Unified: implement local scoping

[asgerf]

This adds local scoping and does a few other things in order to get that working:

• Moves libraries into codeql.unified.internal and imports their Public modules into unified.qll. Makes it easy to share internal code between the libraries.
• The last commit sets out to use Yeast context-passing to correctly translate identifers in patterns to either name_pattern or expr_equality_pattern wrapping a name_expr. In the future we might want to move this logic into QL but I wanted to make sure that Yeast can handle this kind of problem if we need it to. The commit also fixes a bunch of potential context-leaking issues where modifiers would leak into expr/stmt subtrees.

guard statements could not be natively handled by the shared library, but it turns out can handle it by flattening their children into the enclosing Block.

[Copilot]

Pull request overview

This PR introduces lexical (local) scoping support to the Unified libraries by adding a name-binding–based Variables library, restructuring Unified’s public surface to re-export internal Public modules via unified.qll, and updating the Swift Yeast translation to correctly distinguish binding patterns from expression-equality patterns while preventing modifier/context leakage into unrelated subtrees.

Changes:

• Add a Unified local-variable model (Variables) backed by codeql/namebinding, plus a developer debug query for the scope graph.
• Update Swift extractor translation to use context-passing + context resets so patterns are translated correctly and binding modifiers don’t leak into initializers/bodies.
• Add/expand Swift corpus and Unified library-tests covering variable binding, shadowing, and guard/conditional scoping behaviors.

Show a summary per file

File	Description
unified/ql/test/library-tests/variables/variables.ql	Adds an InlineExpectationsTest query to validate VariableAccess→Variable resolution via inline comments.
unified/ql/test/library-tests/variables/variables.expected	Inline-expectations .expected placeholder for the new test (expected to be empty).
unified/ql/test/library-tests/variables/test.swift	Adds a comprehensive Swift fixture exercising shadowing and scoping scenarios.
unified/ql/lib/unified.qll	Switches Unified’s public imports to re-export internal Public modules (Variables/Ast extras).
unified/ql/lib/qlpack.yml	Adds dependency on codeql/namebinding to support local name binding.
unified/ql/lib/codeql/unified/internal/Variables.qll	Implements local variable declarations/accesses and scope lookup wiring for Unified.
unified/ql/lib/codeql/unified/internal/dev/debugScopeGraph.ql	Adds a dev-only graph query to render/debug the local scope graph.
unified/ql/lib/codeql/unified/internal/AstExtra.qll	Adds non-generated AST helper classes (including Comment) under an internal module.
unified/ql/lib/codeql/unified/Comments.qll	Removes the old comments helper (moved under internal AstExtra).
unified/extractor/tests/corpus/swift/variables/tuple-destructuring-binding.output	Updates expected AST output for tuple destructuring bindings.
unified/extractor/tests/corpus/swift/variables/binding-modifier-does-not-leak-into-initializer.swift	Adds corpus fixture ensuring binding modifiers don’t leak into initializer translation.
unified/extractor/tests/corpus/swift/variables/binding-modifier-does-not-leak-into-initializer.output	Adds expected output for the initializer leakage fixture.
unified/extractor/tests/corpus/swift/types/binding-modifier-does-not-leak-into-accessor-body.swift	Adds corpus fixture ensuring binding modifiers don’t leak into accessor bodies.
unified/extractor/tests/corpus/swift/types/binding-modifier-does-not-leak-into-accessor-body.output	Adds expected output for the accessor-body leakage fixture.
unified/extractor/tests/corpus/swift/control-flow/binding-modifier-does-not-leak-to-sibling.swift	Adds corpus fixture ensuring binding modifiers don’t leak to sibling statements.
unified/extractor/tests/corpus/swift/control-flow/binding-modifier-does-not-leak-to-sibling.output	Adds expected output for the sibling leakage fixture.
unified/extractor/src/languages/swift/swift.rs	Updates Swift Yeast rules to publish binding context, translate/reset subtrees, and pattern-translate identifiers appropriately.
shared/yeast/src/build.rs	Adds translate_reset helper to translate captures under a fresh user context.
shared/namebinding/codeql/namebinding/LocalNameBinding.qll	Adjusts the namebinding interface and adds a debug scope graph helper module.
ruby/ql/lib/codeql/ruby/ast/internal/Variable.qll	Updates Ruby implementation to match the adjusted namebinding signature.

Review details

• Files reviewed: 19/20 changed files
• Comments generated: 7
• Review effort level: Low

[hvitved]

QL changes LGTM, I mostly have some minor comments. I have approved in case we want to merge in order to unblock other work; my comments can be addressed follow-up if needed.

[hvitved]

We do something similar in Rust for let chains; perhaps we should consider making this transformation inside the shared library.

[hvitved]

Again, something similar is done for Rust, so there may be potential for sharing.

[tausbn]

I think the changes here look good. My only concern is the new translate_reset mechanism, which is a bit too "all or nothing" for my taste. I've come up with a slightly different API that I think is equally good, but a bit more flexible. In the interest of moving things along, I'll approve and merge this PR, and then make the necessary improvements later on.