feat(evals): add PR impact analysis workflow

.github/workflows/eval-pr.yml

@@ -0,0 +1,88 @@
+name: 'Evals: PR Impact'
+
+on:
+  pull_request:
+    paths:
+      - 'packages/core/src/prompts/**'
+      - 'packages/core/src/tools/**'
+      - 'packages/core/src/agents/**'
+      - 'evals/**'
+
+permissions:
+  contents: 'read'
+  checks: 'write'
+  pull-requests: 'write'
+
+jobs:
+  eval-impact:
+    name: 'Eval Impact Analysis'
+    runs-on: 'gemini-cli-ubuntu-16-core'
+    if: "github.repository == 'google-gemini/gemini-cli'"
+    steps:
+      - name: 'Checkout'
+        uses: 'actions/checkout@v4'
+
+      - name: 'Set up Node.js'
+        uses: 'actions/setup-node@v4'
+        with:
+          node-version-file: '.nvmrc'
+          cache: 'npm'
+
+      - name: 'Install dependencies'
+        run: 'npm ci'
+
+      - name: 'Build project'
+        run: 'npm run build'
+
+      - name: 'Create logs directory'
+        run: 'mkdir -p evals/logs'
+
+      - name: 'Run Evals (Lite)'
+        env:
+          GEMINI_API_KEY: '${{ secrets.GEMINI_API_KEY }}'
+          RUN_EVALS: 'true'
+        run: |
+          # Run 1 attempt on critical models for speed in PR
+          MODELS=("gemini-3.1-pro-preview-customtools" "gemini-3-flash-preview")
+          for model in "${MODELS[@]}"; do
+            echo "Running evals for $model..."
+            mkdir -p "evals/logs/eval-logs-$model-1"
+            # We redirect to report.json in a subfolder so aggregate_evals.js can find it via subfolder name
+            GEMINI_MODEL=$model npm run test:all_evals -- --outputFile.json="evals/logs/eval-logs-$model-1/report.json"
+          done
+
+      - name: 'Generate Impact Report'
+        id: 'generate-report'
+        env:
+          GH_TOKEN: '${{ secrets.GITHUB_TOKEN }}'
+        run: |
+          echo "<!-- eval-impact-report -->" > report.md
+          node scripts/aggregate_evals.js evals/logs --compare-main --pr-comment >> report.md
+          cat report.md >> "$GITHUB_STEP_SUMMARY"
+          
+          # Check if there are any regressions (🔴)
+          if grep -q "🔴" report.md; then
+            echo "REGRESSION_DETECTED=true" >> "$GITHUB_ENV"
+          fi
+
+      - name: 'Comment on PR'
+        env:
+          GH_TOKEN: '${{ secrets.GITHUB_TOKEN }}'
+        run: |
+          PR_NUMBER=${{ github.event.pull_request.number }}
+          # Try to find existing comment to avoid spamming
+          EXISTING_COMMENT=$(gh pr view $PR_NUMBER --json comments --jq '.comments[] | select(.body | contains("eval-impact-report")) | .id' | head -n 1)
+          
+          if [ -n "$EXISTING_COMMENT" ]; then
+            # We can't easily edit by ID with 'gh pr comment', so we just post a new one for now
+            # but in the future we could use 'gh api' to update.
+            gh pr comment $PR_NUMBER --body-file report.md
+          else
+            gh pr comment $PR_NUMBER --body-file report.md
+          fi
+
+      - name: 'Fail if regression detected'
+        if: "env.REGRESSION_DETECTED == 'true'"
+        run: |
+          echo "Behavioral evaluation regressions detected. Please check the impact report."
+          exit 1

evals/README.md

@@ -200,10 +200,30 @@ Results for evaluations are available on GitHub Actions:
 - **CI Evals**: Included in the
   [E2E (Chained)](https://github.com/google-gemini/gemini-cli/actions/workflows/chained_e2e.yml)
   workflow. These must pass 100% for every PR.
+- **PR Impact Analysis**: Run automatically on PRs that modify prompts, tools,
+  or agent logic via the
+  [Evals: PR Impact](https://github.com/google-gemini/gemini-cli/actions/workflows/eval-pr.yml)
+  workflow. This provides a "before and after" comparison of behavioral eval
+  stability and will fail the PR if regressions are detected.
 - **Nightly Evals**: Run daily via the
   [Evals: Nightly](https://github.com/google-gemini/gemini-cli/actions/workflows/evals-nightly.yml)
   workflow. These track the long-term health and stability of model steering.
 
+### PR Impact Report
+
+When a PR triggers the impact analysis, a bot will post a table to the PR
+commenting on the change in pass rates for critical models (e.g. Gemini 3.1 Pro
+and Gemini 3 Flash).
+
+- **Baseline**: The pass rate from the latest successful nightly run on `main`.
+- **Current**: The pass rate on the PR branch (based on a "lite" run of 1
+  attempt).
+- **Impact**: A delta showing if stability improved (🟢), regressed (🔴), or
+  remained stable (⚪).
+
+A PR that introduces a regression (🔴) in any behavioral evaluation will fail
+this check and require investigation before merging.
+
 ### Nightly Report Format
 
 The nightly workflow executes the full evaluation suite multiple times

scripts/aggregate_evals.js

@@ -11,8 +11,10 @@ import path from 'node:path';
 import { execSync } from 'node:child_process';
 import os from 'node:os';
 
-const artifactsDir = process.argv[2] || '.';
-const MAX_HISTORY = 10;
+const args = process.argv.slice(2);
+const artifactsDir = args.find((arg) => !arg.startsWith('--')) || '.';
+const isPrComment = args.includes('--pr-comment');
+const MAX_HISTORY = isPrComment ? 1 : 10;
 
 // Find all report.json files recursively
 function findReports(dir) {
@@ -87,8 +89,20 @@ function fetchHistoricalData() {
   const history = [];
 
   try {
-    // Determine branch
+    // Check if gh is available
+    try {
+      execSync('gh --version', { stdio: 'ignore' });
+    } catch {
+      if (!isPrComment) {
+        console.warn(
+          'Warning: GitHub CLI (gh) not found. Historical data will be unavailable.',
+        );
+      }
+      return history;
+    }
+
     const branch = 'main';
+    // ... rest of the function ...
 
     // Get recent runs
     const cmd = `gh run list --workflow evals-nightly.yml --branch "${branch}" --limit ${
@@ -145,18 +159,23 @@ function fetchHistoricalData() {
 }
 
 function generateMarkdown(currentStatsByModel, history) {
-  console.log('### Evals Nightly Summary\n');
-  console.log(
-    'See [evals/README.md](https://github.com/google-gemini/gemini-cli/tree/main/evals) for more details.\n',
-  );
+  if (isPrComment) {
+    console.log('### 🤖 Model Steering Impact Report\n');
+    console.log(
+      "This PR modifies files that affect the model's behavior. Below is the impact on behavioral evaluations.\n",
+    );
+  } else {
+    console.log('### Evals Nightly Summary\n');
+    console.log(
+      'See [evals/README.md](https://github.com/google-gemini/gemini-cli/tree/main/evals) for more details.\n',
+    );
+  }
 
-  // Reverse history to show oldest first
   const reversedHistory = [...history].reverse();
-
   const models = Object.keys(currentStatsByModel).sort();
 
   const getPassRate = (statsForModel) => {
-    if (!statsForModel) return '-';
+    if (!statsForModel) return null;
     const totalStats = Object.values(statsForModel).reduce(
       (acc, stats) => {
         acc.passed += stats.passed;
@@ -166,67 +185,89 @@ function generateMarkdown(currentStatsByModel, history) {
       { passed: 0, total: 0 },
     );
     return totalStats.total > 0
-      ? ((totalStats.passed / totalStats.total) * 100).toFixed(1) + '%'
-      : '-';
+      ? (totalStats.passed / totalStats.total) * 100
+      : null;
   };
 
+  const formatPassRate = (rate) =>
+    rate === null ? '-' : rate.toFixed(1) + '%';
+
   for (const model of models) {
     const currentStats = currentStatsByModel[model];
-    const totalPassRate = getPassRate(currentStats);
+    const currentPassRate = getPassRate(currentStats);
+
+    // Baseline is the most recent history entry
+    const baselineStats =
+      reversedHistory.length > 0
+        ? reversedHistory[reversedHistory.length - 1].stats[model]
+        : null;
+    const baselinePassRate = getPassRate(baselineStats);
 
     console.log(`#### Model: ${model}`);
-    console.log(`**Total Pass Rate: ${totalPassRate}**\n`);
+    if (isPrComment && baselinePassRate !== null) {
+      const delta = currentPassRate - baselinePassRate;
+      const deltaStr =
+        delta === 0
+          ? ' (No Change)'
+          : ` (${delta > 0 ? '↑' : '↓'} ${Math.abs(delta).toFixed(1)}%)`;
+      console.log(
+        `**Pass Rate: ${formatPassRate(currentPassRate)}** from ${formatPassRate(baselinePassRate)}${deltaStr}\n`,
+      );
+    } else {
+      console.log(`**Total Pass Rate: ${formatPassRate(currentPassRate)}**\n`);
+    }
 
     // Header
     let header = '| Test Name |';
     let separator = '| :--- |';
-    let passRateRow = '| **Overall Pass Rate** |';
 
-    for (const item of reversedHistory) {
-      header += ` [${item.run.databaseId}](${item.run.url}) |`;
+    if (!isPrComment) {
+      for (const item of reversedHistory) {
+        header += ` [${item.run.databaseId}](${item.run.url}) |`;
+        separator += ' :---: |';
+      }
+    } else if (baselinePassRate !== null) {
+      header += ' Baseline |';
       separator += ' :---: |';
-      passRateRow += ` **${getPassRate(item.stats[model])}** |`;
     }
 
-    // Add Current column last
-    header += ' Current |';
-    separator += ' :---: |';
-    passRateRow += ` **${totalPassRate}** |`;
+    header += ' Current | Impact |';
+    separator += ' :---: | :---: |';
 
     console.log(header);
     console.log(separator);
-    console.log(passRateRow);
 
-    // Collect all test names for this model
     const allTestNames = new Set(Object.keys(currentStats));
-    for (const item of reversedHistory) {
-      if (item.stats[model]) {
-        Object.keys(item.stats[model]).forEach((name) =>
-          allTestNames.add(name),
-        );
-      }
+    if (baselineStats) {
+      Object.keys(baselineStats).forEach((name) => allTestNames.add(name));
     }
 
     for (const name of Array.from(allTestNames).sort()) {
       const searchUrl = `https://github.com/search?q=repo%3Agoogle-gemini%2Fgemini-cli%20%22${encodeURIComponent(name)}%22&type=code`;
       let row = `| [${name}](${searchUrl}) |`;
 
-      // History
-      for (const item of reversedHistory) {
-        const stat = item.stats[model] ? item.stats[model][name] : null;
-        if (stat) {
-          const passRate = ((stat.passed / stat.total) * 100).toFixed(0) + '%';
-          row += ` ${passRate} |`;
-        } else {
-          row += ' - |';
+      const curr = currentStats[name];
+      const base = baselineStats ? baselineStats[name] : null;
+
+      if (!isPrComment) {
+        for (const item of reversedHistory) {
+          const stat = item.stats[model] ? item.stats[model][name] : null;
+          row += ` ${stat ? ((stat.passed / stat.total) * 100).toFixed(0) + '%' : '-'} |`;
         }
+      } else if (baselinePassRate !== null) {
+        row += ` ${base ? ((base.passed / base.total) * 100).toFixed(0) + '%' : '-'} |`;
       }
 
-      // Current
-      const curr = currentStats[name];
-      if (curr) {
-        const passRate = ((curr.passed / curr.total) * 100).toFixed(0) + '%';
-        row += ` ${passRate} |`;
+      const currRate = curr ? (curr.passed / curr.total) * 100 : null;
+      const baseRate = base ? (base.passed / base.total) * 100 : null;
+
+      row += ` ${formatPassRate(currRate)} |`;
+
+      if (currRate !== null && baseRate !== null) {
+        const delta = currRate - baseRate;
+        if (delta > 0) row += ` 🟢 +${delta.toFixed(0)}% |`;
+        else if (delta < 0) row += ` 🔴 ${delta.toFixed(0)}% |`;
+        else row += ' ⚪ 0% |';
       } else {
         row += ' - |';
       }
@@ -242,9 +283,6 @@ function generateMarkdown(currentStatsByModel, history) {
 const currentReports = findReports(artifactsDir);
 if (currentReports.length === 0) {
   console.log('No reports found.');
-  // We don't exit here because we might still want to see history if available,
-  // but practically if current has no reports, something is wrong.
-  // Sticking to original behavior roughly, but maybe we can continue.
   process.exit(0);
 }