WF checks on closure arguments.

compiler/rustc_borrowck/src/type_check/canonical.rs

@@ -323,53 +323,4 @@ impl<'a, 'tcx> TypeChecker<'a, 'tcx> {
                 .and(type_op::ascribe_user_type::AscribeUserType { mir_ty, user_ty }),
         );
     }
-
-    /// *Incorrectly* skips the WF checks we normally do in `ascribe_user_type`.
-    ///
-    /// FIXME(#104478, #104477): This is a hack for backward-compatibility.
-    #[instrument(skip(self), level = "debug")]
-    pub(super) fn ascribe_user_type_skip_wf(
-        &mut self,
-        mir_ty: Ty<'tcx>,
-        user_ty: ty::UserType<'tcx>,
-        span: Span,
-    ) {
-        let ty::UserTypeKind::Ty(user_ty) = user_ty.kind else { bug!() };
-
-        // A fast path for a common case with closure input/output types.
-        if let ty::Infer(_) = user_ty.kind() {
-            self.eq_types(user_ty, mir_ty, Locations::All(span), ConstraintCategory::Boring)
-                .unwrap();
-            return;
-        }
-
-        // This is a hack. `body.local_decls` are not necessarily normalized in the old
-        // solver due to not deeply normalizing in writeback. So we must re-normalize here.
-        //
-        // I am not sure of a test case where this actually matters. There is a similar
-        // hack in `equate_inputs_and_outputs` which does have associated test cases.
-        let mir_ty = match self.infcx.next_trait_solver() {
-            true => mir_ty,
-            false => self.normalize(mir_ty, Locations::All(span)),
-        };
-
-        let cause = ObligationCause::dummy_with_span(span);
-        let param_env = self.infcx.param_env;
-        let _: Result<_, ErrorGuaranteed> = self.fully_perform_op(
-            Locations::All(span),
-            ConstraintCategory::Boring,
-            type_op::custom::CustomTypeOp::new(
-                |ocx| {
-                    // The `AscribeUserType` query would normally emit a wf
-                    // obligation for the unnormalized user_ty here. This is
-                    // where the "incorrectly skips the WF checks we normally do"
-                    // happens
-                    let user_ty = ocx.normalize(&cause, param_env, user_ty);
-                    ocx.eq(&cause, param_env, user_ty, mir_ty)?;
-                    Ok(())
-                },
-                "ascribe_user_type_skip_wf",
-            ),
-        );
-    }
 }

compiler/rustc_borrowck/src/type_check/input_output.rs

@@ -111,7 +111,7 @@ impl<'a, 'tcx> TypeChecker<'a, 'tcx> {
                 .skip(1 + if is_coroutine_with_implicit_resume_ty { 1 } else { 0 })
                 .map(|local| &self.body.local_decls[local]),
         ) {
-            self.ascribe_user_type_skip_wf(
+            self.ascribe_user_type(
                 arg_decl.ty,
                 ty::UserType::new(ty::UserTypeKind::Ty(user_ty)),
                 arg_decl.source_info.span,
@@ -120,7 +120,7 @@ impl<'a, 'tcx> TypeChecker<'a, 'tcx> {
 
         // If the user explicitly annotated the output type, enforce it.
         let output_decl = &self.body.local_decls[RETURN_PLACE];
-        self.ascribe_user_type_skip_wf(
+        self.ascribe_user_type(
             output_decl.ty,
             ty::UserType::new(ty::UserTypeKind::Ty(user_provided_sig.output())),
             output_decl.source_info.span,

tests/ui/implied-bounds/hrlt-implied-trait-bounds-roundtrip.rs

@@ -1,4 +1,3 @@
-//@ check-pass
 struct Foo<'a>(&'a ())
 where
     (): Trait<'a>;
@@ -21,7 +20,7 @@ where
 }
 
 fn main() {
-    let bar: for<'a, 'b> fn(Foo<'a>, &'b ()) = |_, _| {};
+    let bar: for<'a, 'b> fn(Foo<'a>, &'b ()) = |_, _| {}; //~ ERROR: lifetime may not live long enough
 
     // If `could_use_implied_bounds` were to use implied bounds,
     // keeping 'a late-bound, then we could assign that function

tests/ui/implied-bounds/hrlt-implied-trait-bounds-roundtrip.stderr

@@ -0,0 +1,11 @@
+error: lifetime may not live long enough
+  --> $DIR/hrlt-implied-trait-bounds-roundtrip.rs:23:49
+   |
+LL |     let bar: for<'a, 'b> fn(Foo<'a>, &'b ()) = |_, _| {};
+   |                                                 ^
+   |                                                 |
+   |                                                 has type `Foo<'1>`
+   |                                                 requires that `'1` must outlive `'static`
+
+error: aborting due to 1 previous error
+

tests/ui/nll/closure-requirements/escape-argument-callee.stderr

@@ -20,7 +20,7 @@ LL |         let mut closure = expect_sig(|p, y| *p = y);
    |                                       -  -  ^^^^^^ assignment requires that `'1` must outlive `'2`
    |                                       |  |
    |                                       |  has type `&'1 i32`
-   |                                       has type `&'?1 mut &'2 i32`
+   |                                       has type `&'2 mut &'?2 i32`
 
 note: no external requirements
   --> $DIR/escape-argument-callee.rs:20:1

tests/ui/nll/closure-requirements/propagate-approximated-ref.stderr

@@ -19,6 +19,8 @@ LL |     establish_relationships(&cell_a, &cell_b, |_outlives1, _outlives2, x, y
    = note: late-bound region is '?4
    = note: number of external vids: 5
    = note: where '?1: '?2
+   = note: where '?1: '?2
+   = note: where '?1: '?2
 
 note: no external requirements
   --> $DIR/propagate-approximated-ref.rs:42:1

tests/ui/nll/closure-requirements/propagate-approximated-shorter-to-static-no-bound.stderr

@@ -18,6 +18,7 @@ LL |     establish_relationships(&cell_a, &cell_b, |_outlives, x, y| {
    = note: late-bound region is '?3
    = note: number of external vids: 4
    = note: where '?1: '?0
+   = note: where '?1: '?0
 
 note: no external requirements
   --> $DIR/propagate-approximated-shorter-to-static-no-bound.rs:31:1

tests/ui/nll/closure-requirements/propagate-approximated-shorter-to-static-wrong-bound.stderr

@@ -18,6 +18,9 @@ LL |     establish_relationships(&cell_a, &cell_b, |_outlives1, _outlives2, x, y
    = note: late-bound region is '?3
    = note: late-bound region is '?4
    = note: number of external vids: 5
+   = note: where '?1: '?2
+   = note: where '?1: '?2
+   = note: where '?1: '?0
    = note: where '?1: '?0
 
 note: no external requirements

tests/ui/nll/closure-requirements/propagate-fail-to-approximate-longer-no-bounds.stderr

@@ -23,7 +23,7 @@ error: lifetime may not live long enough
 LL |     establish_relationships(&cell_a, &cell_b, |_outlives, x, y| {
    |                                                ---------  - has type `&'?6 Cell<&'1 u32>`
    |                                                |
-   |                                                has type `&'?4 Cell<&'2 &'?1 u32>`
+   |                                                has type `&'2 Cell<&'?5 &'?1 u32>`
 LL |         // Only works if 'x: 'y:
 LL |         demand_y(x, y, x.get())
    |         ^^^^^^^^^^^^^^^^^^^^^^^ argument requires that `'1` must outlive `'2`

tests/ui/nll/closure-requirements/propagate-fail-to-approximate-longer-wrong-bounds.rs

@@ -36,7 +36,7 @@ fn demand_y<'x, 'y>(_cell_x: &Cell<&'x u32>, _cell_y: &Cell<&'y u32>, _y: &'y u3
 
 #[rustc_regions]
 fn supply<'a, 'b>(cell_a: Cell<&'a u32>, cell_b: Cell<&'b u32>) {
-    establish_relationships(&cell_a, &cell_b, |_outlives1, _outlives2, x, y| {
+    establish_relationships(&cell_a, &cell_b, |_outlives1, _outlives2, x, y| { //~ ERROR: lifetime may not live long enough
         // Only works if 'x: 'y:
         demand_y(x, y, x.get())
         //~^ ERROR

tests/ui/nll/closure-requirements/propagate-fail-to-approximate-longer-wrong-bounds.stderr

@@ -1,4 +1,4 @@
-note: no external requirements
+note: external requirements
   --> $DIR/propagate-fail-to-approximate-longer-wrong-bounds.rs:39:47
    |
 LL |     establish_relationships(&cell_a, &cell_b, |_outlives1, _outlives2, x, y| {
@@ -17,12 +17,16 @@ LL |     establish_relationships(&cell_a, &cell_b, |_outlives1, _outlives2, x, y
    = note: late-bound region is '?10
    = note: late-bound region is '?3
    = note: late-bound region is '?4
+   = note: number of external vids: 5
+   = note: where '?1: '?2
+   = note: where '?1: '?2
+   = note: where '?1: '?2
 
 error: lifetime may not live long enough
   --> $DIR/propagate-fail-to-approximate-longer-wrong-bounds.rs:41:9
    |
 LL |     establish_relationships(&cell_a, &cell_b, |_outlives1, _outlives2, x, y| {
-   |                                                ----------  ---------- has type `&'?7 Cell<&'2 &'?2 u32>`
+   |                                                ----------  ---------- has type `&'2 Cell<&'?8 &'?2 u32>`
    |                                                |
    |                                                has type `&'?5 Cell<&'1 &'?1 u32>`
 LL |         // Only works if 'x: 'y:
@@ -41,5 +45,24 @@ LL | fn supply<'a, 'b>(cell_a: Cell<&'a u32>, cell_b: Cell<&'b u32>) {
    |
    = note: defining type: supply
 
-error: aborting due to 1 previous error
+error: lifetime may not live long enough
+  --> $DIR/propagate-fail-to-approximate-longer-wrong-bounds.rs:39:5
+   |
+LL |   fn supply<'a, 'b>(cell_a: Cell<&'a u32>, cell_b: Cell<&'b u32>) {
+   |             --  -- lifetime `'b` defined here
+   |             |
+   |             lifetime `'a` defined here
+LL | /     establish_relationships(&cell_a, &cell_b, |_outlives1, _outlives2, x, y| {
+LL | |         // Only works if 'x: 'y:
+LL | |         demand_y(x, y, x.get())
+LL | |
+LL | |     });
+   | |______^ argument requires that `'a` must outlive `'b`
+   |
+   = help: consider adding the following bound: `'a: 'b`
+   = note: requirement occurs because of the type `Cell<&'?11 u32>`, which makes the generic argument `&'?11 u32` invariant
+   = note: the struct `Cell<T>` is invariant over the parameter `T`
+   = help: see <https://doc.rust-lang.org/nomicon/subtyping.html> for more information about variance
+
+error: aborting due to 2 previous errors
 

tests/ui/unboxed-closures/unboxed-closures-infer-argument-types-two-region-pointers.stderr

@@ -4,7 +4,7 @@ error: lifetime may not live long enough
 LL |     doit(0, &|x, y| {
    |               -  - has type `&'1 i32`
    |               |
-   |               has type `&Cell<&'2 i32>`
+   |               has type `&'2 Cell<&i32>`
 LL |         x.set(y);
    |         ^^^^^^^^ argument requires that `'1` must outlive `'2`
    |

tests/ui/wf/check-wf-of-closure-args.rs

@@ -0,0 +1,14 @@
+// Checks that we perform WF checks on closure args, regardless of wether they
+// are used in the closure it self.
+// related to issue #104478
+
+struct MyTy<T: Trait>(T);
+trait Trait {}
+impl Trait for &'static str {}
+fn wf<T>(_: T) {}
+
+fn main() {
+    let _: for<'x> fn(MyTy<&'x str>) = |_| {}; //~ ERROR: lifetime may not live long enough
+
+    let _: for<'x> fn(MyTy<&'x str>) = |x| wf(x); //~ ERROR: lifetime may not live long enough
+}

tests/ui/wf/check-wf-of-closure-args.stderr

@@ -0,0 +1,20 @@
+error: lifetime may not live long enough
+  --> $DIR/check-wf-of-closure-args.rs:11:41
+   |
+LL |     let _: for<'x> fn(MyTy<&'x str>) = |_| {};
+   |                                         ^
+   |                                         |
+   |                                         has type `MyTy<&'1 str>`
+   |                                         requires that `'1` must outlive `'static`
+
+error: lifetime may not live long enough
+  --> $DIR/check-wf-of-closure-args.rs:13:41
+   |
+LL |     let _: for<'x> fn(MyTy<&'x str>) = |x| wf(x);
+   |                                         ^
+   |                                         |
+   |                                         has type `MyTy<&'1 str>`
+   |                                         requires that `'1` must outlive `'static`
+
+error: aborting due to 2 previous errors
+