Extract shared isRegression() to deduplicate hybrid coverage check

andimarek · claude · andimarek · commit a12be23714ca · 2026-03-10T08:12:56.000+10:00
The hybrid regression check (percentage drop + missed count increase)
was duplicated between pull_request.yml and pr-report.yml. Extract it
into parse-jacoco.js and update both workflows. The PR report now shows
🟡 instead of 🔴 for classes where coverage percentage dropped but
missed count did not increase (e.g. code extraction/refactoring).

Co-Authored-By: Claude Opus 4.6 &lt;noreply@anthropic.com&gt;
diff --git a/.github/scripts/parse-jacoco.js b/.github/scripts/parse-jacoco.js
@@ -92,4 +92,12 @@ function pct(covered, missed) {
   return total === 0 ? 0 : (covered / total * 100);
 }
 
-module.exports = { parseJacocoXml, pct, zeroCov };
+// A coverage metric is a "real regression" when BOTH the percentage drops
+// beyond the tolerance AND the absolute number of missed items increases.
+// This avoids false positives when well-covered code is extracted/moved out
+// of a class (which lowers the percentage without actually losing coverage).
+function isRegression(currPct, basePct, currMissed, baseMissed, tolerance = 0.05) {
+  return currPct < basePct - tolerance && currMissed > baseMissed;
+}
+
+module.exports = { parseJacocoXml, pct, zeroCov, isRegression };
diff --git a/.github/workflows/pr-report.yml b/.github/workflows/pr-report.yml
@@ -64,7 +64,7 @@ jobs:
             }
             console.log(`Posting report for PR #${prNumber}`);
 
-            const { parseJacocoXml, pct, zeroCov } = require('./.github/scripts/parse-jacoco.js');
+            const { parseJacocoXml, pct, zeroCov, isRegression } = require('./.github/scripts/parse-jacoco.js');
 
             const versions = ['java11', 'java17', 'java21', 'java25', 'jcstress'];
             const zeroTest = { total: 0, passed: 0, failed: 0, errors: 0, skipped: 0 };
@@ -232,20 +232,25 @@ jobs:
                 return result.replace(/\$/g, '<br>\\$');
               }
 
-              function fmtClassDelta(delta) {
-                return fmtPctDelta(delta, 0);
+              function fmtClassDelta(delta, currMissed, baseMissed) {
+                if (Math.abs(delta) < 0.05) return '±0.0%';
+                const str = delta > 0 ? `+${delta.toFixed(1)}%` : `${delta.toFixed(1)}%`;
+                if (delta > 0) return str + ' 🟢';
+                // Negative delta: use hybrid check — only 🔴 if missed count also increased
+                if (currMissed !== undefined && baseMissed !== undefined && currMissed <= baseMissed) {
+                  return str + ' 🟡';
+                }
+                return str + ' 🔴';
               }
 
               // Build a method-level detail block for classes with coverage decreases.
               // Uses method name+desc as a stable key to match between baseline and current.
               function buildMethodDetails(c) {
                 if (c.removed) return '';
-                // Use the same hybrid check as the coverage gate: percentage
-                // dropped AND absolute missed count increased. This avoids
-                // showing details for classes where code was merely extracted/moved.
-                const lineRegressed = c.lineDelta < -0.05 && c.currMissed.line > c.baseMissed.line;
-                const branchRegressed = c.branchDelta < -0.05 && c.currMissed.branch > c.baseMissed.branch;
-                const methodRegressed = c.methodDelta < -0.05 && c.currMissed.method > c.baseMissed.method;
+                // Only show method details for true regressions (hybrid check)
+                const lineRegressed = isRegression(c.linePct, c.linePct - c.lineDelta, c.currMissed.line, c.baseMissed.line);
+                const branchRegressed = isRegression(c.branchPct, c.branchPct - c.branchDelta, c.currMissed.branch, c.baseMissed.branch);
+                const methodRegressed = isRegression(c.methodPct, c.methodPct - c.methodDelta, c.currMissed.method, c.baseMissed.method);
                 if (!lineRegressed && !branchRegressed && !methodRegressed) return '';
 
                 const currMethods = c.currMethods || [];
@@ -328,7 +333,7 @@ jobs:
                   if (c.removed) {
                     body += `| ${shortenClass(c.name)} | *removed* | *removed* | *removed* |\n`;
                   } else {
-                    body += `| ${shortenClass(c.name)} | ${fmtClassDelta(c.lineDelta)} | ${fmtClassDelta(c.branchDelta)} | ${fmtClassDelta(c.methodDelta)} |\n`;
+                    body += `| ${shortenClass(c.name)} | ${fmtClassDelta(c.lineDelta, c.currMissed.line, c.baseMissed.line)} | ${fmtClassDelta(c.branchDelta, c.currMissed.branch, c.baseMissed.branch)} | ${fmtClassDelta(c.methodDelta, c.currMissed.method, c.baseMissed.method)} |\n`;
                   }
                 }
                 body += '\n';
diff --git a/.github/workflows/pull_request.yml b/.github/workflows/pull_request.yml
@@ -132,7 +132,7 @@ jobs:
           script: |
             const fs = require('fs');
             const path = require('path');
-            const { parseJacocoXml, pct, zeroCov } = require('./.github/scripts/parse-jacoco.js');
+            const { parseJacocoXml, pct, zeroCov, isRegression } = require('./.github/scripts/parse-jacoco.js');
 
             // --- Read baseline from repo ---
             const baselineFile = 'test-baseline.json';
@@ -165,7 +165,7 @@ jobs:
                 const basePct = pct(base[key].covered, base[key].missed);
                 const currMissed = curr[key].missed;
                 const baseMissed = base[key].missed;
-                if (currPct < basePct - 0.05 && currMissed > baseMissed) {
+                if (isRegression(currPct, basePct, currMissed, baseMissed)) {
                   classRegressions.push(`  ${cls} ${metric}: ${currPct.toFixed(1)}% (was ${basePct.toFixed(1)}%, delta ${(currPct - basePct).toFixed(1)}%, missed: ${currMissed} was ${baseMissed})`);
                 }
               }
