Rollup merge of rust-lang#137742 - mu001999-contrib:fix-137708, r=compiler-errors

unconditionally lower match arm even if it's unneeded for never pattern in match

fixes rust-lang#137708

Lowering arm body is skipped when lowering match arm with never pattern, but we may need the HirId for DefId in the body in later passes. And then we got the ICE `No HirId for DefId`.

Fixes this by lowering the arm body even if it's unneeded for never pattern in match, so that we can generate HirId and use it then.

r? `@compiler-errors`

Author: matthiaskrgr

compiler/rustc_ast_lowering/src/expr.rs

@@ -671,10 +671,13 @@ impl<'hir> LoweringContext<'_, 'hir> {
         let span = self.lower_span(arm.span);
         self.lower_attrs(hir_id, &arm.attrs, arm.span);
         let is_never_pattern = pat.is_never_pattern();
-        let body = if let Some(body) = &arm.body
+        // We need to lower the body even if it's unneeded for never pattern in match,
+        // ensure that we can get HirId for DefId if need (issue #137708).
+        let body = arm.body.as_ref().map(|x| self.lower_expr(x));
+        let body = if let Some(body) = body
             && !is_never_pattern
         {
-            self.lower_expr(body)
+            body
         } else {
             // Either `body.is_none()` or `is_never_pattern` here.
             if !is_never_pattern {

tests/ui/never_type/unused_trait_in_never_pattern_body.rs

@@ -0,0 +1,12 @@
+fn a() {
+    match 0 {
+        ! => || { //~ ERROR `!` patterns are experimental
+        //~^ ERROR a never pattern is always unreachable
+        //~^^ ERROR mismatched types
+            use std::ops::Add;
+            0.add(1)
+        },
+    }
+}
+
+fn main() {}

tests/ui/never_type/unused_trait_in_never_pattern_body.stderr

@@ -0,0 +1,36 @@
+error[E0658]: `!` patterns are experimental
+  --> $DIR/unused_trait_in_never_pattern_body.rs:3:9
+   |
+LL |         ! => || {
+   |         ^
+   |
+   = note: see issue #118155 <https://github.com/rust-lang/rust/issues/118155> for more information
+   = help: add `#![feature(never_patterns)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error: a never pattern is always unreachable
+  --> $DIR/unused_trait_in_never_pattern_body.rs:3:14
+   |
+LL |           ! => || {
+   |  ______________^
+LL | |
+LL | |
+LL | |             use std::ops::Add;
+LL | |             0.add(1)
+LL | |         },
+   | |         ^
+   | |         |
+   | |_________this will never be executed
+   |           help: remove this expression
+
+error: mismatched types
+  --> $DIR/unused_trait_in_never_pattern_body.rs:3:9
+   |
+LL |         ! => || {
+   |         ^ a never pattern must be used on an uninhabited type
+   |
+   = note: the matched value is of type `i32`
+
+error: aborting due to 3 previous errors
+
+For more information about this error, try `rustc --explain E0658`.