Rust: Do not dispatch to all implementations when trait target is accurate

[paldepind]

Currently when a call resolves to a trait function we enable dispatching to all implementations of that trait function. However, sometimes when a trait function has a default implementation, it is actually the one and only correct result. See the tests for an example.

This PR restrict the dispatching to the cases where the trait function is the resolved target because type information is not enough to find a single correct target.

[Copilot]

Pull request overview

This PR refines Rust trait function call resolution by distinguishing between cases where trait dispatch is necessary and cases where the target can be precisely determined. The key improvement is adding a dispatch boolean parameter to track whether a resolved target is a trait item due to type ambiguity (requiring dispatch to all implementations) or a precise target (no dispatch needed).

• Modified resolveCallTarget to return a dispatch flag indicating whether the resolved target requires trait dispatch
• Updated call target resolution logic to only dispatch to all trait implementations when type information is insufficient to determine a single target
• Added comprehensive test cases demonstrating correct resolution of trait default implementations vs. overridden implementations

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
rust/ql/lib/codeql/rust/internal/TypeInference.qll	Added dispatch parameter to resolveCallTarget to distinguish between precise targets and trait items requiring dispatch
rust/ql/lib/codeql/rust/elements/internal/CallImpl.qll	Updated getARuntimeTarget to only dispatch to implementations when dispatch=true, ensuring precise targets don't trigger unnecessary dispatch
rust/ql/lib/codeql/rust/elements/internal/InvocationExprImpl.qll	Updated getResolvedTarget to accommodate new resolveCallTarget signature
rust/ql/test/library-tests/dataflow/global/main.rs	Added test module demonstrating trait default implementations vs. overridden implementations with proper call resolution
rust/ql/test/library-tests/dataflow/global/viableCallable.expected	Updated expected test results showing correct resolution of trait calls without unnecessary dispatch
rust/ql/test/library-tests/dataflow/global/inline-flow.expected	Updated expected dataflow results for new test cases

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