Rust: Model String -> str implicit conversion in type inference
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Pull Request Overview
Adds hard-coded support for implicit String -> str conversion in CodeQL’s Rust type inference, updates related tests, and defines the StringStruct.
- Extends
TypeInference.qllto special-caseStringderef tostrwhen resolving method calls. - Introduces
StringStructinStdlib.qlland updates expected outputs across multiple test suites to includeas_strtargets. - Adds a demonstration test in
main.rsforString->strconversion viaparse.
Reviewed Changes
Copilot reviewed 10 out of 10 changed files in this pull request and generated 1 comment.
| File | Description |
|---|---|
| rust/ql/lib/codeql/rust/internal/TypeInference.qll | Adds special-case logic for String → str conversion in calls |
| rust/ql/lib/codeql/rust/frameworks/stdlib/Stdlib.qll | Defines StringStruct mapping to alloc::string::String |
| rust/ql/test/library-tests/type-inference/main.rs | Adds example test case showing implicit conversion with parse |
| rust/ql/test/**/PathResolutionConsistency.expected (many) | Updates expected outputs to include new as_str and conversion targets |
Comments suppressed due to low confidence (1)
rust/ql/lib/codeql/rust/internal/TypeInference.qll:845
- [nitpick] Consider adding a brief comment above this condition to explain why the
StringStruct→Builtins::Strexclusion is needed, to aid future maintainers.
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geoffw0
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Jun 12, 2025
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We will also want the same feature in data flow access paths at some point, but I guess the logic isn't shared between them.
| // See also https://doc.rust-lang.org/reference/expressions/method-call-expr.html#r-expr.method.autoref-deref | ||
| path.isEmpty() and | ||
| t0.(StructType).asItemNode() instanceof StringStruct and | ||
| result.(StructType).asItemNode() instanceof Builtins::Str |
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Is it OK that we also still get the result from result = t0 as well in this situation, i.e. that we get two results (of which only one applies depending on context)?
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Yes, that is deliberate.
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paldepind
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Jun 13, 2025
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Eventually we will want to generally support the
Dereftrait in type inference, but for now hard-code knowledge aboutString -> strconversion.