report: use source maps to show original file name

lighthouse-core/audits/byte-efficiency/legacy-javascript.js

@@ -396,6 +396,23 @@ class LegacyJavascript extends ByteEfficiencyAudit {
     return transferRatio;
   }
 
+  /**
+   * @param {LH.Artifacts.Bundle} bundle
+   * @param {number} generatedLine
+   * @param {number} generatedColumn
+   * @return {LH.Audit.Details.SourceLocationValue['original']}
+   */
+  static _findOriginalLocation(bundle, generatedLine, generatedColumn) {
+    const entry = bundle && bundle.map.findEntry(generatedLine, generatedColumn);
+    if (!entry) return;
+
+    return {
+      file: entry.sourceURL || '',
+      line: entry.sourceLineNumber || 0,
+      column: entry.sourceColumnNumber || 0,
+    };
+  }
+
   /**
    * @param {LH.Artifacts} artifacts
    * @param {Array<LH.Artifacts.NetworkRequest>} networkRecords
@@ -434,8 +451,11 @@ class LegacyJavascript extends ByteEfficiencyAudit {
         // Not needed, but keeps typescript happy.
         totalBytes: 0,
       };
+
+      const bundle = bundles.find(bundle => bundle.script.src === url);
       for (const match of matches) {
         const {name, line, column} = match;
+
         /** @type {SubItem} */
         const subItem = {
           signal: name,
@@ -444,6 +464,7 @@ class LegacyJavascript extends ByteEfficiencyAudit {
             url,
             line,
             column,
+            original: bundle && this._findOriginalLocation(bundle, line, column),
             urlProvider: 'network',
           },
         };

lighthouse-core/report/html/renderer/details-renderer.js

@@ -144,7 +144,7 @@ class DetailsRenderer {
 
   /**
    * @param {{text: string, url: string}} details
-   * @return {Element}
+   * @return {HTMLElement}
    */
   _renderLink(details) {
     const allowedProtocols = ['https:', 'http:'];
@@ -550,22 +550,39 @@ class DetailsRenderer {
     }
 
     // Lines are shown as one-indexed.
-    const line = item.line + 1;
-    const column = item.column;
+    const generatedLocation = `${item.url}:${item.line + 1}:${item.column}`;
+    let sourceMappedOriginalLocation;
+    if (item.original) {
+      const file = item.original.file || '<unmapped>';
+      sourceMappedOriginalLocation = `${file}:${item.original.line + 1}:${item.original.column}`;
+    }
 
+    // We render slightly differently based on presence of source map and provenance of URL.
     let element;
-    if (item.urlProvider === 'network') {
+    if (item.urlProvider === 'network' && sourceMappedOriginalLocation) {
+      element = this._renderLink({
+        url: item.url,
+        text: sourceMappedOriginalLocation,
+      });
+      element.title = `maps to generated location ${generatedLocation}`;
+    } else if (item.urlProvider === 'network' && !sourceMappedOriginalLocation) {
       element = this.renderTextURL(item.url);
-      this._dom.find('.lh-link', element).textContent += `:${line}:${column}`;
+      this._dom.find('.lh-link', element).textContent += `:${item.line + 1}:${item.column}`;
+    } else if (item.urlProvider === 'comment' && sourceMappedOriginalLocation) {
+      element = this._renderText(`${sourceMappedOriginalLocation} (from source map)`);
+      element.title = `${generatedLocation} (from sourceURL)`;
+    } else if (item.urlProvider === 'comment' && !sourceMappedOriginalLocation) {
+      element = this._renderText(`${generatedLocation} (from sourceURL)`);
     } else {
-      element = this._renderText(`${item.url}:${line}:${column} (from sourceURL)`);
+      return null;
     }
 
     element.classList.add('lh-source-location');
     element.setAttribute('data-source-url', item.url);
     // DevTools expects zero-indexed lines.
     element.setAttribute('data-source-line', String(item.line));
     element.setAttribute('data-source-column', String(item.column));
+
     return element;
   }
 

lighthouse-core/test/audits/byte-efficiency/legacy-javascript-test.js

@@ -102,6 +102,7 @@ describe('LegacyJavaScript audit', () => {
               "location": Object {
                 "column": 0,
                 "line": 0,
+                "original": undefined,
                 "type": "source-location",
                 "url": "https://www.googletagmanager.com/a.js",
                 "urlProvider": "network",

lighthouse-core/test/report/html/renderer/details-renderer-test.js

@@ -491,6 +491,37 @@ describe('DetailsRenderer', () => {
       assert.equal(sourceLocationEl.getAttribute('data-source-column'), `${sourceLocation.column}`);
     });
 
+    it('renders source-location values using source map data', () => {
+      const sourceLocation = {
+        type: 'source-location',
+        url: 'https://www.example.com/script.js',
+        urlProvider: 'network',
+        line: 10,
+        column: 5,
+        original: {
+          file: 'main.js',
+          line: 100,
+          column: 10,
+        },
+      };
+      const details = {
+        type: 'table',
+        headings: [{key: 'content', itemType: 'source-location', text: 'Heading'}],
+        items: [{content: sourceLocation}],
+      };
+
+      const el = renderer.render(details);
+      const sourceLocationEl = el.querySelector('.lh-source-location.lh-link');
+      assert.strictEqual(sourceLocationEl.localName, 'a');
+      assert.equal(sourceLocationEl.href, 'https://www.example.com/script.js');
+      assert.equal(sourceLocationEl.textContent, 'main.js:101:10');
+      assert.equal(sourceLocationEl.title, 'maps to generated location https://www.example.com/script.js:11:5');
+      // DevTools should still use the generated location.
+      assert.equal(sourceLocationEl.getAttribute('data-source-url'), sourceLocation.url);
+      assert.equal(sourceLocationEl.getAttribute('data-source-line'), `${sourceLocation.line}`);
+      assert.equal(sourceLocationEl.getAttribute('data-source-column'), `${sourceLocation.column}`);
+    });
+
     it('renders source-location with lh-link class for relative url', () => {
       const sourceLocation = {
         type: 'source-location',

types/audit-details.d.ts

@@ -218,12 +218,23 @@ declare global {
        */
       export interface SourceLocationValue {
         type: 'source-location';
-        /** urls from the network are always valid urls. otherwise, urls come from either a comment or header, and may not be well-formed. */
+        /** A "url" representing the source file. May not be a valid URL, see `urlProvider`. */
         url: string;
-        /** 'network' when the url is the actual, observed resource url. 'comment' when the url comes from a sourceMapURL comment or X-SourceMap header */
+        /**
+         * - `network` when the url is the actual, observed resource url. This is always a valid URL.
+         * - `comment` when the url comes from a sourceURL comment. This could be anything, really.
+         */
         urlProvider: 'network' | 'comment';
+        /** Zero-indexed. */
         line: number;
         column: number;
+        /** The original file location from the source map. */
+        original?: {
+          /** The relevant file from the map's `sources` array. */
+          file: string;
+          line: number;
+          column: number;
+        };
       }
 
       /**