Redirect babel parser to babel-flow (#9071)

Co-authored-by: Georgii Dolzhykov <thorn.mailbox@gmail.com>

changelog_unreleased/flow/pr-9071.md

@@ -0,0 +1,18 @@
+#### Switch the `babel` parser to `babel-flow` if the `@flow` pragma is found (#9071 by @fisker)
+
+In practice, this means that as long as your Flow files have the pragma, it's safe to use the `.js` extension for them. Prettier will correctly parse and print them without any additional configuration. Previously, the pragma was recognized by the parser, but there existed minor correctness issues with the printer. E.g. it's not safe to unquote number keys in Flow.
+
+<!-- prettier-ignore -->
+```jsx
+// Input (with --parser babel)
+// @flow
+f<T>({ "2": 2 })
+
+// Prettier stable
+// @flow
+f<T>({ 2: 2 });
+
+// Prettier master
+// @flow
+f<T>({ "2": 2 });
+```

src/language-js/parser-babel.js

@@ -1,6 +1,10 @@
 "use strict";
 
 const createError = require("../common/parser-create-error");
+const {
+  getNextNonSpaceNonCommentCharacterIndexWithStartIndex,
+  getShebang,
+} = require("../common/util");
 const { hasPragma } = require("./pragma");
 const { locStart, locEnd } = require("./loc");
 const postprocess = require("./postprocess");
@@ -58,13 +62,43 @@ function resolvePluginsConflict(
   return combinations;
 }
 
+// Similar to babel
+// https://github.com/babel/babel/pull/7934/files#diff-a739835084910b0ee3ea649df5a4d223R67
+const FLOW_PRAGMA_REGEX = /@(?:no)?flow\b/;
+function isFlowFile(text, options) {
+  if (options.filepath && options.filepath.endsWith(".js.flow")) {
+    return true;
+  }
+
+  const shebang = getShebang(text);
+  if (shebang) {
+    text = text.slice(shebang.length);
+  }
+
+  const firstNonSpaceNonCommentCharacterIndex = getNextNonSpaceNonCommentCharacterIndexWithStartIndex(
+    text,
+    0
+  );
+
+  if (firstNonSpaceNonCommentCharacterIndex !== false) {
+    text = text.slice(0, firstNonSpaceNonCommentCharacterIndex);
+  }
+
+  return FLOW_PRAGMA_REGEX.test(text);
+}
+
 function createParse(parseMethod, ...pluginCombinations) {
-  return (text, parsers, opts) => {
+  return (text, parsers, opts = {}) => {
+    if (opts.parser === "babel" && isFlowFile(text, opts)) {
+      opts.parser = "babel-flow";
+      return parseFlow(text, parsers, opts);
+    }
+
     // Inline the require to avoid loading all the JS if we don't use it
     const babel = require("@babel/parser");
 
     const sourceType =
-      opts && opts.__babelSourceType === "script" ? "script" : "module";
+      opts.__babelSourceType === "script" ? "script" : "module";
 
     let ast;
     try {

tests/misc/babel-redirect-to-babel-flow/__snapshots__/jsfmt.spec.js.snap

@@ -0,0 +1,333 @@
+// Jest Snapshot v1, https://goo.gl/fbAQLP
+
+exports[`block-comment.js format 1`] = `
+====================================options=====================================
+parsers: ["babel"]
+printWidth: 80
+                                                                                | printWidth
+=====================================input======================================
+/* @flow */
+
+foo = {"1":bar} // "1" should quoted
+
+=====================================output=====================================
+/* @flow */
+
+foo = { "1": bar }; // "1" should quoted
+
+================================================================================
+`;
+
+exports[`block-comment-2.js format 1`] = `
+====================================options=====================================
+parsers: ["babel"]
+printWidth: 80
+                                                                                | printWidth
+=====================================input======================================
+/*                     @noflow */
+
+foo = {"1":bar} // "1" should quoted
+
+=====================================output=====================================
+/*                     @noflow */
+
+foo = { "1": bar }; // "1" should quoted
+
+================================================================================
+`;
+
+exports[`filename.js.flow format 1`] = `
+====================================options=====================================
+parsers: ["babel"]
+printWidth: 80
+                                                                                | printWidth
+=====================================input======================================
+foo = {"1":bar} // "1" should quoted
+
+=====================================output=====================================
+foo = { "1": bar }; // "1" should quoted
+
+================================================================================
+`;
+
+exports[`inline-comment.js format 1`] = `
+====================================options=====================================
+parsers: ["babel"]
+printWidth: 80
+                                                                                | printWidth
+=====================================input======================================
+// @flow
+
+foo = {"1":bar} // "1" should quoted
+
+=====================================output=====================================
+// @flow
+
+foo = { "1": bar }; // "1" should quoted
+
+================================================================================
+`;
+
+exports[`inline-comment-2.js format 1`] = `
+====================================options=====================================
+parsers: ["babel"]
+printWidth: 80
+                                                                                | printWidth
+=====================================input======================================
+//                     @noflow
+
+foo = {"1":bar} // "1" should quoted
+
+=====================================output=====================================
+//                     @noflow
+
+foo = { "1": bar }; // "1" should quoted
+
+================================================================================
+`;
+
+exports[`inline-comment-3.js format 1`] = `
+====================================options=====================================
+parsers: ["babel"]
+printWidth: 80
+                                                                                | printWidth
+=====================================input======================================
+//  another comment
+//                     @flow
+
+foo = {"1":bar} // "1" should quoted
+
+=====================================output=====================================
+//  another comment
+//                     @flow
+
+foo = { "1": bar }; // "1" should quoted
+
+================================================================================
+`;
+
+exports[`like-a-pragma.js format 1`] = `
+====================================options=====================================
+parsers: ["babel"]
+printWidth: 80
+                                                                                | printWidth
+=====================================input======================================
+// by fisker@flow.prettier.com :)
+
+foo = {"1":bar} // "1" should quoted
+
+=====================================output=====================================
+// by fisker@flow.prettier.com :)
+
+foo = { "1": bar }; // "1" should quoted
+
+================================================================================
+`;
+
+exports[`not-flow.js format 1`] = `
+====================================options=====================================
+parsers: ["babel"]
+printWidth: 80
+                                                                                | printWidth
+=====================================input======================================
+foo = {"1":bar} // "1" should unquoted
+
+=====================================output=====================================
+foo = { 1: bar }; // "1" should unquoted
+
+================================================================================
+`;
+
+exports[`not-flow-2.js format 1`] = `
+====================================options=====================================
+parsers: ["babel"]
+printWidth: 80
+                                                                                | printWidth
+=====================================input======================================
+// @flowflow
+
+foo = {"1":bar} // "1" should unquoted
+
+=====================================output=====================================
+// @flowflow
+
+foo = { 1: bar }; // "1" should unquoted
+
+================================================================================
+`;
+
+exports[`not-flow-3.js format 1`] = `
+====================================options=====================================
+parsers: ["babel"]
+printWidth: 80
+                                                                                | printWidth
+=====================================input======================================
+a = "  @flow "
+foo = {"1":bar} // "1" should unquoted
+
+=====================================output=====================================
+a = "  @flow ";
+foo = { 1: bar }; // "1" should unquoted
+
+================================================================================
+`;
+
+exports[`not-flow-4.js format 1`] = `
+====================================options=====================================
+parsers: ["babel"]
+printWidth: 80
+                                                                                | printWidth
+=====================================input======================================
+a = "  // @flow "
+foo = {"1":bar} // "1" should unquoted
+
+=====================================output=====================================
+a = "  // @flow ";
+foo = { 1: bar }; // "1" should unquoted
+
+================================================================================
+`;
+
+exports[`not-flow-5.js format 1`] = `
+====================================options=====================================
+parsers: ["babel"]
+printWidth: 80
+                                                                                | printWidth
+=====================================input======================================
+#!/usr/bin/env @flow
+foo = {"1":bar} // "1" should unquoted
+
+=====================================output=====================================
+#!/usr/bin/env @flow
+foo = { 1: bar }; // "1" should unquoted
+
+================================================================================
+`;
+
+exports[`pragma.js format 1`] = `
+====================================options=====================================
+parsers: ["babel"]
+printWidth: 80
+                                                                                | printWidth
+=====================================input======================================
+/**
+ * @flow
+ */
+
+foo = {"1":bar} // "1" should quoted
+
+=====================================output=====================================
+/**
+ * @flow
+ */
+
+foo = { "1": bar }; // "1" should quoted
+
+================================================================================
+`;
+
+exports[`pragma-2.js format 1`] = `
+====================================options=====================================
+parsers: ["babel"]
+printWidth: 80
+                                                                                | printWidth
+=====================================input======================================
+/**
+ *                      @noflow
+ */
+
+foo = {"1":bar} // "1" should quoted
+
+=====================================output=====================================
+/**
+ *                      @noflow
+ */
+
+foo = { "1": bar }; // "1" should quoted
+
+================================================================================
+`;
+
+exports[`pragma-react.js format 1`] = `
+====================================options=====================================
+parsers: ["babel"]
+printWidth: 80
+                                                                                | printWidth
+=====================================input======================================
+/**
+ * Copyright (c) Facebook, Inc. and its affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ *
+ * @flow
+ */
+
+// DocBlock above is copied from https://github.com/facebook/react/blob/8da0da0937af154b775b243c9d28b6aa50db696b/packages/react-dom/index.js#L1-L8
+
+foo = {"1":bar} // "1" should quoted
+
+=====================================output=====================================
+/**
+ * Copyright (c) Facebook, Inc. and its affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ *
+ * @flow
+ */
+
+// DocBlock above is copied from https://github.com/facebook/react/blob/8da0da0937af154b775b243c9d28b6aa50db696b/packages/react-dom/index.js#L1-L8
+
+foo = { "1": bar }; // "1" should quoted
+
+================================================================================
+`;
+
+exports[`shebang-inline-comment.js format 1`] = `
+====================================options=====================================
+parsers: ["babel"]
+printWidth: 80
+                                                                                | printWidth
+=====================================input======================================
+#!/usr/bin/env node
+//  another comment
+//                     @flow
+
+foo = {"1":bar} // "1" should quoted
+
+=====================================output=====================================
+#!/usr/bin/env node
+//  another comment
+//                     @flow
+
+foo = { "1": bar }; // "1" should quoted
+
+================================================================================
+`;
+
+exports[`shebang-pragma.js format 1`] = `
+====================================options=====================================
+parsers: ["babel"]
+printWidth: 80
+                                                                                | printWidth
+=====================================input======================================
+#!/usr/bin/env node
+/**
+ * @format
+ *                      @noflow
+ */
+
+foo = {"1":bar} // "1" should quoted
+
+=====================================output=====================================
+#!/usr/bin/env node
+/**
+ * @format
+ *                      @noflow
+ */
+
+foo = { "1": bar }; // "1" should quoted
+
+================================================================================
+`;

tests/misc/babel-redirect-to-babel-flow/block-comment-2.js

@@ -0,0 +1,3 @@
+/*                     @noflow */
+
+foo = {"1":bar} // "1" should quoted

tests/misc/babel-redirect-to-babel-flow/block-comment.js

@@ -0,0 +1,3 @@
+/* @flow */
+
+foo = {"1":bar} // "1" should quoted

tests/misc/babel-redirect-to-babel-flow/filename.js.flow

@@ -0,0 +1 @@
+foo = {"1":bar} // "1" should quoted

tests/misc/babel-redirect-to-babel-flow/inline-comment-2.js

@@ -0,0 +1,3 @@
+//                     @noflow
+
+foo = {"1":bar} // "1" should quoted

tests/misc/babel-redirect-to-babel-flow/inline-comment-3.js

@@ -0,0 +1,4 @@
+//  another comment
+//                     @flow
+
+foo = {"1":bar} // "1" should quoted

tests/misc/babel-redirect-to-babel-flow/inline-comment.js

@@ -0,0 +1,3 @@
+// @flow
+
+foo = {"1":bar} // "1" should quoted

tests/misc/babel-redirect-to-babel-flow/jsfmt.spec.js

@@ -0,0 +1 @@
+run_spec(__dirname, ["babel"]);

tests/misc/babel-redirect-to-babel-flow/like-a-pragma.js

@@ -0,0 +1,3 @@
+// by fisker@flow.prettier.com :)
+
+foo = {"1":bar} // "1" should quoted

tests/misc/babel-redirect-to-babel-flow/not-flow-2.js

@@ -0,0 +1,3 @@
+// @flowflow
+
+foo = {"1":bar} // "1" should unquoted

tests/misc/babel-redirect-to-babel-flow/not-flow-3.js

@@ -0,0 +1,2 @@
+a = "  @flow "
+foo = {"1":bar} // "1" should unquoted

tests/misc/babel-redirect-to-babel-flow/not-flow-4.js

@@ -0,0 +1,2 @@
+a = "  // @flow "
+foo = {"1":bar} // "1" should unquoted

tests/misc/babel-redirect-to-babel-flow/not-flow-5.js

@@ -0,0 +1,2 @@
+#!/usr/bin/env @flow
+foo = {"1":bar} // "1" should unquoted

tests/misc/babel-redirect-to-babel-flow/not-flow.js

@@ -0,0 +1 @@
+foo = {"1":bar} // "1" should unquoted

tests/misc/babel-redirect-to-babel-flow/pragma-2.js

@@ -0,0 +1,5 @@
+/**
+ *                      @noflow
+ */
+
+foo = {"1":bar} // "1" should quoted

tests/misc/babel-redirect-to-babel-flow/pragma-react.js

@@ -0,0 +1,12 @@
+/**
+ * Copyright (c) Facebook, Inc. and its affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ *
+ * @flow
+ */
+
+// DocBlock above is copied from https://github.com/facebook/react/blob/8da0da0937af154b775b243c9d28b6aa50db696b/packages/react-dom/index.js#L1-L8
+
+foo = {"1":bar} // "1" should quoted

tests/misc/babel-redirect-to-babel-flow/pragma.js

@@ -0,0 +1,5 @@
+/**
+ * @flow
+ */
+
+foo = {"1":bar} // "1" should quoted

tests/misc/babel-redirect-to-babel-flow/shebang-inline-comment.js

@@ -0,0 +1,5 @@
+#!/usr/bin/env node
+//  another comment
+//                     @flow
+
+foo = {"1":bar} // "1" should quoted

tests/misc/babel-redirect-to-babel-flow/shebang-pragma.js

@@ -0,0 +1,7 @@
+#!/usr/bin/env node
+/**
+ * @format
+ *                      @noflow
+ */
+
+foo = {"1":bar} // "1" should quoted