Support @types typescript typedef packages

Fixes depcheck#163

src/check.js

@@ -7,6 +7,8 @@ import builtInModules from 'builtin-modules';
 import requirePackageName from 'require-package-name';
 import { readJSON } from './utils';
 import getNodes from './utils/parser';
+import { getAtTypesName } from './utils/typescript';
+import { availableParsers } from './constants';
 
 function isModule(dir) {
   try {
@@ -71,6 +73,19 @@ function getDependencies(dir, filename, deps, parser, detectors) {
         .flatten()
         .uniq()
         .map(requirePackageName)
+        .thru(_dependencies => (
+          parser === availableParsers.typescript
+            // If this is a typescript file, importing foo would also use @types/foo, but
+            // only if @types/foo is already a specified dependency.
+            ? lodash(_dependencies)
+              .map((dependency) => {
+                const atTypesName = getAtTypesName(dependency);
+                return deps.includes(atTypesName) ? [dependency, atTypesName] : [dependency];
+              })
+              .flatten()
+              .value()
+            : _dependencies
+        ))
         .value();
 
     const discover = lodash.partial(discoverPropertyDep, dir, deps);

src/utils/typescript.js

@@ -0,0 +1,10 @@
+/* eslint-disable import/prefer-default-export */
+const orgDepRegex = /@(.*?)\/(.*)/;
+
+// The name of the DefinitelyTyped package for a given package
+export function getAtTypesName(dep) {
+  const match = orgDepRegex.exec(dep);
+  const pkgName = match ? `${match[1]}__${match[2]}` : dep;
+
+  return `@types/${pkgName}`;
+}

test/fake_modules/typescript/esnext.ts

@@ -1,4 +1,5 @@
 import Dep from 'ts-dep-esnext';
+import '@org/org-pkg';
 
 export const ObjRestSpread = () => {
   const a = {a: 1, b: 2};

test/fake_modules/typescript/package.json

@@ -1,5 +1,8 @@
 {
   "dependencies": {
+    "@org/org-pkg": "0.0.1",
+    "@types/org__org-pkg": "0.0.1",
+    "@types/react": "0.0.1",
     "react": "0.0.1",
     "ts-dep-1": "0.0.1",
     "ts-dep-2": "0.0.1",

test/fake_modules/typescript/typedef.d.ts

@@ -0,0 +1 @@
+import 'ts-dep-typedef';

test/spec.js

@@ -222,6 +222,9 @@ export default [
       missing: {},
       using: {
         react: ['component.tsx'],
+        '@types/react': ['component.tsx'],
+        '@types/org__org-pkg': ['esnext.ts'],
+        '@org/org-pkg': ['esnext.ts'],
         'ts-dep-1': ['index.ts'],
         'ts-dep-2': ['index.ts'],
         'ts-dep-esnext': ['esnext.ts'],