feat: add prepare upstream script (Yelp#223)

prepare-upstream-contribution.sh

@@ -0,0 +1,77 @@
+#!/bin/bash
+# Description:
+#
+# This script allows you to generate a baseline commit history maintains the
+# original author / committor information before making upstream contribution.
+# Inspired by https://stosb.com/blog/retaining-history-when-moving-files-across-repositories-in-git/
+#
+# See usage for more detailed description.
+
+function usage() {
+cat <<DOCEND
+Description:
+
+  This script takes a list of file as input. Find out all the commits containing the input
+  file list, then rewrites the history from START_COMMIT to END_COMMIT, removing all commits
+  does not contain file within input file list. For the remaining commits, trim out all the
+  changes not applied to input file list. The end result is a commit history after START_COMMIT,
+  all commits are specific for input file list.
+
+  Note: after you get a rewrite history, you might want to review it and use 'git rebase' to get
+  an even cleaner history.
+
+Environment variables:
+
+  START_COMMIT   default is the commit right before message "Apply IBM specific changes".
+                 This commit won't be changed.
+  END_COMMIT     default is "head" which is the last commit to be rewrite.
+
+Parameters:
+
+  List of files to collect commits from
+
+Example:
+
+  env START_COMMIT=a3a8b85 END_COMMIT=head ./prepare-upstream-contribution.sh detect_secrets/plugins/softlayer.py tests/plugins/softlayer_test.py
+DOCEND
+  exit 1
+}
+
+if [[ "$1" == "-h" || "$1" == "--help" ]]; then
+  usage
+fi
+
+echo "File to filter is ${FILES:=$@}"
+if [ -z "$FILES" ]; then
+  echo "Incoming file list is empty"
+  exit 1
+fi
+
+echo "START_COMMIT is ${START_COMMIT:=$(git log --grep='Apply IBM specific changes' --pretty=format:'%h')~1}"
+echo "END_COMMIT is ${END_COMMIT:=head}"
+echo "Temp branch is ${TEMP_BRANCH:=rewrite-$(head /dev/urandom | base64 | tr -dc a-z0-9 | head -c8)}"
+
+TEMP_GIT_DIR=${TEMP_BRANCH}-newroot
+CURRENT_BRANCH=$(git rev-parse --abbrev-ref HEAD)
+git checkout -b ${TEMP_BRANCH}
+
+# Use filter to copy file to a temporarity location
+git filter-branch --force --prune-empty --tree-filter "mkdir -p ${TEMP_GIT_DIR}; for f in $FILES; do mv \$f ${TEMP_GIT_DIR}/ 2>/dev/null; done; true;" ${START_COMMIT}..${END_COMMIT}
+# Set the temp location as root
+git filter-branch --prune-empty -f --subdirectory-filter ${TEMP_BRANCH}-newroot
+# Add filtered off commits to the top of starting commit
+git rebase ${START_COMMIT}
+
+# move files back to their original location and make a new commit
+for f in $FILES; do
+    mv $(basename $f) $f 2>/dev/null
+    git add $f
+    git add $(basename $f)
+done
+git commit -m 'Move files back'
+git checkout ${CURRENT_BRANCH}
+
+echo "The prepared branch is ${TEMP_BRANCH}. Use command below to view the history"
+echo ""
+echo "  git log --oneline -n10 ${TEMP_BRANCH}"
+echo ""