Make line counts reflect all line endings (#691)

Summary:
**Summary**

Metro included a few functions to count source lines, some of which didn't correctly count all [line terminators specified in the ECMAScript standard](https://262.ecma-international.org/12.0/#sec-line-terminators). This PR replaces those implementations with the correct one found in `packages/metro/src/shared/output/RamBundle/util.js`.

The user-facing issue which led me to this was that importing a file with CRLF line endings caused `/symbolicate` to return incorrect mappings for all files after that one in the bundle. Metro-transform-worker was double-counting the line endings and getExplodedSourceMap was carrying that erroneous offset through.

**Test plan**

There's a new test for a variety of line endings, and the several existing tests that exercise countLines pass without modification.

Pull Request resolved: #691

Reviewed By: feedthejim

Differential Revision: D30607069

Pulled By: motiz88

fbshipit-source-id: c83d5cd87de40b204e9b7ade08ce831360751bf6

packages/metro-source-map/src/source-map.js

@@ -277,9 +277,10 @@ function addMapping(generator, mapping, carryOver) {
   }
 }
 
-function countLines(string) {
-  return string.split('\n').length;
-}
+const newline = /\r\n?|\n|\u2028|\u2029/g;
+
+const countLines = (string: string): number =>
+  (string.match(newline) || []).length + 1;
 
 module.exports = {
   BundleBuilder,

packages/metro-transform-worker/src/__tests__/index-test.js

@@ -600,3 +600,24 @@ it('skips minification in Hermes canary transform profile', async () => {
     });"
   `);
 });
+
+it('counts all line endings correctly', async () => {
+  const transformStr = str =>
+    Transformer.transform(baseConfig, '/root', 'local/file.js', str, {
+      dev: false,
+      minify: false,
+      type: 'module',
+    });
+
+  const differentEndingsResult = await transformStr(
+    'one\rtwo\r\nthree\nfour\u2028five\u2029six',
+  );
+
+  const standardEndingsResult = await transformStr(
+    'one\ntwo\nthree\nfour\nfive\nsix',
+  );
+
+  expect(differentEndingsResult.output[0].data.lineCount).toEqual(
+    standardEndingsResult.output[0].data.lineCount,
+  );
+});

packages/metro/src/lib/countLines.js

@@ -10,12 +10,9 @@
 
 'use strict';
 
-const nullthrows = require('nullthrows');
+const newline = /\r\n?|\n|\u2028|\u2029/g;
 
-const reLine = /^/gm;
-
-function countLines(s: string): number {
-  return nullthrows(s.match(reLine)).length;
-}
+const countLines = (string: string): number =>
+  (string.match(newline) || []).length + 1;
 
 module.exports = countLines;

packages/metro/src/shared/output/RamBundle/util.js

@@ -12,6 +12,7 @@
 
 const invariant = require('invariant');
 
+import countLines from '../../../lib/countLines';
 import type {ModuleGroups, ModuleTransportLike} from '../../types.flow';
 import type {
   IndexMap,
@@ -20,11 +21,6 @@ import type {
   BasicSourceMap,
 } from 'metro-source-map';
 
-const newline = /\r\n?|\n|\u2028|\u2029/g;
-// fastest implementation
-const countLines = (string: string): number =>
-  (string.match(newline) || []).length + 1;
-
 function lineToLineSourceMap(
   source: string,
   filename: string = '',