Rust: Type inference for macro expressions

[hvitved]

DCA shows a nice 1 percentage point increase in resolvable calls.

[Copilot]

Pull Request Overview

Adds support for inferring types from macro expressions in the Rust CodeQL type inference engine.

• Extended the typeEquality predicate to treat MacroExpr expansions as equivalent nodes.
• Added a new macros test module with a format! invocation in main.rs.
• Updated the type-inference.expected file to include expected entries for macro expressions and their expansions.

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

File	Description
rust/ql/lib/codeql/rust/internal/TypeInference.qll	Added an or clause in typeEquality to equate macro expressions with their expansions.
rust/ql/test/library-tests/type-inference/main.rs	Introduced a macros module and a format! call to exercise macro-based type inference.
rust/ql/test/library-tests/type-inference/type-inference.expected	Updated expected output to list MacroExpr nodes and their expanded types for the tests.

Comments suppressed due to low confidence (2)

rust/ql/test/library-tests/type-inference/main.rs:1808

• [nitpick] The module name macros could be confused with Rust's built-in macros. Consider renaming it to something more descriptive like macro_tests or macro_expr_tests.

mod macros {

rust/ql/test/library-tests/type-inference/main.rs:1810

• This inline TODO references an open PR. Remove or update this comment once that change is merged to avoid stale test markers.

let x = format!("Hello, {}", "World!"); // $ MISSING: type=x:String -- needs https://github.com/github/codeql/pull/19658

[Copilot]

[nitpick] Consider adding a brief comment above this clause explaining why macro expressions require special handling here, improving future maintainability.

Suggested change

	or
	or
	// Macro expressions require special handling because they can expand into multiple
	// expressions or statements, which affects type inference.

[paldepind]

👍