Add option to enforce certain line endings

docs/api.md

@@ -51,6 +51,7 @@ prettier.resolveConfig(filePath).then(options => {
 
 If `options.editorconfig` is `true` and an [`.editorconfig` file](http://editorconfig.org/) is in your project, Prettier will parse it and convert its properties to the corresponding prettier configuration. This configuration will be overridden by `.prettierrc`, etc. Currently, the following EditorConfig properties are supported:
 
+- `end_of_line`
 - `indent_style`
 - `indent_size`/`tab_width`
 - `max_line_length`

docs/options.md

@@ -271,3 +271,45 @@ Valid options:
 | Default      | CLI Override                                                | API Override                                                |
 | ------------ | ----------------------------------------------------------- | ----------------------------------------------------------- |
 | `"preserve"` | <code>--prose-wrap <always&#124;never&#124;preserve></code> | <code>proseWrap: "<always&#124;never&#124;preserve>"</code> |
+
+<!--TODO(1.15)
+
+## End of Line
+
+_available in 1.15.0+_
+
+For historical reasons, there exist two commonly used flavors of line endings in text files. That is `\n` (or `LF` for _Line Feed_) and `\r\n` (or `CRLF` for _Carriage Return + Line Feed_).
+The former is common on Linux and macOS, while the latter is prevalent on Windows.
+Some details explaining why it is so [can be found on Wikipedia](https://en.wikipedia.org/wiki/Newline).
+
+By default, Prettier preserves a flavor of line endings a given file has already used.
+It also converts mixed line endings within one file to what it finds at the end of the first line.
+
+When people collaborate on a project from different operating systems, it becomes easy to end up with mixed line endings in the central git repository.
+It is also possible for Windows users to accidentally change line endings in an already committed file from `LF` to `CRLF`.
+Doing so produces a large `git diff`, and if it get unnoticed during code review, all line-by-line history for the file (`git blame`) gets lost.
+
+If you want to make sure that your git repository only contains Linux-style line endings in files covered by Prettier:
+
+1. Set `endOfLine` option to `lf`
+1. Configure [a pre-commit hook](./precommit.md) that will run Prettier
+1. Configure Prettier to run in your CI pipeline (e.g. using [`prettier-check` npm package](https://www.npmjs.com/package/prettier-check))
+1. Ask Windows users to run `git config core.autocrlf false` before working on your repo so that git did not convert `LF` to `CRLF` on checkout.
+   Alternatively, you can add `* text=auto eol=lf` to the repo's `.gitattributes` file to achieve this.
+
+All modern text editors in all operating systems are able to correctly display line endings when `\n` (`LF`) is used.
+However, old versions of Notepad for Windows will visually squash such lines into one.
+
+Valid options:
+
+- `"auto"` - Maintain existing line endings
+  (mixed values within one file are normalised by looking at what's used after the first line)
+- `"lf"` – Line Feed only (`\n`), common on Linux and macOS as well as inside git repos
+- `"crlf"` - Carriage Return + Line Feed characters (`\r\n`), common on Windows
+- `"cr"` - Carriage Return character only (`\r`), used very rarely
+
+| Default  | CLI Override                                                | API Override                                               |
+| -------- | ----------------------------------------------------------- | ---------------------------------------------------------- |
+| `"auto"` | <code>--end-of-line <auto&#124;cr&#124;crlf&#124;lf></code> | <code>endOfLine: "<auto&#124;cr&#124;crlf&#124;lf>"</code> |
+
+-->

package.json

@@ -29,7 +29,7 @@
     "dedent": "0.7.0",
     "diff": "3.2.0",
     "editorconfig": "0.15.2",
-    "editorconfig-to-prettier": "0.0.6",
+    "editorconfig-to-prettier": "0.1.0",
     "emoji-regex": "6.5.1",
     "escape-string-regexp": "1.0.5",
     "esutils": "2.0.2",

src/common/end-of-line.js

@@ -0,0 +1,25 @@
+"use strict";
+
+function guessEndOfLine(text) {
+  const index = text.indexOf("\r");
+  if (index >= 0) {
+    return text.charAt(index + 1) === "\n" ? "crlf" : "cr";
+  }
+  return "lf";
+}
+
+function convertEndOfLineToChars(value) {
+  switch (value) {
+    case "cr":
+      return "\r";
+    case "crlf":
+      return "\r\n";
+    default:
+      return "\n";
+  }
+}
+
+module.exports = {
+  guessEndOfLine,
+  convertEndOfLineToChars
+};

src/doc/doc-printer.js

@@ -1,6 +1,7 @@
 "use strict";
 
 const { getStringWidth } = require("../common/util");
+const { convertEndOfLineToChars } = require("../common/end-of-line");
 const { concat, fill, cursor } = require("./doc-builders");
 
 /** @type {{[groupId: PropertyKey]: MODE}} */
@@ -241,7 +242,7 @@ function printDocToString(doc, options) {
   groupModeMap = {};
 
   const width = options.printWidth;
-  const newLine = options.newLine || "\n";
+  const newLine = convertEndOfLineToChars(options.endOfLine);
   let pos = 0;
   // cmds is basically a stack. We've turned a recursive call into a
   // while loop which is much faster. The while loop below adds new

src/language-js/pragma.js

@@ -10,10 +10,12 @@ function hasPragma(text) {
 function insertPragma(text) {
   const parsedDocblock = docblock.parseWithComments(docblock.extract(text));
   const pragmas = Object.assign({ format: "" }, parsedDocblock.pragmas);
-  const newDocblock = docblock.print({
-    pragmas,
-    comments: parsedDocblock.comments.replace(/^(\s+?\r?\n)+/, "") // remove leading newlines
-  });
+  const newDocblock = docblock
+    .print({
+      pragmas,
+      comments: parsedDocblock.comments.replace(/^(\s+?\r?\n)+/, "") // remove leading newlines
+    })
+    .replace(/(\r\n|\r)/g, "\n"); // normalise newlines (mitigate use of os.EOL by jest-docblock)
   const strippedText = docblock.strip(text);
   const separatingNewlines = strippedText.startsWith("\n") ? "\n" : "\n\n";
   return newDocblock + separatingNewlines + strippedText;

src/main/core-options.js

@@ -62,6 +62,36 @@ const options = {
     `,
     cliCategory: CATEGORY_EDITOR
   },
+  endOfLine: {
+    since: "1.15.0",
+    category: CATEGORY_GLOBAL,
+    type: "choice",
+    default: "auto",
+    description: "Which end of line characters to apply.",
+    choices: [
+      {
+        value: "auto",
+        description: dedent`
+          Maintain existing
+          (mixed values within one file are normalised by looking at what's used after the first line)
+        `
+      },
+      {
+        value: "lf",
+        description:
+          "Line Feed only (\\n), common on Linux and macOS as well as inside git repos"
+      },
+      {
+        value: "crlf",
+        description:
+          "Carriage Return + Line Feed characters (\\r\\n), common on Windows"
+      },
+      {
+        value: "cr",
+        description: "Carriage Return character only (\\r), used very rarely"
+      }
+    ]
+  },
   filepath: {
     since: "1.4.0",
     category: CATEGORY_SPECIAL,

src/main/core.js

@@ -7,6 +7,10 @@ const massageAST = require("./massage-ast");
 const comments = require("./comments");
 const parser = require("./parser");
 const printAstToDoc = require("./ast-to-doc");
+const {
+  guessEndOfLine,
+  convertEndOfLineToChars
+} = require("../common/end-of-line");
 const rangeUtil = require("./range-util");
 const privateUtil = require("../common/util");
 const {
@@ -18,14 +22,6 @@ const UTF8BOM = 0xfeff;
 
 const CURSOR = Symbol("cursor");
 
-function guessLineEnding(text) {
-  const index = text.indexOf("\n");
-  if (index >= 0 && text.charAt(index - 1) === "\r") {
-    return "\r\n";
-  }
-  return "\n";
-}
-
 function ensureAllCommentsPrinted(astComments) {
   if (!astComments) {
     return;
@@ -84,7 +80,9 @@ function coreFormat(text, opts, addAlignmentSize) {
 
   const astComments = attachComments(text, ast, opts);
   const doc = printAstToDoc(ast, opts, addAlignmentSize);
-  opts.newLine = guessLineEnding(originalText);
+  if (opts.endOfLine === "auto") {
+    opts.endOfLine = guessEndOfLine(originalText);
+  }
 
   const result = printDocToString(doc, opts);
 
@@ -97,7 +95,7 @@ function coreFormat(text, opts, addAlignmentSize) {
       result.cursorNodeStart -= result.formatted.indexOf(trimmed);
     }
 
-    result.formatted = trimmed + opts.newLine;
+    result.formatted = trimmed + convertEndOfLineToChars(opts.endOfLine);
   }
 
   if (opts.cursorOffset >= 0) {

tests/end_of_line/__snapshots__/jsfmt.spec.js.snap

@@ -0,0 +1,83 @@
+// Jest Snapshot v1, https://goo.gl/fbAQLP
+
+exports[`usingCrlf.js - babylon-verify 1`] = `
+function f() {
+  console.log("testing line endings");
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+function f() {
+  console.log("testing line endings");
+}
+
+`;
+
+exports[`usingCrlf.js - babylon-verify 2`] = `
+function f() {
+  console.log("testing line endings");
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+function f() {/*CR*/  console.log("testing line endings");/*CR*/}/*CR*/
+`;
+
+exports[`usingCrlf.js - babylon-verify 3`] = `
+function f() {
+  console.log("testing line endings");
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+function f() {/*CR*/
+  console.log("testing line endings");/*CR*/
+}/*CR*/
+
+`;
+
+exports[`usingCrlf.js - babylon-verify 4`] = `
+function f() {
+  console.log("testing line endings");
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+function f() {
+  console.log("testing line endings");
+}
+
+`;
+
+exports[`usingLf.js - babylon-verify 1`] = `
+function f() {
+  console.log("testing line endings");
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+function f() {
+  console.log("testing line endings");
+}
+
+`;
+
+exports[`usingLf.js - babylon-verify 2`] = `
+function f() {
+  console.log("testing line endings");
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+function f() {/*CR*/  console.log("testing line endings");/*CR*/}/*CR*/
+`;
+
+exports[`usingLf.js - babylon-verify 3`] = `
+function f() {
+  console.log("testing line endings");
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+function f() {/*CR*/
+  console.log("testing line endings");/*CR*/
+}/*CR*/
+
+`;
+
+exports[`usingLf.js - babylon-verify 4`] = `
+function f() {
+  console.log("testing line endings");
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+function f() {
+  console.log("testing line endings");
+}
+
+`;

tests/end_of_line/jsfmt.spec.js

@@ -0,0 +1,4 @@
+run_spec(__dirname, ["babylon"]);
+run_spec(__dirname, ["babylon"], { endOfLine: "cr" });
+run_spec(__dirname, ["babylon"], { endOfLine: "crlf" });
+run_spec(__dirname, ["babylon"], { endOfLine: "lf" });

tests/end_of_line/usingCrlf.js

@@ -0,0 +1,3 @@
+function f() {
+  console.log("testing line endings");
+}

tests/end_of_line/usingLf.js

@@ -0,0 +1,3 @@
+function f() {
+  console.log("testing line endings");
+}

tests/end_of_line_in_css/__snapshots__/jsfmt.spec.js.snap

@@ -0,0 +1,75 @@
+// Jest Snapshot v1, https://goo.gl/fbAQLP
+
+exports[`usingCrlf.css - css-verify 1`] = `
+.foo {
+        margin: 42px;
+}~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+.foo {
+  margin: 42px;
+}
+
+`;
+
+exports[`usingCrlf.css - css-verify 2`] = `
+.foo {
+        margin: 42px;
+}~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+.foo {/*CR*/  margin: 42px;/*CR*/}/*CR*/
+`;
+
+exports[`usingCrlf.css - css-verify 3`] = `
+.foo {
+        margin: 42px;
+}~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+.foo {/*CR*/
+  margin: 42px;/*CR*/
+}/*CR*/
+
+`;
+
+exports[`usingCrlf.css - css-verify 4`] = `
+.foo {
+        margin: 42px;
+}~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+.foo {
+  margin: 42px;
+}
+
+`;
+
+exports[`usingLf.css - css-verify 1`] = `
+.foo {
+        margin: 42px;
+}~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+.foo {
+  margin: 42px;
+}
+
+`;
+
+exports[`usingLf.css - css-verify 2`] = `
+.foo {
+        margin: 42px;
+}~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+.foo {/*CR*/  margin: 42px;/*CR*/}/*CR*/
+`;
+
+exports[`usingLf.css - css-verify 3`] = `
+.foo {
+        margin: 42px;
+}~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+.foo {/*CR*/
+  margin: 42px;/*CR*/
+}/*CR*/
+
+`;
+
+exports[`usingLf.css - css-verify 4`] = `
+.foo {
+        margin: 42px;
+}~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+.foo {
+  margin: 42px;
+}
+
+`;

tests/end_of_line_in_css/jsfmt.spec.js

@@ -0,0 +1,4 @@
+run_spec(__dirname, ["css"]);
+run_spec(__dirname, ["css"], { endOfLine: "cr" });
+run_spec(__dirname, ["css"], { endOfLine: "crlf" });
+run_spec(__dirname, ["css"], { endOfLine: "lf" });

tests/end_of_line_in_css/usingCrlf.css

@@ -0,0 +1,3 @@
+.foo {
+        margin: 42px;
+}

tests/end_of_line_in_css/usingLf.css

@@ -0,0 +1,3 @@
+.foo {
+        margin: 42px;
+}