Unified: Basic support for extensions

[asgerf]

Adds support for Swift extension blocks, aka extension methods.

class A {}
extension A {
  func foo() { ... }
}
A().foo() // calls 'foo' from the extension

This adds a new field, ClassLikeNode.getExtensionTarget() for storing the extension target.

Two features are not yet handled:

• Scoping: We assume extensions are in scope everywhere, though in reality they are only visible from files the import the file containing the extension. I'd like to build support this together with access levels (protected, etc) as I expect we can use the same mechanism for both. The idea is that an extension method can be seen as having an access level that only permits access within certain files.
• Type parameters: Type parameters of the target type are in scope within the extension, without being redeclared locally. Not supported yet.

DCA shows an increase in statically-resolvable names by about 2 percentage points.

[Copilot]

Copilot review overview

🟡 Changes recommended

A new conformance test uses invalid Swift, and extractor documentation contradicts the new mapping.

Get a fresh assessment by requesting another Copilot review.

Review tier: Balanced
Findings: 1 · 1

Open findings (2)

• Use a valid protocol-conformance fixture · New
• Update the obsolete extension-mapping comment · New

What changed in this PR

Adds structured Swift extension targets and integrates extension members into unified static name binding.

Changes:

• Adds extension_target to the unified AST schema and extractor.
• Resolves static and instance members across extensions.
• Adds extraction and name-binding coverage.

File	Description
unified/​extractor/​ast_types.yml	Defines the extension-target field.
unified/​extractor/​src/​languages/​swift/​swift.rs	Maps Swift extended types structurally.
unified/​extractor/​tests/​corpus/​swift/​types/​extension.output	Updates generated extractor expectations.
unified/​ql/​lib/​unified.dbscheme	Adds extension-target storage.
unified/​ql/​lib/​codeql/​unified/​internal/​Ast.qll	Exposes the generated field accessor.
unified/​ql/​lib/​codeql/​unified/​internal/​StaticNameBinding.qll	Connects extension and target namespaces.
unified/​ql/​test/​library-tests/​static-name-binding/​test.swift	Updates qualified-target expectations.
unified/​ql/​test/​library-tests/​static-name-binding/​extensions.swift	Adds extension name-binding scenarios.

---

💡 Add a code-review agent skill or configure MCP servers for context-aware, tailored reviews. Learn more in the docs.

[hvitved]

Should the last access be marked as spurious?

[asgerf]

Added a comment to clarify, based on offline discussion