core: round metric savings to remove false precision (#15721)

GoogleChrome · Jan 4, 2024 · 4e4a835 · 4e4a835
1 parent dd8feb7
commit 4e4a835
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Showing 4 changed files with 73 additions and 26 deletions.
diff --git a/core/audits/audit.js b/core/audits/audit.js
@@ -10,6 +10,15 @@ import {Util} from '../../shared/util.js';
 
 const DEFAULT_PASS = 'defaultPass';
 
+/** @type {LH.Audit.MetricSavings} */
+const METRIC_SAVINGS_PRECISION = {
+  FCP: 50,
+  LCP: 50,
+  INP: 50,
+  TBT: 50,
+  CLS: 0.001,
+};
+
 /**
  * @typedef TableOptions
  * @property {number=} wastedMs
@@ -339,6 +348,33 @@ class Audit {
     return score;
   }
 
+  /**
+   * @param {LH.Audit.MetricSavings|undefined} metricSavings
+   * @return {LH.Audit.MetricSavings|undefined}
+   */
+  static _quantizeMetricSavings(metricSavings) {
+    if (!metricSavings) return;
+
+    /** @type {LH.Audit.MetricSavings} */
+    const normalizedMetricSavings = {...metricSavings};
+
+    for (const key of /** @type {Array<LH.Result.MetricAcronym>} */ (Object.keys(metricSavings))) {
+      let value = metricSavings[key];
+      if (value === undefined) continue;
+
+      value = Math.max(value, 0);
+
+      const precision = METRIC_SAVINGS_PRECISION[key];
+      if (precision !== undefined) {
+        value = Math.round(value / precision) * precision;
+      }
+
+      normalizedMetricSavings[key] = value;
+    }
+
+    return normalizedMetricSavings;
+  }
+
   /**
    * @param {typeof Audit} audit
    * @param {string | LH.IcuMessage} errorMessage
@@ -378,10 +414,13 @@ class Audit {
       scoreDisplayMode = product.scoreDisplayMode;
     }
 
+    const metricSavings = Audit._quantizeMetricSavings(product.metricSavings);
+    const hasSomeSavings = Object.values(metricSavings || {}).some(v => v);
+
     if (scoreDisplayMode === Audit.SCORING_MODES.METRIC_SAVINGS) {
       if (score && score >= Util.PASS_THRESHOLD) {
         score = 1;
-      } else if (Object.values(product.metricSavings || {}).some(v => v)) {
+      } else if (hasSomeSavings) {
         score = 0;
       } else {
         score = 0.5;
@@ -419,7 +458,7 @@ class Audit {
       errorStack: product.errorStack,
       warnings: product.warnings,
       scoringOptions: product.scoringOptions,
-      metricSavings: product.metricSavings,
+      metricSavings,
 
       details: product.details,
       guidanceLevel: audit.meta.guidanceLevel,

diff --git a/core/test/audits/audit-test.js b/core/test/audits/audit-test.js
@@ -178,6 +178,14 @@ describe('Audit', () => {
       assert.strictEqual(auditResult.score, 0.3);
     });
 
+    it('quantizes metric savings', () => {
+      const auditResult = Audit.generateAuditResult(PassOrFailAudit, {
+        score: 0,
+        metricSavings: {LCP: 0.1, FCP: 149, CLS: 0.0015, TBT: -100},
+      });
+      assert.deepStrictEqual(auditResult.metricSavings, {LCP: 0, FCP: 150, CLS: 0.002, TBT: 0});
+    });
+
     it('chooses the title if score is passing', () => {
       const auditResult = Audit.generateAuditResult(PassOrFailAudit, {score: 1});
       assert.strictEqual(auditResult.score, 1);

diff --git a/core/test/fixtures/user-flows/reports/sample-flow-result.json b/core/test/fixtures/user-flows/reports/sample-flow-result.json
@@ -529,7 +529,7 @@
             "numericUnit": "millisecond",
             "displayValue": "1.0 s",
             "metricSavings": {
-              "TBT": 143
+              "TBT": 150
             },
             "details": {
               "type": "table",
@@ -594,7 +594,7 @@
             "numericUnit": "millisecond",
             "displayValue": "0.3 s",
             "metricSavings": {
-              "TBT": 142.50196940171634
+              "TBT": 150
             },
             "details": {
               "type": "table",
@@ -1744,7 +1744,7 @@
             "scoreDisplayMode": "informative",
             "displayValue": "5 elements found",
             "metricSavings": {
-              "CLS": 0.002631263732910156
+              "CLS": 0.003
             },
             "details": {
               "type": "table",
@@ -1869,7 +1869,7 @@
             "scoreDisplayMode": "informative",
             "displayValue": "3 long tasks found",
             "metricSavings": {
-              "TBT": 143
+              "TBT": 150
             },
             "details": {
               "type": "table",
@@ -8996,7 +8996,7 @@
             "numericUnit": "millisecond",
             "displayValue": "0.9 s",
             "metricSavings": {
-              "TBT": 122.83299999999986
+              "TBT": 100
             },
             "details": {
               "type": "table",
@@ -9066,7 +9066,7 @@
             "numericUnit": "millisecond",
             "displayValue": "0.4 s",
             "metricSavings": {
-              "TBT": 106.76186411159928
+              "TBT": 100
             },
             "details": {
               "type": "table",
@@ -9874,7 +9874,7 @@
             "scoreDisplayMode": "metricSavings",
             "displayValue": "1 element found",
             "metricSavings": {
-              "CLS": 0.13125
+              "CLS": 0.131
             },
             "details": {
               "type": "table",
@@ -9923,7 +9923,7 @@
             "scoreDisplayMode": "informative",
             "displayValue": "1 long task found",
             "metricSavings": {
-              "TBT": 122.83299999999986
+              "TBT": 100
             },
             "details": {
               "type": "table",
@@ -10713,7 +10713,7 @@
             "scoreDisplayMode": "informative",
             "displayValue": "60 ms spent on event 'keypress'",
             "metricSavings": {
-              "INP": 64
+              "INP": 50
             },
             "details": {
               "type": "list",
@@ -18485,7 +18485,7 @@
             "numericUnit": "millisecond",
             "displayValue": "0.5 s",
             "metricSavings": {
-              "TBT": 13
+              "TBT": 0
             },
             "details": {
               "type": "table",
@@ -18550,7 +18550,7 @@
             "numericUnit": "millisecond",
             "displayValue": "0.2 s",
             "metricSavings": {
-              "TBT": 25.85177364864864
+              "TBT": 50
             },
             "details": {
               "type": "table",
@@ -19676,7 +19676,7 @@
             "scoreDisplayMode": "informative",
             "displayValue": "2 long tasks found",
             "metricSavings": {
-              "TBT": 13
+              "TBT": 0
             },
             "details": {
               "type": "table",
@@ -20988,7 +20988,7 @@
             "warnings": [],
             "metricSavings": {
               "FCP": 0,
-              "LCP": 330
+              "LCP": 350
             },
             "details": {
               "type": "opportunity",

diff --git a/core/test/results/sample_v2.json b/core/test/results/sample_v2.json
@@ -390,8 +390,8 @@
       "numericUnit": "millisecond",
       "displayValue": "Root document took 570 ms",
       "metricSavings": {
-        "FCP": 468.46799999999996,
-        "LCP": 468.46799999999996
+        "FCP": 450,
+        "LCP": 450
       },
       "details": {
         "type": "opportunity",
@@ -1106,7 +1106,7 @@
       "numericUnit": "millisecond",
       "displayValue": "2.2 s",
       "metricSavings": {
-        "TBT": 1220.691999999999
+        "TBT": 1200
       },
       "details": {
         "type": "table",
@@ -1171,7 +1171,7 @@
       "numericUnit": "millisecond",
       "displayValue": "1.3 s",
       "metricSavings": {
-        "TBT": 1209.4020894768312
+        "TBT": 1200
       },
       "details": {
         "type": "table",
@@ -2349,7 +2349,7 @@
       "scoreDisplayMode": "informative",
       "displayValue": "Third-party code blocked the main thread for 0 ms",
       "metricSavings": {
-        "TBT": 23.424291876693196
+        "TBT": 0
       },
       "details": {
         "type": "table",
@@ -2430,7 +2430,7 @@
       "scoreDisplayMode": "metricSavings",
       "displayValue": "13,320 ms",
       "metricSavings": {
-        "LCP": 10819.961
+        "LCP": 10800
       },
       "details": {
         "type": "list",
@@ -2530,7 +2530,7 @@
       "scoreDisplayMode": "metricSavings",
       "displayValue": "5 elements found",
       "metricSavings": {
-        "CLS": 0.13570762803819444
+        "CLS": 0.136
       },
       "details": {
         "type": "table",
@@ -2655,7 +2655,7 @@
       "scoreDisplayMode": "informative",
       "displayValue": "2 long tasks found",
       "metricSavings": {
-        "TBT": 1220.691999999999
+        "TBT": 1200
       },
       "details": {
         "type": "table",
@@ -4609,7 +4609,7 @@
       "warnings": [],
       "metricSavings": {
         "FCP": 0,
-        "LCP": 610
+        "LCP": 600
       },
       "details": {
         "type": "opportunity",
@@ -4919,7 +4919,7 @@
       "displayValue": "Potential savings of 143 KiB",
       "metricSavings": {
         "FCP": 150,
-        "LCP": 1060
+        "LCP": 1050
       },
       "details": {
         "type": "opportunity",
@@ -5195,7 +5195,7 @@
       "numericUnit": "element",
       "displayValue": "153 elements",
       "metricSavings": {
-        "TBT": 1
+        "TBT": 0
       },
       "details": {
         "type": "table",