Support merging sourcemaps when transformed file is fully replaced (#…

…14247)

* Support merging sourcemaps when transformed file is fully replaced

A follow-up to #14246. I finally thought of a case where the
sourceFileName's content is fully replaced, leading to only the injected
file existing in the output sourcemap. This can happen where only one
output source is created, or multiple.

In the single output source case, we'd incorrectly associate the
mappings through the inputMap, even though none of the content actually
comes from there.

In the multiple source case, we'd silently fail and output empty mappings.

Both cases are now fixed, with the correct remapping being done through
in all possible output cases now.

* Update to remapping@2.1.0 to support source location override

packages/babel-core/package.json

@@ -48,7 +48,7 @@
     "./src/transformation/util/clone-deep.ts": "./src/transformation/util/clone-deep-browser.ts"
   },
   "dependencies": {
-    "@ampproject/remapping": "^2.0.0",
+    "@ampproject/remapping": "^2.1.0",
     "@babel/code-frame": "workspace:^",
     "@babel/generator": "workspace:^",
     "@babel/helper-compilation-targets": "workspace:^",

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

@@ -6,77 +6,27 @@ export default function mergeSourceMap(
   map: SourceMap,
   source: string,
 ): SourceMap {
-  const outputSources = map.sources;
-
-  let result;
-  if (outputSources.length > 1) {
-    // When there are multiple output sources, we can't always be certain which
-    // source represents the file we just transformed.
-    const index = outputSources.indexOf(source);
-
-    // If we can't find the source, we fall back to the legacy behavior of
-    // outputting an empty sourcemap.
-    if (index === -1) {
-      result = emptyMap(inputMap);
-    } else {
-      result = mergeMultiSource(inputMap, map, index);
+  const result = remapping(rootless(map), (s, ctx) => {
+    if (s === source) {
+      // 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
+      // same directory, the expected output is just `baz.js`. Without this step,
+      // it would become `foo/baz.js`.
+      ctx.source = "";
+
+      return rootless(inputMap);
     }
-  } else {
-    result = mergeSingleSource(inputMap, map);
-  }
+
+    return null;
+  });
 
   if (typeof inputMap.sourceRoot === "string") {
     result.sourceRoot = inputMap.sourceRoot;
   }
   return result;
 }
 
-// A single source transformation is the default, and easiest to handle.
-function mergeSingleSource(inputMap: SourceMap, map: SourceMap): SourceMap {
-  return remapping([rootless(map), rootless(inputMap)], () => null);
-}
-
-// Transformation generated an output from multiple source files. When this
-// happens, it's ambiguous which source was the transformed file, and which
-// source is from the transformation process. We use remapping's multisource
-// behavior, returning the input map when we encounter the transformed file.
-function mergeMultiSource(inputMap: SourceMap, map: SourceMap, index: number) {
-  // We empty the source index, which will prevent the sourcemap from becoming
-  // relative the 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 same
-  // directory, the expected output is just `baz.js`. Without this step, it
-  // would become `foo/baz.js`.
-  map.sources[index] = "";
-
-  let count = 0;
-  return remapping(rootless(map), () => {
-    if (count++ === index) return rootless(inputMap);
-    return null;
-  });
-}
-
-// Legacy behavior of the old merger was to output a sourcemap without any
-// mappings but with copied sourcesContent. This only happens if there are
-// multiple output files and it's ambiguous which one is the transformed file.
-function emptyMap(inputMap: SourceMap) {
-  const inputSources = inputMap.sources;
-
-  const sources = [];
-  const sourcesContent = inputMap.sourcesContent?.filter((content, i) => {
-    if (typeof content !== "string") return false;
-
-    sources.push(inputSources[i]);
-    return true;
-  });
-
-  return {
-    ...inputMap,
-    sources,
-    sourcesContent,
-    mappings: "",
-  };
-}
-
 function rootless(map: SourceMap): SourceMap {
   return {
     ...map,

packages/babel-core/test/fixtures/transformation/source-maps/input-source-map-multiple-output-sources-complete-replace/options.json

@@ -0,0 +1,4 @@
+{
+  "inputSourceMap": true,
+  "plugins": ["./plugin.js"]
+}

packages/babel-core/test/fixtures/transformation/source-maps/input-source-map-multiple-output-sources-complete-replace/output.js

@@ -0,0 +1,2 @@
+"bar";
+"baz";

packages/babel-core/test/fixtures/transformation/source-maps/input-source-map-multiple-output-sources-complete-replace/plugin.js

@@ -0,0 +1,52 @@
+module.exports = function (babel) {
+  const { types: t } = babel;
+
+  return {
+    visitor: {
+      Program(path) {
+        const { file } = this;
+        const { sourceFileName } = file.opts.generatorOpts;
+
+        // This injects the sourcesContent, though I don't imagine anyone's
+        // doing it.
+        file.code = {
+            [sourceFileName]: file.code,
+            'bar.js': '<bar />',
+            'baz.js': 'baz();',
+        };
+      },
+
+      CallExpression(path) {
+        const callee = path.node;
+        const { loc } = callee;
+
+        // This filename will cause a second source file to be generated in the
+        // output sourcemap.
+        loc.filename = "bar.js";
+        loc.start.column = 1;
+        loc.end.column = 4;
+
+        const node = t.stringLiteral('bar');
+        node.loc = loc;
+        path.replaceWith(node);
+      },
+
+      Function(path) {
+        const callee = path.node;
+        const { loc } = callee;
+
+        // This filename will cause a second source file to be generated in the
+        // output sourcemap.
+        loc.filename = "baz.js";
+        loc.start.column = 0;
+        loc.start.line = 1;
+        loc.end.column = 3;
+        loc.end.line = 1;
+
+        const node = t.stringLiteral('baz');
+        node.loc = loc;
+        path.replaceWith(node);
+      },
+    },
+  };
+};

packages/babel-core/test/fixtures/transformation/source-maps/input-source-map-multiple-output-sources-complete-replace/source-map.json

@@ -0,0 +1,13 @@
+{
+  "mappings": "AAAC;ACAD,K",
+  "names": [],
+  "sources": [
+    "bar.js",
+    "baz.js"
+  ],
+  "sourcesContent": [
+    "<bar />",
+    "baz();"
+  ],
+  "version": 3
+}

packages/babel-core/test/fixtures/transformation/source-maps/input-source-map-multiple-output-sources/plugin.js

@@ -20,7 +20,7 @@ module.exports = function (babel) {
         path.replaceWith(node);
 
         // This injects the sourcesContent, though I don't imagine anyone's
-          // doing it.
+        // doing it.
         file.code = {
             [sourceFileName]: file.code,
             'test.js': '<bar />',

packages/babel-core/test/fixtures/transformation/source-maps/input-source-map-sources-complete-replace/options.json

@@ -0,0 +1,4 @@
+{
+  "inputSourceMap": true,
+  "plugins": ["./plugin.js"]
+}

packages/babel-core/test/fixtures/transformation/source-maps/input-source-map-sources-complete-replace/output.js

@@ -0,0 +1 @@
+"bar";

packages/babel-core/test/fixtures/transformation/source-maps/input-source-map-sources-complete-replace/plugin.js

@@ -0,0 +1,38 @@
+module.exports = function (babel) {
+  const { types: t } = babel;
+
+  return {
+    visitor: {
+      Program(path) {
+        const { file } = this;
+        const { sourceFileName } = file.opts.generatorOpts;
+
+        // This injects the sourcesContent, though I don't imagine anyone's
+        // doing it.
+        file.code = {
+            [sourceFileName]: file.code,
+            'test.js': '<bar />',
+        };
+      },
+
+      CallExpression(path) {
+        const callee = path.node;
+        const { loc } = callee;
+
+        // This filename will cause a second source file to be generated in the
+        // output sourcemap.
+        loc.filename = "test.js";
+        loc.start.column = 1;
+        loc.end.column = 4;
+
+        const node = t.stringLiteral('bar');
+        node.loc = loc;
+        path.replaceWith(node);
+      },
+
+      Function(path) {
+        path.remove();
+      },
+    },
+  };
+};

packages/babel-core/test/fixtures/transformation/source-maps/input-source-map-sources-complete-replace/source-map.json

@@ -0,0 +1,7 @@
+{
+  "mappings": "AAAC",
+  "names": [],
+  "sources": ["test.js"],
+  "sourcesContent": ["<bar />"],
+  "version": 3
+}

yarn.lock

@@ -5,13 +5,12 @@ __metadata:
   version: 5
   cacheKey: 8
 
-"@ampproject/remapping@npm:^2.0.0":
-  version: 2.0.2
-  resolution: "@ampproject/remapping@npm:2.0.2"
+"@ampproject/remapping@npm:^2.0.0, @ampproject/remapping@npm:^2.1.0":
+  version: 2.1.0
+  resolution: "@ampproject/remapping@npm:2.1.0"
   dependencies:
-    "@jridgewell/trace-mapping": ^0.2.2
-    sourcemap-codec: 1.4.8
-  checksum: 5759df3715f0291cbf97099a9bb7202201a1a267e232ee1505418c768b9ae7281cd550b1da563a12808a06529eb1298744a6cabde21ac354fc8450044c7f2213
+    "@jridgewell/trace-mapping": ^0.3.0
+  checksum: 10ff0d4a559f930082f1a4c1b68dc521d5b1a75e0b8ab4829e9eedf6621386893e4a008f0db6c716f64db5d8eed49c0abcfbf3bd6ff11d5a00312454a9351ed4
   languageName: node
   linkType: hard
 
@@ -323,7 +322,7 @@ __metadata:
   version: 0.0.0-use.local
   resolution: "@babel/core@workspace:packages/babel-core"
   dependencies:
-    "@ampproject/remapping": ^2.0.0
+    "@ampproject/remapping": ^2.1.0
     "@babel/code-frame": "workspace:^"
     "@babel/generator": "workspace:^"
     "@babel/helper-compilation-targets": "workspace:^"
@@ -4091,13 +4090,20 @@ __metadata:
   languageName: node
   linkType: hard
 
-"@jridgewell/trace-mapping@npm:^0.2.2":
-  version: 0.2.5
-  resolution: "@jridgewell/trace-mapping@npm:0.2.5"
+"@jridgewell/sourcemap-codec@npm:^1.4.10":
+  version: 1.4.10
+  resolution: "@jridgewell/sourcemap-codec@npm:1.4.10"
+  checksum: 247229218edbe165dcf0a5ae0c4b81bff1b5438818bb09221f756681fe158597fdf25c2a803f9260453b299c98c7e01ddebeb1555cda3157d987cd22c08605ef
+  languageName: node
+  linkType: hard
+
+"@jridgewell/trace-mapping@npm:^0.3.0":
+  version: 0.3.2
+  resolution: "@jridgewell/trace-mapping@npm:0.3.2"
   dependencies:
     "@jridgewell/resolve-uri": ^3.0.3
-    sourcemap-codec: 1.4.8
-  checksum: 7ac0a2992f4a8d16c1cbe03bccbcfbd1e96bf5071b0a794dd97904a7588cc248b73e8091fabcb13dac8f40bc51297ee4ef98a6a870ca5a4dfb8e2dcbf6f33956
+    "@jridgewell/sourcemap-codec": ^1.4.10
+  checksum: b58be6b4133cbcb20bfd28c9ca843b8db9efa0bf1d7e0e9e26b2228dace94ad53161c996ab1d762d7c3955dfc398a7734e7b84a2493ae36b451f232234fbb257
   languageName: node
   linkType: hard
 
@@ -14168,7 +14174,7 @@ fsevents@^1.2.7:
   languageName: node
   linkType: hard
 
-"sourcemap-codec@npm:1.4.8, sourcemap-codec@npm:^1.4.4":
+"sourcemap-codec@npm:^1.4.4":
   version: 1.4.8
   resolution: "sourcemap-codec@npm:1.4.8"
   checksum: b57981c05611afef31605732b598ccf65124a9fcb03b833532659ac4d29ac0f7bfacbc0d6c5a28a03e84c7510e7e556d758d0bb57786e214660016fb94279316