Rust: Handle unqualified UseTrees in path resolution

[hvitved]

Previously, we assumed that use trees { ... } always had a qualifier, but this need not be the case.

DCA looks good; we gain an additional 0.4 %-point call edges, although at the cost of a slowdown on rust (which happens because we compute more data flow, for example the predicate AccessAfterLifetime::AccessAfterLifetimeFlow::Flow::Stage3::fwdFlowThrough grows from 3,626,391,847 tuples to 4,361,916,386 tuples.).

[Copilot]

Pull Request Overview

This PR enhances path resolution for Rust use statements to support complex nested use tree patterns. Specifically, it handles cases like use {{{my::{{self as my_alias, *}}}}} where braces are deeply nested without intervening path segments.

• Introduces getAUseTreeUseTree() to recursively traverse nested use trees that lack path segments
• Updates path resolution logic to handle nested glob imports and aliases within brace groups
• Adds test coverage for the new nested use tree pattern with my_alias::nested_f()

Reviewed Changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated no comments.

File	Description
rust/ql/lib/codeql/rust/internal/PathResolution.qll	Core implementation adding getAUseTreeUseTree() and getAUseUseTree() helpers, and updating resolution logic to handle nested use trees without paths
rust/ql/test/library-tests/path-resolution/main.rs	Test case demonstrating nested braces with alias (use {{{my::{{self as my_alias, *}}}}}) and its usage
rust/ql/test/library-tests/path-resolution/path-resolution.expected	Updated expected output with new path resolutions and shifted line numbers
rust/ql/test/library-tests/path-resolution/CONSISTENCY/PathResolutionConsistency.expected	Updated line numbers for consistency checks

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[paldepind]

LGTM! One question that might need addressing, but I've improved in case it's intended.

[paldepind]

Is the overlap in the disjunction here intended? If not we could do if root.hasPath() then ... else ....

[hvitved]

Yeah, we may as well; this predicate is only called in one place, and it expects the result to have a path.