Rust: Refine Self resolution inside impl blocks

[hvitved]

Before this PR, we would resolve Self inside impl blocks to either (1) the type being implemented, if Self is not a qualifier of another path, or (2) the impl block itself, otherwise.

This PR changes the logic so we always resolve Self to the type being implemented, which enables us to correctly resolve more paths.

We also restrict the scope of default trait implementations in path resolution, similar to @paldepind 's #20723, and finally prevent type parameters from escaping their scope when resolving type mentions.

DCA looks great: A significant reduction in Nodes With Type At Length Limit, and a modest increase in resolved calls.

[Copilot]

Pull Request Overview

This PR refines the resolution of Self inside impl blocks to consistently resolve to the type being implemented rather than the impl block itself. This enables more accurate path resolution, trait method calls, and type inference. The changes include restricting the scope of default trait implementations, preventing type parameters from escaping their scope, and improving consistency in path resolution.

• Resolves Self to the implementing type in all contexts, not to the impl block
• Prevents type parameters from escaping their declared scope during type resolution
• Restricts default trait implementations to only be inherited from the directly implemented trait, not super traits

Reviewed Changes

Copilot reviewed 11 out of 11 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
rust/ql/lib/codeql/rust/internal/PathResolution.qll	Updates Self resolution logic to always resolve to the implementing type; restricts default trait implementation inheritance to direct traits only; simplifies path resolution logic
rust/ql/lib/codeql/rust/internal/TypeMention.qll	Adds type parameter scoping logic to prevent parameters from escaping their declaring item's scope; refactors type resolution into resolvePathTypeAt
rust/ql/lib/codeql/rust/internal/Type.qll	Adds getDeclaringItem() method to TypeParameter to track the scope of type parameters
rust/ql/lib/codeql/rust/internal/TypeInferenceConsistency.qll	Filters out known limitations for escaping type parameters in consistency checks
rust/ql/test/library-tests/path-resolution/main.rs	Adds test cases for improved Self resolution in impl blocks; demonstrates resolution of methods from different traits
rust/ql/test/library-tests/type-inference/main.rs	Removes spurious target annotation that is now correctly resolved
rust/ql/test/library-tests/type-inference/type-inference.expected	Updates expected results reflecting improved type inference with fewer incorrect inferences
rust/ql/test/library-tests/type-inference/CONSISTENCY/PathResolutionConsistency.expected	Removes spurious call target and adds multiple path resolution entries for associated types
rust/ql/test/library-tests/sensitivedata/CONSISTENCY/PathResolutionConsistency.expected	Removes false positive for multiple call targets
rust/ql/test/library-tests/path-resolution/path-resolution.expected	Updates expected path resolutions reflecting improved Self resolution to implementing types
rust/ql/test/library-tests/path-resolution/CONSISTENCY/PathResolutionConsistency.expected	Updates line numbers for multiple call targets after code changes

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