bug(dead-code): exported functions passed as values report as dead — graph-core emits no reference edge

[EivMeyer]

Verified on main @ af09b7c (v0.2.1), built locally, darwin-arm64.

Summary

An exported function that is only ever passed as a value — to map, reduce, filter, a callback, a handler table — is reported as dead. The graph has no edge kind for a symbol reference, so TS_DEAD_CODE_UNUSED_EXPORT fires on code that is plainly in use.

Repro

// src/domain/money.ts
export function money(amount: number, currency: Currency): Money { ... }
export function add(a: Money, b: Money): Money { ... }

// src/domain/cart.ts
export function lineTotal(item: LineItem): Money { ... }

export function cartTotal(items: readonly LineItem[]): Money {
  if (items.length === 0) return money(0, "EUR");
  return items.map(lineTotal).reduce(add);      // <-- both passed as values
}

opcore graph build then opcore --repo .:

TS_DEAD_CODE_UNUSED_EXPORT [warning] src/domain/cart.ts  :: no incoming CALLS graph evidence: lineTotal
TS_DEAD_CODE_UNUSED_EXPORT [warning] src/domain/money.ts :: no incoming CALLS graph evidence: add

money, format, and cartTotal — all invoked with call syntax — are correctly not flagged.

Rewrite the same logic with direct calls:

export function cartTotal(items: readonly LineItem[]): Money {
  let running = money(0, "EUR");
  for (const item of items) {
    running = add(running, lineTotal(item));
  }
  return running;
}

Rebuild the graph, and both warnings disappear. Only the genuinely dead export remains.

Cause

packages/validation-typescript/src/dead-code-entrypoints.ts:21

const symbolReachabilityEdgeKinds = new Set(["CALLS", "INHERITS", "IMPLEMENTS"]);

This is not just a narrow edge-kind set. Grepping crates/graph-core/src, the only edge kinds the graph emits at all are CALLS, IMPLEMENTS, IMPORTS_FROM, INHERITS, TESTED_BY. There is no reference edge, so passing a function as a value records no relationship anywhere — reachability isn't ignoring a weak edge, the edge was never extracted.

That makes this a graph-core change (emit a reference edge from the Rust extractor), not a set-membership change in TypeScript.

Why it matters

Higher-order usage is ordinary TypeScript. Any repo using map/reduce/filter with named functions, or registering handlers in a table, gets false dead-export warnings in proportion to how idiomatic it is. They are warning severity so they do not block, but #285 and #288 both contemplate promoting dead-code to error — this would need fixing first.

Distinct from #287 (entrypoint modeling), which is about package-declared public APIs whose callers live outside the repo. Here the caller is in the same file.