Support tsconfig.json paths in Jest (#698)

Per #696

.changeset/mighty-eagles-rush.md

@@ -0,0 +1,7 @@
+---
+"skuba": minor
+---
+
+jest: Support `tsconfig.json` paths
+
+Module aliases other than `src` are now supported in `skuba test`. Our Jest preset includes a dynamic `moduleNameMapper` that reads the `paths` compiler option from your `tsconfig.json`.

jest-preset.js

@@ -1,28 +1,14 @@
-const { defaults: tsJestDefaults } = require('ts-jest/presets');
+const { defaults } = require('ts-jest/presets');
 
-const TS_JEST_NAME = 'ts-jest';
-
-/**
- * Resolved path of the `ts-jest` preset.
- *
- * This allows Jest to resolve the preset even if it is installed to a nested
- * `./node_modules/skuba/node_modules/ts-jest` directory.
- */
-const TS_JEST_PATH = require.resolve(TS_JEST_NAME);
-
-// Rewrite `ts-jest` transformations using our resolved `TS_JEST_PATH`.
-const tsJestTransform = Object.fromEntries(
-  Object.entries(tsJestDefaults.transform).map(([key, value]) => [
-    key,
-    value === TS_JEST_NAME ? TS_JEST_PATH : value,
-  ]),
-);
+const { createModuleNameMapper } = require('./jest/moduleNameMapper');
+const { transform } = require('./jest/transform');
 
 /** @type {import('@jest/types').Config.InitialOptions} */
 module.exports = {
-  ...tsJestDefaults,
+  ...defaults,
 
-  transform: tsJestTransform,
+  moduleNameMapper: createModuleNameMapper(),
+  transform,
 
   collectCoverageFrom: [
     '**/*.ts',
@@ -35,10 +21,6 @@ module.exports = {
     '!<rootDir>/jest.*.ts',
   ],
   coverageDirectory: 'coverage',
-  moduleNameMapper: {
-    '^src$': '<rootDir>/src',
-    '^src/(.+)$': '<rootDir>/src/$1',
-  },
   testEnvironment: 'node',
   testPathIgnorePatterns: [
     '/node_modules.*/',

jest/moduleNameMapper.js

@@ -0,0 +1,86 @@
+const path = require('path');
+
+const { pathsToModuleNameMapper } = require('ts-jest/utils');
+const {
+  sys,
+  findConfigFile,
+  readConfigFile,
+  parseJsonConfigFileContent,
+} = require('typescript');
+
+/**
+ * Set a default `src` module alias for backward compatibility.
+ *
+ * TODO: drop this default in skuba v4.
+ */
+const DEFAULT_PATHS = { src: ['src'], 'src/*': ['src/*'] };
+
+/**
+ * @returns {unknown}
+ */
+const getConfigFromDisk = () => {
+  const filename =
+    findConfigFile('.', sys.fileExists.bind(this)) || 'tsconfig.json';
+
+  return readConfigFile(filename, sys.readFile.bind(this)).config;
+};
+
+module.exports.createModuleNameMapper = (getConfig = getConfigFromDisk) => {
+  try {
+    const json = getConfig();
+
+    const parsedConfig = parseJsonConfigFileContent(json, sys, '.');
+
+    const paths = Object.fromEntries(
+      Object.entries(parsedConfig.options.paths ?? DEFAULT_PATHS).flatMap(
+        ([key, values]) => [
+          // Pass through the input path entry almost verbatim.
+          // We trim a trailing slash because TypeScript allows `import 'src'`
+          // to be resolved by the alias `src/`, but Jest's mapper does not.
+          [
+            key.replace(/\/$/, ''),
+            values.map((value) => value.replace(/\/$/, '')),
+          ],
+          // Append a variant of the input path entry.
+          // As TypeScript allows both `import 'src'` and `import 'src/nested'`
+          // to be resolved by the alias `src/*` (and likewise for plain `src`),
+          // we need to seed two Jest mappings per path.
+          ...(key.endsWith('/*')
+            ? [
+                [
+                  // Given a path `src/*`, seed an extra `src`.
+                  key.replace(/\/\*$/, ''),
+                  values.map((value) => value.replace(/\/\*$/, '')),
+                ],
+              ]
+            : [
+                [
+                  // Given a path `src`, seed an extra `src/*`.
+                  path.join(key, '*'),
+                  values.map((value) => path.join(value, '*')),
+                ],
+              ]),
+        ],
+      ),
+    );
+
+    const prefix = path.join('<rootDir>', parsedConfig.options.baseUrl || '.');
+
+    const moduleNameMapper = pathsToModuleNameMapper(paths, { prefix });
+
+    // Normalise away any `..`s that may crop up from `baseUrl` usage.
+    // For example, a `baseUrl` of `src` and a path of `../cli` will result in
+    // `<rootDir>/src/../cli`, which can be normalised to `<rootDir>/cli`.
+    return Object.fromEntries(
+      Object.entries(moduleNameMapper).map(([key, values]) => [
+        key,
+        Array.isArray(values)
+          ? values.map((value) => path.normalize(value))
+          : path.normalize(values),
+      ]),
+    );
+  } catch {
+    // Bail out here to support zero-config mode.
+    return pathsToModuleNameMapper(DEFAULT_PATHS, { prefix: '<rootDir>' });
+  }
+};

jest/moduleNameMapper.test.ts

@@ -0,0 +1,75 @@
+import { createModuleNameMapper } from './moduleNameMapper';
+
+describe('moduleNameMapper', () => {
+  const act = (paths?: unknown, baseUrl?: string) =>
+    createModuleNameMapper(() => ({
+      compilerOptions: {
+        baseUrl,
+        paths,
+      },
+    }));
+
+  it('expands wildcard paths', () =>
+    expect(act({ 'src/*': ['src/*'], 'lib/wip/*': ['lib/wip/*'] }))
+      .toMatchInlineSnapshot(`
+      Object {
+        "^lib/wip$": "<rootDir>/lib/wip",
+        "^lib/wip/(.*)$": "<rootDir>/lib/wip/$1",
+        "^src$": "<rootDir>/src",
+        "^src/(.*)$": "<rootDir>/src/$1",
+      }
+    `));
+
+  it('expands non-wildcard paths', () =>
+    expect(act({ cli: ['cli'], 'src/': ['src/'] })).toMatchInlineSnapshot(`
+      Object {
+        "^cli$": "<rootDir>/cli",
+        "^cli/(.*)$": "<rootDir>/cli/$1",
+        "^src$": "<rootDir>/src",
+        "^src/(.*)$": "<rootDir>/src/$1",
+      }
+    `));
+
+  it('expands duplicate asymmetric paths', () =>
+    expect(
+      act({
+        jquery: ['node_modules/jquery/dist/jquery'],
+        'jquery/*': ['node_modules/jquery/dist/jquery/*'],
+      }),
+    ).toMatchInlineSnapshot(`
+      Object {
+        "^jquery$": "<rootDir>/node_modules/jquery/dist/jquery",
+        "^jquery/(.*)$": "<rootDir>/node_modules/jquery/dist/jquery/$1",
+      }
+    `));
+
+  it('respects a base URL', () =>
+    expect(act({ cli: ['../cli'], 'app/*': ['app/*'] }, 'src'))
+      .toMatchInlineSnapshot(`
+      Object {
+        "^app$": "<rootDir>/src/app",
+        "^app/(.*)$": "<rootDir>/src/app/$1",
+        "^cli$": "<rootDir>/cli",
+        "^cli/(.*)$": "<rootDir>/cli/$1",
+      }
+    `));
+
+  it('respects no paths', () =>
+    expect(act({})).toMatchInlineSnapshot(`Object {}`));
+
+  it('falls back on undefined paths', () =>
+    expect(act(undefined)).toMatchInlineSnapshot(`
+      Object {
+        "^src$": "<rootDir>/src",
+        "^src/(.*)$": "<rootDir>/src/$1",
+      }
+    `));
+
+  it('falls back on invalid config', () =>
+    expect(act('INVALID')).toMatchInlineSnapshot(`
+      Object {
+        "^src$": "<rootDir>/src",
+        "^src/(.*)$": "<rootDir>/src/$1",
+      }
+    `));
+});

jest/transform.js

@@ -0,0 +1,19 @@
+const { defaults } = require('ts-jest/presets');
+
+const TS_JEST_NAME = 'ts-jest';
+
+/**
+ * Resolved path of the `ts-jest` preset.
+ *
+ * This allows Jest to resolve the preset even if it is installed to a nested
+ * `./node_modules/skuba/node_modules/ts-jest` directory.
+ */
+const TS_JEST_PATH = require.resolve(TS_JEST_NAME);
+
+// Rewrite `ts-jest` transformations using our resolved `TS_JEST_PATH`.
+module.exports.transform = Object.fromEntries(
+  Object.entries(defaults.transform).map(([key, value]) => [
+    key,
+    value === TS_JEST_NAME ? TS_JEST_PATH : value,
+  ]),
+);

package.json

@@ -12,6 +12,7 @@
   "typings": "lib/index.d.ts",
   "files": [
     "config/**/*",
+    "jest/**/*",
     "lib*/**/*.d.ts",
     "lib*/**/*.js",
     "lib*/**/*.js.map",