fix(dataflow): grouped param wrapper gives every name the same paramIndex

[carlos-alm]

Problem

extractParams (src/ast-analysis/visitor-utils.ts) incremented index once per CHILD of the parameter list, not once per extracted name. Dart's optional_formal_parameters wraps multiple genuinely separate parameter declarations in one child node ({int times, bool loud}), so both times and loud got the same paramIndex.

Fix

Added groupedParamTypes to DataflowRulesConfig: when a child's type is in this set, extractParams iterates that child's own named children as separate slots instead of treating the whole node as one slot. Set for Dart's optional_formal_parameters.

This is deliberately not a blanket "index per extracted name" change (the issue's own caution): true single-slot destructuring (JS/TS function f({a, b})) must keep sharing one index across a/b, since both come from the same argument slot — verified via a new test locking that in.

Also discovered Dart's grammar attaches a parameter's default-value literal (= 1, = false) as a flat sibling inside the optional_formal_parameters group, not nested inside its formal_parameter — so the grouped-slot loop only consumes an index for a slot that actually yields a name, otherwise the literal siblings created off-by-N gaps.

Simplified extractDartParamName by removing its now-dead recursive optional_formal_parameters branch, since extractParams no longer calls it on the group node directly.

TS/WASM-only — the Rust engine has no Dart dataflow rules at all yet (tracked separately by #2359), so there's nothing to mirror there for this fix.

Follow-up filed

While verifying no other language relies on the old shared-index behavior, found Go's func f(a, b int) hits the identical bug class in both engines (TS's go.ts and Rust's extract_params_go) — already shipped, so lower risk tolerance and a differently-shaped fix. Filed as #2501, out of scope here.

Closes #2358

Test plan

• New Dart tests: named-parameter group and optional-positional group each get distinct paramIndex values
• New JS/TS test: destructured object-pattern names still share one paramIndex, non-destructured sibling gets the next one
• Full vitest run suite (5272 passed, 328 files)
• tsc --noEmit, biome check
• cargo test --release, cargo clippy -- -D warnings, cargo fmt --check (unaffected, confirmed clean)
• Dual-engine dataflow parity suite

[greptile-apps]

Greptile Summary

The PR corrects parameter-slot indexing for Dart grouped parameters while preserving shared indices for destructuring and positional indices after unnamed parameters.

• Adds groupedParamTypes to the dataflow-rule contract and enables it for Dart optional parameter groups.
• Iterates each name-producing slot inside grouped wrappers while retaining ordinary unnamed slots in the index count.
• Adds Dart, JavaScript, and C++ regression coverage for the affected indexing behaviors.

Confidence Score: 5/5

The PR appears safe to merge.

No blocking failure remains.

Important Files Changed

Filename	Overview
src/ast-analysis/visitor-utils.ts	Separates grouped parameter-slot traversal from ordinary parameter handling, preserving index advancement for unnamed ordinary parameters.
src/ast-analysis/rules/b2.ts	Configures Dart optional parameter wrappers as grouped slots and removes the obsolete recursive group extraction branch.
src/ast-analysis/shared.ts	Adds an empty grouped-parameter type set to the shared dataflow defaults.
src/types.ts	Extends the dataflow-rule contract with the grouped parameter wrapper configuration.
tests/parsers/dataflow-cpp.test.ts	Covers the previously reported unnamed-parameter regression by asserting the following named parameter remains at index 1.
tests/parsers/dataflow-dart.test.ts	Covers distinct indices for Dart named and optional-positional grouped parameters.
tests/parsers/dataflow-javascript.test.ts	Ensures names from one destructured argument continue sharing a parameter index.

Flowchart

%%{init: {'theme': 'neutral'}}%%
flowchart TD
  A[Parameter-list child] --> B{Grouped parameter type?}
  B -->|No| C[Extract names at current index]
  C --> D[Always advance index]
  B -->|Yes| E[Iterate grouped named children]
  E --> F{Child yields names?}
  F -->|Yes| G[Emit names and advance index]
  F -->|No| H[Skip metadata/default-value child]

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_{Reviews (2): Last reviewed commit: "fix(dataflow): unnamed parameter no long..." | Re-trigger Greptile}

[github-actions]

Codegraph Impact Analysis

2 functions changed → 3 callers affected across 2 files

• extractDartParamName in src/ast-analysis/rules/b2.ts:545 (1 transitive callers)
• extractParams in src/ast-analysis/visitor-utils.ts:89 (2 transitive callers)

[carlos-alm]

@greptileai please re-review — pushed a fix for the unnamed-parameter regression you flagged.