Fix ICE in normalization during closure capture analysis (#149746)

compiler/rustc_hir_typeck/src/upvar.rs

@@ -1553,10 +1553,16 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
     ) -> bool {
         // FIXME(#132279): Using `non_body_analysis` here feels wrong.
         let needs_drop = |ty: Ty<'tcx>| {
-            ty.has_significant_drop(
-                self.tcx,
-                ty::TypingEnv::non_body_analysis(self.tcx, closure_def_id),
-            )
+            let typing_env = ty::TypingEnv::non_body_analysis(self.tcx, closure_def_id);
+
+            // FIX for ICE #149746:
+            // We try to normalize the type first.
+            // If normalization fails, we assume it doesn't have a significant drop (false)
+            // to avoid crashing, allowing the compiler to emit the underlying type error later.
+            self.tcx
+                .try_normalize_erasing_regions(typing_env, ty)
+                .map(|normalized_ty| normalized_ty.has_significant_drop(self.tcx, typing_env))
+                .unwrap_or(false)
         };
 
         let is_drop_defined_for_ty = |ty: Ty<'tcx>| {

tests/ui/associated-types/normalization-ice-issue-149746.rs

@@ -0,0 +1,16 @@
+//@ edition: 2015..2021
+#![warn(rust_2021_incompatible_closure_captures)]
+trait Owner { type Ty<T: FnMut()>; }
+impl Owner for () { type Ty<T: FnMut()> = T; }
+pub struct Warns<T> {
+    _significant_drop: <() as Owner>::Ty<T>,
+    //~^ ERROR expected a `FnMut()` closure, found `T`
+    field: String,
+}
+pub fn test<T>(w: Warns<T>) {
+    //~^ ERROR expected a `FnMut()` closure, found `T`
+    _ = || w.field
+    //~^ ERROR expected a `FnMut()` closure, found `T`
+    //~| ERROR expected a `FnMut()` closure, found `T`
+}
+fn main() {}

tests/ui/associated-types/normalization-ice-issue-149746.stderr

@@ -0,0 +1,60 @@
+error[E0277]: expected a `FnMut()` closure, found `T`
+  --> $DIR/normalization-ice-issue-149746.rs:6:24
+   |
+LL |     _significant_drop: <() as Owner>::Ty<T>,
+   |                        ^^^^^^^^^^^^^^^^^^^^ expected an `FnMut()` closure, found `T`
+   |
+   = note: wrap the `T` in a closure with no arguments: `|| { /* code */ }`
+note: required by a bound in `Owner::Ty`
+  --> $DIR/normalization-ice-issue-149746.rs:3:26
+   |
+LL | trait Owner { type Ty<T: FnMut()>; }
+   |                          ^^^^^^^ required by this bound in `Owner::Ty`
+help: consider restricting type parameter `T` with trait `FnMut`
+   |
+LL | pub struct Warns<T: FnMut()> {
+   |                   +++++++++
+
+error[E0277]: expected a `FnMut()` closure, found `T`
+  --> $DIR/normalization-ice-issue-149746.rs:12:9
+   |
+LL |     _ = || w.field
+   |         ^^^^^^^^^^ expected an `FnMut()` closure, found `T`
+   |
+   = note: wrap the `T` in a closure with no arguments: `|| { /* code */ }`
+note: required by a bound in `Owner::Ty`
+  --> $DIR/normalization-ice-issue-149746.rs:3:26
+   |
+LL | trait Owner { type Ty<T: FnMut()>; }
+   |                          ^^^^^^^ required by this bound in `Owner::Ty`
+
+error[E0277]: expected a `FnMut()` closure, found `T`
+  --> $DIR/normalization-ice-issue-149746.rs:10:16
+   |
+LL | pub fn test<T>(w: Warns<T>) {
+   |                ^ expected an `FnMut()` closure, found `T`
+   |
+   = note: wrap the `T` in a closure with no arguments: `|| { /* code */ }`
+note: required by a bound in `Owner::Ty`
+  --> $DIR/normalization-ice-issue-149746.rs:3:26
+   |
+LL | trait Owner { type Ty<T: FnMut()>; }
+   |                          ^^^^^^^ required by this bound in `Owner::Ty`
+
+error[E0277]: expected a `FnMut()` closure, found `T`
+  --> $DIR/normalization-ice-issue-149746.rs:12:9
+   |
+LL |     _ = || w.field
+   |         ^^^^^^^^^^ expected an `FnMut()` closure, found `T`
+   |
+   = note: wrap the `T` in a closure with no arguments: `|| { /* code */ }`
+note: required by a bound in `Owner::Ty`
+  --> $DIR/normalization-ice-issue-149746.rs:3:26
+   |
+LL | trait Owner { type Ty<T: FnMut()>; }
+   |                          ^^^^^^^ required by this bound in `Owner::Ty`
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
+
+error: aborting due to 4 previous errors
+
+For more information about this error, try `rustc --explain E0277`.