Fix merging sourcemaps on Windows

[jridgewell]

Q	A
Fixed Issues?	Fixes #14277
Patch: Bug Fix?
Major: Breaking Change?
Minor: New Feature?
Tests Added + Pass?	Yes
Documentation PR Link
Any Dependency Changes?
License	MIT

On win32 machines, the sourceFileName uses backslash paths like
C:\foo\bar.js. But sourcemaps are always posix paths, so we need to
normalize to regular slashes before we can merge (else we won't find the
source associated with our input map).

This mirrors code done while generating the output map at

babel/packages/babel-generator/src/source-map.ts

Line 102 in 5c2fcad

: (filename || this._opts.sourceFileName).replace(/\\/g, "/"),

[babel-bot]

Build successful! You can test your changes in the REPL here: https://babeljs.io/repl/build/51311/

[jridgewell]

I've verified this using GH Actions to patch the node_modules file. Compare https://github.com/jridgewell/babel-7.17.3-sourcemaps-issue/runs/5225317890?check_suite_focus=true to https://github.com/jridgewell/babel-7.17.3-sourcemaps-issue/runs/5225382417?check_suite_focus=true (check the Run cat 'app\\*.map' step):

--- a.json	2022-02-16 19:47:50.000000000 -0500
+++ b.json	2022-02-16 19:47:50.000000000 -0500
@@ -1,10 +1,10 @@
 {
   "version": 3,
   "file": "babel-7.13.3-sourcemaps-issue.js",
-  "mappings": "yBAKIA,QAAQC,IAHA,iB",
+  "mappings": "yBAKEA,QAAQC,IAJD,iB",
   "sources": ["webpack://babel-7.17.3-sourcemaps-issue/./src/index.ts"],
   "sourcesContent": [
-    "\"use strict\";\nfunction welcome(user) {\n    return `Hello, ${user}!`;\n}\n(function () {\n    console.log(welcome(\"world\"));\n})();\n"
+    "function welcome(user: string): string {\r\n  return `Hello, ${user}!`;\r\n}\r\n\r\n(function () {\r\n  console.log(welcome(\"world\"));\r\n})();\r\n"
   ],
   "names": ["console", "log"],
   "sourceRoot": ""

It now correctly shows the original TypeScript code in the sourcesContent and the mappings now correctly points the output string to template literal at line 2 column 9.

• Before
• After

[nicolo-ribaudo]

Thanks!