From 3a0c62da351a6453ceda00b3bae267527b2815e2 Mon Sep 17 00:00:00 2001
From: Adam Raine <6752989+adamraine@users.noreply.github.com>
Date: Wed, 10 May 2023 16:31:43 -0700
Subject: [PATCH] core: add metric savings to audit result (#14997)

---
 core/audits/server-response-time.js                  |  7 ++++++-
 .../fraggle-rock/reports/sample-flow-result.json     | 12 ++++++++++--
 core/test/results/sample_v2.json                     |  6 +++++-
 types/lhr/audit-details.d.ts                         | 10 ++++++++++
 types/lhr/audit-result.d.ts                          |  2 ++
 5 files changed, 33 insertions(+), 4 deletions(-)

diff --git a/core/audits/server-response-time.js b/core/audits/server-response-time.js
index c0df87c657c1..a80dde34fa51 100644
--- a/core/audits/server-response-time.js
+++ b/core/audits/server-response-time.js
@@ -70,11 +70,16 @@ class ServerResponseTime extends Audit {
       {key: 'responseTime', valueType: 'timespanMs', label: str_(i18n.UIStrings.columnTimeSpent)},
     ];
 
+    const overallSavingsMs = Math.max(responseTime - TARGET_MS, 0);
     const details = Audit.makeOpportunityDetails(
       headings,
       [{url: mainResource.url, responseTime}],
-      {overallSavingsMs: responseTime - TARGET_MS}
+      {overallSavingsMs}
     );
+    details.metricSavings = {
+      FCP: overallSavingsMs,
+      LCP: overallSavingsMs,
+    };
 
     return {
       numericValue: responseTime,
diff --git a/core/test/fixtures/fraggle-rock/reports/sample-flow-result.json b/core/test/fixtures/fraggle-rock/reports/sample-flow-result.json
index 4d5ce46cdf97..098dd6b5ca9f 100644
--- a/core/test/fixtures/fraggle-rock/reports/sample-flow-result.json
+++ b/core/test/fixtures/fraggle-rock/reports/sample-flow-result.json
@@ -233,7 +233,11 @@
                   "responseTime": 19.687999999999988
                 }
               ],
-              "overallSavingsMs": -80.31200000000001
+              "overallSavingsMs": 0,
+              "metricSavings": {
+                "FCP": 0,
+                "LCP": 0
+              }
             }
           },
           "interactive": {
@@ -16685,7 +16689,11 @@
                   "responseTime": 10.263
                 }
               ],
-              "overallSavingsMs": -89.737
+              "overallSavingsMs": 0,
+              "metricSavings": {
+                "FCP": 0,
+                "LCP": 0
+              }
             }
           },
           "interactive": {
diff --git a/core/test/results/sample_v2.json b/core/test/results/sample_v2.json
index 4cc4e127b822..8bcae53c9ede 100644
--- a/core/test/results/sample_v2.json
+++ b/core/test/results/sample_v2.json
@@ -336,7 +336,11 @@
             "responseTime": 568.468
           }
         ],
-        "overallSavingsMs": 468.46799999999996
+        "overallSavingsMs": 468.46799999999996,
+        "metricSavings": {
+          "FCP": 468.46799999999996,
+          "LCP": 468.46799999999996
+        }
       }
     },
     "interactive": {
diff --git a/types/lhr/audit-details.d.ts b/types/lhr/audit-details.d.ts
index 17611dcf9baf..fc054c6913cf 100644
--- a/types/lhr/audit-details.d.ts
+++ b/types/lhr/audit-details.d.ts
@@ -15,6 +15,8 @@ interface BaseDetails {
   overallSavingsBytes?: number;
   /** Additional information, usually used for including debug or meta information in the LHR */
   debugData?: Details.DebugData;
+  /** Estimates of how much this audit affects various performance metrics. Values will be in the unit of the respective metrics. */
+  metricSavings?: Details.MetricSavings;
 }
 
 type Details =
@@ -303,6 +305,14 @@ declare module Details {
     value: number,
     granularity?: number,
   }
+
+  interface MetricSavings {
+    LCP?: number;
+    FCP?: number;
+    CLS?: number;
+    TBT?: number;
+    INP?: number;
+  }
 }
 
 export default Details;
diff --git a/types/lhr/audit-result.d.ts b/types/lhr/audit-result.d.ts
index b8285eca4bd9..48b3146740e4 100644
--- a/types/lhr/audit-result.d.ts
+++ b/types/lhr/audit-result.d.ts
@@ -50,6 +50,8 @@ export interface Result {
   id: string;
   /** A more detailed description that describes why the audit is important and links to Lighthouse documentation on the audit; markdown links supported. */
   description: string;
+  /** Estimates of how much this audit affects various performance metrics. Values will be in the unit of the respective metrics. */
+  metricSavings?: AuditDetails.MetricSavings;
   /** A numeric value that has a meaning specific to the audit, e.g. the number of nodes in the DOM or the timestamp of a specific load event. More information can be found in the audit details, if present. */
   numericValue?: number;
   /** The unit of `numericValue`, used when the consumer wishes to convert numericValue to a display string. */