Rollup merge of #132668 - ehuss:yield-gate-2024, r=davidtwco

Feature gate yield expressions not in 2024

This changes it so that yield expressions are no longer allowed in the 2024 edition without a feature gate. We are currently only reserving the `gen` keyword in the 2024 edition, and not allowing anything else to be implicitly enabled by the edition.

In practice this doesn't have a significant difference since yield expressions can't really be used outside of coroutines or gen blocks, which have their own feature gates. However, it does affect what is accepted pre-expansion, and I would feel more comfortable not allowing yield expressions.

I believe the stabilization process for gen blocks or coroutines will not need to check the edition here, so this shouldn't ever be needed.

1 files changed, 12 insertions, 3 deletions

diff --git a/compiler/rustc_ast_passes/src/feature_gate.rs b/compiler/rustc_ast_passes/src/feature_gate.rs
index 396aac34515..be6f2c152a4 100644
--- a/compiler/rustc_ast_passes/src/feature_gate.rs
+++ b/compiler/rustc_ast_passes/src/feature_gate.rs
@@ -523,9 +523,18 @@ pub fn check_crate(krate: &ast::Crate, sess: &Session, features: &Features) {
         "consider removing `for<...>`"
     );
     gate_all!(more_qualified_paths, "usage of qualified paths in this context is experimental");
-    for &span in spans.get(&sym::yield_expr).iter().copied().flatten() {
-        if !span.at_least_rust_2024() {
-            gate!(&visitor, coroutines, span, "yield syntax is experimental");
+    // yield can be enabled either by `coroutines` or `gen_blocks`
+    if let Some(spans) = spans.get(&sym::yield_expr) {
+        for span in spans {
+            if (!visitor.features.coroutines() && !span.allows_unstable(sym::coroutines))
+                && (!visitor.features.gen_blocks() && !span.allows_unstable(sym::gen_blocks))
+            {
+                #[allow(rustc::untranslatable_diagnostic)]
+                // Don't know which of the two features to include in the
+                // error message, so I am arbitrarily picking one.
+                feature_err(&visitor.sess, sym::coroutines, *span, "yield syntax is experimental")
+                    .emit();
+            }
         }
     }
     gate_all!(gen_blocks, "gen blocks are experimental");