Support index source maps.

src/actions/receive-profile.ts

@@ -79,7 +79,7 @@ import {
 import { doSourceMapSymbolication } from './source-map-symbolication';
 import type { SourceMapSymbolicationResult } from './source-map-symbolication';
 
-import type { RawSourceMap } from 'source-map';
+import type { SourceMap } from 'firefox-profiler/profile-logic/source-maps/store';
 import type {
   RequestedLib,
   ImplementationFilter,
@@ -849,7 +849,7 @@ async function doResolveSourceMaps(
   browserConnection: BrowserConnection,
   dispatch: Dispatch
 ): Promise<{
-  resolvedSourceMaps: Map<IndexIntoSourceTable, RawSourceMap>;
+  resolvedSourceMaps: Map<IndexIntoSourceTable, SourceMap>;
   compiledSources: Map<IndexIntoSourceTable, string>;
 }> {
   const { sources, stringArray } = profile.shared;
@@ -872,7 +872,7 @@ async function doResolveSourceMaps(
   }
 
   // Fetch source maps and compiled sources in parallel, ignoring individual failures.
-  const resolvedSourceMaps: Map<IndexIntoSourceTable, RawSourceMap> = new Map();
+  const resolvedSourceMaps: Map<IndexIntoSourceTable, SourceMap> = new Map();
   const compiledSources: Map<IndexIntoSourceTable, string> = new Map();
 
   dispatch({ type: 'START_SOURCE_MAP_FETCHING' });

src/actions/source-map-symbolication.ts

@@ -20,7 +20,7 @@ import type {
   EligibleSource,
   SourceMapAmbiguityReason,
 } from 'firefox-profiler/profile-logic/source-maps/matching';
-import type { RawSourceMap } from 'source-map';
+import type { SourceMap } from 'firefox-profiler/profile-logic/source-maps/store';
 import { assertExhaustiveCheck } from 'firefox-profiler/utils/types';
 
 /**
@@ -40,7 +40,7 @@ import { assertExhaustiveCheck } from 'firefox-profiler/utils/types';
 export type SourceMapSymbolicationResult = 'applied' | 'no-match' | 'error';
 
 export function doSourceMapSymbolication(
-  resolvedSourceMaps: Map<IndexIntoSourceTable, RawSourceMap>,
+  resolvedSourceMaps: Map<IndexIntoSourceTable, SourceMap>,
   compiledSources: Map<IndexIntoSourceTable, string>,
   run: SourceMapRunner = _runSourceMapWorker
 ): ThunkAction<Promise<SourceMapSymbolicationResult>> {

src/app-logic/browser-connection.ts

@@ -16,7 +16,7 @@ import {
   getJSSourcesViaWebChannelV7,
   getSourceMapViaWebChannel,
 } from './web-channel';
-import type { RawSourceMap } from 'source-map';
+import type { SourceMap } from 'firefox-profiler/profile-logic/source-maps/store';
 import type {
   Milliseconds,
   FaviconData,
@@ -92,7 +92,7 @@ export interface BrowserConnection {
 
   // Get source map of the given source directly from the browser.
   // Requires WebChannel version 7+.
-  getSourceMap(sourceId: string): Promise<RawSourceMap>;
+  getSourceMap(sourceId: string): Promise<SourceMap>;
 
   // True when the browser exposes GET_SOURCE_MAP (WebChannel version 7+).
   // Callers use this to gate source-map-based features.
@@ -247,7 +247,7 @@ class BrowserConnectionImpl implements BrowserConnection {
     return [];
   }
 
-  async getSourceMap(sourceId: string): Promise<RawSourceMap> {
+  async getSourceMap(sourceId: string): Promise<SourceMap> {
     if (!this.supportsGetSourceMap) {
       throw new Error(
         "Can't use getSourceMap in Firefox versions with the old WebChannel."

src/app-logic/web-channel.ts

@@ -8,7 +8,7 @@ import type {
   ExternalMarkersData,
   FaviconData,
 } from 'firefox-profiler/types';
-import type { RawSourceMap } from 'source-map';
+import type { SourceMap } from 'firefox-profiler/profile-logic/source-maps/store';
 
 /**
  * This file is in charge of handling the message managing between profiler.firefox.com
@@ -162,7 +162,7 @@ type GetPageFaviconsResponse = Array<FaviconData | null>;
 type OpenScriptInTabDebuggerResponse = void;
 type GetJSSourceReponseItem = { sourceText: string } | { error: string };
 type GetJSSourcesResponse = Array<GetJSSourceReponseItem>;
-type GetSourceMapResponse = RawSourceMap;
+type GetSourceMapResponse = SourceMap;
 
 // TypeScript function overloads for request/response pairs.
 function _sendMessageWithResponse(

src/profile-logic/embed-js-sources.ts

@@ -12,7 +12,7 @@ import { parseSourceMapFileContents } from 'firefox-profiler/profile-logic/sourc
 import { base64StringToBytes } from 'firefox-profiler/utils/base64';
 import { StringTable } from 'firefox-profiler/utils/string-table';
 
-import type { RawSourceMap } from 'source-map';
+import type { SourceMap } from 'firefox-profiler/profile-logic/source-maps/store';
 import type { SourceMapRunner } from 'firefox-profiler/profile-logic/source-maps/worker-types';
 import type { IndexIntoSourceTable, Profile } from 'firefox-profiler/types';
 
@@ -70,7 +70,7 @@ function _resolveSourceMapURL(
 async function _readSourceMap(
   resolvedSourceMapURL: string,
   readSource: SourceReader
-): Promise<RawSourceMap | null> {
+): Promise<SourceMap | null> {
   const isInline = resolvedSourceMapURL.startsWith('data:');
   const sourceMapText = isInline
     ? _decodeDataUrl(resolvedSourceMapURL)
@@ -119,7 +119,7 @@ export async function embedJsSources(
   const stringTable = StringTable.withBackingArray(stringArray);
   let embeddedCount = 0;
   const compiledSources = new Map<IndexIntoSourceTable, string>();
-  const resolvedSourceMaps = new Map<IndexIntoSourceTable, RawSourceMap>();
+  const resolvedSourceMaps = new Map<IndexIntoSourceTable, SourceMap>();
   // Gecko keys source rows by their ScriptSource id, so a script that's loaded
   // more than once can have several rows with the same URL.
   const readSourceOnce = _cacheByKey(readSource);

src/profile-logic/source-maps/matching.ts

@@ -3,7 +3,7 @@
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
 import type { IndexIntoSourceTable, SourceTable } from 'firefox-profiler/types';
-import type { RawSourceMap } from 'source-map';
+import type { SourceMap } from './store';
 
 /**
  * A source row that already carries a sourceMapURL, and is therefore eligible
@@ -60,45 +60,69 @@ export function getSourcesWithSourceMapURL(
   return eligible;
 }
 
-/**
- * Parse the text contents of a `.map` file into a RawSourceMap. Returns null
- * for invalid JSON, for JSON that isn't a source map (missing version /
- * mappings / sources), and for index maps.
- *
- * An index map replaces the top-level `mappings` string with a `sections`
- * array, each section pairing a generated-code offset with an embedded source
- * map (ECMA-426 section 10: https://tc39.es/ecma426/#sec-index-source-map).
- * We skip them because no mainstream web bundler emits one, and we currently
- * don't support it.
- */
-export function parseSourceMapFileContents(text: string): RawSourceMap | null {
-  let parsed: unknown;
-  try {
-    parsed = JSON.parse(text);
-  } catch {
-    return null;
+function _isPosition(value: unknown): boolean {
+  if (value === null || typeof value !== 'object') {
+    return false;
   }
+  const position = value as Record<string, unknown>;
+  return (
+    typeof position.line === 'number' && typeof position.column === 'number'
+  );
+}
 
-  if (parsed === null || typeof parsed !== 'object') {
-    return null;
+function _isRegularSourceMap(value: unknown): boolean {
+  if (value === null || typeof value !== 'object') {
+    return false;
   }
+  const map = value as Record<string, unknown>;
+  return (
+    typeof map.version === 'number' &&
+    typeof map.mappings === 'string' &&
+    Array.isArray(map.sources)
+  );
+}
 
-  const map = parsed as Record<string, unknown>;
+// An index map replaces the top-level `mappings` string with a `sections`
+// array, each section pairing a generated-code offset with an embedded source
+// map (ECMA-426 section 10: https://tc39.es/ecma426/#sec-index-source-map).
+// The embedded maps must be regular source maps: the spec decodes them with
+// DecodeSourceMap, so index maps can't be nested. Sections that reference
+// their map by `url` instead are not supported by the source-map library.
+function _isIndexSourceMap(map: Record<string, unknown>): boolean {
+  return (
+    typeof map.version === 'number' &&
+    Array.isArray(map.sections) &&
+    map.sections.every(
+      (section) =>
+        section !== null &&
+        typeof section === 'object' &&
+        _isPosition(section.offset) &&
+        _isRegularSourceMap(section.map)
+    )
+  );
+}
 
-  // Index maps use `sections` instead of top-level `mappings`. Reject them.
-  if ('sections' in map) {
-    return null;
+function _isSourceMap(value: unknown): value is SourceMap {
+  if (value === null || typeof value !== 'object') {
+    return false;
   }
+  const map = value as Record<string, unknown>;
+  return 'sections' in map ? _isIndexSourceMap(map) : _isRegularSourceMap(map);
+}
 
-  if (
-    typeof map.version !== 'number' ||
-    typeof map.mappings !== 'string' ||
-    !Array.isArray(map.sources)
-  ) {
+/**
+ * Parse the text contents of a `.map` file into a source map. Returns null
+ * for invalid JSON, and for JSON that isn't a source map (missing version /
+ * mappings / sources, or malformed index map sections).
+ */
+export function parseSourceMapFileContents(text: string): SourceMap | null {
+  let parsed: unknown;
+  try {
+    parsed = JSON.parse(text);
+  } catch {
     return null;
   }
-
-  return parsed as RawSourceMap;
+  return _isSourceMap(parsed) ? parsed : null;
 }
 
 /**
@@ -158,7 +182,7 @@ function matchByBasename(
  * one, which we match unconditionally regardless of name.
  */
 export function matchSourceMapToSource(
-  map: RawSourceMap,
+  map: SourceMap,
   uploadedFileName: string,
   eligible: EligibleSource[]
 ): SourceMapMatchResult {

src/profile-logic/source-maps/store.ts

@@ -3,11 +3,16 @@
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
 import { SourceMapConsumer as LibSourceMapConsumer } from 'source-map';
-import type { RawSourceMap } from 'source-map';
+import type { RawIndexMap, RawSourceMap } from 'source-map';
 import type { IndexIntoSourceTable } from 'firefox-profiler/types';
 
 export type SourceMapConsumer = LibSourceMapConsumer;
 
+/**
+ * A parsed source map, either a regular one or an index map made of sections.
+ */
+export type SourceMap = RawSourceMap | RawIndexMap;
+
 /**
  * Holds pre-parsed SourceMapConsumer instances keyed by IndexIntoSourceTable.
  * Initialized from the resolvedSourceMaps already fetched at profile load time.
@@ -20,7 +25,7 @@ export class SourceMapStore {
   }
 
   static async create(
-    resolvedSourceMaps: Map<IndexIntoSourceTable, RawSourceMap>,
+    resolvedSourceMaps: Map<IndexIntoSourceTable, SourceMap>,
     wasmUrl: string
   ): Promise<SourceMapStore> {
     const consumers = new Map<IndexIntoSourceTable, SourceMapConsumer>();

src/profile-logic/source-maps/worker-types.ts

@@ -7,15 +7,15 @@ import type {
   IndexIntoFrameTable,
   IndexIntoSourceTable,
 } from 'firefox-profiler/types';
-import type { RawSourceMap } from 'source-map';
+import type { SourceMap } from './store';
 import type { SourceMapSymbolicationInput } from './symbolication';
 
 /**
  * Data sent from the main thread to the source map symbolication worker.
  * All values are structured-cloned (copied) across the thread boundary.
  */
 export type WorkerInput = SourceMapSymbolicationInput & {
-  resolvedSourceMaps: Map<IndexIntoSourceTable, RawSourceMap>;
+  resolvedSourceMaps: Map<IndexIntoSourceTable, SourceMap>;
   // Compiled source texts keyed by bundle source index.
   compiledSources: Map<IndexIntoSourceTable, string>;
 };

src/profile-query/function-annotate.ts

@@ -26,7 +26,7 @@ import {
 import { fetchAssembly } from 'firefox-profiler/utils/fetch-assembly';
 import { fetchSource } from 'firefox-profiler/utils/fetch-source';
 import type { ExternalCommunicationDelegate } from 'firefox-profiler/utils/query-api';
-import type { RawSourceMap } from 'source-map';
+import type { SourceMap } from 'firefox-profiler/profile-logic/source-maps/store';
 import type {
   Profile,
   IndexIntoFuncTable,
@@ -64,7 +64,7 @@ class NodeExternalCommunicationDelegate implements ExternalCommunicationDelegate
     throw new Error('No browser connection available in profiler-cli');
   }
 
-  async fetchSourceMapFromBrowser(_sourceId: string): Promise<RawSourceMap> {
+  async fetchSourceMapFromBrowser(_sourceId: string): Promise<SourceMap> {
     throw new Error('No browser connection available in profiler-cli');
   }
 }

src/test/unit/embed-js-sources.test.ts

@@ -129,6 +129,43 @@ describe('embedJsSources', function () {
     });
   });
 
+  it('applies an index source map', async function () {
+    // The bundle is a concatenation of two chunks, and the function is in the
+    // second one, on the bundle's second line.
+    const firstChunk = 'var c=1;';
+    const firstChunkMap = new SourceMapGenerator({ file: 'first.js' });
+    firstChunkMap.addMapping({
+      source: '../src/first.js',
+      original: { line: 1, column: 0 },
+      generated: { line: 1, column: 0 },
+    });
+    const indexMap = JSON.stringify({
+      version: 3,
+      file: 'bundle.js',
+      sections: [
+        { offset: { line: 0, column: 0 }, map: firstChunkMap.toJSON() },
+        { offset: { line: 1, column: 0 }, map: JSON.parse(buildSourceMap()) },
+      ],
+    });
+    const profile = makeProfile(BUNDLE_URL, { sourceMapURL: 'bundle.js.map' });
+    profile.shared.funcTable.lineNumber[0] = 2;
+    profile.shared.frameTable.line[0] = 2;
+    await embedJsSources(
+      profile,
+      makeReader({
+        [BUNDLE_URL]: firstChunk + '\n' + BUNDLE_SOURCE,
+        [BUNDLE_URL + '.map']: indexMap,
+      }),
+      runSourceMapSymbolicationNode
+    );
+    expect(getOriginalLocationOfFunc(profile)).toEqual({
+      name: 'greet',
+      filename: ORIGINAL_FILENAME,
+      line: 1,
+      content: ORIGINAL_SOURCE,
+    });
+  });
+
   it('falls back to the sourceMappingURL comment', async function () {
     const profile = makeProfile(BUNDLE_URL);
     const bundleWithComment =

src/test/unit/source-map-matching.test.ts

@@ -81,9 +81,35 @@ describe('parseSourceMapFileContents', function () {
     expect(parseSourceMapFileContents('null')).toBeNull();
   });
 
-  it('rejects index maps (with a sections field)', function () {
-    const indexMap = JSON.stringify({ version: 3, sections: [] });
-    expect(parseSourceMapFileContents(indexMap)).toBeNull();
+  it('parses an index map', function () {
+    const indexMap = {
+      version: 3,
+      file: 'bundle.js',
+      sections: [
+        { offset: { line: 0, column: 0 }, map: makeMap() },
+        { offset: { line: 10, column: 0 }, map: makeMap() },
+      ],
+    };
+    expect(parseSourceMapFileContents(JSON.stringify(indexMap))).toEqual(
+      indexMap
+    );
+  });
+
+  it('returns null for malformed index maps', function () {
+    const section = { offset: { line: 0, column: 0 }, map: makeMap() };
+    for (const indexMap of [
+      { version: 3, sections: 'not an array' },
+      { version: 3, sections: [{ ...section, offset: { line: 0 } }] },
+      { version: 3, sections: [{ ...section, map: { version: 3 } }] },
+      { version: 3, sections: [{ offset: section.offset, url: 'a.map' }] },
+      // Nested index maps are not allowed.
+      {
+        version: 3,
+        sections: [{ ...section, map: { version: 3, sections: [section] } }],
+      },
+    ]) {
+      expect(parseSourceMapFileContents(JSON.stringify(indexMap))).toBeNull();
+    }
   });
 });