fix Type aliases are expanded in the hover text #2707

[asukaminato0721]

Summary

Fixes #2707

non-call hovers on plain functions render the declared source header instead of the normalized solved signature.

That preserves aliases like Messages in hover text while leaving call-site hover behavior unchanged for constructors, __call__, and expanded **kwargs.

Test Plan

add test

[Copilot]

Pull request overview

This PR aims to improve Pyrefly’s LSP hover output for function signatures so that user-authored type alias names (e.g. Messages) are preserved in hover text instead of being expanded (e.g. list[str]), addressing issue #2707.

Changes:

• Add a hover regression test ensuring function signature hover preserves a TypeAlias name.
• Update hover rendering to prefer displaying the declared function header text (from source) for non-call-site hovers, instead of the fully-resolved type display.
• Refactor hover definition lookup plumbing to retain the definition range/module for the new display path.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 3 comments.

File	Description
pyrefly/lib/test/lsp/hover.rs	Adds a test asserting hover shows def func(msgs: Messages) -> None: ... and not the expanded alias.
pyrefly/lib/lsp/wasm/hover.rs	Introduces source-based function header extraction to preserve alias names in hover signatures.

---

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[Copilot]

declared_function_hover_display slices from the start of the StmtFunctionDef to the start of the first statement in the body. Because comments/blank lines are not AST statements, this slice can include leading body comments (e.g. def f(...):\n # comment\n pass), causing trim_end() to end with # comment instead of :, so the function returns None and hover falls back to the type-based display (re-expanding aliases). Consider finding the end of the signature colon directly (e.g., by tokenizing or scanning the slice for the signature-terminating : while skipping trailing whitespace/comments) rather than using the first body statement as the cutoff.

[Copilot]

This introduces an Ast::parse(module.contents(), ...) on the hover path for functions. Hover can be called very frequently, and parsing the full module each time can become a noticeable CPU cost on larger files. If possible, reuse an already-cached AST (e.g. use transaction.get_ast(handle) when the definition module is the current handle; or extend the definition result to carry a handle/key that lets you retrieve a cached AST) and only fall back to parsing when no cached AST is available.

[Copilot]

The new test covers a TypeAlias-style alias and a simple body (pass). Given the signature extraction logic in declared_function_hover_display, it would be good to add coverage for (1) type Messages = list[str] aliases (PEP 695) and (2) a function whose body begins with a comment/blank line before the first statement, which currently affects whether the signature header is detected and aliases are preserved.

Suggested change

	#[test]
	#[test]
	fn hover_over_function_preserves_pep695_type_alias() {
	let code = r#"
	type Messages = list[str]
	def func(msgs: Messages) -> None:
	pass
	func
	#^
	"#;
	let report = get_batched_lsp_operations_report(&[("main", code)], |state, handle, position| {
	match get_hover(&state.transaction(), handle, position, false) {
	Some(Hover {
	contents: HoverContents::Markup(markup),
	..
	}) => markup.value,
	_ => "None".to_owned(),
	}
	});
	assert!(
	report.contains("def func(msgs: Messages) -> None: ..."),
	"Expected hover to preserve the PEP 695 alias name, got: {report}"
	);
	assert!(
	!report.contains("def func(msgs: list[str]) -> None: ..."),
	"Expected hover not to expand the PEP 695 alias, got: {report}"
	);
	}
	#[test]
	fn hover_over_function_with_leading_blank_and_comment_preserves_alias() {
	let code = r#"
	from typing import TypeAlias
	Messages: TypeAlias = list[str]
	def func(msgs: Messages) -> None:
	# leading comment before the first statement
	pass
	func
	#^
	"#;
	let report = get_batched_lsp_operations_report(&[("main", code)], |state, handle, position| {
	match get_hover(&state.transaction(), handle, position, false) {
	Some(Hover {
	contents: HoverContents::Markup(markup),
	..
	}) => markup.value,
	_ => "None".to_owned(),
	}
	});
	assert!(
	report.contains("def func(msgs: Messages) -> None: ..."),
	"Expected hover to preserve the alias name when the body starts with blank/comment lines, got: {report}"
	);
	assert!(
	!report.contains("def func(msgs: list[str]) -> None: ..."),
	"Expected hover not to expand the alias when the body starts with blank/comment lines, got: {report}"
	);
	}
	#[test]

[github-actions]

According to mypy_primer, this change doesn't affect type check results on a corpus of open source code. ✅