core: correctly truncate unicode strings

cli/test/smokehouse/test-definitions/byte-efficiency.js

@@ -192,12 +192,12 @@ const expectations = {
             },
             {
               // /some-custom-url.js,
-              url: 'inline: \n  function unusedFunction() {\n    // Un...',
+              url: 'inline: \n  function unusedFunction() {\n    // U…',
               wastedBytes: '6690 +/- 100',
               wastedPercent: '99.6 +/- 0.1',
             },
             {
-              url: 'inline: \n  // Used block #1\n  // FILLER DATA JUS...',
+              url: 'inline: \n  // Used block #1\n  // FILLER DATA JU…',
               wastedBytes: '6569 +/- 100',
               wastedPercent: 100,
             },

core/audits/audit.js

@@ -225,7 +225,7 @@ class Audit {
       const lineNumber = lineIndex + 1;
       /** @type LH.Audit.Details.SnippetValue['lines'][0] */
       const lineDetail = {
-        content: line.slice(0, maxLineLength),
+        content: Util.truncate(line, maxLineLength),
         lineNumber,
       };
       if (line.length > maxLineLength) {

core/audits/byte-efficiency/unminified-javascript.js

@@ -8,6 +8,7 @@ import {ByteEfficiencyAudit} from './byte-efficiency-audit.js';
 import * as i18n from '../../lib/i18n/i18n.js';
 import {computeJSTokenLength as computeTokenLength} from '../../lib/minification-estimator.js';
 import {getRequestForScript, isInline} from '../../lib/script-helpers.js';
+import {Util} from '../../../shared/util.js';
 
 const UIStrings = {
   /** Imperative title of a Lighthouse audit that tells the user to minify the page’s JS code to reduce file size. This is displayed in a list of audit titles that Lighthouse generates. */
@@ -84,7 +85,7 @@ class UnminifiedJavaScript extends ByteEfficiencyAudit {
       const networkRecord = getRequestForScript(networkRecords, script);
 
       const displayUrl = isInline(script) ?
-        `inline: ${script.content.substring(0, 40)}...` :
+        `inline: ${Util.truncate(script.content, 40)}` :
         script.url;
       try {
         const result = UnminifiedJavaScript.computeWaste(script.content, displayUrl, networkRecord);

core/computed/unused-css.js

@@ -7,6 +7,7 @@
 import {makeComputedArtifact} from './computed-artifact.js';
 import {ByteEfficiencyAudit} from '../audits/byte-efficiency/byte-efficiency-audit.js';
 import {NetworkRecords} from './network-records.js';
+import {Util} from '../../shared/util.js';
 
 const PREVIEW_LENGTH = 100;
 
@@ -87,8 +88,7 @@ class UnusedCSS {
    * @return {string}
    */
   static determineContentPreview(content) {
-    let preview = (content || '')
-        .slice(0, PREVIEW_LENGTH * 5)
+    let preview = Util.truncate(content || '', PREVIEW_LENGTH * 5, '')
         .replace(/( {2,}|\t)+/g, '  ') // remove leading indentation if present
         .replace(/\n\s+}/g, '\n}') // completely remove indentation of closing braces
         .trim(); // trim the leading whitespace
@@ -101,16 +101,17 @@ class UnusedCSS {
           firstRuleStart > firstRuleEnd ||
           firstRuleStart > PREVIEW_LENGTH) {
         // We couldn't determine the first rule-set or it's not within the preview
-        preview = preview.slice(0, PREVIEW_LENGTH) + '...';
+        preview = Util.truncate(preview, PREVIEW_LENGTH);
       } else if (firstRuleEnd < PREVIEW_LENGTH) {
         // The entire first rule-set fits within the preview
-        preview = preview.slice(0, firstRuleEnd + 1) + ' ...';
+        preview = preview.slice(0, firstRuleEnd + 1) + ' …';
       } else {
         // The first rule-set doesn't fit within the preview, just show as many as we can
-        const lastSemicolonIndex = preview.slice(0, PREVIEW_LENGTH).lastIndexOf(';');
+        const truncated = Util.truncate(preview, PREVIEW_LENGTH, '');
+        const lastSemicolonIndex = truncated.lastIndexOf(';');
         preview = lastSemicolonIndex < firstRuleStart ?
-            preview.slice(0, PREVIEW_LENGTH) + '... } ...' :
-            preview.slice(0, lastSemicolonIndex + 1) + ' ... } ...';
+            truncated + '… } …' :
+            preview.slice(0, lastSemicolonIndex + 1) + ' … } …';
       }
     }
 

core/gather/driver/prepare.js

@@ -167,10 +167,23 @@ async function prepareTargetForTimespanMode(driver, settings) {
     disableThrottling: false,
     blockedUrlPatterns: undefined,
   });
+  await warmUpIntlSegmenter(driver);
 
   log.timeEnd(status);
 }
 
+/**
+ * Ensure the `Intl.Segmenter` created in `pageFunctions.truncate` is cached by v8 before
+ * recording the trace begins.
+ *
+ * @param {LH.Gatherer.FRTransitionalDriver} driver
+ */
+async function warmUpIntlSegmenter(driver) {
+  await driver.executionContext.evaluate(pageFunctions.truncate, {
+    args: ['aaa', 2],
+  });
+}
+
 /**
  * Prepares a target to be analyzed in navigation mode by enabling protocol domains, emulation, and new document
  * handlers for global APIs or error handling.
@@ -197,6 +210,8 @@ async function prepareTargetForNavigationMode(driver, settings) {
     await shimRequestIdleCallbackOnNewDocument(driver, settings);
   }
 
+  await warmUpIntlSegmenter(driver);
+
   log.timeEnd(status);
 }
 

core/lib/page-functions.js

@@ -4,6 +4,8 @@
  * Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License.
  */
 
+import {Util} from '../../shared/util.js';
+
 /**
  * @fileoverview
  * Helper functions that are passed by `toString()` by Driver to be evaluated in target page.
@@ -132,10 +134,9 @@ function getOuterHTMLSnippet(element, ignoreAttrs = [], snippetCharacterLimit =
       }
 
       // Elide attribute value if too long.
-      if (attributeValue.length > ATTRIBUTE_CHAR_LIMIT) {
-        attributeValue = attributeValue.slice(0, ATTRIBUTE_CHAR_LIMIT - 1) + '…';
-        dirty = true;
-      }
+      const truncatedString = truncate(attributeValue, ATTRIBUTE_CHAR_LIMIT);
+      if (truncatedString !== attributeValue) dirty = true;
+      attributeValue = truncatedString;
 
       if (dirty) {
         // Style attributes can be blocked by the CSP if they are set via `setAttribute`.
@@ -372,22 +373,6 @@ function isPositionFixed(element) {
  * @return {string | null}
  */
 function getNodeLabel(element) {
-  // Inline so that audits that import getNodeLabel don't
-  // also need to import truncate
-  /**
-   * @param {string} str
-   * @param {number} maxLength
-   * @return {string}
-   */
-  function truncate(str, maxLength) {
-    if (str.length <= maxLength) {
-      return str;
-    }
-    // Take advantage of string iterator multi-byte character awareness.
-    // Regular `.slice` will ignore unicode character boundaries and lead to malformed text.
-    return Array.from(str).slice(0, maxLength - 1).join('') + '…';
-  }
-
   const tagName = element.tagName.toLowerCase();
   // html and body content is too broad to be useful, since they contain all page content
   if (tagName !== 'html' && tagName !== 'body') {
@@ -518,14 +503,47 @@ function getNodeDetails(element) {
   return details;
 }
 
+/**
+ *
+ * @param {string} string
+ * @param {number} characterLimit
+ * @return {string}
+ */
+function truncate(string, characterLimit) {
+  return Util.truncate(string, characterLimit);
+}
+
+/** @type {string} */
+const truncateRawString = truncate.toString();
+truncate.toString = () => `function truncate(string, characterLimit) {
+  const Util = { ${Util.truncate} };
+  return (${truncateRawString})(string, characterLimit);
+}`;
+
+/** @type {string} */
+const getNodeLabelRawString = getNodeLabel.toString();
+getNodeLabel.toString = () => `function getNodeLabel(element) {
+  ${truncate};
+  return (${getNodeLabelRawString})(element);
+}`;
+
+/** @type {string} */
+const getOuterHTMLSnippetRawString = getOuterHTMLSnippet.toString();
+// eslint-disable-next-line max-len
+getOuterHTMLSnippet.toString = () => `function getOuterHTMLSnippet(element, ignoreAttrs = [], snippetCharacterLimit = 500) {
+  ${truncate};
+  return (${getOuterHTMLSnippetRawString})(element, ignoreAttrs, snippetCharacterLimit);
+}`;
+
 /** @type {string} */
 const getNodeDetailsRawString = getNodeDetails.toString();
 getNodeDetails.toString = () => `function getNodeDetails(element) {
+  ${truncate};
   ${getNodePath};
   ${getNodeSelector};
   ${getBoundingClientRect};
-  ${getOuterHTMLSnippet};
-  ${getNodeLabel};
+  ${getOuterHTMLSnippetRawString};
+  ${getNodeLabelRawString};
   return (${getNodeDetailsRawString})(element);
 }`;
 
@@ -541,4 +559,5 @@ export const pageFunctions = {
   isPositionFixed,
   wrapRequestIdleCallback,
   getBoundingClientRect,
+  truncate,
 };

core/lib/url-utils.js

@@ -138,7 +138,7 @@ class UrlUtils {
   static elideDataURI(url) {
     try {
       const parsed = new URL(url);
-      return parsed.protocol === 'data:' ? url.slice(0, 100) : url;
+      return parsed.protocol === 'data:' ? Util.truncate(url, 100) : url;
     } catch (e) {
       return url;
     }

core/test/computed/unused-css-test.js

@@ -6,6 +6,8 @@
 
 import assert from 'assert/strict';
 
+import {expect} from 'expect';
+
 import {UnusedCSS} from '../../computed/unused-css.js';
 
 describe('UnusedCSS computed artifact', () => {
@@ -22,7 +24,7 @@ describe('UnusedCSS computed artifact', () => {
   describe('#determineContentPreview', () => {
     function assertLinesContained(actual, expected) {
       expected.split('\n').forEach(line => {
-        assert.ok(actual.includes(line.trim()), `${line} is found in preview`);
+        expect(actual).toContain(line.trim());
       });
     }
 
@@ -50,7 +52,7 @@ describe('UnusedCSS computed artifact', () => {
       assertLinesContained(preview(longContent), `
             body {
               color: white;
-            } ...
+            } …
           `.trim());
     });
 
@@ -66,7 +68,7 @@ describe('UnusedCSS computed artifact', () => {
       assertLinesContained(preview(longContent), `
             body {
               color: white;
-              font-size: 20px; ... } ...
+              font-size: 20px; … } …
           `.trim());
     });
 
@@ -77,7 +79,7 @@ describe('UnusedCSS computed artifact', () => {
            */
           `.trim();
 
-      assert.ok(/aaa\.\.\./.test(preview(longContent)));
+      assert.ok(/aaa…/.test(preview(longContent)));
     });
   });
 

shared/test/util-test.js

@@ -211,4 +211,26 @@ describe('util helpers', () => {
       ]);
     });
   });
+
+  describe('truncate', () => {
+    it('truncates based on visual characters', () => {
+      expect(Util.truncate('aaa', 30)).toEqual('aaa');
+      expect(Util.truncate('aaa', 3)).toEqual('aaa');
+      expect(Util.truncate('aaa', 2)).toEqual('a…');
+      expect(Util.truncate('aaa🥳', 4)).toEqual('aaa🥳');
+      expect(Util.truncate('aaa🥳', 3)).toEqual('aa…');
+      expect(Util.truncate('aaa👨‍👨‍👦‍👦', 4)).toEqual('aaa👨‍👨‍👦‍👦');
+      expect(Util.truncate('aaa👨‍👨‍👦‍👦', 3)).toEqual('aa…');
+      expect(Util.truncate('देवनागरी', 5)).toEqual('देवनागरी');
+      expect(Util.truncate('देवनागरी', 4)).toEqual('देवना…');
+
+      expect(Util.truncate('aaa', 3, '')).toEqual('aaa');
+      expect(Util.truncate('aaa', 2, '')).toEqual('aa');
+
+      expect(Util.truncate('aaaaa', 5, '...')).toEqual('aaaaa');
+      expect(Util.truncate('aaaaa', 4, '...')).toEqual('a...');
+      expect(Util.truncate('aaaaa', 3, '...')).toEqual('...');
+      expect(Util.truncate('aaaaa', 1, '...')).toEqual('...');
+    });
+  });
 });

shared/tsconfig.json

@@ -2,7 +2,7 @@
   "extends": "../tsconfig-base.json",
   "compilerOptions": {
     // Limit defs to base JS.
-    "lib": ["es2020"],
+    "lib": ["es2020", "es2022.intl"],
     // Only include `@types/node` from node_modules/.
     "types": ["node"],
     // "listFiles": true,

shared/util.js

@@ -153,6 +153,39 @@ class Util {
     return segments;
   }
 
+  /**
+   * @param {string} string
+   * @param {number} characterLimit
+   * @param {string} ellipseSuffix
+   */
+  static truncate(string, characterLimit, ellipseSuffix = '…') {
+    // Early return for the case where there are fewer bytes than the character limit.
+    if (string.length <= characterLimit) {
+      return string;
+    }
+
+    const segmenter = new Intl.Segmenter(undefined, {granularity: 'grapheme'});
+    const iterator = segmenter.segment(string)[Symbol.iterator]();
+
+    let lastSegmentIndex = 0;
+    for (let i = 0; i <= characterLimit - ellipseSuffix.length; i++) {
+      const result = iterator.next();
+      if (result.done) {
+        return string;
+      }
+
+      lastSegmentIndex = result.value.index;
+    }
+
+    for (let i = 0; i < ellipseSuffix.length; i++) {
+      if (iterator.next().done) {
+        return string;
+      }
+    }
+
+    return string.slice(0, lastSegmentIndex) + ellipseSuffix;
+  }
+
   /**
    * @param {URL} parsedUrl
    * @param {{numPathParts?: number, preserveQuery?: boolean, preserveHost?: boolean}=} options