Rust: Fix context-based type inference explosion

[hvitved]

The following simple program would make our type inference implementation explode:

#[derive(Default)]
struct S;

fn f() -> S {
    let x = Default::default();
    From::from(x)
}

Firstly, because of a getSuccessor vs getAssocItem bug, From::from would allow for any sub trait of From, for example the Int trait, which meant that x could be inferred to have type bool. Secondly, since many from implementations are polymorphic in their argument, we should really be checking that the return type matches the type of the calling context.

This PR makes those two adjustments, and adds the regression test.

DCA looks good; we loose some call edges, but nothing too serious.

[hvitved]

This conjunction has non-linear recursion, hence the magic'ed version of hasTypeConstraint.

[Copilot]

Pull request overview

This PR fixes a type inference explosion issue in Rust queries by correcting two bugs in the type inference implementation:

1. Path resolution bug: Changed getASuccessor(_) to getAnAssocItem() to correctly resolve trait functions only from the trait itself, not from sub-traits
2. Context-based return type checking: Enhanced the logic to only use return type for disambiguation when all argument positions are trivially satisfied

Changes:

• Fixed trait function resolution to prevent matching sub-trait implementations
• Added logic to check return type matches calling context for polymorphic functions
• Refactored Input modules into a unified structure
• Added regression test for the Default::default() and From::from() pattern

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
shared/typeinference/codeql/typeinference/internal/TypeInference.qll	Added helper predicate with pragma[nomagic] to optimize type constraint checking
rust/ql/lib/codeql/rust/internal/typeinference/TypeInference.qll	Fixed getASuccessor → getAnAssocItem bug, merged Input modules, fixed parameter ordering in context typing
rust/ql/lib/codeql/rust/internal/typeinference/FunctionOverloading.qll	Split predicate and added return type disambiguation logic
rust/ql/test/library-tests/type-inference/main.rs	Added regression test for from_default module
rust/ql/test/library-tests/type-inference/type-inference.expected	Updated expected test output
rust/ql/test/query-tests/security/CWE-312/CONSISTENCY/PathResolutionConsistency.expected	Removed spurious multiple resolution error

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[geoffw0]

Looks helpful.

Is there a reason this is still draft?

[hvitved]

Is there a reason this is still draft?

I would like to rework this a bit more; while it does fix the example posted in the description, there are still cases resulting in timeouts that I would like to cover as well.