fix: implement fail-fast fallback and single-commit git diff strategy

- Fix fallback logic to fail fast instead of building entire project when no modules detected
- Change git diff strategy to use HEAD~1..HEAD for maintenance branches (single cherry-pick commits)
- Add local testing script for debugging without GitHub Actions cycles
- Update verbose logging to show which git diff strategy is being used

Root cause: Cherry-picked commits on maintenance branches were compared against themselves
using origin/branch...HEAD, resulting in 0 changed files and fallback to full builds.

Now maintenance branches always use single-commit diff which correctly detects changes.

Author: markpollack

.github/scripts/test_discovery.py

@@ -57,45 +57,25 @@ def _get_changed_files(self, base_ref: Optional[str] = None) -> List[str]:
         try:
             # Determine the reference to diff against
             pr_base = os.environ.get('GITHUB_BASE_REF')   # PRs
-            pr_head = os.environ.get('GITHUB_HEAD_REF')   # PRs  
+            pr_head = os.environ.get('GITHUB_HEAD_HEAD')   # PRs  
             branch = os.environ.get('GITHUB_REF_NAME')    # pushes
 
-            # Prefer explicit flag if provided
-            if base_ref:
-                ref_for_diff = base_ref
+            # For maintenance branches (cherry-picks), always use single commit diff
+            if branch and branch.endswith('.x'):
+                # Maintenance branch - cherry-picks are always single commits
+                cmd = ["git", "diff", "--name-only", "HEAD~1..HEAD"]
+            elif base_ref:
+                # Explicit base reference provided - use two-dot diff for direct comparison
+                cmd = ["git", "diff", "--name-only", f"{base_ref}..HEAD"]
             elif pr_base and pr_head:
                 # PR context - compare against base branch
-                ref_for_diff = f"origin/{pr_base}"
+                cmd = ["git", "diff", "--name-only", f"origin/{pr_base}..HEAD"]
             elif pr_base:
                 # PR context fallback
-                ref_for_diff = f"origin/{pr_base}"
-            elif branch:
-                # Push context - compare against remote tracking branch
-                ref_for_diff = f"origin/{branch}"
+                cmd = ["git", "diff", "--name-only", f"origin/{pr_base}..HEAD"]
             else:
-                # Final fallback - find merge base with main
-                ref_for_diff = None
-            
-            if ref_for_diff:
-                # Compare remote tracking branch tip to HEAD (handles multi-commit pushes)
-                cmd = ["git", "diff", "--name-only", f"{ref_for_diff}...HEAD"]
-            else:
-                # Push context or other - compare with previous commit
-                # First try to find a reasonable base commit
-                merge_base_cmd = ["git", "merge-base", "HEAD", "origin/main"]
-                try:
-                    merge_base_result = subprocess.run(
-                        merge_base_cmd, 
-                        cwd=self.repo_root,
-                        capture_output=True, 
-                        text=True, 
-                        check=True
-                    )
-                    base_commit = merge_base_result.stdout.strip()
-                    cmd = ["git", "diff", "--name-only", f"{base_commit}...HEAD"]
-                except subprocess.CalledProcessError:
-                    # Fallback to last commit
-                    cmd = ["git", "diff", "--name-only", "HEAD~1..HEAD"]
+                # Final fallback - single commit diff (most reliable)
+                cmd = ["git", "diff", "--name-only", "HEAD~1..HEAD"]
 
             # Execute the git diff command
             result = subprocess.run(
@@ -189,12 +169,15 @@ def _detect_default_base(self) -> str:
         pr_base = os.environ.get('GITHUB_BASE_REF')
         branch = os.environ.get('GITHUB_REF_NAME')
 
-        if pr_base:
-            return f"origin/{pr_base}"
+        # Show the actual strategy being used
+        if branch and branch.endswith('.x'):
+            return f"HEAD~1 (single commit - maintenance branch {branch})"
+        elif pr_base:
+            return f"origin/{pr_base} (PR base)"
         elif branch:
-            return f"origin/{branch}"
+            return f"HEAD~1 (single commit - branch {branch})"
         else:
-            return "origin/main (merge-base)"
+            return "HEAD~1 (single commit - fallback)"
 
 
 def modules_from_diff_cli():

.github/scripts/test_local.sh

@@ -0,0 +1,79 @@
+#!/bin/bash
+
+# Local testing script to simulate GitHub Actions maintenance-fast.yml workflow
+# Usage: ./test_local.sh [branch_name]
+
+set -e
+
+BRANCH_NAME=${1:-"1.0.x"}
+SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
+
+echo "=== Local GitHub Actions Simulation ==="
+echo "Branch: $BRANCH_NAME"
+echo "Script dir: $SCRIPT_DIR"
+echo ""
+
+# Simulate GitHub Actions environment variables
+export GITHUB_REF_NAME="$BRANCH_NAME"
+export GITHUB_REF="refs/heads/$BRANCH_NAME"
+
+echo "=== Step 1: Show commit range ==="
+echo "Base ref: origin/$GITHUB_REF_NAME"
+if git rev-parse "origin/$GITHUB_REF_NAME" >/dev/null 2>&1; then
+    git log --oneline "origin/$GITHUB_REF_NAME...HEAD" | head -5
+else
+    echo "WARNING: origin/$GITHUB_REF_NAME not found, using HEAD~1"
+    git log --oneline HEAD~1..HEAD
+fi
+echo ""
+
+echo "=== Step 2: Compute impacted modules ==="
+cd "$SCRIPT_DIR/../.."
+echo "Working directory: $(pwd)"
+
+# Test different git diff strategies locally
+echo "--- Testing git diff strategies ---"
+
+echo "Strategy 1: origin/$GITHUB_REF_NAME...HEAD (three-dot)"
+FILES_3DOT=$(git diff --name-only "origin/$GITHUB_REF_NAME...HEAD" 2>/dev/null || echo "")
+echo "Files found: $(echo "$FILES_3DOT" | wc -l)"
+echo "$FILES_3DOT" | head -3
+
+echo ""
+echo "Strategy 2: origin/$GITHUB_REF_NAME..HEAD (two-dot)"
+FILES_2DOT=$(git diff --name-only "origin/$GITHUB_REF_NAME..HEAD" 2>/dev/null || echo "")
+echo "Files found: $(echo "$FILES_2DOT" | wc -l)"
+echo "$FILES_2DOT" | head -3
+
+echo ""
+echo "Strategy 3: HEAD~1..HEAD (single commit)"
+FILES_1COMMIT=$(git diff --name-only "HEAD~1..HEAD" 2>/dev/null || echo "")
+echo "Files found: $(echo "$FILES_1COMMIT" | wc -l)"
+echo "$FILES_1COMMIT" | head -3
+
+echo ""
+echo "--- Running test_discovery.py ---"
+MODS=$(python3 .github/scripts/test_discovery.py modules-from-diff --base "origin/$GITHUB_REF_NAME" --verbose 2>&1)
+MODULE_LIST=$(echo "$MODS" | tail -1)
+
+echo "Script output:"
+echo "$MODS"
+echo ""
+echo "Final modules: '$MODULE_LIST'"
+
+echo ""
+echo "=== Step 3: Test build logic ==="
+if [ -z "$MODULE_LIST" ]; then 
+    echo "ERROR: No modules detected - git diff failed to find changes"
+    echo "This likely indicates a problem with the git diff strategy"
+    echo "Failing fast to avoid wasted resources and investigate the issue"
+    echo "Check the 'Compute impacted modules' step output for debugging info"
+    exit 1
+else
+    echo "SUCCESS: Would build modules: $MODULE_LIST"
+    echo "Build command would be:"
+    echo "./mvnw -B -T 1C -Pintegration-tests -DfailIfNoTests=false -pl \"$MODULE_LIST\" -amd verify"
+fi
+
+echo ""
+echo "=== Local test complete ==="

.github/workflows/maintenance-fast.yml

@@ -47,5 +47,11 @@ jobs:
           SPRING_AI_OPENAI_API_KEY: ${{ secrets.OPENAI_API_KEY }}
         run: |
           MODS="${{ steps.mods.outputs.modules }}"
-          if [ -z "$MODS" ]; then MODS="."; fi
+          if [ -z "$MODS" ]; then 
+            echo "ERROR: No modules detected - git diff failed to find changes"
+            echo "This likely indicates a problem with the git diff strategy"
+            echo "Failing fast to avoid wasted resources and investigate the issue"
+            echo "Check the 'Compute impacted modules' step output for debugging info"
+            exit 1
+          fi
           ./mvnw -B -T 1C -Pintegration-tests -DfailIfNoTests=false -pl "$MODS" -amd verify