Rust: Adjust the taint reach metric for better stability.

[geoffw0]

Adjust the taint reach metric for better stability.

When models are added the number of flow summary nodes generated often increases, and we've recently found this tends to cause the taint reach metric to wobble (even when the amount of actual flow and regular nodes associated with the database remains constant). We now exclude flow summary nodes from both the numerator and denominator of the taint reach calculation. I have locally verified this makes the taint reach number stable under deletion (and therefore also addition) of irrelevant summary models.

I expect to see [hopefully quite small] wobbles in the taint reach calculation in the DCA run for this change.

[Copilot]

Pull Request Overview

This PR refines the taint reach metric by excluding flow summary nodes from both the numerator and denominator, stabilizing the calculation when models change.

• Import FlowSummaryNode to identify summary nodes.
• Update getTaintedNodesCount and getTaintReach to filter out summary nodes and introduce getTotalNodesCount.
• Expose the new “total non-summary nodes” statistic in taintStats.

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
rust/ql/src/queries/summary/TaintReach.qll	Import FlowSummaryNode, filter it out in tainted/total counts.
rust/ql/src/queries/summary/Stats.qll	Add new stat key for total non-summary nodes in taintStats.

Comments suppressed due to low confidence (3)

rust/ql/src/queries/summary/TaintReach.qll:39

• There aren’t any existing tests covering getTotalNodesCount or the new stat; consider adding or updating tests to validate its behavior and catch regressions.

int getTotalNodesCount() { result = count(DataFlow::Node n | not n instanceof FlowSummaryNode) }

rust/ql/src/queries/summary/Stats.qll:192

• [nitpick] The label "total non-summary nodes" doesn’t exactly match the method name getTotalNodesCount; consider renaming it to something like "total nodes (excluding summary)" for clarity and consistency.

  key = "Taint reach - total non-summary nodes" and value = getTotalNodesCount()

rust/ql/src/queries/summary/Stats.qll:192

• Indentation for this new entry should align with the existing 4-space indent on other key = ... lines to maintain consistent formatting.

  key = "Taint reach - total non-summary nodes" and value = getTotalNodesCount()

[geoffw0]

DCA looks as expected (apart from one spurious build failure)