_, T>` is implemented for `(S,)`
+note: required by a bound in `X::f`
+  --> $DIR/hr-associated-type-bound-param-6.rs:3:16
+   |
+LL |     for<'b> T: X<'b, T>,
+   |                ^^^^^^^^ required by this bound in `X::f`
+...
+LL |     fn f(x: &<T as X<'_, T>>::U) {
+   |        - required by a bound in this associated function
+
 error[E0277]: the trait bound `i32: X<'_, i32>` is not satisfied
   --> $DIR/hr-associated-type-bound-param-6.rs:18:27
    |
@@ -25,6 +41,6 @@ LL |     <(i32,) as X<i32>>::f("abc");
    |
    = help: the trait `X<'_, T>` is implemented for `(S,)`
 
-error: aborting due to 3 previous errors
+error: aborting due to 4 previous errors
 
 For more information about this error, try `rustc --explain E0277`.

tests/ui/higher-ranked/leak-check/candidate-from-env-universe-err-2.next.stderr

@@ -1,8 +1,8 @@
 error[E0277]: the trait bound `for<'a> T: Trait<'a, '_>` is not satisfied
-  --> $DIR/candidate-from-env-universe-err-2.rs:15:5
+  --> $DIR/candidate-from-env-universe-err-2.rs:15:15
    |
 LL |     impl_hr::<T>();
-   |     ^^^^^^^^^^^^^^ the trait `for<'a> Trait<'a, '_>` is not implemented for `T`
+   |               ^ the trait `for<'a> Trait<'a, '_>` is not implemented for `T`
    |
 note: required by a bound in `impl_hr`
   --> $DIR/candidate-from-env-universe-err-2.rs:12:19