Rust: Include synthetic type parameters in Type.getATypeParameter

[hvitved]

#20179 follow-up: The not certainType.getATypeParameter() = tp check in certainTypeConflict does not work as intended for synthetic type parameters.

DCA is uneventful.

[Copilot]

Pull Request Overview

This PR modifies the type parameter handling in Rust to properly include synthetic type parameters (such as associated types in traits) in Type.getATypeParameter(). The changes address an issue where the certainTypeConflict check wasn't working correctly for synthetic type parameters.

• Separates positional type parameters from all type parameters by introducing getPositionalTypeParameter()
• Updates getATypeParameter() to include both positional and synthetic type parameters
• Adds specific handling for trait and dynamic trait types to include their associated types

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
rust/ql/lib/codeql/rust/internal/Type.qll	Refactors type parameter methods and adds synthetic type parameter support for trait types
rust/ql/lib/codeql/rust/internal/TypeMention.qll	Updates call to use the new positional type parameter method

[Copilot]

The default implementation of getATypeParameter() only returns positional type parameters. This means that types like StructType, EnumType, etc. won't include their synthetic type parameters unless they override this method. Consider making this method abstract or providing a more comprehensive default implementation.

Suggested change

	TypeParameter getATypeParameter() { result = this.getPositionalTypeParameter(_) }
	abstract TypeParameter getATypeParameter();

[paldepind]

I think this is a great change!

The way I understand it, #19847 got rid of the annoying traitAliasIndex that assigned arbitrary indices to associated types for traits. But, it also meant that getTypeParameter on traits no longer gave the tp's for associated types.

With this PR we get the best of both worlds: A getATypeParameter that gives the full set of type parameters (without requiring one to invent positions where it doesn't make much sense) and a getPositionalTypeParameter that holds for the subset of the TPs that have a meaningful position.