part of Support gen syntax (feature gen_blocks) #16156

[asukaminato0721]

part of #16156

add basic supports for gen { } async gen { } gen fn async gen fn

fix some type signature show.

add some tests.

[Copilot]

Pull request overview

Adds initial support for the gen / async gen syntax (blocks and functions) across HIR lowering, type inference, and type display, including wiring up an AsyncIterator lang item and adding regression tests.

Changes:

• Introduce new HIR expression variants for gen {} / async gen {} and lower gen fn / async gen fn bodies into them.
• Extend type inference / solver interop and type display to represent gen as impl Iterator<Item = ...> and async gen as impl AsyncIterator<Item = ...>.
• Add AsyncIterator minicore + lang item plumbing and new inference/coercion tests.

Reviewed changes

Copilot reviewed 22 out of 22 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
crates/test-utils/src/minicore.rs	Adds minicore support for core::async_iter::AsyncIterator plus #[lang] wiring for Option/Poll.
crates/intern/src/symbol/symbols.rs	Registers new symbols used by the async iterator/lang item plumbing.
crates/hir/src/display.rs	Displays gen fn/async gen fn and strips wrapped return types similarly to async fn.
crates/hir-ty/src/tests/simple.rs	Adds inference tests for gen/async gen blocks and functions.
crates/hir-ty/src/tests/coercion.rs	Adds coercion tests for yield inside gen/async gen blocks.
crates/hir-ty/src/next_solver/interner.rs	Updates solver interner to recognize Gen/AsyncGen and map AsyncIterator lang item.
crates/hir-ty/src/mir/lower.rs	Explicitly marks gen/async gen blocks as not supported in MIR lowering.
crates/hir-ty/src/infer/mutability.rs	Includes Gen/AsyncGen in mutability inference traversal.
crates/hir-ty/src/infer/expr.rs	Implements inference + coroutine type lowering for Gen/AsyncGen blocks.
crates/hir-ty/src/infer/closure/analysis.rs	Includes Gen/AsyncGen in closure capture analysis traversal.
crates/hir-ty/src/display.rs	Displays coroutine types originating from gen/async gen as impl Iterator/AsyncIterator.
crates/hir-ty/src/diagnostics/unsafe_check.rs	Traverses Gen/AsyncGen blocks in unsafe diagnostics.
crates/hir-ty/src/diagnostics/expr.rs	Validates Gen/AsyncGen blocks like other block expressions.
crates/hir-expand/src/mod_path.rs	Adds known path for core::async_iter::AsyncIterator.
crates/hir-def/src/signatures.rs	Adds GEN flag and is_gen() on function signatures.
crates/hir-def/src/lang_item.rs	Adds AsyncIterator to the lang item table.
crates/hir-def/src/hir.rs	Adds Expr::Gen and Expr::AsyncGen HIR variants.
crates/hir-def/src/expr_store/scope.rs	Ensures scopes are computed for Gen/AsyncGen blocks.
crates/hir-def/src/expr_store/pretty.rs	Pretty-prints gen and async gen blocks.
crates/hir-def/src/expr_store/lower.rs	Lowers gen/async gen blocks and wraps gen fn/async gen fn bodies; wraps function return type in Iterator/AsyncIterator impl-trait.
crates/hir-def/src/expr_store/body.rs	Threads is_gen_fn into body lowering.
crates/hir-def/src/expr_store.rs	Traversal updates to treat Gen/AsyncGen as block-like expressions.

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.

View changes since this review

[Copilot]

In this async gen block inference test, the binding result is expected to have type {unknown}, but the initializer expression is inferred as Poll<Option<<impl AsyncIterator<Item = i8> as AsyncIterator>::Item>> in the same snapshot. This looks like an inference/display gap for local bindings (it should likely resolve to Poll<Option<i8>>, consistent with the async_gen_fn_types_inferred test below). Consider updating the implementation so result gets a concrete type here, and then tighten the expectation accordingly so the test doesn't lock in {unknown}.

Suggested change

	let result = Pin::new(&mut generator).poll_next(&mut cx);
	}
	"#,
	expect![[r#"
	91..97 'mut cx': Context<'?>
	112..239 '{ ...cx); }': ()
	122..135 'mut generator': impl AsyncIterator<Item = i8>
	138..174 'async ... }': impl AsyncIterator<Item = i8>
	158..167 'yield 1i8': ()
	164..167 '1i8': i8
	184..190 'result': {unknown}
	193..201 'Pin::new': fn new<&'? mut impl AsyncIterator<Item = i8>>(&'? mut impl AsyncIterator<Item = i8>) -> Pin<&'? mut impl AsyncIterator<Item = i8>>
	193..217 'Pin::n...rator)': Pin<&'? mut impl AsyncIterator<Item = i8>>
	193..236 'Pin::n...ut cx)': Poll<Option<<impl AsyncIterator<Item = i8> as AsyncIterator>::Item>>
	202..216 '&mut generator': &'? mut impl AsyncIterator<Item = i8>
	207..216 'generator': impl AsyncIterator<Item = i8>
	228..235 '&mut cx': &'? mut Context<'?>
	233..235 'cx': Context<'?>
	let result: core::task::Poll<Option<i8>> = Pin::new(&mut generator).poll_next(&mut cx);
	}
	"#,
	expect![[r#"
	91..97 'mut cx': Context<'?>
	112..264 '{ ...cx); }': ()
	122..135 'mut generator': impl AsyncIterator<Item = i8>
	138..174 'async ... }': impl AsyncIterator<Item = i8>
	158..167 'yield 1i8': ()
	164..167 '1i8': i8
	184..190 'result': Poll<Option<i8>>
	223..231 'Pin::new': fn new<&'? mut impl AsyncIterator<Item = i8>>(&'? mut impl AsyncIterator<Item = i8>) -> Pin<&'? mut impl AsyncIterator<Item = i8>>
	223..247 'Pin::n...rator)': Pin<&'? mut impl AsyncIterator<Item = i8>>
	223..266 'Pin::n...ut cx)': Poll<Option<i8>>
	232..246 '&mut generator': &'? mut impl AsyncIterator<Item = i8>
	237..246 'generator': impl AsyncIterator<Item = i8>
	258..265 '&mut cx': &'? mut Context<'?>
	263..265 'cx': Context<'?>