feat(babel-preset-gatsby-package): add conditional compilation plugin

.eslintrc.js

@@ -36,6 +36,7 @@ module.exports = {
     __PATH_PREFIX__: true,
     __BASE_PATH__: true,
     __ASSET_PREFIX__: true,
+    _CFLAGS_: true,
   },
   rules: {
     "@babel/no-unused-expressions": [

package.json

@@ -117,8 +117,8 @@
   },
   "scripts": {
     "bootstrap": "npm-run-all -s check-versions \"lerna-prepare -- --{@}\" --",
-    "check-repo-fields": "babel-node scripts/check-repo-fields.js",
-    "check-versions": "babel-node scripts/check-versions.js",
+    "check-repo-fields": "node scripts/check-repo-fields.js",
+    "check-versions": "node scripts/check-versions.js",
     "format": "npm run format:code && npm run format:other && npm run format:svg",
     "format:code": "npm run lint:code -- --fix",
     "format:other": "npm run prettier -- --write",

packages/babel-preset-gatsby-package/.babelrc

@@ -0,0 +1,11 @@
+{
+  "plugins": [
+    ["@babel/plugin-transform-modules-commonjs"]
+  ],
+  "overrides": [
+    {
+      "test": ["**/*.ts", "**/*.tsx"],
+      "plugins": [["@babel/plugin-transform-typescript", { "isTSX": true }]],
+    }
+  ]
+}

packages/babel-preset-gatsby-package/.gitignore

@@ -1 +1,2 @@
 yarn.lock
+dist/

packages/babel-preset-gatsby-package/__tests__/__snapshots__/index.js.snap

@@ -54,6 +54,29 @@ Array [
 ]
 `;
 
+exports[`babel-preset-gatsby-package in browser mode specifies proper presets for esm 1`] = `
+Array [
+  Array [
+    "@babel/preset-env",
+    Object {
+      "bugfixes": true,
+      "debug": false,
+      "loose": true,
+      "modules": false,
+      "shippedProposals": true,
+      "targets": Object {
+        "esmodules": true,
+      },
+      "useBuiltIns": false,
+    },
+  ],
+  Array [
+    "@babel/preset-react",
+  ],
+  "@babel/preset-flow",
+]
+`;
+
 exports[`babel-preset-gatsby-package in browser mode specifies the proper plugins 1`] = `
 Array [
   "@babel/plugin-proposal-nullish-coalescing-operator",
@@ -64,6 +87,25 @@ Array [
 ]
 `;
 
+exports[`babel-preset-gatsby-package in node mode can enable compilerFlags 1`] = `
+Array [
+  "@babel/plugin-proposal-nullish-coalescing-operator",
+  "@babel/plugin-proposal-optional-chaining",
+  "@babel/plugin-transform-runtime",
+  "@babel/plugin-syntax-dynamic-import",
+  "babel-plugin-dynamic-import-node",
+  Array [
+    "./babel-transform-compiler-flags",
+    Object {
+      "availableFlags": Array [
+        "MAJOR",
+      ],
+      "flags": Object {},
+    },
+  ],
+]
+`;
+
 exports[`babel-preset-gatsby-package in node mode specifies proper presets 1`] = `
 Array [
   Array [

packages/babel-preset-gatsby-package/__tests__/babel-transform-compiler-flags.js

@@ -0,0 +1,3 @@
+const runner = require(`@babel/helper-plugin-test-runner`).default
+
+runner(__dirname)

packages/babel-preset-gatsby-package/__tests__/fixtures/compiler-flags/default/input.js

@@ -0,0 +1,17 @@
+
+if (_CFLAGS_.MAJOR === '4') {
+  console.log('We only load this for Gatsby 4')
+} else {
+  console.log('Old code path')
+}
+
+function isGatsby4() {
+  return _CFLAGS_.MAJOR === '4'
+}
+
+
+if (isGatsby4()) {
+  console.log('We only load this for Gatsby 4')
+} else {
+  console.log('Old code path')
+}

packages/babel-preset-gatsby-package/__tests__/fixtures/compiler-flags/default/output.mjs

@@ -0,0 +1,15 @@
+if ("4" === '4') {
+  console.log('We only load this for Gatsby 4');
+} else {
+  console.log('Old code path');
+}
+
+function isGatsby4() {
+  return "4" === '4';
+}
+
+if (isGatsby4()) {
+  console.log('We only load this for Gatsby 4');
+} else {
+  console.log('Old code path');
+}

packages/babel-preset-gatsby-package/__tests__/fixtures/compiler-flags/unused/input.js

@@ -0,0 +1,6 @@
+
+if (_CFLAGS_.UNKNOWN === 'true') {
+  console.log('We only load this when true')
+} else {
+  console.log('Old code path')
+}

packages/babel-preset-gatsby-package/__tests__/fixtures/compiler-flags/unused/options.json

@@ -0,0 +1,3 @@
+{
+  "throws": "UNKNOWN is not part of the available compiler flags."
+}

packages/babel-preset-gatsby-package/__tests__/fixtures/options.js

@@ -0,0 +1,17 @@
+const path = require("path")
+
+module.exports = {
+  sourceType: "module",
+  plugins: [
+    [path.resolve(__dirname, "../../src/babel-transform-compiler-flags.ts"),
+      {
+        availableFlags: ['MAJOR'],
+        flags: {
+          MAJOR: '4',
+        }
+      }
+    ],
+  ],
+  babelrc: false,
+  configFile: false,
+}

packages/babel-preset-gatsby-package/__tests__/index.js

@@ -1,12 +1,20 @@
-const preset = require(`../`)
+const preset = require(`../src/index.js`)
 
-jest.mock(`../resolver`, () => jest.fn(moduleName => moduleName))
+jest.mock(`../src/resolver`, () => jest.fn(moduleName => moduleName))
 
-beforeEach(() => {
-  delete process.env.BABEL_ENV
-})
 
 describe(`babel-preset-gatsby-package`, () => {
+  let babelEnv;
+
+  beforeEach(() => {
+    babelEnv = process.env.BABEL_ENV
+    delete process.env.BABEL_ENV;
+  })
+
+  afterEach(() => {
+    process.env.BABEL_ENV = babelEnv
+  })
+
   describe(`in node mode`, () => {
     it(`specifies the proper plugins`, () => {
       const { plugins } = preset()
@@ -29,12 +37,15 @@ describe(`babel-preset-gatsby-package`, () => {
         nodeVersion,
       })
 
-      const [, opts] = presets.find(preset =>
-        [].concat(preset).includes(`@babel/preset-env`)
-      )
+      const [, opts] = presets.find(preset => [].concat(preset).includes(`@babel/preset-env`))
 
       expect(opts.targets.node).toBe(nodeVersion)
     })
+
+    it(`can enable compilerFlags`, () => {
+      const { plugins } = preset(null, { availableCompilerFlags: [`MAJOR`] })
+      expect(plugins).toMatchSnapshot()
+    })
   })
 
   describe(`in browser mode`, () => {
@@ -52,5 +63,10 @@ describe(`babel-preset-gatsby-package`, () => {
       const { presets } = preset(null, { browser: true, debug: true })
       expect(presets).toMatchSnapshot()
     })
+
+    it(`specifies proper presets for esm`, () => {
+      const { presets } = preset(null, { browser: true, esm: true })
+      expect(presets).toMatchSnapshot()
+    })
   })
 })

packages/babel-preset-gatsby-package/package.json

@@ -20,12 +20,24 @@
     "babel-plugin-dynamic-import-node": "^2.3.3",
     "core-js": "^3.10.0"
   },
+  "devDependencies": {
+    "@types/babel__core": "^7.1.15",
+    "@babel/cli": "^7.14.8",
+    "@babel/core": "^7.14.8",
+    "@babel/helper-plugin-test-runner": "7.14.5",
+    "@babel/plugin-transform-modules-commonjs": "^7.14.5"
+  },
   "peerDependencies": {
     "@babel/core": "^7.11.6"
   },
   "license": "MIT",
-  "main": "index.js",
+  "main": "dist/index.js",
   "engines": {
     "node": ">=12.13.0"
+  },
+  "scripts": {
+    "build": "babel src --out-dir dist/ --ignore \"**/__tests__\" --ignore \"**/__mocks__\" --extensions \".ts,.js\"",
+    "prepare": "cross-env NODE_ENV=production npm run build",
+    "watch": "babel -w src --out-dir dist/ --ignore \"**/__tests__\" --extensions \".ts,.js\""
   }
 }

packages/babel-preset-gatsby-package/src/babel-transform-compiler-flags.ts

@@ -0,0 +1,52 @@
+import type { NodePath, PluginObj, types, PluginPass } from "@babel/core"
+
+interface IPluginOptions {
+  flags: Record<string, string>
+  availableFlags: Array<string>
+}
+
+export default function compilerFlags(
+  {
+    types: t,
+  }: {
+    types: typeof types
+  },
+  opts: Partial<IPluginOptions>
+): PluginObj {
+  if (!opts.flags) {
+    throw new Error(`flags option needs to be set`)
+  }
+  if (!opts.availableFlags) {
+    throw new Error(`availableFlags option needs to be set`)
+  }
+
+  return {
+    name: `babel-transform-compiler-flags`,
+    visitor: {
+      Identifier(
+        nodePath: NodePath<types.Identifier>,
+        state: PluginPass
+      ): void {
+        const flags = (state.opts as IPluginOptions).flags
+        const availableFlags = (state.opts as IPluginOptions).availableFlags
+
+        if (
+          nodePath.node.name === `_CFLAGS_` &&
+          t.isMemberExpression(nodePath.parent)
+        ) {
+          const cFlag = (nodePath.parent.property as types.Identifier).name
+
+          if (!availableFlags.includes(cFlag)) {
+            throw new Error(
+              `${cFlag} is not part of the available compiler flags.`
+            )
+          }
+
+          nodePath.parentPath.replaceWith(
+            t.stringLiteral(flags[cFlag] ? flags[cFlag] : ``)
+          )
+        }
+      },
+    },
+  }
+}

packages/babel-preset-gatsby-package/index.js → packages/babel-preset-gatsby-package/src/index.js

@@ -1,8 +1,14 @@
 const r = require(`./resolver`)
 
 function preset(context, options = {}) {
-  const { browser = false, debug = false, nodeVersion = `12.13.0`, esm = false } = options
-  const { NODE_ENV, BABEL_ENV } = process.env
+  const {
+    browser = false,
+    debug = false,
+    nodeVersion = `12.13.0`,
+    esm = false,
+    availableCompilerFlags = [],
+  } = options
+  const { NODE_ENV, BABEL_ENV, COMPILER_OPTIONS } = process.env
 
   const IS_TEST = (BABEL_ENV || NODE_ENV) === `test`
 
@@ -13,11 +19,11 @@ function preset(context, options = {}) {
   if (browser) {
     if (esm) {
       browserConfig.targets = {
-        esmodules: true
+        esmodules: true,
       }
     } else {
       browserConfig.targets = {
-        browsers: [`last 2 versions`, `not ie <= 11`, `not android 4.4.3`]
+        browsers: [`last 2 versions`, `not ie <= 11`, `not android 4.4.3`],
       }
     }
   }
@@ -30,6 +36,20 @@ function preset(context, options = {}) {
     },
   }
 
+  let parsedCompilerOptions = {}
+  if (COMPILER_OPTIONS) {
+    // COMPILER_OPTIONS syntax is key=value,key2=value2
+    parsedCompilerOptions = COMPILER_OPTIONS.split(`,`).reduce((acc, curr) => {
+      const [key, value] = curr.split(`=`)
+
+      if (key) {
+        acc[key] = value
+      }
+
+      return acc
+    }, Object.create(null))
+  }
+
   return {
     presets: [
       [
@@ -54,6 +74,13 @@ function preset(context, options = {}) {
       r(`@babel/plugin-transform-runtime`),
       r(`@babel/plugin-syntax-dynamic-import`),
       IS_TEST && r(`babel-plugin-dynamic-import-node`),
+      availableCompilerFlags.length && [
+        r(`./babel-transform-compiler-flags`),
+        {
+          flags: parsedCompilerOptions,
+          availableFlags: availableCompilerFlags,
+        },
+      ],
     ].filter(Boolean),
     overrides: [
       {

packages/babel-preset-gatsby-package/resolver.js → packages/babel-preset-gatsby-package/src/resolver.js

@@ -1,3 +1,3 @@
 const r = m => require.resolve(m)
 
-module.exports = r;
+module.exports = r

packages/babel-preset-gatsby-package/tsconfig.json

@@ -0,0 +1,4 @@
+{
+  "extends": "../../tsconfig.json",
+  "strict": true
+}

tsconfig.json

@@ -15,6 +15,7 @@
     "resolveJsonModule": true,
     "esModuleInterop": true,
     "jsx": "preserve",
+    "typeRoots": ["./types", "**/node_modules/@types", "node_modules/@types"],
     "paths": {
       "@reach/router/*": ["./node_modules/@gatsbyjs/reach-router/*"]
     }

types/gatsby-monorepo/global.d.ts

@@ -0,0 +1,3 @@
+declare const _CFLAGS_: {
+  GATSBY_MAJOR: string
+}

types/gatsby-monorepo/package.json

@@ -0,0 +1,5 @@
+{
+  "name": "gatsby-monorepo",
+  "types": "./global.d.ts",
+  "private": true
+}