Rust: Support Argument[x] MaD source definitions

[hvitved]

Adds support for writing MaD sources like

extensions:
  - addsTo:
      pack: codeql/rust-all
      extensible: sourceModel
    data:
      - ["repo::test", "crate::arg_source", "Argument[0]", "test-source", "manual"]

which interprets post-update nodes of first arguments in calls to arg_source as sources.

[Copilot]

Pull Request Overview

This PR adds support for interpreting post-update nodes of the first argument in calls to arg_source by introducing a new MaD source definition.

• Adds a new MaD source definition for "Argument[0]" in the YAML models file.
• Introduces an arg_source function and an associated test (test_arg_source) in main.rs that demonstrates the new source flow.

Reviewed Changes

Copilot reviewed 2 out of 4 changed files in this pull request and generated 1 comment.

File	Description
rust/ql/test/library-tests/dataflow/models/models.ext.yml	Added a new row defining a source model for arg_source with "Argument[0]"
rust/ql/test/library-tests/dataflow/models/main.rs	Added the arg_source function and a corresponding test to invoke it

Files not reviewed (2)

• rust/ql/lib/codeql/rust/dataflow/internal/FlowSummaryImpl.qll: Language not supported
• rust/ql/test/library-tests/dataflow/models/models.expected: Language not supported

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[Copilot]

Consider adding a semicolon after the sink(i) call for consistency with other test cases and to prevent potential compilation issues.

Suggested change

	sink(i) // $ hasValueFlow=i
	sink(i); // $ hasValueFlow=i

[paldepind]

We could make this a member predicate on ParameterPosition?

[hvitved]

Done.

[geoffw0]

LGTM, thanks for addressing this!

[paldepind]

🎉