Rust: Distinguish &mut T from &T in type inference
#20973
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| string derefChain, boolean borrow, TypePath path | ||
| ) { | ||
| result = substituteLookupTraits(this.getACandidateReceiverTypeAt(derefChain, borrow, path)) | ||
| Type getANonPseudoCandidateReceiverTypeAt(string derefChain, BorrowKind borrow, TypePath path) { |
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Missing QLDoc for parameter Warning
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Pull request overview
This PR improves Rust type inference by distinguishing between mutable references (&mut T) and shared references (&T), which were previously treated as a single RefType. The change significantly reduces path resolution inconsistencies by eliminating ambiguity when methods are implemented for both borrow types.
Key Changes:
- Split
RefTypeintoRefSharedTypeandRefMutTypein the type system - Updated method resolution to prioritize shared borrows over mutable borrows when constructing candidate receiver types
- Enhanced type inference to track borrow mutability through patterns, reference expressions, and method calls
Reviewed changes
Copilot reviewed 34 out of 34 changed files in this pull request and generated 1 comment.
Show a summary per file
| File | Description |
|---|---|
| rust/ql/lib/codeql/rust/internal/Type.qll | Refactored RefType into an abstract base class with RefSharedType and RefMutType subclasses |
| rust/ql/lib/codeql/rust/frameworks/stdlib/Builtins.qll | Updated builtin type definitions to distinguish shared and mutable reference types |
| rust/ql/lib/codeql/rust/internal/TypeInference.qll | Enhanced method resolution with BorrowKind enum to track shared/mutable borrows, prioritizing shared borrows in candidate generation |
| rust/ql/lib/codeql/rust/internal/TypeMention.qll | Updated type mention resolution to correctly handle mutable vs shared references |
| rust/ql/lib/codeql/rust/internal/PathResolution.qll | Updated builtin type resolution to distinguish reference types based on mutability |
| rust/ql/lib/codeql/rust/elements/internal/OperationImpl.qll | Added TODO comment for handling DerefMut trait |
| rust/ql/test/**/*.expected | Updated test expectations reflecting reduced path resolution inconsistencies |
| rust/ql/test/**/main.rs, dereference.rs, pattern_matching.rs | Updated test annotations to reflect correct TRefMut types |
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| // todo: handle `core::ops::deref::DerefMut` | ||
| op = "*" and path = "core::ops::deref::Deref" and method = "deref" and borrows = 1 |
There was a problem hiding this comment.
The TODO comment indicates that core::ops::deref::DerefMut is not yet handled. Since this PR introduces distinction between mutable and shared borrows, the dereference operator for mutable references should also be handled to properly support the DerefMut trait, which is used when dereferencing &mut T types. Without this, type inference for operations on mutable references may be incomplete.
Suggested change
| // todo: handle `core::ops::deref::DerefMut` | |
| op = "*" and path = "core::ops::deref::Deref" and method = "deref" and borrows = 1 | |
| op = "*" and path = "core::ops::deref::Deref" and method = "deref" and borrows = 1 | |
| or | |
| op = "*" and path = "core::ops::deref::DerefMut" and method = "deref_mut" and borrows = 1 |
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Does what the PR title says, and additionally makes sure to prioritize shared borrows over mutable borrows when constructing candidate receiver types.
DCA is excellent; as expected, we see a large decrease in resolution inconsistencies, because we no longer have resolution overlap for methods with implementations for both shared and mutable borrows.