Feature gate gen blocks, even in 2024 edition

compiler/rustc_ast_passes/src/feature_gate.rs

@@ -554,7 +554,12 @@ 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");
-    gate_all!(coroutines, "yield syntax is experimental");
+    for &span in spans.get(&sym::yield_expr).iter().copied().flatten() {
+        if !span.at_least_rust_2024() {
+            gate_feature_post!(&visitor, coroutines, span, "yield syntax is experimental");
+        }
+    }
+    gate_all!(gen_blocks, "gen blocks are experimental");
     gate_all!(raw_ref_op, "raw address of syntax is experimental");
     gate_all!(const_trait_impl, "const trait impls are experimental");
     gate_all!(

compiler/rustc_feature/src/unstable.rs

@@ -456,6 +456,8 @@ declare_features! (
     (unstable, ffi_returns_twice, "1.34.0", Some(58314), None),
     /// Allows using `#[repr(align(...))]` on function items
     (unstable, fn_align, "1.53.0", Some(82232), None),
+    /// Allows defining gen blocks and `gen fn`.
+    (unstable, gen_blocks, "CURRENT_RUSTC_VERSION", Some(117078), None),
     /// Infer generic args for both consts and types.
     (unstable, generic_arg_infer, "1.55.0", Some(85077), None),
     /// An extension to the `generic_associated_types` feature, allowing incomplete features.

compiler/rustc_parse/src/parser/expr.rs

@@ -1850,7 +1850,7 @@ impl<'a> Parser<'a> {
         let lo = self.prev_token.span;
         let kind = ExprKind::Yield(self.parse_expr_opt()?);
         let span = lo.to(self.prev_token.span);
-        self.sess.gated_spans.gate(sym::coroutines, span);
+        self.sess.gated_spans.gate(sym::yield_expr, span);
         let expr = self.mk_expr(span, kind);
         self.maybe_recover_from_bad_qpath(expr)
     }
@@ -3075,6 +3075,7 @@ impl<'a> Parser<'a> {
             GenBlockKind::Async
         } else {
             assert!(self.eat_keyword(kw::Gen));
+            self.sess.gated_spans.gate(sym::gen_blocks, lo.to(self.token.span));
             GenBlockKind::Gen
         };
         let capture_clause = self.parse_capture_clause()?;

compiler/rustc_span/src/symbol.rs

@@ -819,6 +819,7 @@ symbols! {
         future_trait,
         gdb_script_file,
         ge,
+        gen_blocks,
         gen_future,
         gen_kill,
         generator_clone,
@@ -1780,6 +1781,7 @@ symbols! {
         xmm_reg,
         yeet_desugar_details,
         yeet_expr,
+        yield_expr,
         ymm_reg,
         zmm_reg,
     }

tests/ui/coroutine/gen_block.rs

@@ -1,6 +1,6 @@
 // revisions: e2024 none
 //[e2024] compile-flags: --edition 2024 -Zunstable-options
-#![cfg_attr(e2024, feature(coroutines))]
+#![cfg_attr(e2024, feature(gen_blocks))]
 
 fn main() {
     let x = gen {};

tests/ui/coroutine/gen_block_is_coro.rs

@@ -1,5 +1,5 @@
 //compile-flags: --edition 2024 -Zunstable-options
-#![feature(coroutines, coroutine_trait)]
+#![feature(coroutines, coroutine_trait, gen_blocks)]
 
 use std::ops::Coroutine;
 

tests/ui/coroutine/gen_block_is_iter.rs

@@ -2,7 +2,7 @@
 //compile-flags: --edition 2024 -Zunstable-options
 //[next] compile-flags: -Ztrait-solver=next
 // check-pass
-#![feature(coroutines)]
+#![feature(gen_blocks)]
 
 fn foo() -> impl Iterator<Item = u32> {
     gen { yield 42 }

tests/ui/coroutine/gen_block_is_no_future.rs

@@ -1,5 +1,5 @@
 //compile-flags: --edition 2024 -Zunstable-options
-#![feature(coroutines)]
+#![feature(gen_blocks)]
 
 fn foo() -> impl std::future::Future { //~ ERROR is not a future
     gen { yield 42 }

tests/ui/coroutine/gen_block_iterate.rs

@@ -2,7 +2,7 @@
 //compile-flags: --edition 2024 -Zunstable-options
 //[next] compile-flags: -Ztrait-solver=next
 // run-pass
-#![feature(coroutines)]
+#![feature(gen_blocks)]
 
 fn foo() -> impl Iterator<Item = u32> {
     gen { yield 42; for x in 3..6 { yield x } }

tests/ui/feature-gates/feature-gate-coroutines.e2024.stderr

@@ -0,0 +1,9 @@
+error[E0627]: yield expression outside of coroutine literal
+  --> $DIR/feature-gate-coroutines.rs:5:5
+   |
+LL |     yield true;
+   |     ^^^^^^^^^^
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0627`.

tests/ui/feature-gates/feature-gate-coroutines.none.stderr

@@ -1,5 +1,5 @@
 error[E0658]: yield syntax is experimental
-  --> $DIR/feature-gate-coroutines.rs:2:5
+  --> $DIR/feature-gate-coroutines.rs:5:5
    |
 LL |     yield true;
    |     ^^^^^^^^^^
@@ -8,7 +8,16 @@ LL |     yield true;
    = help: add `#![feature(coroutines)]` to the crate attributes to enable
 
 error[E0658]: yield syntax is experimental
-  --> $DIR/feature-gate-coroutines.rs:8:5
+  --> $DIR/feature-gate-coroutines.rs:8:16
+   |
+LL |     let _ = || yield true;
+   |                ^^^^^^^^^^
+   |
+   = note: see issue #43122 <https://github.com/rust-lang/rust/issues/43122> for more information
+   = help: add `#![feature(coroutines)]` to the crate attributes to enable
+
+error[E0658]: yield syntax is experimental
+  --> $DIR/feature-gate-coroutines.rs:14:5
    |
 LL |     yield;
    |     ^^^^^
@@ -17,7 +26,7 @@ LL |     yield;
    = help: add `#![feature(coroutines)]` to the crate attributes to enable
 
 error[E0658]: yield syntax is experimental
-  --> $DIR/feature-gate-coroutines.rs:9:5
+  --> $DIR/feature-gate-coroutines.rs:15:5
    |
 LL |     yield 0;
    |     ^^^^^^^
@@ -26,12 +35,12 @@ LL |     yield 0;
    = help: add `#![feature(coroutines)]` to the crate attributes to enable
 
 error[E0627]: yield expression outside of coroutine literal
-  --> $DIR/feature-gate-coroutines.rs:2:5
+  --> $DIR/feature-gate-coroutines.rs:5:5
    |
 LL |     yield true;
    |     ^^^^^^^^^^
 
-error: aborting due to 4 previous errors
+error: aborting due to 5 previous errors
 
 Some errors have detailed explanations: E0627, E0658.
 For more information about an error, try `rustc --explain E0627`.

tests/ui/feature-gates/feature-gate-coroutines.rs

@@ -1,10 +1,16 @@
+// revisions: e2024 none
+//[e2024] compile-flags: --edition 2024 -Zunstable-options
+
 fn main() {
-    yield true; //~ ERROR yield syntax is experimental
+    yield true; //[none]~ ERROR yield syntax is experimental
                 //~^ ERROR yield expression outside of coroutine literal
+
+    let _ = || yield true; //[none]~ ERROR yield syntax is experimental
 }
 
 #[cfg(FALSE)]
 fn foo() {
-    yield; //~ ERROR yield syntax is experimental
-    yield 0; //~ ERROR yield syntax is experimental
+    // Ok in 2024 edition
+    yield; //[none]~ ERROR yield syntax is experimental
+    yield 0; //[none]~ ERROR yield syntax is experimental
 }

tests/ui/feature-gates/feature-gate-gen_blocks.e2024.stderr

@@ -0,0 +1,28 @@
+error[E0658]: gen blocks are experimental
+  --> $DIR/feature-gate-gen_blocks.rs:5:5
+   |
+LL |     gen {};
+   |     ^^^^^
+   |
+   = note: see issue #117078 <https://github.com/rust-lang/rust/issues/117078> for more information
+   = help: add `#![feature(gen_blocks)]` to the crate attributes to enable
+
+error[E0658]: gen blocks are experimental
+  --> $DIR/feature-gate-gen_blocks.rs:13:5
+   |
+LL |     gen {};
+   |     ^^^^^
+   |
+   = note: see issue #117078 <https://github.com/rust-lang/rust/issues/117078> for more information
+   = help: add `#![feature(gen_blocks)]` to the crate attributes to enable
+
+error[E0282]: type annotations needed
+  --> $DIR/feature-gate-gen_blocks.rs:5:9
+   |
+LL |     gen {};
+   |         ^^ cannot infer type
+
+error: aborting due to 3 previous errors
+
+Some errors have detailed explanations: E0282, E0658.
+For more information about an error, try `rustc --explain E0282`.

tests/ui/feature-gates/feature-gate-gen_blocks.none.stderr

@@ -0,0 +1,9 @@
+error[E0422]: cannot find struct, variant or union type `gen` in this scope
+  --> $DIR/feature-gate-gen_blocks.rs:5:5
+   |
+LL |     gen {};
+   |     ^^^ not found in this scope
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0422`.

tests/ui/feature-gates/feature-gate-gen_blocks.rs

@@ -0,0 +1,15 @@
+// revisions: e2024 none
+//[e2024] compile-flags: --edition 2024 -Zunstable-options
+
+fn main() {
+    gen {};
+    //[none]~^ ERROR: cannot find struct, variant or union type `gen`
+    //[e2024]~^^ ERROR: gen blocks are experimental
+    //[e2024]~| ERROR: type annotations needed
+}
+
+#[cfg(FALSE)]
+fn foo() {
+    gen {};
+    //[e2024]~^ ERROR: gen blocks are experimental
+}