Add support of 'extends' property in tsconfig.json (#33)

* Move code related to reading tsconfig.json into a function

* Make getCompilerOptions options support "extends" prop in tsconfig

* Add a test for extends functionality

* Simplify base tsconfig

* Simplify tsconfig

* Remove not important comment

* Run prettier

check.js

@@ -1,13 +1,14 @@
 import { dirname, basename, join, relative } from 'path'
-import { existsSync, promises as fs } from 'fs'
+import { promises as fs } from 'fs'
 import { createRequire } from 'module'
 import { fileURLToPath } from 'url'
 import { createSpinner } from 'nanospinner'
 import { location } from 'vfile-location'
 import { Worker } from 'worker_threads'
 import pico from 'picocolors'
 import glob from 'fast-glob'
-import JSON5 from 'json5'
+
+import { getCompilerOptions } from './get-compiler-options.js'
 
 let require = createRequire(import.meta.url)
 
@@ -74,12 +75,7 @@ export async function check(
   let spinner = createSpinner('Check types', { stream: stderr })
   spinner.start()
 
-  let compilerOptions
-  let tsconfigPath = join(cwd, 'tsconfig.json')
-  if (existsSync(tsconfigPath)) {
-    let tsconfig = JSON5.parse(await fs.readFile(tsconfigPath))
-    compilerOptions = tsconfig.compilerOptions
-  }
+  let compilerOptions = getCompilerOptions(cwd)
 
   let all = await glob(globs, { cwd, ignore: ['node_modules'], absolute: true })
 

create-program.js

@@ -6,34 +6,13 @@ let require = createRequire(import.meta.url)
 
 const TS_DIR = dirname(require.resolve('typescript'))
 
-const DEFAULT = {
-  allowSyntheticDefaultImports: true,
-  strictFunctionTypes: false,
-  noUnusedParameters: true,
-  noImplicitReturns: true,
-  moduleResolution: 'NodeJs',
-  noUnusedLocals: true,
-  stripInternal: true,
-  allowJs: true,
-  module: 'esnext',
-  strict: true,
-  noEmit: true,
-  jsx: 'react'
-}
-
-export function createProgram(files, opts = DEFAULT) {
-  opts.moduleResolution = 'node'
-
-  let { options, errors } = ts.convertCompilerOptionsFromJson(opts, './')
-
-  if (errors.length) {
-    throw errors
-  }
+export function createProgram(files, options) {
+  options.moduleResolution = ts.ModuleResolutionKind.NodeJs
 
   if (options.lib) {
-    options.lib.forEach(path => {
+    for (let path of options.lib) {
       files.push(join(TS_DIR, path))
-    })
+    }
     options.lib.length = 0
   }
 

get-compiler-options.js

@@ -0,0 +1,33 @@
+import ts from 'typescript'
+
+const DEFAULT_OPTIONS = ts.convertCompilerOptionsFromJson(
+  {
+    allowSyntheticDefaultImports: true,
+    strictFunctionTypes: false,
+    noUnusedParameters: true,
+    noImplicitReturns: true,
+    moduleResolution: 'NodeJs',
+    noUnusedLocals: true,
+    stripInternal: true,
+    allowJs: true,
+    module: 'esnext',
+    strict: true,
+    noEmit: true,
+    jsx: 'react'
+  },
+  './'
+).options
+
+export function getCompilerOptions(cwd, configName = 'tsconfig.json') {
+  let configFileName = ts.findConfigFile(cwd, ts.sys.fileExists, configName)
+  if (configFileName === undefined) {
+    return DEFAULT_OPTIONS
+  }
+  let configFile = ts.readConfigFile(configFileName, ts.sys.readFile)
+  let parsedCommandLine = ts.parseJsonConfigFileContent(
+    configFile.config,
+    ts.sys,
+    cwd
+  )
+  return parsedCommandLine.options
+}

package.json

@@ -21,7 +21,6 @@
   },
   "dependencies": {
     "fast-glob": "^3.2.12",
-    "json5": "^2.2.3",
     "nanospinner": "^1.1.0",
     "picocolors": "^1.0.0",
     "vfile-location": "^4.0.1"

test/__snapshots__/check.test.js.snap

@@ -91,6 +91,13 @@ exports[`loads custom tsconfig.json 1`] = `
 "
 `;
 
+exports[`loads custom tsconfig.json with extends property 1`] = `
+"- Check types
+✔ Check types
+✔ index.errors.ts
+"
+`;
+
 exports[`supports simple cases 1`] = `
 "- Check types
 ✔ Check types

test/check.test.js

@@ -58,6 +58,10 @@ it('loads custom tsconfig.json', async () => {
   expect(await good('tsconfig')).toMatchSnapshot()
 })
 
+it('loads custom tsconfig.json with extends property', async () => {
+  expect(await good('tsconfig-with-extends')).toMatchSnapshot()
+})
+
 it('accepts files', async () => {
   expect(await good('negative', 'b.*')).toMatchSnapshot()
 })

test/fixtures/tsconfig-with-extends/index.errors.ts

@@ -0,0 +1,6 @@
+declare const a: number | null
+
+// THROWS Type 'number | null' is not assignable to type 'number'.
+export const b: number = a
+
+// This file checks whether the compiler performs strictNullChecks if it is enabled in the config file specified via extends

test/fixtures/tsconfig-with-extends/tsconfig.base.json

@@ -0,0 +1,5 @@
+{
+  "compilerOptions": {
+    "strictNullChecks": true
+  }
+}

test/fixtures/tsconfig-with-extends/tsconfig.json

@@ -0,0 +1,9 @@
+{
+  // tsconfig should support extends
+  "extends": "./tsconfig.base.json",
+  "compilerOptions": {
+    "noUnusedLocals": false,
+    "target": "ES5",
+    "moduleResolution": "Node"
+  }
+}