fix(resolution): follow alias bindings to the function they name (#1482) (#1808)

Adapt upstream PR #1485 by @valkyriweb (cc791cfc51b100097571421b4ab7c53b96ceb202)
onto current main. Keep the upstream alias-binding module and six-test suite
verbatim, preserve target-kind gating and default-export bindings, and add
one credited Unreleased changelog entry.

Linux verification (x86_64, Node 22.19.0): TypeScript build and asset copy
pass; the fresh ./impl.js repro changes callers/impact of realImpl from
missing consumerFn to including it. All 6 upstream tests and 231 related
resolver regression tests pass.

Fixes #1482

The Forge PR will supersede upstream PR #1485.

Co-authored-by: Colby McHenry <colbymchenry@users.noreply.github.com>

__tests__/alias-binding-resolution.test.ts

@@ -0,0 +1,107 @@
+/**
+ * Calls through an alias binding.
+ *
+ * A name bound to nothing but another symbol — `export const alias = fn`,
+ * `export { fn as alias }`, `export const api = { run: fn }`, or a same-file
+ * `const local = fn` — used to resolve to the BINDING, one hop short of the
+ * function. The edge existed, so nothing looked broken, but `callers fn` omitted
+ * every caller that went through the alias and reported a confident zero while
+ * `callers alias` found them.
+ *
+ * Specifiers here are extensionless so these cases stand independently of
+ * `.js`-specifier resolution.
+ */
+import { describe, it, expect, afterEach } from 'vitest';
+import * as fs from 'fs';
+import * as path from 'path';
+import * as os from 'os';
+import CodeGraph from '../src/index';
+
+describe('calls through an alias binding reach the aliased symbol', () => {
+  let cg: CodeGraph;
+  let dir: string;
+
+  afterEach(() => {
+    if (cg) cg.destroy();
+    if (dir && fs.existsSync(dir)) fs.rmSync(dir, { recursive: true, force: true });
+  });
+
+  const index = async (files: Record<string, string>): Promise<void> => {
+    dir = fs.mkdtempSync(path.join(os.tmpdir(), 'codegraph-alias-'));
+    for (const [name, content] of Object.entries(files)) {
+      fs.writeFileSync(path.join(dir, name), content);
+    }
+    cg = CodeGraph.initSync(dir, { config: { include: ['**/*.ts'], exclude: [] } });
+    await cg.indexAll();
+  };
+
+  const callersOf = (name: string): string[] => {
+    const target = cg.getNodesByKind('function').find((n) => n.name === name);
+    expect(target, `fixture symbol ${name} was not indexed`).toBeDefined();
+    return cg.getCallers(target!.id).map((c) => c.node.name);
+  };
+
+  it('follows `export const alias = fn`', async () => {
+    await index({
+      'impl.ts': 'export function realImpl(): number { return 1; }\nexport const aliasName = realImpl;\n',
+      'consumer.ts': "import { aliasName } from './impl';\nexport function consumerFn(): number { return aliasName(); }\n",
+    });
+    expect(callersOf('realImpl')).toContain('consumerFn');
+  });
+
+  it('follows a local `export { fn as alias }` clause', async () => {
+    // The declaration carries no `export` keyword, so extraction does not flag
+    // it exported — the export index must still bind the renamed export to it.
+    await index({
+      'impl.ts': 'function realImpl(): number { return 1; }\nexport { realImpl as aliasName };\n',
+      'consumer.ts': "import { aliasName } from './impl';\nexport function consumerFn(): number { return aliasName(); }\n",
+    });
+    expect(callersOf('realImpl')).toContain('consumerFn');
+  });
+
+  it('follows a function reference held in an object-literal property', async () => {
+    await index({
+      'impl.ts': 'export function realImpl(): number { return 1; }\nexport const api = { run: realImpl };\n',
+      'consumer.ts': "import { api } from './impl';\nexport function consumerFn(): number { return api.run(); }\n",
+    });
+    expect(callersOf('realImpl')).toContain('consumerFn');
+  });
+
+  it('follows a same-file alias binding', async () => {
+    await index({
+      'impl.ts':
+        'function realImpl(): number { return 1; }\n' +
+        'const localAlias = realImpl;\n' +
+        'export function consumerFn(): number { return localAlias(); }\n',
+    });
+    expect(callersOf('realImpl')).toContain('consumerFn');
+  });
+
+  it('leaves a genuine wrapper pointing at the wrapper, not the wrapped function', async () => {
+    // `wrapper` is a real function, not an alias: the call site calls IT.
+    await index({
+      'impl.ts':
+        'export function realImpl(): number { return 1; }\n' +
+        'export const wrapper = (): number => realImpl();\n',
+      'consumer.ts': "import { wrapper } from './impl';\nexport function consumerFn(): number { return wrapper(); }\n",
+    });
+    expect(callersOf('realImpl')).not.toContain('consumerFn');
+  });
+
+  it('does not hop when the aliased name is ambiguous across files', async () => {
+    // Two same-named callables and no same-file declaration to prefer: a hop
+    // would have to guess, and a wrong edge is worse than a missing one.
+    await index({
+      'one.ts': 'export function shared(): number { return 1; }\n',
+      'two.ts': 'export function shared(): number { return 2; }\n',
+      'alias.ts': "import { shared } from './one';\nexport const aliasName = shared;\n",
+      'consumer.ts': "import { aliasName } from './alias';\nexport function consumerFn(): number { return aliasName(); }\n",
+    });
+
+    const sharedNodes = cg.getNodesByKind('function').filter((n) => n.name === 'shared');
+    expect(sharedNodes).toHaveLength(2);
+    for (const node of sharedNodes) {
+      expect(cg.getCallers(node.id).map((c) => c.node.name)).not.toContain('consumerFn');
+    }
+  });
+});