makes asset saving use computed artifacts

fixes screenshots not being saved

lighthouse-core/lib/asset-saver.js

@@ -85,28 +85,53 @@ function saveArtifacts(artifacts, filename) {
   log.log('artifacts file saved to disk', artifactsFilename);
 }
 
+/**
+ * Filter traces and extract screenshots to prepare for saving.
+ * @param {!Object} options
+ * @param {!Artifacts} artifacts
+ * @return {!Promise<!Array<{traceData: !Object, html: string}>>}
+ */
 function prepareAssets(options, artifacts) {
-  const traceData = Object.keys(artifacts.traces).map(passName => {
-    const filteredTrace = Object.assign({}, artifacts.traces[passName]);
-    filteredTrace.traceEvents = filterForSize(filteredTrace.traceEvents);
-    return filteredTrace;
-  });
-  const html = screenshotDump(options, artifacts.ScreenshotFilmstrip);
-  return {traceData, html};
+  const passNames = Object.keys(artifacts.traces);
+  const assets = [];
+
+  return passNames.reduce((chain, passName) => {
+    const trace = artifacts.traces[passName];
+
+    return chain.then(_ => artifacts.requestScreenshots(trace))
+      .then(screenshots => {
+        const traceData = Object.assign({}, trace);
+        traceData.traceEvents = filterForSize(traceData.traceEvents);
+        const html = screenshotDump(options, screenshots);
+
+        assets.push({
+          traceData,
+          html
+        });
+      });
+  }, Promise.resolve())
+    .then(_ => assets);
 }
 
+/**
+ * Writes trace(s) and associated screenshot(s) to disk.
+ * @param {!Object} options
+ * @param {!Artifacts} artifacts
+ * @return {!Promise}
+ */
 function saveAssets(options, artifacts) {
-  const assets = prepareAssets(options, artifacts);
+  return prepareAssets(options, artifacts).then(assets => {
+    assets.forEach((data, index) => {
+      const filenamePrefix = getFilenamePrefix(options);
 
-  assets.traceData.forEach((data, index) => {
-    const traceFilename = getFilenamePrefix(options);
-    fs.writeFileSync(`${traceFilename}${index}.trace.json`, stringify(data, null, 2));
-    log.log('trace file saved to disk', traceFilename);
-  });
+      const traceData = data.traceData;
+      fs.writeFileSync(`${filenamePrefix}-${index}.trace.json`, stringify(traceData, null, 2));
+      log.log('trace file saved to disk', filenamePrefix);
 
-  const screenshotsFilename = getFilenamePrefix(options);
-  fs.writeFileSync(screenshotsFilename + '.screenshots.html', assets.html);
-  log.log('screenshots saved to disk', screenshotsFilename);
+      fs.writeFileSync(`${filenamePrefix}-${index}.screenshots.html`, data.html);
+      log.log('screenshots saved to disk', filenamePrefix);
+    });
+  });
 }
 
 module.exports = {

lighthouse-core/runner.js

@@ -80,13 +80,18 @@ class Runner {
 
       // Ignoring these two flags for coverage as this functionality is not exposed by the module.
       /* istanbul ignore next */
-      if (opts.flags.saveArtifacts || opts.flags.saveAssets) {
+      if (opts.flags.saveArtifacts) {
         run = run.then(artifacts => {
           opts.flags.saveArtifacts && assetSaver.saveArtifacts(artifacts);
-          opts.flags.saveAssets && assetSaver.saveAssets(opts, artifacts);
           return artifacts;
         });
       }
+      if (opts.flags.saveAssets) {
+        run = run.then(artifacts => {
+          return assetSaver.saveAssets(opts, artifacts)
+            .then(_ => artifacts);
+        });
+      }
 
       // Now run the audits.
       let auditResults = [];

lighthouse-core/test/lib/asset-saver-test.js

@@ -21,17 +21,25 @@ const assetSaver = require('../../lib/asset-saver');
 const assert = require('assert');
 const fs = require('fs');
 
-const ScreenshotFilmstrip = require('../fixtures/traces/screenshots.json');
+const screenshotFilmstrip = require('../fixtures/traces/screenshots.json');
 const traceEvents = require('../fixtures/traces/progressive-app.json');
 const Audit = require('../../audits/audit.js');
 
 /* eslint-env mocha */
 describe('asset-saver helper', () => {
   it('generates HTML', () => {
     const options = {url: 'https://testexample.com'};
-    const artifacts = {screenshots: [], traces: []};
-    const output = assetSaver.prepareAssets(options, artifacts);
-    assert.ok(/<!doctype/gim.test(output.html));
+    const artifacts = {
+      traces: {
+        [Audit.DEFAULT_PASS]: {
+          traceEvents: []
+        }
+      },
+      requestScreenshots: () => Promise.resolve([]),
+    };
+    return assetSaver.prepareAssets(options, artifacts).then(assets => {
+      assert.ok(/<!doctype/gim.test(assets[0].html));
+    });
   });
 
   describe('saves files to disk with real filenames', function() {
@@ -48,20 +56,20 @@ describe('asset-saver helper', () => {
           traceEvents
         }
       },
-      ScreenshotFilmstrip
+      requestScreenshots: () => Promise.resolve(screenshotFilmstrip)
     };
 
     assetSaver.saveAssets(options, artifacts);
 
     it('trace file saved to disk with data', () => {
-      const traceFilename = assetSaver.getFilenamePrefix(options) + '0.trace.json';
+      const traceFilename = assetSaver.getFilenamePrefix(options) + '-0.trace.json';
       const traceFileContents = fs.readFileSync(traceFilename, 'utf8');
       assert.ok(traceFileContents.length > 3000000);
       fs.unlinkSync(traceFilename);
     });
 
     it('screenshots file saved to disk with data', () => {
-      const ssFilename = assetSaver.getFilenamePrefix(options) + '.screenshots.html';
+      const ssFilename = assetSaver.getFilenamePrefix(options) + '-0.screenshots.html';
       const ssFileContents = fs.readFileSync(ssFilename, 'utf8');
       assert.ok(/<!doctype/gim.test(ssFileContents));
       assert.ok(ssFileContents.includes('{"timestamp":674089419.919'));