Fix infinite recursion when merging sourcemaps (#14274)

* Fix infinite recursion when merge sourcemaps

* Add test case

* Externalize the sourcemap

packages/babel-core/src/transformation/file/merge-map.ts

@@ -6,8 +6,14 @@ export default function mergeSourceMap(
   map: SourceMap,
   source: string,
 ): SourceMap {
+  // Prevent an infinite recursion if one of the input map's sources has the
+  // same resolved path as the input map. In the case, it would keep find the
+  // input map, then get it's sources which will include a path like the input
+  // map, on and on.
+  let found = false;
   const result = remapping(rootless(map), (s, ctx) => {
-    if (s === source) {
+    if (s === source && !found) {
+      found = true;
       // We empty the source location, which will prevent the sourcemap from
       // becoming relative to the input's location. Eg, if we're transforming a
       // file 'foo/bar.js', and it is a transformation of a `baz.js` file in the

packages/babel-core/test/fixtures/transformation/source-maps/input-source-map-same-location/input.js

@@ -0,0 +1,6 @@
+var foo = function () {
+  return 4;
+};
+
+//# sourceMappingURL=input.js.map
+

packages/babel-core/test/fixtures/transformation/source-maps/input-source-map-same-location/options.json

@@ -0,0 +1,3 @@
+{
+  "inputSourceMap": true
+}

packages/babel-core/test/fixtures/transformation/source-maps/input-source-map-same-location/output.js

@@ -0,0 +1,3 @@
+var foo = function () {
+  return 4;
+};

packages/babel-core/test/fixtures/transformation/source-maps/input-source-map-same-location/source-map.json

@@ -0,0 +1,7 @@
+{
+  "mappings": "AAAA,UAAU,Y;SAAM;AAAC,CAAjB",
+  "names": [],
+  "sources": ["source-maps/input-source-map-same-location/input.js"],
+  "sourcesContent": ["var foo = () => 4;"],
+  "version": 3
+}