chore(lambda-nodejs): improve node modules versions extraction

Lookup the version in the `package.json` and then fallback to requiring
the module's `package.json`. This allows to mark transitive dependencies
as externals and install them.

See aws#11289 (comment)

packages/@aws-cdk/aws-lambda-nodejs/lib/util.ts

@@ -92,7 +92,10 @@ export function exec(cmd: string, args: string[], options?: SpawnSyncOptions) {
 }
 
 /**
- * Extract dependencies from a package.json
+ * Extract versions for a list of modules.
+ *
+ * First lookup the version in the package.json and then fallback to requiring
+ * the module's package.json. The fallback is needed for transitive dependencies.
  */
 export function extractDependencies(pkgPath: string, modules: string[]): { [key: string]: string } {
   const dependencies: { [key: string]: string } = {};
@@ -107,10 +110,13 @@ export function extractDependencies(pkgPath: string, modules: string[]): { [key:
   };
 
   for (const mod of modules) {
-    if (!pkgDependencies[mod]) {
-      throw new Error(`Cannot extract version for module '${mod}' in package.json`);
+    try {
+      // eslint-disable-next-line @typescript-eslint/no-require-imports
+      const version = pkgDependencies[mod] ?? require(`${mod}/package.json`).version;
+      dependencies[mod] = version;
+    } catch (err) {
+      throw new Error(`Cannot extract version for module '${mod}'. Check that it's referenced in your package.json or installed.`);
     }
-    dependencies[mod] = pkgDependencies[mod];
   }
 
   return dependencies;

packages/@aws-cdk/aws-lambda-nodejs/test/util.test.ts

@@ -89,7 +89,7 @@ describe('exec', () => {
 });
 
 describe('extractDependencies', () => {
-  test('with depencies referenced in package.json', () => {
+  test('with dependencies referenced in package.json', () => {
     expect(extractDependencies(
       path.join(__dirname, '../package.json'),
       ['@aws-cdk/aws-lambda', '@aws-cdk/core'],
@@ -99,11 +99,22 @@ describe('extractDependencies', () => {
     });
   });
 
+  test('with transitive dependencies', () => {
+    expect(extractDependencies(
+      path.join(__dirname, '../package.json'),
+      ['typescript'],
+    )).toEqual({
+      // eslint-disable-next-line @typescript-eslint/no-require-imports, import/no-extraneous-dependencies
+      typescript: require('typescript/package.json').version,
+    });
+    /* eslint-enable @typescript-eslint/no-require-imports */
+  });
+
   test('with unknown dependency', () => {
     expect(() => extractDependencies(
       path.join(__dirname, '../package.json'),
       ['unknown'],
-    )).toThrow(/Cannot extract version for module 'unknown' in package.json/);
+    )).toThrow(/Cannot extract version for module 'unknown'/);
   });
 });