From 6497e8ef995cd3c31c3db72f2528ef231963dafa Mon Sep 17 00:00:00 2001
From: Tonye Jack <jtonye@ymail.com>
Date: Tue, 13 Dec 2022 13:24:35 -0700
Subject: [PATCH] Updated to fetch the common ancestor

---
 action.yml  |  1 +
 diff-sha.sh | 34 ++++++++++++++++++++++++++++------
 2 files changed, 29 insertions(+), 6 deletions(-)

diff --git a/action.yml b/action.yml
index 1c047883..310ccec8 100644
--- a/action.yml
+++ b/action.yml
@@ -176,6 +176,7 @@ runs:
         GITHUB_EVENT_HEAD_REPO_FORK: ${{ github.event.pull_request.head.repo.fork }}
         GITHUB_EVENT_PULL_REQUEST_BASE_SHA: ${{ github.event.pull_request.base.sha }}
         GITHUB_EVENT_PULL_REQUEST_HEAD_SHA: ${{ github.event.pull_request.head.sha }}
+        GITHUB_EVENT_PULL_REQUEST_COMMITS: ${{ github.event.pull_request.commits }}
         GITHUB_EVENT_BEFORE: ${{ github.event.before }}
         GITHUB_EVENT_FORCED: ${{ github.event.forced }}
         GITHUB_REFNAME: ${{ github.ref_name }}
diff --git a/diff-sha.sh b/diff-sha.sh
index ce320c60..f51e3ac0 100644
--- a/diff-sha.sh
+++ b/diff-sha.sh
@@ -4,13 +4,13 @@ set -euo pipefail
 
 INITIAL_COMMIT="false"
 GITHUB_OUTPUT=${GITHUB_OUTPUT:-""}
-EXTRA_ARGS="--no-tags"
+EXTRA_ARGS="--no-tags --prune --no-recurse-submodules"
 PREVIOUS_SHA=""
 CURRENT_SHA=""
 DIFF="..."
 
 if [[ "$GITHUB_REF" == "refs/tags/"* ]]; then
-  EXTRA_ARGS=""
+  EXTRA_ARGS="--prune --no-recurse-submodules"
 fi
 
 if [[ "$GITHUB_EVENT_HEAD_REPO_FORK" == "true" ]]; then
@@ -162,6 +162,28 @@ else
     # shellcheck disable=SC2086
     git fetch -u --progress $EXTRA_ARGS --depth="$INPUT_FETCH_DEPTH" origin +refs/heads/"$TARGET_BRANCH":refs/remotes/origin/"$TARGET_BRANCH" 1>/dev/null 2>&1
     git branch --track "$TARGET_BRANCH" origin/"$TARGET_BRANCH" 1>/dev/null 2>&1 || true
+    # shellcheck disable=SC2086
+    git fetch $EXTRA_ARGS -u --progress --depth=$(( GITHUB_EVENT_PULL_REQUEST_COMMITS + 1 )) origin +"$GITHUB_REF":refs/remotes/origin/"$CURRENT_BRANCH" 1>/dev/null 2>&1
+
+    COMMON_ANCESTOR=$(git rev-list --first-parent --max-parents=0 --max-count=1 origin/"$CURRENT_BRANCH" 2>&1) && exit_status=$? || exit_status=$?
+
+    if [[ -z "$COMMON_ANCESTOR" ]]; then
+      echo "::error::Unable to locate a common ancestor for the current branch: $CURRENT_BRANCH"
+      exit 1
+    else
+      echo "::debug::Common ancestor: $COMMON_ANCESTOR"
+    fi
+
+    DATE=$(git log --date=iso8601 --format=%cd "${COMMON_ANCESTOR}")
+
+    if [[ -z "$DATE" ]]; then
+      echo "::error::Unable to locate a date for the common ancestor: $COMMON_ANCESTOR"
+      exit 1
+    else
+      # shellcheck disable=SC2086
+      git fetch $EXTRA_ARGS --shallow-since="${DATE}" origin +refs/heads/"$TARGET_BRANCH":refs/remotes/origin/"$TARGET_BRANCH" 1>/dev/null 2>&1
+      echo "::debug::Date: $DATE"
+    fi
   else
     # shellcheck disable=SC2086
     git fetch $EXTRA_ARGS -u --progress --depth="$INPUT_FETCH_DEPTH" origin +"$GITHUB_REF":refs/remotes/origin/"$CURRENT_BRANCH" 1>/dev/null 2>&1
@@ -221,14 +243,14 @@ else
         max_depth=$INPUT_MAX_FETCH_DEPTH
 
         for ((i=depth; i<max_depth; i+=depth)); do
+          if git diff --name-only --ignore-submodules=all "$PREVIOUS_SHA$DIFF$CURRENT_SHA" 1>/dev/null 2>&1; then
+            break
+          fi
+
           echo "Fetching $i commits..."
 
           # shellcheck disable=SC2086
           git fetch $EXTRA_ARGS -u --progress --depth="$i" origin +"$GITHUB_REF":refs/remotes/origin/"$CURRENT_BRANCH" 1>/dev/null 2>&1
-
-          if git diff --name-only --ignore-submodules=all "$PREVIOUS_SHA$DIFF$CURRENT_SHA" 1>/dev/null 2>&1; then
-            break
-          fi
         done
 
         if ((i >= max_depth)); then