Rollup merge of #144666 - compiler-errors:correct-late, r=lqd

Make sure to account for the right item universal regions in borrowck

Fixes #144608.

The ICE comes from a mismatch between the liberated late bound regions (i.e. "`ReLateParam`"s) that come from promoting closure outlives, and the regions we have in our region vid mapping from `UniversalRegions`.

When building `UniversalRegions`, we end up using the liberated regions from the binder of the closure's signature:

https://github.com/rust-lang/rust/blob/c8bb4e8a126cf38cff70cea488a3a423a5321954/compiler/rustc_borrowck/src/universal_regions.rs#L521

Notably, this signature may be anonymized if the closure signature being deduced comes from an external constraints:

https://github.com/rust-lang/rust/blob/c8bb4e8a126cf38cff70cea488a3a423a5321954/compiler/rustc_hir_typeck/src/closure.rs#L759-L762

This is true in the test file I committed, where the signature is influenced by the `impl FnMut(&mut ())` RPIT.

However, when promoting a type outlives constraint we end up creating a late bound lifetime mapping that disagrees with those liberated late bound regions we constructed in `UniversalRegions`:

https://github.com/rust-lang/rust/blob/c8bb4e8a126cf38cff70cea488a3a423a5321954/compiler/rustc_borrowck/src/universal_regions.rs#L299

Specifically, in `for_each_late_bound_region_in_item` (which is called by `for_each_late_bound_region_in_recursive_scope`), we were using `tcx.late_bound_vars` which uses the late bound regions *from the HIR*. This query both undercounts the late bound regions (e.g. those that end up being deduced from bounds), and also doesn't account for the fact that we anonymize them in the signature as mentioned above.

https://github.com/rust-lang/rust/blob/c8bb4e8a126cf38cff70cea488a3a423a5321954/compiler/rustc_borrowck/src/universal_regions.rs#L977

This PR fixes that function to use the *correct signature*, which properly considers the bound vars that come from deducing the signature of the closure, and which comes from the closure's args from the `type_of` query.

Author: Zalathar

compiler/rustc_borrowck/src/universal_regions.rs

@@ -969,13 +969,28 @@ fn for_each_late_bound_region_in_item<'tcx>(
     mir_def_id: LocalDefId,
     mut f: impl FnMut(ty::Region<'tcx>),
 ) {
-    if !tcx.def_kind(mir_def_id).is_fn_like() {
-        return;
-    }
+    let bound_vars = match tcx.def_kind(mir_def_id) {
+        DefKind::Fn | DefKind::AssocFn => {
+            tcx.late_bound_vars(tcx.local_def_id_to_hir_id(mir_def_id))
+        }
+        // We extract the bound vars from the deduced closure signature, since we may have
+        // only deduced that a param in the closure signature is late-bound from a constraint
+        // that we discover during typeck.
+        DefKind::Closure => {
+            let ty = tcx.type_of(mir_def_id).instantiate_identity();
+            match *ty.kind() {
+                ty::Closure(_, args) => args.as_closure().sig().bound_vars(),
+                ty::CoroutineClosure(_, args) => {
+                    args.as_coroutine_closure().coroutine_closure_sig().bound_vars()
+                }
+                ty::Coroutine(_, _) | ty::Error(_) => return,
+                _ => unreachable!("unexpected type for closure: {ty}"),
+            }
+        }
+        _ => return,
+    };
 
-    for (idx, bound_var) in
-        tcx.late_bound_vars(tcx.local_def_id_to_hir_id(mir_def_id)).iter().enumerate()
-    {
+    for (idx, bound_var) in bound_vars.iter().enumerate() {
         if let ty::BoundVariableKind::Region(kind) = bound_var {
             let kind = ty::LateParamRegionKind::from_bound(ty::BoundVar::from_usize(idx), kind);
             let liberated_region = ty::Region::new_late_param(tcx, mir_def_id.to_def_id(), kind);

tests/ui/borrowck/liberated-region-from-outer-closure.rs

@@ -0,0 +1,12 @@
+// Regression test for <https://github.com/rust-lang/rust/issues/144608>.
+
+fn example<T: Copy>(x: T) -> impl FnMut(&mut ()) {
+    move |_: &mut ()| {
+        move || needs_static_lifetime(x);
+        //~^ ERROR the parameter type `T` may not live long enough
+    }
+}
+
+fn needs_static_lifetime<T: 'static>(obj: T) {}
+
+fn main() {}

tests/ui/borrowck/liberated-region-from-outer-closure.stderr

@@ -0,0 +1,17 @@
+error[E0310]: the parameter type `T` may not live long enough
+  --> $DIR/liberated-region-from-outer-closure.rs:5:17
+   |
+LL |         move || needs_static_lifetime(x);
+   |                 ^^^^^^^^^^^^^^^^^^^^^^^^
+   |                 |
+   |                 the parameter type `T` must be valid for the static lifetime...
+   |                 ...so that the type `T` will meet its required lifetime bounds
+   |
+help: consider adding an explicit lifetime bound
+   |
+LL | fn example<T: Copy + 'static>(x: T) -> impl FnMut(&mut ()) {
+   |                    +++++++++
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0310`.

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

@@ -9,6 +9,9 @@ LL |         let mut closure = expect_sig(|p, y| *p = y);
                for<Region(BrAnon), Region(BrAnon), Region(BrAnon)> extern "rust-call" fn((&'^0 mut &'^1 i32, &'^2 i32)),
                (),
            ]
+   = note: late-bound region is '?1
+   = note: late-bound region is '?2
+   = note: late-bound region is '?3
 
 error: lifetime may not live long enough
   --> $DIR/escape-argument-callee.rs:26:45

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

@@ -9,6 +9,8 @@ LL |         let mut closure = expect_sig(|p, y| *p = y);
                for<Region(BrAnon), Region(BrAnon)> extern "rust-call" fn((&'^0 mut &'^1 i32, &'^1 i32)),
                (),
            ]
+   = note: late-bound region is '?1
+   = note: late-bound region is '?2
 
 note: no external requirements
   --> $DIR/escape-argument.rs:20:1

tests/ui/nll/closure-requirements/propagate-approximated-fail-no-postdom.stderr

@@ -9,6 +9,8 @@ LL |         |_outlives1, _outlives2, _outlives3, x, y| {
                for<Region(BrAnon), Region(BrAnon)> extern "rust-call" fn((std::cell::Cell<&'?1 &'^0 u32>, std::cell::Cell<&'?2 &'^0 u32>, std::cell::Cell<&'^1 &'?3 u32>, std::cell::Cell<&'^0 u32>, std::cell::Cell<&'^1 u32>)),
                (),
            ]
+   = note: late-bound region is '?7
+   = note: late-bound region is '?8
    = note: late-bound region is '?4
    = note: late-bound region is '?5
    = note: late-bound region is '?6

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

@@ -9,6 +9,12 @@ LL |     establish_relationships(&cell_a, &cell_b, |_outlives1, _outlives2, x, y
                for<Region(BrAnon), Region(BrAnon), Region(BrAnon), Region(BrAnon), Region(BrAnon), Region(BrAnon)> extern "rust-call" fn((&'^0 std::cell::Cell<&'?1 &'^1 u32>, &'^2 std::cell::Cell<&'^3 &'?2 u32>, &'^4 std::cell::Cell<&'^1 u32>, &'^5 std::cell::Cell<&'^3 u32>)),
                (),
            ]
+   = note: late-bound region is '?5
+   = note: late-bound region is '?6
+   = note: late-bound region is '?7
+   = note: late-bound region is '?8
+   = note: late-bound region is '?9
+   = note: late-bound region is '?10
    = note: late-bound region is '?3
    = note: late-bound region is '?4
    = note: number of external vids: 5

tests/ui/nll/closure-requirements/propagate-approximated-shorter-to-static-comparing-against-free.stderr

@@ -9,6 +9,7 @@ LL |     foo(cell, |cell_a, cell_x| {
                for<Region(BrAnon)> extern "rust-call" fn((std::cell::Cell<&'?1 u32>, std::cell::Cell<&'^0 u32>)),
                (),
            ]
+   = note: late-bound region is '?2
 
 error[E0521]: borrowed data escapes outside of closure
   --> $DIR/propagate-approximated-shorter-to-static-comparing-against-free.rs:22:9
@@ -43,6 +44,7 @@ LL |     foo(cell, |cell_a, cell_x| {
                for<Region(BrAnon)> extern "rust-call" fn((std::cell::Cell<&'?1 u32>, std::cell::Cell<&'^0 u32>)),
                (),
            ]
+   = note: late-bound region is '?2
    = note: number of external vids: 2
    = note: where '?1: '?0
 

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

@@ -9,6 +9,11 @@ LL |     establish_relationships(&cell_a, &cell_b, |_outlives, x, y| {
                for<Region(BrAnon), Region(BrAnon), Region(BrAnon), Region(BrAnon), Region(BrAnon)> extern "rust-call" fn((&'^0 std::cell::Cell<&'?1 &'^1 u32>, &'^2 std::cell::Cell<&'^1 u32>, &'^3 std::cell::Cell<&'^4 u32>)),
                (),
            ]
+   = note: late-bound region is '?4
+   = note: late-bound region is '?5
+   = note: late-bound region is '?6
+   = note: late-bound region is '?7
+   = note: late-bound region is '?8
    = note: late-bound region is '?2
    = note: late-bound region is '?3
    = note: number of external vids: 4

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

@@ -9,6 +9,12 @@ LL |     establish_relationships(&cell_a, &cell_b, |_outlives1, _outlives2, x, y
                for<Region(BrAnon), Region(BrAnon), Region(BrAnon), Region(BrAnon), Region(BrAnon), Region(BrAnon)> extern "rust-call" fn((&'^0 std::cell::Cell<&'?1 &'^1 u32>, &'^2 std::cell::Cell<&'?2 &'^3 u32>, &'^4 std::cell::Cell<&'^1 u32>, &'^5 std::cell::Cell<&'^3 u32>)),
                (),
            ]
+   = note: late-bound region is '?5
+   = note: late-bound region is '?6
+   = note: late-bound region is '?7
+   = note: late-bound region is '?8
+   = note: late-bound region is '?9
+   = note: late-bound region is '?10
    = note: late-bound region is '?3
    = note: late-bound region is '?4
    = note: number of external vids: 5