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-rw-r--r--compiler/rustc_infer/src/infer/error_reporting/mod.rs1
-rw-r--r--compiler/rustc_infer/src/infer/mod.rs12
-rw-r--r--compiler/rustc_middle/src/ty/error.rs12
-rw-r--r--compiler/rustc_trait_selection/src/traits/error_reporting/mod.rs30
-rw-r--r--src/test/ui/mismatched_types/E0631.rs2
-rw-r--r--src/test/ui/mismatched_types/E0631.stderr8
-rw-r--r--src/test/ui/mismatched_types/closure-arg-count.rs2
-rw-r--r--src/test/ui/mismatched_types/closure-arg-count.stderr8
-rw-r--r--src/test/ui/unboxed-closures/non-tupled-arg-mismatch.rs8
-rw-r--r--src/test/ui/unboxed-closures/non-tupled-arg-mismatch.stderr17
10 files changed, 87 insertions, 13 deletions
diff --git a/compiler/rustc_infer/src/infer/error_reporting/mod.rs b/compiler/rustc_infer/src/infer/error_reporting/mod.rs
index fcb87a9f32f..3c7dac2bfd8 100644
--- a/compiler/rustc_infer/src/infer/error_reporting/mod.rs
+++ b/compiler/rustc_infer/src/infer/error_reporting/mod.rs
@@ -1750,6 +1750,7 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
         if let Some(ValuePairs::PolyTraitRefs(exp_found)) = values
             && let ty::Closure(def_id, _) = exp_found.expected.skip_binder().self_ty().kind()
             && let Some(def_id) = def_id.as_local()
+            && terr.involves_regions()
         {
             let span = self.tcx.def_span(def_id);
             diag.span_note(span, "this closure does not fulfill the lifetime requirements");
diff --git a/compiler/rustc_infer/src/infer/mod.rs b/compiler/rustc_infer/src/infer/mod.rs
index 1e26e7bb86e..444817f396e 100644
--- a/compiler/rustc_infer/src/infer/mod.rs
+++ b/compiler/rustc_infer/src/infer/mod.rs
@@ -1935,6 +1935,18 @@ impl<'tcx> TypeTrace<'tcx> {
         }
     }
 
+    pub fn poly_trait_refs(
+        cause: &ObligationCause<'tcx>,
+        a_is_expected: bool,
+        a: ty::PolyTraitRef<'tcx>,
+        b: ty::PolyTraitRef<'tcx>,
+    ) -> TypeTrace<'tcx> {
+        TypeTrace {
+            cause: cause.clone(),
+            values: PolyTraitRefs(ExpectedFound::new(a_is_expected, a.into(), b.into())),
+        }
+    }
+
     pub fn consts(
         cause: &ObligationCause<'tcx>,
         a_is_expected: bool,
diff --git a/compiler/rustc_middle/src/ty/error.rs b/compiler/rustc_middle/src/ty/error.rs
index 8e6af936ded..ac89bec702e 100644
--- a/compiler/rustc_middle/src/ty/error.rs
+++ b/compiler/rustc_middle/src/ty/error.rs
@@ -74,6 +74,18 @@ pub enum TypeError<'tcx> {
     TargetFeatureCast(DefId),
 }
 
+impl TypeError<'_> {
+    pub fn involves_regions(self) -> bool {
+        match self {
+            TypeError::RegionsDoesNotOutlive(_, _)
+            | TypeError::RegionsInsufficientlyPolymorphic(_, _)
+            | TypeError::RegionsOverlyPolymorphic(_, _)
+            | TypeError::RegionsPlaceholderMismatch => true,
+            _ => false,
+        }
+    }
+}
+
 /// Explains the source of a type err in a short, human readable way. This is meant to be placed
 /// in parentheses after some larger message. You should also invoke `note_and_explain_type_err()`
 /// afterwards to present additional details, particularly when it comes to lifetime-related
diff --git a/compiler/rustc_trait_selection/src/traits/error_reporting/mod.rs b/compiler/rustc_trait_selection/src/traits/error_reporting/mod.rs
index 4260cb53adc..1a39a168038 100644
--- a/compiler/rustc_trait_selection/src/traits/error_reporting/mod.rs
+++ b/compiler/rustc_trait_selection/src/traits/error_reporting/mod.rs
@@ -22,6 +22,7 @@ use rustc_hir::intravisit::Visitor;
 use rustc_hir::GenericParam;
 use rustc_hir::Item;
 use rustc_hir::Node;
+use rustc_infer::infer::TypeTrace;
 use rustc_infer::traits::TraitEngine;
 use rustc_middle::traits::select::OverflowError;
 use rustc_middle::ty::abstract_const::NotConstEvaluatable;
@@ -941,9 +942,14 @@ impl<'a, 'tcx> InferCtxtExt<'tcx> for InferCtxt<'a, 'tcx> {
 
                 self.reported_closure_mismatch.borrow_mut().insert((span, found_span));
 
+                let mut not_tupled = false;
+
                 let found = match found_trait_ref.skip_binder().substs.type_at(1).kind() {
                     ty::Tuple(ref tys) => vec![ArgKind::empty(); tys.len()],
-                    _ => vec![ArgKind::empty()],
+                    _ => {
+                        not_tupled = true;
+                        vec![ArgKind::empty()]
+                    }
                 };
 
                 let expected_ty = expected_trait_ref.skip_binder().substs.type_at(1);
@@ -951,10 +957,28 @@ impl<'a, 'tcx> InferCtxtExt<'tcx> for InferCtxt<'a, 'tcx> {
                     ty::Tuple(ref tys) => {
                         tys.iter().map(|t| ArgKind::from_expected_ty(t, Some(span))).collect()
                     }
-                    _ => vec![ArgKind::Arg("_".to_owned(), expected_ty.to_string())],
+                    _ => {
+                        not_tupled = true;
+                        vec![ArgKind::Arg("_".to_owned(), expected_ty.to_string())]
+                    }
                 };
 
-                if found.len() == expected.len() {
+                // If this is a `Fn` family trait and either the expected or found
+                // is not tupled, then fall back to just a regular mismatch error.
+                // This shouldn't be common unless manually implementing one of the
+                // traits manually, but don't make it more confusing when it does
+                // happen.
+                if Some(expected_trait_ref.def_id()) != tcx.lang_items().gen_trait() && not_tupled {
+                    self.report_and_explain_type_error(
+                        TypeTrace::poly_trait_refs(
+                            &obligation.cause,
+                            true,
+                            expected_trait_ref,
+                            found_trait_ref,
+                        ),
+                        ty::error::TypeError::Mismatch,
+                    )
+                } else if found.len() == expected.len() {
                     self.report_closure_arg_mismatch(
                         span,
                         found_span,
diff --git a/src/test/ui/mismatched_types/E0631.rs b/src/test/ui/mismatched_types/E0631.rs
index a2939465830..83dbdb77abe 100644
--- a/src/test/ui/mismatched_types/E0631.rs
+++ b/src/test/ui/mismatched_types/E0631.rs
@@ -1,7 +1,7 @@
 #![feature(unboxed_closures)]
 
 fn foo<F: Fn(usize)>(_: F) {}
-fn bar<F: Fn<usize>>(_: F) {}
+fn bar<F: Fn<(usize,)>>(_: F) {}
 fn main() {
     fn f(_: u64) {}
     foo(|_: isize| {}); //~ ERROR type mismatch
diff --git a/src/test/ui/mismatched_types/E0631.stderr b/src/test/ui/mismatched_types/E0631.stderr
index 4d673d45559..410ea4b0b34 100644
--- a/src/test/ui/mismatched_types/E0631.stderr
+++ b/src/test/ui/mismatched_types/E0631.stderr
@@ -27,8 +27,8 @@ LL |     bar(|_: isize| {});
 note: required by a bound in `bar`
   --> $DIR/E0631.rs:4:11
    |
-LL | fn bar<F: Fn<usize>>(_: F) {}
-   |           ^^^^^^^^^ required by this bound in `bar`
+LL | fn bar<F: Fn<(usize,)>>(_: F) {}
+   |           ^^^^^^^^^^^^ required by this bound in `bar`
 
 error[E0631]: type mismatch in function arguments
   --> $DIR/E0631.rs:9:9
@@ -65,8 +65,8 @@ LL |     bar(f);
 note: required by a bound in `bar`
   --> $DIR/E0631.rs:4:11
    |
-LL | fn bar<F: Fn<usize>>(_: F) {}
-   |           ^^^^^^^^^ required by this bound in `bar`
+LL | fn bar<F: Fn<(usize,)>>(_: F) {}
+   |           ^^^^^^^^^^^^ required by this bound in `bar`
 
 error: aborting due to 4 previous errors
 
diff --git a/src/test/ui/mismatched_types/closure-arg-count.rs b/src/test/ui/mismatched_types/closure-arg-count.rs
index e817631ad5d..65c8d6a7e93 100644
--- a/src/test/ui/mismatched_types/closure-arg-count.rs
+++ b/src/test/ui/mismatched_types/closure-arg-count.rs
@@ -1,6 +1,6 @@
 #![feature(unboxed_closures)]
 
-fn f<F: Fn<usize>>(_: F) {}
+fn f<F: Fn<(usize,)>>(_: F) {}
 fn main() {
     [1, 2, 3].sort_by(|| panic!());
     //~^ ERROR closure is expected to take
diff --git a/src/test/ui/mismatched_types/closure-arg-count.stderr b/src/test/ui/mismatched_types/closure-arg-count.stderr
index 3968774e357..a02ec819838 100644
--- a/src/test/ui/mismatched_types/closure-arg-count.stderr
+++ b/src/test/ui/mismatched_types/closure-arg-count.stderr
@@ -56,8 +56,8 @@ LL |     f(|| panic!());
 note: required by a bound in `f`
   --> $DIR/closure-arg-count.rs:3:9
    |
-LL | fn f<F: Fn<usize>>(_: F) {}
-   |         ^^^^^^^^^ required by this bound in `f`
+LL | fn f<F: Fn<(usize,)>>(_: F) {}
+   |         ^^^^^^^^^^^^ required by this bound in `f`
 help: consider changing the closure to take and ignore the expected argument
    |
 LL |     f(|_| panic!());
@@ -74,8 +74,8 @@ LL |     f(  move    || panic!());
 note: required by a bound in `f`
   --> $DIR/closure-arg-count.rs:3:9
    |
-LL | fn f<F: Fn<usize>>(_: F) {}
-   |         ^^^^^^^^^ required by this bound in `f`
+LL | fn f<F: Fn<(usize,)>>(_: F) {}
+   |         ^^^^^^^^^^^^ required by this bound in `f`
 help: consider changing the closure to take and ignore the expected argument
    |
 LL |     f(  move    |_| panic!());
diff --git a/src/test/ui/unboxed-closures/non-tupled-arg-mismatch.rs b/src/test/ui/unboxed-closures/non-tupled-arg-mismatch.rs
new file mode 100644
index 00000000000..925463d6dee
--- /dev/null
+++ b/src/test/ui/unboxed-closures/non-tupled-arg-mismatch.rs
@@ -0,0 +1,8 @@
+#![feature(unboxed_closures)]
+
+fn a<F: Fn<usize>>(f: F) {}
+
+fn main() {
+    a(|_: usize| {});
+    //~^ ERROR mismatched types
+}
diff --git a/src/test/ui/unboxed-closures/non-tupled-arg-mismatch.stderr b/src/test/ui/unboxed-closures/non-tupled-arg-mismatch.stderr
new file mode 100644
index 00000000000..9a24fb8c2be
--- /dev/null
+++ b/src/test/ui/unboxed-closures/non-tupled-arg-mismatch.stderr
@@ -0,0 +1,17 @@
+error[E0308]: mismatched types
+  --> $DIR/non-tupled-arg-mismatch.rs:6:5
+   |
+LL |     a(|_: usize| {});
+   |     ^ types differ
+   |
+   = note: expected trait `Fn<usize>`
+              found trait `Fn<(usize,)>`
+note: required by a bound in `a`
+  --> $DIR/non-tupled-arg-mismatch.rs:3:9
+   |
+LL | fn a<F: Fn<usize>>(f: F) {}
+   |         ^^^^^^^^^ required by this bound in `a`
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0308`.
generated by cgit-pink 1.4.1-3-g733a5 (git 2.37.1) at 2026-04-26 04:38:09 +0000