Rollup merge of rust-lang#148872 - ShoyuVanilla:issue-148192, r=chenyukang

fix: Do not ICE when missing match arm with ill-formed subty is met

Fixes rust-lang#148192

The ICE comes from the following line, calling `normalize_erasing_regions` to a projection type whose trait bound is not met:
https://github.com/rust-lang/rust/blob/2fcbda6c1a70606bdb09857e01d01fc6229da712/compiler/rustc_pattern_analysis/src/rustc.rs#L185-L194

The above function is called while trying to lint missing match arms, or scrutinize ctors of missing(not necessary error) match arms.

So, the following code can trigger ICEs.
```rust
trait WhereTrait {
    type Type;
}

fn foo(e: Enum) {
    match e {
        Enum::Map(_) => (), // ICE, while trying to lint missing arms
    }

    if let Enum::Map(_) = e {} // ICE, while trying to scrutinize missing ctors (even worse)
}

enum Enum {
    Map(()),
    Map2(<() as WhereTrait>::Type),
}
```

This ICE won't be triggered with the following code, as this is filtered out before `check_match` as the existence of ill-formed type inside the variant marks the body as tainted by error in `hir_typeck`, but for the above code, the `hir_typeck` complains nothing because everything it sees is locally correct.

```rust
fn foo(e: Enum) {
    match e {
        Enum::Map2(_) => (), // No ICE
    }
}
```

I've considered visiting and wf checking for the match scrutinee before entering `check_match`, but that might regress the perf and I think just emitting delayed bug would enough as the normalization failure would be originated by other errors like ill-formdness.

Author: Zalathar

compiler/rustc_pattern_analysis/src/rustc.rs

@@ -191,7 +191,18 @@ impl<'p, 'tcx: 'p> RustcPatCtxt<'p, 'tcx> {
         variant.fields.iter().map(move |field| {
             let ty = field.ty(self.tcx, args);
             // `field.ty()` doesn't normalize after instantiating.
-            let ty = self.tcx.normalize_erasing_regions(self.typing_env, ty);
+            let ty =
+                self.tcx.try_normalize_erasing_regions(self.typing_env, ty).unwrap_or_else(|e| {
+                    self.tcx.dcx().span_delayed_bug(
+                        self.scrut_span,
+                        format!(
+                            "Failed to normalize {:?} in typing_env={:?} while getting variant sub tys for {ty:?}",
+                            e.get_type_for_failure(),
+                            self.typing_env,
+                        ),
+                    );
+                    ty
+                });
             let ty = self.reveal_opaque_ty(ty);
             (field, ty)
         })

tests/ui/pattern/missing-ctor-with-ill-formed-inner-ty-issue-148192.rs

@@ -0,0 +1,20 @@
+trait WhereTrait {
+    type Type;
+}
+
+fn foo(e: Enum) {
+    if let Enum::Map(_) = e {}
+
+    match e {
+        //~^ ERROR: non-exhaustive patterns: `Enum::Map2(_)` not covered
+        Enum::Map(_) => (),
+    }
+}
+
+enum Enum {
+    Map(()),
+    Map2(<() as WhereTrait>::Type),
+    //~^ ERROR: the trait bound `(): WhereTrait` is not satisfied
+}
+
+fn main() {}

tests/ui/pattern/missing-ctor-with-ill-formed-inner-ty-issue-148192.stderr

@@ -0,0 +1,37 @@
+error[E0277]: the trait bound `(): WhereTrait` is not satisfied
+  --> $DIR/missing-ctor-with-ill-formed-inner-ty-issue-148192.rs:16:10
+   |
+LL |     Map2(<() as WhereTrait>::Type),
+   |          ^^^^^^^^^^^^^^^^^^^^^^^^ the trait `WhereTrait` is not implemented for `()`
+   |
+help: this trait has no implementations, consider adding one
+  --> $DIR/missing-ctor-with-ill-formed-inner-ty-issue-148192.rs:1:1
+   |
+LL | trait WhereTrait {
+   | ^^^^^^^^^^^^^^^^
+
+error[E0004]: non-exhaustive patterns: `Enum::Map2(_)` not covered
+  --> $DIR/missing-ctor-with-ill-formed-inner-ty-issue-148192.rs:8:11
+   |
+LL |     match e {
+   |           ^ pattern `Enum::Map2(_)` not covered
+   |
+note: `Enum` defined here
+  --> $DIR/missing-ctor-with-ill-formed-inner-ty-issue-148192.rs:14:6
+   |
+LL | enum Enum {
+   |      ^^^^
+LL |     Map(()),
+LL |     Map2(<() as WhereTrait>::Type),
+   |     ---- not covered
+   = note: the matched value is of type `Enum`
+help: ensure that all possible cases are being handled by adding a match arm with a wildcard pattern or an explicit pattern as shown
+   |
+LL ~         Enum::Map(_) => (),
+LL ~         Enum::Map2(_) => todo!(),
+   |
+
+error: aborting due to 2 previous errors
+
+Some errors have detailed explanations: E0004, E0277.
+For more information about an error, try `rustc --explain E0004`.