feat(config): adds a helper to build moduleNameMapper from paths

Closes #364

README.md

@@ -204,6 +204,19 @@ module.exports = {
 };
 ```
 
+TS Jest provides a helper to automatically create this map from the `paths` compiler option of your TS config:
+
+```js
+// jest.config.js
+const { pathsToModuleNameMapper } = require('ts-jest');
+const { compilerOptions } = require('./tsconfig'); // replace with the path to your tsconfig.json file
+
+module.exports = {
+  // [...]
+  moduleNameMapper: pathsToModuleNameMapper(compilerOptions.paths /*, { prefix: '<rootDir>/' } */ )
+};
+```
+
 ### Using `babel-jest`
 By default ts-jest does not rely on babel-jest. But you may want to use some babel plugins and stll be able to write TypeScript. This can be achieved using the `babelConfig` config key. It can be:
 

src/config/paths-to-module-name-mapper.spec.ts

@@ -0,0 +1,71 @@
+import { pathsToModuleNameMapper } from './paths-to-module-name-mapper'
+import { logTargetMock } from '../__helpers__/mocks'
+
+const tsconfigMap = {
+  log: ['src/util/log'],
+  server: ['src/server'],
+  'util/*': ['src/util/*'],
+  'api/*': ['src/api/*'],
+  'test/*': ['test/*'],
+  'mocks/*': ['test/mocks/*'],
+  'test/*/mock': ['test/mocks/*'],
+}
+
+describe('pathsToModuleNameMapper', () => {
+  it('should convert tsconfig mapping', () => {
+    expect(pathsToModuleNameMapper(tsconfigMap)).toMatchInlineSnapshot(`
+Object {
+  "^api/(.*)$": "src/api/$1",
+  "^log$": "src/util/log",
+  "^mocks/(.*)$": "test/mocks/$1",
+  "^server$": "src/server",
+  "^test/(.*)$": "test/$1",
+  "^test/(.*)/mock$": "test/mocks/$1",
+  "^util/(.*)$": "src/util/$1",
+}
+`)
+  })
+
+  it('should use the given prefix', () => {
+    expect(pathsToModuleNameMapper(tsconfigMap, { prefix: '<rootDir>/' }))
+      .toMatchInlineSnapshot(`
+Object {
+  "^api/(.*)$": "<rootDir>/src/api/$1",
+  "^log$": "<rootDir>/src/util/log",
+  "^mocks/(.*)$": "<rootDir>/test/mocks/$1",
+  "^server$": "<rootDir>/src/server",
+  "^test/(.*)$": "<rootDir>/test/$1",
+  "^test/(.*)/mock$": "<rootDir>/test/mocks/$1",
+  "^util/(.*)$": "<rootDir>/src/util/$1",
+}
+`)
+  })
+
+  it('should warn about mapping it cannot handle', () => {
+    const log = logTargetMock()
+    log.clear()
+    expect(
+      pathsToModuleNameMapper({
+        kept: ['src/kept'],
+        'no-target': [],
+        'too-many-target': ['one', 'two'],
+        'too/*/many/*/stars': ['to/*/many/*/stars'],
+      }),
+    ).toMatchInlineSnapshot(`
+Object {
+  "^kept$": "src/kept",
+  "^too\\\\-many\\\\-target$": "one",
+}
+`)
+    expect(log.lines.warn).toMatchInlineSnapshot(`
+Array [
+  "[level:40] Not mapping \\"no-target\\" because it has no target.
+",
+  "[level:40] Mapping only to first target of \\"too-many-target\\" becuase it has more than one (2).
+",
+  "[level:40] Not mapping \\"too/*/many/*/stars\\" because it has more than one star (\`*\`).
+",
+]
+`)
+  })
+})

src/config/paths-to-module-name-mapper.ts

@@ -0,0 +1,55 @@
+import { CompilerOptions } from 'typescript'
+import { rootLogger } from '../util/logger'
+import { interpolate, Errors } from '../util/messages'
+import { LogContexts } from 'bs-logger'
+
+type TsPathMapping = Exclude<CompilerOptions['paths'], undefined>
+type JestPathMapping = jest.InitialOptions['moduleNameMapper']
+
+// we don't need to escape all chars, so commented out is the real one
+// const escapeRegex = (str: string) => str.replace(/[-\/\\^$*+?.()|[\]{}]/g, '\\$&')
+const escapeRegex = (str: string) => str.replace(/[-\\^$*+?.()|[\]{}]/g, '\\$&')
+
+const logger = rootLogger.child({ [LogContexts.namespace]: 'path-mapper' })
+
+export const pathsToModuleNameMapper = (
+  mapping: TsPathMapping,
+  { prefix = '' }: { prefix?: string } = {},
+): JestPathMapping => {
+  const jestMap: JestPathMapping = {}
+  for (const fromPath of Object.keys(mapping)) {
+    let pattern: string
+    const toPaths = mapping[fromPath]
+    // check that we have only one target path
+    if (toPaths.length === 0) {
+      logger.warn(
+        interpolate(Errors.NotMappingPathWithEmptyMap, { path: fromPath }),
+      )
+      continue
+    } else if (toPaths.length > 1) {
+      logger.warn(
+        interpolate(Errors.MappingOnlyFirstTargetOfPath, {
+          path: fromPath,
+          count: toPaths.length,
+        }),
+      )
+    }
+    const target = toPaths[0]
+
+    // split with '*'
+    const segments = fromPath.split(/\*/g)
+    if (segments.length === 1) {
+      pattern = `^${escapeRegex(fromPath)}$`
+      jestMap[pattern] = `${prefix}${target}`
+    } else if (segments.length === 2) {
+      pattern = `^${escapeRegex(segments[0])}(.*)${escapeRegex(segments[1])}$`
+      jestMap[pattern] = `${prefix}${target.replace(/\*/g, '$1')}`
+    } else {
+      logger.warn(
+        interpolate(Errors.NotMappingMultiStarPath, { path: fromPath }),
+      )
+      continue
+    }
+  }
+  return jestMap
+}

src/index.ts

@@ -2,6 +2,7 @@ import { TsJestTransformer } from './ts-jest-transformer'
 import { createJestPreset } from './config/create-jest-preset'
 import { TsJestGlobalOptions } from './types'
 import { VersionCheckers } from './util/version-checkers'
+import { pathsToModuleNameMapper } from './config/paths-to-module-name-mapper'
 
 // tslint:disable-next-line:no-var-requires
 const version: string = require('../package.json').version
@@ -39,6 +40,7 @@ export {
   // extra ==================
   createJestPreset,
   jestPreset,
+  pathsToModuleNameMapper,
   // tests ==================
   __singleton,
   __resetModule,

src/types.ts

@@ -1,6 +1,5 @@
 import _ts, { CompilerOptions } from 'typescript'
 import * as _babel from 'babel__core'
-import { Writable } from 'stream'
 
 export type TBabelCore = typeof _babel
 export type TTypeScript = typeof _ts

src/util/messages.ts

@@ -8,6 +8,9 @@ export enum Errors {
   UntestedDependencyVersion = "Version {{actualVersion}} of {{module}} installed has not been tested with ts-jest. If you're experiencing issues, consider using a supported version ({{expectedVersion}}). Please do not report issues in ts-jest if you are using unsupported versions.",
   MissingDependency = "Module {{module}} is not installed. If you're experiencing issues, consider installing a supported version ({{expectedVersion}}).",
   UnableToCompileTypeScript = 'Unable to compile TypeScript ({{help}}):\n{{diagnostics}}',
+  NotMappingMultiStarPath = 'Not mapping "{{path}}" because it has more than one star (`*`).',
+  NotMappingPathWithEmptyMap = 'Not mapping "{{path}}" because it has no target.',
+  MappingOnlyFirstTargetOfPath = 'Mapping only to first target of "{{path}}" becuase it has more than one ({{count}}).',
 }
 
 export enum Helps {