Auto merge of #112953 - compiler-errors:interpolated-block-exprs, r=WaffleLapkin

Support interpolated block for `try` and `async`

I'm putting this up for T-lang discussion, to decide whether or not they feel like this should be supported. This was raised in #112952, which surprised me. There doesn't seem to be a *technical* reason why we don't support this.

### Precedent:

This is supported:

```rust
macro_rules! always {
  ($block:block) => {
    if true $block
  }
}

fn main() {
    always!({});
}
```

### Counterpoint:

However, for context, this is *not* supported:

```rust
macro_rules! unsafe_block {
  ($block:block) => {
    unsafe $block
  }
}

fn main() {
    unsafe_block!({});
}
```

If this support for `async` and `try` with interpolated blocks is *not* desirable, then I can convert them to instead the same diagnostic as `unsafe $block` and make this situation a lot less ambiguous.

----

I'll try to write up more before T-lang triage on Tuesday. I couldn't find anything other than #69760 for why something like `unsafe $block` is not supported, and even that PR doesn't have much information.

Fixes #112952

1 files changed, 10 insertions, 4 deletions

diff --git a/compiler/rustc_parse/src/parser/expr.rs b/compiler/rustc_parse/src/parser/expr.rs
index 3ecdbc36248..769415b614b 100644
--- a/compiler/rustc_parse/src/parser/expr.rs
+++ b/compiler/rustc_parse/src/parser/expr.rs
@@ -3003,7 +3003,8 @@ impl<'a> Parser<'a> {
     fn is_do_catch_block(&self) -> bool {
         self.token.is_keyword(kw::Do)
             && self.is_keyword_ahead(1, &[kw::Catch])
-            && self.look_ahead(2, |t| *t == token::OpenDelim(Delimiter::Brace))
+            && self
+                .look_ahead(2, |t| *t == token::OpenDelim(Delimiter::Brace) || t.is_whole_block())
             && !self.restrictions.contains(Restrictions::NO_STRUCT_LITERAL)
     }
 
@@ -3013,7 +3014,8 @@ impl<'a> Parser<'a> {
 
     fn is_try_block(&self) -> bool {
         self.token.is_keyword(kw::Try)
-            && self.look_ahead(1, |t| *t == token::OpenDelim(Delimiter::Brace))
+            && self
+                .look_ahead(1, |t| *t == token::OpenDelim(Delimiter::Brace) || t.is_whole_block())
             && self.token.uninterpolated_span().at_least_rust_2018()
     }
 
@@ -3032,10 +3034,14 @@ impl<'a> Parser<'a> {
             && ((
                 // `async move {`
                 self.is_keyword_ahead(1, &[kw::Move])
-                    && self.look_ahead(2, |t| *t == token::OpenDelim(Delimiter::Brace))
+                    && self.look_ahead(2, |t| {
+                        *t == token::OpenDelim(Delimiter::Brace) || t.is_whole_block()
+                    })
             ) || (
                 // `async {`
-                self.look_ahead(1, |t| *t == token::OpenDelim(Delimiter::Brace))
+                self.look_ahead(1, |t| {
+                    *t == token::OpenDelim(Delimiter::Brace) || t.is_whole_block()
+                })
             ))
     }