aosp-merger: Improve merge commit message

* Merge and commit separately,
  to get newline between commit content and Change-Id
* Install prepare-commit-msg git hook, for nicer conflict messages
  https://gist.github.com/mikeNG/e55ef8e7a1e5cd596a950386503054fd/

Change-Id: I97370b352ccf4f146b4b6ea89af75e032fb13730

aosp-merger/_merge_helper.sh

@@ -32,6 +32,8 @@ readonly vars_path="${script_path}/../vars"
 
 source "${vars_path}/common"
 
+readonly hook="${script_path}/prepare-commit-msg"
+
 TOP="${script_path}/../../.."
 BRANCH="${calyxos_branch}"
 STAGINGBRANCH="staging/${BRANCH}_${OPERATION}-${NEWTAG}"
@@ -40,6 +42,9 @@ cd "${TOP}/${PROJECTPATH}"
 repo start "${STAGINGBRANCH}" .
 git fetch -q --tags aosp "${NEWTAG}"
 
+[[ ! -e .git/hooks/prepare-commit-msg ]] && cp "${hook}" .git/hooks/
+chmod +x .git/hooks/prepare-commit-msg
+
 PROJECTOPERATION="${OPERATION}"
 
 # Check if we've actually changed anything before attempting to merge
@@ -69,7 +74,7 @@ fi
 
 if [[ "${PROJECTOPERATION}" == "merge" ]]; then
     echo "#### Merging ${NEWTAG} into ${PROJECTPATH} ####"
-    git merge --no-edit --log "${NEWTAG}"
+    git merge --no-commit --log "${NEWTAG}" && git commit --no-edit
 elif [[ "${PROJECTOPERATION}" == "rebase" ]]; then
     echo "#### Rebasing ${PROJECTPATH} onto ${NEWTAG} ####"
     git rebase --onto "${NEWTAG}" "${OLDTAG}"

aosp-merger/prepare-commit-msg

@@ -0,0 +1,14 @@
+#!/bin/sh
+
+case "$2,$3" in
+  merge,)
+    if grep -q "# It looks like you may be committing a merge." "$1"; then
+        sed -i -e '/# ------------------------ >8 ------------------------/,+3d' "$1"
+        /usr/bin/perl -i.bak -ne 's/^#// if /^# Conflicts/ .. /^#\R/; print' "$1"
+        sed -i '/ It looks like you may be committing a merge./i # ------------------------ >8 ------------------------' "$1"
+    fi
+    ;;
+
+  *)
+    ;;
+esac