core(js-bundles): return error object when sizes cannot be determined

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

@@ -104,15 +104,20 @@ class UnusedJavaScript extends ByteEfficiencyAudit {
       };
 
       if (item.wastedBytes <= unusedThreshold) continue;
+      items.push(item);
+
+      // If there was an error calculating the bundle sizes, we can't
+      // create any sub-items.
+      if (!bundle || 'errorMessage' in bundle.sizes) continue;
+      const sizes = bundle.sizes;
 
       // Augment with bundle data.
-      if (bundle && unusedJsSummary.sourcesWastedBytes) {
+      if (unusedJsSummary.sourcesWastedBytes) {
         const topUnusedSourceSizes = Object.entries(unusedJsSummary.sourcesWastedBytes)
           .sort((a, b) => b[1] - a[1])
           .slice(0, 5)
           .map(([source, unused]) => {
-            const total =
-              source === '(unmapped)' ? bundle.sizes.unmappedBytes : bundle.sizes.files[source];
+            const total = source === '(unmapped)' ? sizes.unmappedBytes : sizes.files[source];
             return {
               source,
               unused: Math.round(unused * transferRatio),
@@ -133,8 +138,6 @@ class UnusedJavaScript extends ByteEfficiencyAudit {
           }),
         };
       }
-
-      items.push(item);
     }
 
     return {

lighthouse-core/computed/js-bundles.js

@@ -22,10 +22,6 @@ function computeGeneratedFileSizes(map, content) {
   const totalBytes = content.length;
   let unmappedBytes = totalBytes;
 
-  // If the map + contents don't line up, return a result that
-  // denotes nothing is mapped.
-  const failureResult = {files: {}, unmappedBytes, totalBytes};
-
   // @ts-expect-error: This function is added in SDK.js. This will eventually be added to CDT.
   map.computeLastGeneratedColumns();
 
@@ -43,23 +39,27 @@ function computeGeneratedFileSizes(map, content) {
     // Lines and columns are zero-based indices. Visually, lines are shown as a 1-based index.
 
     const line = lines[lineNum];
-    if (line === null) {
-      log.error('JSBundles', `${map.url()} mapping for line out of bounds: ${lineNum + 1}`);
-      return failureResult;
+    if (line === null || line === undefined) {
+      const errorMessage = `${map.url()} mapping for line out of bounds: ${lineNum + 1}`;
+      log.error('JSBundles', errorMessage);
+      return {errorMessage};
     }
 
     if (colNum > line.length) {
-      // eslint-disable-next-line max-len
-      log.error('JSBundles', `${map.url()} mapping for column out of bounds: ${lineNum + 1}:${colNum}`);
-      return failureResult;
+      const errorMessage =
+        `${map.url()} mapping for column out of bounds: ${lineNum + 1}:${colNum}`;
+      log.error('JSBundles', errorMessage);
+      return {errorMessage};
     }
 
     let mappingLength = 0;
     if (lastColNum !== undefined) {
       if (lastColNum > line.length) {
         // eslint-disable-next-line max-len
-        log.error('JSBundles', `${map.url()} mapping for last column out of bounds: ${lineNum + 1}:${lastColNum}`);
-        return failureResult;
+        const errorMessage =
+          `${map.url()} mapping for last column out of bounds: ${lineNum + 1}:${lastColNum}`;
+        log.error('JSBundles', errorMessage);
+        return {errorMessage};
       }
       mappingLength = lastColNum - colNum;
     } else {

lighthouse-core/computed/module-duplication.js

@@ -91,6 +91,8 @@ class ModuleDuplication {
 
     // Determine size of each `sources` entry.
     for (const {rawMap, sizes} of bundles) {
+      if ('errorMessage' in sizes) continue;
+
       /** @type {SourceData[]} */
       const sourceDataArray = [];
       sourceDatasMap.set(rawMap, sourceDataArray);

lighthouse-core/scripts/legacy-javascript/create-polyfill-size-estimation.js

@@ -88,6 +88,7 @@ async function main() {
     SourceMaps: [{scriptUrl: '', map: bundleMap}],
   };
   const bundles = await JsBundles.compute_(artifacts);
+  if ('errorMessage' in bundles[0].sizes) throw new Error(bundles[0].sizes.errorMessage);
   const bundleFileSizes = bundles[0].sizes.files;
 
   const allModules = Object.keys(bundleFileSizes).filter(s => s.startsWith('node_modules'));

lighthouse-core/test/computed/js-bundles-test.js

@@ -292,9 +292,7 @@ describe('JsBundles computed artifact', () => {
             "sourceURL": "src/foo.js",
           },
           "sizes": Object {
-            "files": Object {},
-            "totalBytes": 13,
-            "unmappedBytes": 13,
+            "errorMessage": "compiled.js.map mapping for last column out of bounds: 1:14",
           },
         }
       `);
@@ -314,9 +312,7 @@ describe('JsBundles computed artifact', () => {
             "sourceURL": "src/foo.js",
           },
           "sizes": Object {
-            "files": Object {},
-            "totalBytes": 0,
-            "unmappedBytes": 0,
+            "errorMessage": "compiled.js.map mapping for column out of bounds: 1:1",
           },
         }
       `);
@@ -347,5 +343,46 @@ describe('JsBundles computed artifact', () => {
         }
       `);
     });
+
+    it('emits error when column out of bounds', async () => {
+      const newMappings = map.mappings.split(',');
+      expect(newMappings[1]).toBe('SAAAA');
+      // Make the column offset very big, force out of bounds.
+      // See https://www.mattzeunert.com/2016/02/14/how-do-source-maps-work.html
+      newMappings[1] = 'kD' + 'AAAA';
+      map.mappings = newMappings.join(',');
+      expect(await test()).toMatchInlineSnapshot(`
+        Object {
+          "entry": SourceMapEntry {
+            "columnNumber": 642,
+            "lastColumnNumber": 651,
+            "lineNumber": 0,
+            "name": undefined,
+            "sourceColumnNumber": 18,
+            "sourceLineNumber": 1,
+            "sourceURL": "src/foo.js",
+          },
+          "sizes": Object {
+            "errorMessage": "compiled.js.map mapping for last column out of bounds: 1:685",
+          },
+        }
+      `);
+    });
+
+    it('emits error when line out of bounds', async () => {
+      const newMappings = map.mappings.split(',');
+      expect(newMappings[1]).toBe('SAAAA');
+      // Make the line offset very big, force out of bounds.
+      // See https://sourcemaps.info/spec.html#:~:text=broken%20down%20as%20follows
+      map.mappings = ';'.repeat(10) + map.mappings;
+      expect(await test()).toMatchInlineSnapshot(`
+        Object {
+          "entry": null,
+          "sizes": Object {
+            "errorMessage": "compiled.js.map mapping for line out of bounds: 11",
+          },
+        }
+      `);
+    });
   });
 });

types/artifacts.d.ts

@@ -326,7 +326,7 @@ declare global {
           files: Record<string, number>;
           unmappedBytes: number;
           totalBytes: number;
-        };
+        } | {errorMessage: string};
       }
 
       /** @see https://developer.mozilla.org/en-US/docs/Web/HTML/Element/a#Attributes */