Type inference 2.0

[hvitved]

By lack of a better title, I named this PR 'Type inference 2.0', because it makes a lot of changes (improvements) to our implementation of type inference for Rust. At a high level, a lot of code is moved from the Rust codebase to the shared type inference library (in preparation for unified/Swift), and there is now a very clear distinction between bottom-up type inference and top-down (contextual) type inference.

Before this PR

• The shared type inference library contained the core functionality for propagating type information through for example function calls, but all logic for mapping AST nodes to types was done outside of the library.
• Rust type inference allowed for types to propagate bidirectionally (as a classical constrained-based implementation would), but since this could easily lead to explosions in inferred types, advanced logic existed for inferring types with certainty, and this logic also tried to infer certain types for calls.

Note for the reviewer

As usual, commit-by-commit reviewing is encouraged. The first commit (which compiles and works) moves a bunch of logic around in the Rust implementation, which is then removed in the subsequent commit (which doesn't compile). I found that doing it like this resulted in a cleaner diff on the last commit, and it also makes it more clear which parts of the logic are now handled by shared code.

Impact

Future work

• Handle more AST constructs in the shared library, such as patterns (should be relatively straightforward).
• Shared logic for type-based overload resolution; logic currently exists for Rust, and perhaps some of this logic can be shared.

[Copilot]

Pull request overview

Refactors Rust type inference around the shared library’s new bottom-up and contextual inference architecture.

Changes:

• Adds shared AST inference, contextual typing, closure handling, and diagnostics.
• Reimplements Rust inference through the shared Make3 interface.
• Updates Rust tests and consistency expectations.

Show a summary per file

File	Description
shared/util/codeql/util/UnboundList.qll	Adds list append helper.
shared/typeinference/codeql/typeinference/internal/TypeInference.qll	Implements shared inference framework.
rust/ql/test/library-tests/type-inference/type-inference.ql	Uses shared type-test support.
rust/ql/test/library-tests/type-inference/pattern_matching.rs	Updates inference expectations.
rust/ql/test/library-tests/type-inference/overloading.rs	Records contextual inference regression.
rust/ql/test/library-tests/type-inference/main.rs	Updates coverage and expectations.
rust/ql/test/library-tests/type-inference/dereference.rs	Exercises inferred generic arguments.
rust/ql/test/library-tests/type-inference/CONSISTENCY/PathResolutionConsistency.expected	Updates generated consistency output.
rust/ql/test/library-tests/type-inference/closure.rs	Updates closure expectations.
rust/ql/test/library-tests/dataflow/sources/web_frameworks/CONSISTENCY/TypeInferenceConsistency.expected	Updates generated consistency output.
rust/ql/test/library-tests/dataflow/models/CONSISTENCY/PathResolutionConsistency.expected	Updates generated consistency output.
rust/ql/lib/codeql/rust/internal/typeinference/TypeMention.qll	Adds contextual and constructor type mentions.
rust/ql/lib/codeql/rust/internal/typeinference/TypeInferenceConsistency.qll	Adopts shared consistency checks.
rust/ql/lib/codeql/rust/internal/typeinference/TypeInference.qll	Adapts Rust inference to Make3.
rust/ql/lib/codeql/rust/internal/typeinference/Type.qll	Introduces generalized pseudo-types.
rust/ql/lib/codeql/rust/internal/typeinference/FunctionType.qll	Generalizes pseudo-type filtering.
rust/ql/lib/codeql/rust/internal/typeinference/BlanketImplementation.qll	Generalizes pseudo-type filtering.
rust/ql/lib/codeql/rust/internal/CachedStages.qll	Uses the shared inference cache stage.

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Suppressed comments (1)

shared/typeinference/codeql/typeinference/internal/TypeInference.qll:3345

• Remove the duplicated article.

       * Holds if the the textual representation `repr` should be used for `n` in

• Files reviewed: 17/19 changed files
• Comments generated: 4
• Review effort level: Balanced