fix(dataflow): Dart local variable declarations and calls never tracked

[carlos-alm]

Summary

• dataflowDart left varDeclaratorNode entirely unconfigured, and callNode pointed at 'call_expression' — a node type that doesn't exist at all in tree-sitter-dart's grammar.
• Confirmed empirically (by dumping real parsed trees) that the grammar's own documented postfix_expression wrapper (per node-types.json) never actually materializes either: a call is a flat sequence of siblings under whatever encloses it — helper(x) parses as [identifier "helper", selector "(x)"] as direct siblings, obj.method(x) as [identifier "obj", selector ".method", selector "(x)"] — not a single self-contained node with fields, which the existing field-based callFunctionField/callArgsField extraction fundamentally assumes.
• Adds two new opt-in DataflowRulesConfig fields (null for every other language, zero behavior change elsewhere):
  • resolveCallParts — override for grammars with no field-based call structure. Dart's resolveDartCallParts dispatches from the call selector and resolves the callee by walking backward to the preceding sibling (another selector's property, for method calls, or a bare identifier, for bare calls).
  • callChainSiblingType — lets a new findCallSelector helper walk forward from a call-sourced value expression (e.g. a var declarator's resolved value field, which lands on the callee's bare identifier, not the call itself) to the trailing call-node sibling — the symmetric counterpart, needed so var x = helper(y); is recognized as call-sourced the same way it already is for languages whose call node IS the value node directly.
• Also sets varDeclaratorNode/varNameField/varValueField (the grammar does have real name/value fields on initialized_variable_definition) and argumentWrapperType: 'argument' (matching the same wrapper name PHP's config already unwraps).
• Rust's native engine has no Dart dataflow rules at all yet (tracked separately as follow-up: Rust engine needs DartDataflowRules to match TS's now-fixed dataflowDart #2359), so this is legitimately TS/WASM-only.
• Closes follow-up: Dart dataflow — calls nested inside a return/other expression are never tracked #2497 as a duplicate — that follow-up (calls nested in return expressions never tracked) is fully subsumed by this fix.

Test plan

• Empirically verified against real parsed trees for bare calls, method calls, non-call postfix expressions (x++), call-sourced and plain variable declarations, before writing any test
• New tests in tests/parsers/dataflow-dart.test.ts: bare call (as return expr and as statement), method call, non-call postfix rejection, call-sourced assignment, plain-assignment rejection
• Full test suite: 328 files / 5269 tests passed
• npm run lint clean
• diff-impact — contained (6 functions changed, 6 transitive callers)

Closes #2357

[greptile-apps]

Greptile Summary

The PR enables Dart call and local-variable dataflow extraction in the TypeScript/WASM analysis path.

• Configures Dart initialized-variable fields and argument wrappers.
• Adds grammar-specific resolution for Dart’s flat selector-based call representation.
• Adds sibling-chain lookup for call-sourced variable declarations.
• Adds coverage for bare calls, method calls, postfix rejection, and call-sourced assignments.

Confidence Score: 5/5

The PR appears safe to merge, with no concrete blocking or independently actionable non-blocking issue established.

The Dart-specific behavior is opt-in, existing languages retain the prior field-based resolution path, and the added tests exercise the primary call and assignment cases without revealing a reachable regression.

Important Files Changed

Filename	Overview
src/ast-analysis/rules/b2.ts	Adds Dart-specific variable declaration fields and selector-based call-part resolution; no actionable defect was established.
src/ast-analysis/visitors/dataflow-visitor.ts	Generalizes call resolution and adds opt-in sibling lookup while preserving the existing field-based path for other languages.
src/ast-analysis/shared.ts	Adds null defaults for the two opt-in dataflow configuration fields.
src/types.ts	Extends the dataflow rules contract with typed call-resolution and sibling-chain options.
tests/parsers/dataflow-dart.test.ts	Adds focused positive and negative coverage for newly supported Dart calls and declarations.

Flowchart

%%{init: {'theme': 'neutral'}}%%
flowchart LR
  AST["Dart flat AST siblings"] --> Selector["Call selector"]
  Selector --> Resolve["resolveDartCallParts"]
  Resolve --> Callee["Callee name"]
  Resolve --> Args["Arguments node"]
  Args --> Flows["Argument flows"]
  Value["Variable value node"] --> Find["findCallSelector"]
  Find --> Selector
  Callee --> Assignment["Call-sourced assignment"]

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[github-actions]

Codegraph Impact Analysis

6 functions changed → 6 callers affected across 2 files

• prevNamedSibling in src/ast-analysis/rules/b2.ts:574 (2 transitive callers)
• resolveDartCallParts in src/ast-analysis/rules/b2.ts:608 (1 transitive callers)
• resolveCallExprParts in src/ast-analysis/visitors/dataflow-visitor.ts:218 (4 transitive callers)
• findCallSelector in src/ast-analysis/visitors/dataflow-visitor.ts:248 (3 transitive callers)
• handleVarDeclarator in src/ast-analysis/visitors/dataflow-visitor.ts:269 (2 transitive callers)
• handleCallExpr in src/ast-analysis/visitors/dataflow-visitor.ts:372 (2 transitive callers)