Rust: skip unexpanded stuff in library emission

[redsun82]

This will skip all unexpanded entities in library extraction, where we only really care about expanded things. This means skipping:

• the token tree of macro calls
• the unexpanded AST of attribute macros

In the latter case, in order to replace the single Item with its expansion (which is a MacroItems entity), we wrap the MacroItems in a dummy MacroCall with null path.

[redsun82]

DCA shows a moderate speedup, and improvement in call graph resolution (with one exception being bevy going very slightly worse). I think this is worth taking in.

[Copilot]

Pull Request Overview

This PR enhances library-mode emission by skipping unexpanded macro entities and only emitting fully expanded items.

• Updated pre_emit! to use prepare_item_expansion for early returns of attribute macro expansions.
• Added logic to skip nodes inside unexpanded macro call token trees during library extraction.
• Introduced prepare_item_expansion and emit_attribute_macro_expansion to wrap attribute macro expansions in a dummy MacroCall and refactored emit_item_expansion.

Comments suppressed due to low confidence (1)

rust/extractor/src/translate/base.rs:692

• New skip logic for nodes inside unexpanded macro call token trees lacks accompanying tests; consider adding unit tests to verify that these nodes are correctly ignored in library mode.

if syntax

[Copilot]

emit_attribute_macro_expansion is invoked both in prepare_item_expansion and again in emit_item_expansion, which may lead to duplicate work or inconsistent emission. Consider caching the result or ensuring it's only called once.

Suggested change

	if let Some(expanded) = self.emit_attribute_macro_expansion(node) {
	let node_id = node.syntax().text_range().start().into(); // Use a unique identifier for the node
	if let Some(expanded) = self.macro_expansion_cache.get(&node_id).cloned()
	.or_else(|| {
	let result = self.emit_attribute_macro_expansion(node);
	if let Some(ref expansion) = result {
	self.macro_expansion_cache.insert(node_id, expansion.clone());
	}
	result
	})
	{

[Copilot]

[nitpick] Using a magic identifier (TrapId::Star) for dummy MacroCall may be unclear—consider defining a named constant or adding a comment explaining its special purpose.

Suggested change

	id: TrapId::Star,
	id: DUMMY_MACRO_CALL_ID,

[Copilot]

prepare_item_expansion is a new public method and would benefit from a doc comment explaining its behavior, parameters, and return value.

Suggested change

	/// Prepares an item for macro expansion if applicable.
	///
	/// This method handles items that may expand via attribute macros. If the item is part of a
	/// library source and expands through an attribute macro, it emits the expansion and wraps
	/// it in a dummy `MacroCall` to produce a single `Item` label. Otherwise, it checks if the
	/// item is an attribute macro call and adjusts the macro context depth accordingly.
	///
	/// # Parameters
	/// - `node`: A reference to the AST node representing the item to be prepared for expansion.
	///
	/// # Returns
	/// - `Some(Label<generated::Item>)` if the item is expanded and wrapped in a `MacroCall`.
	/// - `None` if no expansion is performed or the item is not an attribute macro call.

[aibaars]

I think we can simply drop any node of type TokenTree. That includes macro call arguments, as well as macro rule/definition bodies. Like done in #19581