Rust: Fix bad join

[hvitved]

Before

Evaluated relational algebra for predicate TypeInference::MethodResolution::MethodCall.getTrait/0#dispred#fc13ba6e@914858bt with tuple counts:
          153112   ~2%    {2} r1 = SCAN `Operation::Operation.isOverloaded/3#f0e64084` OUTPUT In.0, In.1
          153112   ~2%    {2}    | STREAM DEDUP

           18807   ~0%    {2} r2 = JOIN `TypeInference::getCallExprTraitQualifier/1#c084fe9f` WITH TypeInference::MethodResolution::MethodCallCallExpr#6eae461f ON FIRST 1 OUTPUT Lhs.0, Lhs.1

        65859035   ~3%    {3} r3 = JOIN `_IndexExpr::Generated::IndexExpr#9975e37a_TypeInference::MethodResolution::MethodCallIndexExpr.isInM__#shared` WITH Trait::Generated::Trait#ecf50173 CARTESIAN PRODUCT OUTPUT Rhs.0, _, Lhs.0
        65859035   ~0%    {3}    | REWRITE WITH Out.1 := "core::ops::index::Index"
           11191   ~0%    {2}    | JOIN WITH `Addressable::Addressable.getCanonicalPath/0#dispred#6044348f#bb` ON FIRST 2 OUTPUT Lhs.2, Lhs.0

             671   ~0%    {1} r4 = JOIN IndexExpr::Generated::IndexExpr#9975e37a WITH `TypeInference::MethodResolution::MethodCallIndexExpr.isInMutableContext/0#dispred#8c8ad425` ON FIRST 1 OUTPUT Lhs.0
         3948835   ~2%    {3}    | JOIN WITH Trait::Generated::Trait#ecf50173 CARTESIAN PRODUCT OUTPUT Rhs.0, _, Lhs.0
         3948835   ~2%    {3}    | REWRITE WITH Out.1 := "core::ops::index::IndexMut"
             671   ~1%    {2}    | JOIN WITH `Addressable::Addressable.getCanonicalPath/0#dispred#6044348f#bb` ON FIRST 2 OUTPUT Lhs.2, Lhs.0

          183781   ~0%    {2} r5 = r1 UNION r2 UNION r3 UNION r4
                          return r5

After

Evaluated relational algebra for predicate TypeInference::MethodResolution::MethodCall.getTrait/0#dispred#fc13ba6e@1b4a55e3 with tuple counts:
        153112   ~2%    {2} r1 = SCAN `Operation::Operation.isOverloaded/3#f0e64084` OUTPUT In.0, In.1
        153112   ~2%    {2}    | STREAM DEDUP

         11191   ~0%    {2} r2 = JOIN `_IndexExpr::Generated::IndexExpr#9975e37a_TypeInference::MethodResolution::MethodCallIndexExpr.isInM__#shared` WITH Stdlib::IndexTrait#e80543a5 CARTESIAN PRODUCT OUTPUT Lhs.0, Rhs.0

         18807   ~0%    {2} r3 = JOIN `TypeInference::getCallExprTraitQualifier/1#c084fe9f` WITH TypeInference::MethodResolution::MethodCallCallExpr#6eae461f ON FIRST 1 OUTPUT Lhs.0, Lhs.1

           671   ~0%    {1} r4 = JOIN IndexExpr::Generated::IndexExpr#9975e37a WITH `TypeInference::MethodResolution::MethodCallIndexExpr.isInMutableContext/0#dispred#8c8ad425` ON FIRST 1 OUTPUT Lhs.0
           671   ~1%    {2}    | JOIN WITH Stdlib::IndexMutTrait#4d6c31bd CARTESIAN PRODUCT OUTPUT Lhs.0, Rhs.0

        183781   ~0%    {2} r5 = r1 UNION r2 UNION r3 UNION r4
                        return r5

[Copilot]

Pull request overview

This PR optimizes a QL query by refactoring trait lookups for index operations. Instead of using string comparisons with getCanonicalPath(), the code now uses instanceof checks with dedicated trait classes, significantly improving performance by reducing tuple counts in the relational algebra evaluation from ~66 million to ~4 million.

• Introduces a new IndexMutTrait class in the Stdlib module
• Refactors MethodCallIndexExpr.getTrait() to use instanceof checks instead of string comparisons

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
rust/ql/lib/codeql/rust/frameworks/stdlib/Stdlib.qll	Adds the IndexMutTrait class to represent the core::ops::index::IndexMut trait, following the same pattern as the existing IndexTrait class
rust/ql/lib/codeql/rust/internal/TypeInference.qll	Refactors getTrait() method to use instanceof IndexMutTrait and instanceof IndexTrait instead of string comparisons with getCanonicalPath()

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