Auto merge of #96376 - scottmcm:do-yeet, r=oli-obk

Add `do yeet` expressions to allow experimentation in nightly

Two main goals for this:
- Ensure that trait restructuring in https://github.com/rust-lang/rust/issues/84277#issuecomment-1066120333 doesn't accidentally close us off from the possibility of doing this in future, as sketched in https://rust-lang.github.io/rfcs/3058-try-trait-v2.html#possibilities-for-yeet
- Experiment with the *existence* of syntax for this, to be able to weight the syntax-vs-library tradeoffs better than we can right now.  Notably the syntax (with `do`) and name in this PR are not intended as candidates for stabilization, but they make a good v0 PR for adding this with minimal impact to compiler maintenance or priming one possible name choice over another.

r? `@oli-obk`
The lang `second` for doing this: https://github.com/rust-lang/lang-team/issues/160#issuecomment-1107896716

Tracking issues
- Lang, https://github.com/rust-lang/rust/issues/96373
- Libs-api, https://github.com/rust-lang/rust/issues/96374

1 files changed, 21 insertions, 0 deletions

diff --git a/compiler/rustc_parse/src/parser/expr.rs b/compiler/rustc_parse/src/parser/expr.rs
index 13e9a5e660f..6114e7aaa7b 100644
--- a/compiler/rustc_parse/src/parser/expr.rs
+++ b/compiler/rustc_parse/src/parser/expr.rs
@@ -1374,6 +1374,8 @@ impl<'a> Parser<'a> {
             self.parse_break_expr(attrs)
         } else if self.eat_keyword(kw::Yield) {
             self.parse_yield_expr(attrs)
+        } else if self.is_do_yeet() {
+            self.parse_yeet_expr(attrs)
         } else if self.eat_keyword(kw::Let) {
             self.parse_let_expr(attrs)
         } else if self.eat_keyword(kw::Underscore) {
@@ -1605,6 +1607,21 @@ impl<'a> Parser<'a> {
         self.maybe_recover_from_bad_qpath(expr, true)
     }
 
+    /// Parse `"do" "yeet" expr?`.
+    fn parse_yeet_expr(&mut self, attrs: AttrVec) -> PResult<'a, P<Expr>> {
+        let lo = self.token.span;
+
+        self.bump(); // `do`
+        self.bump(); // `yeet`
+
+        let kind = ExprKind::Yeet(self.parse_expr_opt()?);
+
+        let span = lo.to(self.prev_token.span);
+        self.sess.gated_spans.gate(sym::yeet_expr, span);
+        let expr = self.mk_expr(span, kind, attrs);
+        self.maybe_recover_from_bad_qpath(expr, true)
+    }
+
     /// Parse `"break" (('label (:? expr)?) | expr?)` with `"break"` token already eaten.
     /// If the label is followed immediately by a `:` token, the label and `:` are
     /// parsed as part of the expression (i.e. a labeled loop). The language team has
@@ -2676,6 +2693,10 @@ impl<'a> Parser<'a> {
             && !self.restrictions.contains(Restrictions::NO_STRUCT_LITERAL)
     }
 
+    fn is_do_yeet(&self) -> bool {
+        self.token.is_keyword(kw::Do) && self.is_keyword_ahead(1, &[kw::Yeet])
+    }
+
     fn is_try_block(&self) -> bool {
         self.token.is_keyword(kw::Try)
             && self.look_ahead(1, |t| *t == token::OpenDelim(Delimiter::Brace))