Rust: Add ConstAccess class with getConst() predicate

[Copilot]

Adds ConstAccess class for identifying constant accesses in Rust code, analogous to the existing VariableAccess class.

Changes

• ConstAccess class in ConstImpl.qll extends PathExprBase, uses resolvePath() to resolve paths to Const items
• getConst() predicate returns the constant being accessed
• Test suite in rust/ql/test/library-tests/const_access/ covers global, associated, and module constants

Example Usage

import rust

from ConstAccess ca
where ca.getConst().getName().getText() = "MAX_SIZE"
select ca, "Access to MAX_SIZE constant"

Example code patterns matched:

const GLOBAL: i32 = 42;
impl MyStruct {
    const ASSOC: i32 = 100;
}

let x = GLOBAL;                    // ConstAccess
let y = MyStruct::ASSOC;           // ConstAccess
let z = module::CONST;             // ConstAccess

Implementation follows the same pattern as resolveSelfTy()/resolveTraitTy() in PathResolution.qll.

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Original prompt

---

This section details on the original issue you should resolve

<issue_title>Rust: Add new ConstAccess class</issue_title>
<issue_description>Just like we have the VariableAccess class, we should have a ConstAccess class with a Const getConst() predicate for retrieving that constant being accessed. getConst can be implemented by directly calling resolvePath from PathResolution.qll library. Test cases should be added as well.</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes Rust: Add new ConstAccess class #20735

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[Copilot]

Pull Request Overview

This PR introduces support for identifying and querying constant accesses in Rust code. It adds a new ConstAccess class that extends PathExpr to represent expressions that access constant declarations.

Key changes:

• Created a new ConstAccess class that uses path resolution to identify when a path expression refers to a constant
• Added comprehensive test coverage including global constants, associated constants, and module constants
• Updated the extractor test expectations to reflect that constant accesses are now identified as ConstAccess rather than just PathExpr

Reviewed Changes

Copilot reviewed 9 out of 10 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
rust/ql/lib/codeql/rust/elements/internal/ConstImpl.qll	Added ConstAccess class definition that extends PathExpr and resolves paths to constants
rust/ql/lib/codeql/rust/elements/ConstAccess.qll	Created public interface for the ConstAccess class
rust/ql/lib/rust.qll	Added import for the new ConstAccess element
rust/ql/.gitattributes	Removed linguist-generated marker from ConstImpl.qll to allow manual edits
rust/ql/.generated.list	Removed ConstImpl.qll entry as it's now manually maintained
rust/ql/test/library-tests/const_access/*	Added comprehensive test suite for constant access functionality
rust/ql/test/extractor-tests/macro-expansion/PrintAst.expected	Updated expected output to reflect ConstAccess classification

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[geoffw0]

I would have expected ConstAccess to extend VariableAccess (and re-use the getVariable() method).

[hvitved]

I think keeping them separate is easier, and also makes more sense IMO (a "constant variable" is a bit of an oxymoron).

[geoffw0]

a "constant variable" is a bit of an oxymoron

That's true.

I was thinking more about how typical QL involving variables (e.g. looking for initializers) is likely to want to look at constants just the same.

[geoffw0]

I think in most other languages we model a constant as a variable with a const flag or specifier or some such.

[geoffw0]

We had a discussion about this, conclusion is that we can address this later if there turns out to be a need.