repo-tools/type-deps: support nested declaration files

Signed-off-by: Patrik Oldsberg <poldsberg@gmail.com>

.changeset/repo-tools-type-deps-ambient-jest.md

@@ -2,4 +2,4 @@
 '@backstage/repo-tools': patch
 ---
 
-The `type-deps` command now detects ambient global types from the `jest` namespace in declaration files, rather than only looking for explicit imports and reference directives.
+The `type-deps` command now follows relative imports and re-exports into declaration chunk files, and detects ambient global types such as the `jest` namespace.

packages/repo-tools/src/commands/type-deps/type-deps.ts

@@ -78,6 +78,50 @@ function shouldCheckTypes(pkg: Package & PackageJsonWithTypes) {
   );
 }
 
+/**
+ * Read a declaration file and recursively follow all relative imports and
+ * re-exports, collecting the source content of each file encountered.
+ */
+function collectDeclSources(entryPath: string): string[] {
+  const visited = new Set<string>();
+  const sources: string[] = [];
+
+  function visit(filePath: string) {
+    const resolved = resolvePath(filePath);
+    if (visited.has(resolved)) {
+      return;
+    }
+    visited.add(resolved);
+
+    // Handle .js -> .d.ts extension mapping used by declaration chunk files
+    let actualPath = resolved;
+    if (!fs.existsSync(actualPath)) {
+      actualPath = resolved.replace(/\.js$/, '.d.ts');
+    }
+    if (!fs.existsSync(actualPath)) {
+      return;
+    }
+
+    const src = fs.readFileSync(actualPath, 'utf8');
+    sources.push(src);
+
+    // Follow relative imports and re-exports into chunk files
+    const relativeRefs = (
+      src.match(/^(?:import|export) .* from '\..*';$/gm) || []
+    )
+      .map(match => match.match(/from '(.*)'/)?.[1] ?? '')
+      .filter(n => n.startsWith('.'));
+
+    const dir = resolvePath(actualPath, '..');
+    for (const ref of relativeRefs) {
+      visit(resolvePath(dir, ref));
+    }
+  }
+
+  visit(entryPath);
+  return sources;
+}
+
 function findAllDeps(declSrc: string) {
   const importedDeps = (declSrc.match(/^import .* from '.*';$/gm) || [])
     .map(match => match.match(/from '(.*)'/)?.[1] ?? '')
@@ -112,11 +156,8 @@ function findAllDeps(declSrc: string) {
  */
 function checkTypes(pkg: Package) {
   const allDeps = getPackageExportDetails(pkg.packageJson).flatMap(exp => {
-    const typeDecl = fs.readFileSync(
-      resolvePath(pkg.dir, 'dist', exp.distPath),
-      'utf8',
-    );
-    return findAllDeps(typeDecl);
+    const entryPath = resolvePath(pkg.dir, 'dist', exp.distPath);
+    return collectDeclSources(entryPath).flatMap(src => findAllDeps(src));
   });
   const deps = Array.from(new Set(allDeps));