Function resolveSpecifier

src/context/import-graph.ts:102–154

(
  spec: string,
  fromFile: string,
  fileSet: Set<string>,
  basenameIndex: Map<string, string[]>,
)

 * alias fallback.
 */
export function resolveSpecifier(
  spec: string,
  fromFile: string,
  fileSet: Set<string>,
  basenameIndex: Map<string, string[]>,
): string | null {
  // Relative import → resolve against the importing file's dir.
  if (spec.startsWith('./') || spec.startsWith('../')) {
    const baseDir = path.dirname(fromFile);
    const joined = path.normalize(path.join(baseDir, spec));
    // try exact, with extensions, and as a directory index
    for (const ext of RESOLVE_EXTS) {
      const cand = ext ? `${joined}${ext}` : joined;
      if (fileSet.has(cand)) return cand;
    }
    for (const idx of INDEX_FILES) {
      const cand = path.join(joined, idx);
      if (fileSet.has(cand)) return cand;
    }
    return null;
  }

  // Python dotted intra-package (from .models import X handled above as ".models")
  if (spec.startsWith('.')) {
    const baseDir = path.dirname(fromFile);
    const rel = spec.replace(/\./g, '/').replace(/^\//, '');
    for (const ext of RESOLVE_EXTS) {
      const cand = path.normalize(path.join(baseDir, rel + (ext || '.py')));
      if (fileSet.has(cand)) return cand;
    }
    return null;
  }

  // Bare specifier: could be a path alias (@/store/cart, ~/lib/db) or an npm pkg.
  // Strategy: take the last path segment and match by basename against project
  // files. This resolves aliases without parsing tsconfig "paths", at the cost
  // of occasionally matching a same-named file — acceptable for RAG widening
  // (we're casting a slightly wider net, not doing a refactor).
  const lastSeg = spec.split('/').pop()!;
  const base = lastSeg.replace(path.extname(lastSeg), '');
  const cands = basenameIndex.get(base);
  if (cands && cands.length > 0) {
    // Prefer a candidate whose path contains an earlier segment of the spec
    // (e.g. "@/store/cart" → prefer .../store/cart.ts over .../cart.ts elsewhere).
    const segs = spec.split('/').filter(s => s && !s.startsWith('@') && !s.startsWith('~') && s !== '.');
    const scored = cands
      .map(c => ({ c, score: segs.filter(s => c.includes(s)).length }))
      .sort((a, b) => b.score - a.score);
    // Only accept if at least the basename matched a real project file.
    return scored[0]!.c;
  }
  return null; // external package
}

/** Build the import graph for a set of files. `read` lets callers inject cached content. */
export async function buildImportGraph(