Remove unnecessary PR updates for indirect children (#23)

* Remove indirect children updates - diffs stay correct without them

The action now only updates direct children of a merged PR. Indirect
descendants (grandchildren, etc.) are intentionally not modified.

This simplification is possible because:
- PR diffs remain correct without updating indirect children
- The merge-base calculation still works correctly since the synthetic
  merge commit includes the original parent commit as an ancestor
- Indirect children become direct children when their parent is merged,
  at which point they get updated properly

Benefits:
- Simpler code: removed ~140 lines
- Fewer API calls and git operations
- No risk of cascading merge conflicts through the stack
- Clearer mental model: each merge only affects direct children

The e2e tests still verify that indirect children's diffs remain correct
after their grandparent is merged.

* Clean up unit tests: remove dead code, add actual verification

- Remove unused simulate_delete_remote_branch() helper function
- Actually verify feature3 wasn't modified instead of just logging

* Fix outdated comment about feature4 purpose in e2e test

---------

Co-authored-by: Claude <noreply@anthropic.com>

Author: Phlogistique

README.md

@@ -17,11 +17,12 @@ This action tries to fix that in a transparent way. Install it, and hopefully th
 ### How it works
 
 1. Triggers when a PR is squash merged
-2. Finds PRs that were based on the merged branch
-3. For direct children: creates a synthetic merge commit with three parents (child tip, deleted branch tip, squash commit) to preserve history without re-introducing code
-4. For indirect descendants: merges the updated parent branch
-5. Updates the direct child PRs to base on trunk now that the bottom change has landed; higher PRs stay based on their parent
-6. Force-pushes updated branches and deletes the merged branch
+2. Finds PRs that were based on the merged branch (direct children only)
+3. Creates a synthetic merge commit with three parents (child tip, deleted branch tip, squash commit) to preserve history without re-introducing code
+4. Updates the direct child PRs to base on trunk now that the bottom change has landed
+5. Force-pushes updated branches and deletes the merged branch
+
+**Note:** Indirect descendants (grandchildren, etc.) are intentionally not modified. Their PR diffs remain correct because the merge-base calculation still works—the synthetic merge commit includes the original parent commit as an ancestor. When their direct parent is eventually merged, they become direct children and get updated at that point.
 
 ### Conflict handling
 
@@ -38,7 +39,6 @@ After you manually resolve the conflict and push:
 2. The action detects the conflict label and removes it
 3. Updates the PR's base branch to trunk
 4. Deletes the old base branch (if no other conflicted PRs still depend on it)
-5. Continues updating any dependent PRs in the stack
 
 ---
 

tests/mock_gh.sh

@@ -1,31 +1,24 @@
 #!/bin/bash
 
+# Mock gh CLI for unit tests.
+# Only direct children are queried now (no recursive updates of indirect children).
+
 if [[ "$1" == "pr" && "$2" == "list" ]]; then
     # Parse the --base argument to determine which PRs to return
     base=""
-    jq_flag=""
     for ((i=1; i<=$#; i++)); do
         if [[ "${!i}" == "--base" ]]; then
             next=$((i+1))
             base="${!next}"
         fi
-        if [[ "${!i}" == "--jq" ]]; then
-            next=$((i+1))
-            jq_flag="${!next}"
-        fi
     done
 
-    if [[ "$base" == "main" ]]; then
-        : # No PRs target main in our test
-    elif [[ "$base" == "feature1" ]]; then
+    if [[ "$base" == "feature1" ]]; then
+        # feature2 is a direct child of feature1
         echo 'feature2'
-    elif [[ "$base" == "feature2" ]]; then
-        echo feature3
-    elif [[ "$base" == "feature3" ]]; then
-        :
     else
-        echo "Unknown base branch: $@" >&2
-        exit 1
+        # No other bases have direct children in our test scenario
+        :
     fi
 elif [[ "$1" == "pr" && "$2" == "edit" ]]; then
     # Just log the edit command

tests/test_e2e.sh

@@ -47,14 +47,15 @@
 #   - The action should detect that PR2 (feature2) was based on feature1
 #   - Update PR2's base branch from feature1 to main
 #   - Merge main into feature2 to incorporate the squash commit
-#   - Propagate the merge to feature3 and feature4 as well
 #   - Delete the merged branch (feature1)
+#   - NOTE: Indirect children (feature3, feature4) are NOT updated - their diffs
+#     remain correct because the merge-base calculation works correctly
 #
 # Verifications:
 #   - feature1 branch is deleted from remote
 #   - PR2 base branch is updated from feature1 to main
-#   - PR3 base branch remains feature2 (only direct children are updated)
-#   - feature2, feature3, and feature4 branches contain the squash merge commit
+#   - PR3 base branch remains feature2 (only direct children's base is updated)
+#   - feature2 contains the squash merge commit (feature3/feature4 do NOT)
 #   - PR diffs are IDENTICAL before and after (action preserves incremental diffs)
 #
 # SCENARIO 2: Conflict Handling (Steps 8-13)
@@ -94,13 +95,7 @@
 #   - The action detects the conflict label and removes it
 #   - Updates PR3's base branch to main
 #   - Deletes feature2 branch (no other conflicted PRs depend on it)
-#   - The continuation workflow updates feature4 (grandchild) recursively
-#   - Verify the label is removed, base updated, branch deleted, and feature4 is updated
-#
-# Grandchild Update (feature4):
-#   - Tests that update_branch_recursive properly handles grandchildren
-#   - Even when SQUASH_COMMIT is undefined (in conflict-resolved mode)
-#   - The skip_if_clean guard must handle the missing SQUASH_COMMIT ref
+#   - NOTE: feature4 is NOT updated (indirect children are not modified)
 #
 # =============================================================================
 set -e # Exit immediately if a command exits with a non-zero status.
@@ -654,14 +649,14 @@ PR3_URL=$(log_cmd gh pr create --repo "$REPO_FULL_NAME" --base feature2 --head f
 PR3_NUM=$(echo "$PR3_URL" | awk -F'/' '{print $NF}')
 echo >&2 "Created PR #$PR3_NUM: $PR3_URL"
 
-# Branch feature4 (base: feature3) - tests grandchildren in conflict resolution
+# Branch feature4 (base: feature3) - tests that indirect children's diffs remain correct
 log_cmd git checkout -b feature4 feature3
 sed -i '2s/.*/Feature 4 content line 2/' file.txt # Edit line 2 (shared)
 sed -i '5s/.*/Feature 4 content line 5/' file.txt # Edit line 5 (unique)
 log_cmd git add file.txt
 log_cmd git commit -m "Add feature 4"
 log_cmd git push origin feature4
-PR4_URL=$(log_cmd gh pr create --repo "$REPO_FULL_NAME" --base feature3 --head feature4 --title "Feature 4" --body "This is PR 4, based on PR 3 (grandchild for conflict resolution test)")
+PR4_URL=$(log_cmd gh pr create --repo "$REPO_FULL_NAME" --base feature3 --head feature4 --title "Feature 4" --body "This is PR 4, based on PR 3 (indirect child, tests diff preservation)")
 PR4_NUM=$(echo "$PR4_URL" | awk -F'/' '{print $NF}')
 echo >&2 "Created PR #$PR4_NUM: $PR4_URL"
 
@@ -718,37 +713,20 @@ else
     echo >&2 "❌ Verification Failed: PR #$PR3_NUM base branch is '$PR3_BASE', expected 'feature2'."
     exit 1
 fi
-# Verify local branches are updated to include the squash commit
-echo >&2 "Checking if branches incorporate the squash commit..."
-log_cmd git checkout feature2 # Checkout local branch first
-log_cmd git pull origin feature2 # Pull updates pushed by the action
-log_cmd git checkout feature3
-log_cmd git pull origin feature3
-log_cmd git checkout feature4
-log_cmd git pull origin feature4
-
-# Check ancestry
+# Verify feature2 (direct child) is updated to include the squash commit
+echo >&2 "Checking if feature2 incorporates the squash commit..."
+log_cmd git checkout feature2
+log_cmd git pull origin feature2
 if log_cmd git merge-base --is-ancestor "$MERGE_COMMIT_SHA1" feature2; then
     echo >&2 "✅ Verification Passed: feature2 correctly incorporates the squash commit $MERGE_COMMIT_SHA1."
 else
     echo >&2 "❌ Verification Failed: feature2 does not include the squash commit $MERGE_COMMIT_SHA1."
     log_cmd git log --graph --oneline feature2 main
     exit 1
 fi
-if log_cmd git merge-base --is-ancestor "$MERGE_COMMIT_SHA1" feature3; then
-    echo >&2 "✅ Verification Passed: feature3 correctly incorporates the squash commit $MERGE_COMMIT_SHA1."
-else
-    echo >&2 "❌ Verification Failed: feature3 does not include the squash commit $MERGE_COMMIT_SHA1."
-    log_cmd git log --graph --oneline feature3 main
-    exit 1
-fi
-if log_cmd git merge-base --is-ancestor "$MERGE_COMMIT_SHA1" feature4; then
-    echo >&2 "✅ Verification Passed: feature4 correctly incorporates the squash commit $MERGE_COMMIT_SHA1."
-else
-    echo >&2 "❌ Verification Failed: feature4 does not include the squash commit $MERGE_COMMIT_SHA1."
-    log_cmd git log --graph --oneline feature4 main
-    exit 1
-fi
+# Note: feature3 and feature4 are NOT updated (indirect children are not modified).
+# Their diffs remain correct because the merge-base calculation still works.
+echo >&2 "✅ feature3 and feature4 intentionally not updated (indirect children)"
 # Verify diffs are preserved (identical to initial)
 echo >&2 "Verifying diffs are preserved after action..."
 PR2_DIFF_AFTER=$(get_pr_diff "$PR2_URL")
@@ -950,8 +928,6 @@ echo >&2 "15. Verifying conflict resolution content..."
 log_cmd git fetch origin
 log_cmd git checkout feature3
 log_cmd git pull origin feature3
-log_cmd git checkout feature4
-log_cmd git pull origin feature4
 
 # Verify feature3 now incorporates main (including PR2 merge commit and main's conflict commit)
 if log_cmd git merge-base --is-ancestor origin/main feature3; then
@@ -962,15 +938,9 @@ else
     exit 1
 fi
 
-# Verify feature4 (grandchild) was updated by continuation workflow
-# This tests that update_branch_recursive properly handles grandchildren even when SQUASH_COMMIT is undefined
-if log_cmd git merge-base --is-ancestor origin/feature3 feature4; then
-    echo >&2 "✅ Verification Passed: feature4 (grandchild) correctly incorporates resolved feature3."
-else
-    echo >&2 "❌ Verification Failed: feature4 does not include the resolved feature3."
-    log_cmd git log --graph --oneline feature4 feature3
-    exit 1
-fi
+# Note: feature4 is NOT updated (indirect children are not modified).
+# It will be updated when feature3 is merged (becoming a direct child at that point).
+echo >&2 "✅ feature4 intentionally not updated (indirect child of resolved PR)"
 
 # Verify the final content of file.txt on feature3
 # Line 1: Original base

tests/test_update_pr_stack.sh

@@ -16,12 +16,6 @@ simulate_push() {
     log_cmd git update-ref "refs/remotes/origin/$branch_name" "$branch_name"
 }
 
-# Helper function to simulate 'git push origin :<branch>'
-simulate_delete_remote_branch() {
-    local branch_name="$1"
-    log_cmd git update-ref -d "refs/remotes/origin/$branch_name"
-}
-
 # Create a temporary directory for the test repository
 TEST_REPO=$(mktemp -d)
 cd "$TEST_REPO"
@@ -101,22 +95,21 @@ else
     exit 1
 fi
 
-# Test if the squash commit is incorporated into feature3
-if log_cmd git merge-base --is-ancestor "$SQUASH_COMMIT" feature3; then
-    echo "✅ feature3 includes the squash commit"
+# Verify feature3 is NOT modified (indirect children are not updated)
+# We stored the original SHA before running the script, now verify it hasn't changed
+FEATURE3_AFTER=$(log_cmd git rev-parse feature3)
+FEATURE3_BEFORE=$(log_cmd git rev-parse origin/feature3)
+if [[ "$FEATURE3_AFTER" == "$FEATURE3_BEFORE" ]]; then
+    echo "✅ feature3 remains unchanged (indirect children not updated)"
 else
-    echo "❌ feature3 does not include the squash commit"
-    log_cmd git log --graph --oneline --all
+    echo "❌ feature3 was modified unexpectedly"
     exit 1
 fi
 
-# Show the contents of feature2 and feature3 to verify they contain all changes
+# Show the contents of feature2 to verify it contains the expected changes
 echo -e "\nContent of feature2 branch:"
 log_cmd git show feature2:file.txt
 
-echo -e "\nContent of feature3 branch:"
-log_cmd git show feature3:file.txt
-
 # Test triple dot diff on feature2
 # After rebase, the diff should only contain the changes unique to feature2
 # In this conflict scenario, feature2's change should overwrite feature1's change
@@ -150,22 +143,24 @@ else
 fi
 
 
-# Test triple dot diff on feature3
-# After rebase, the diff should only contain the changes unique to feature3 relative to main
+# Test triple dot diff on feature3 relative to feature2 (simulates PR diff)
+# Even though feature3 was NOT updated, its diff vs feature2 should remain correct
+# because the merge-base calculation still works (feature2's synthetic merge has
+# the original feature2 commit as a parent via BEFORE_MERGE)
 EXPECTED_DIFF3=$(cat <<EOF
 diff --git a/file.txt b/file.txt
 --- a/file.txt
 +++ b/file.txt
 @@ -1,3 +1,3 @@
  Initial line 1
--Feature 1 content line 2
+-Feature 2 content line 2
 +Feature 3 content line 2
  Initial line 3
 EOF
 )
-ACTUAL_DIFF3=$(log_cmd git diff main...feature3 | grep -v '^index')
+ACTUAL_DIFF3=$(log_cmd git diff feature2...feature3 | grep -v '^index')
 if [[ "$ACTUAL_DIFF3" == "$EXPECTED_DIFF3" ]]; then
-    echo "✅ Triple dot diff for feature3 shows expected changes"
+    echo "✅ Triple dot diff for feature3 (vs feature2) shows expected changes"
 else
     echo "❌ Triple dot diff for feature3 doesn't show expected changes"
     echo "Expected:"
@@ -179,16 +174,14 @@ fi
 # Test idempotence by running the update again
 echo -e "\nRunning update script again to test idempotence..."
 
-# Store current commit hashes
+# Store current commit hash for feature2 (the only branch modified by the action)
 FEATURE2_COMMIT_BEFORE=$(log_cmd git rev-parse feature2)
-FEATURE3_COMMIT_BEFORE=$(log_cmd git rev-parse feature3)
 
 # Run update script again with mocked push
 run_update_pr_stack
 
 # Check that no new commits were created
 FEATURE2_COMMIT_AFTER=$(log_cmd git rev-parse feature2)
-FEATURE3_COMMIT_AFTER=$(log_cmd git rev-parse feature3)
 
 if [[ "$FEATURE2_COMMIT_BEFORE" == "$FEATURE2_COMMIT_AFTER" ]]; then
     echo "✅ Idempotence test passed for feature2"
@@ -198,14 +191,6 @@ else
     exit 1
 fi
 
-if [[ "$FEATURE3_COMMIT_BEFORE" == "$FEATURE3_COMMIT_AFTER" ]]; then
-    echo "✅ Idempotence test passed for feature3"
-else
-    echo "❌ Idempotence test failed for feature3"
-    log_cmd git log --graph --oneline --all
-    exit 1
-fi
-
 echo -e "\nAll tests passed! 🎉"
 
 # Clean up