Update commit-msg hook to version from Gerrit 3.1.3

Includes the following commits (redacted to those that are relevant):

da300bd9bd8 - Do not create a change id if gerrit.createChangeId == false
731eb42b8ae - Do not strip out "-- >8 --" comment in commit-msg hook
627d07c2bfc - Handle messages with only comments in the commit-msg hook
68296f71804 - Simplify the hook script using git-interpret-trailers

Change-Id: I7a82836495427df3c5437ba88a9576b47629065f
Reviewed-on: https://gerrit-review.googlesource.com/c/git-repo/+/255393
Reviewed-by: Mike Frysinger <vapier@google.com>
Tested-by: David Pursehouse <dpursehouse@collab.net>

hooks/commit-msg

@@ -1,5 +1,5 @@
 #!/bin/sh
-# From Gerrit Code Review 2.14.6
+# From Gerrit Code Review 3.1.3
 #
 # Part of Gerrit Code Review (https://www.gerritcodereview.com/)
 #
@@ -16,176 +16,48 @@
 # WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 # See the License for the specific language governing permissions and
 # limitations under the License.
-#
-
-unset GREP_OPTIONS
-
-CHANGE_ID_AFTER="Bug|Depends-On|Issue|Test|Feature|Fixes|Fixed"
-MSG="$1"
-
-# Check for, and add if missing, a unique Change-Id
-#
-add_ChangeId() {
-	clean_message=`sed -e '
-		/^diff --git .*/{
-			s///
-			q
-		}
-		/^Signed-off-by:/d
-		/^#/d
-	' "$MSG" | git stripspace`
-	if test -z "$clean_message"
-	then
-		return
-	fi
-
-	# Do not add Change-Id to temp commits
-	if echo "$clean_message" | head -1 | grep -q '^\(fixup\|squash\)!'
-	then
-		return
-	fi
-
-	if test "false" = "`git config --bool --get gerrit.createChangeId`"
-	then
-		return
-	fi
-
-	# Does Change-Id: already exist? if so, exit (no change).
-	if grep -i '^Change-Id:' "$MSG" >/dev/null
-	then
-		return
-	fi
-
-	id=`_gen_ChangeId`
-	T="$MSG.tmp.$$"
-	AWK=awk
-	if [ -x /usr/xpg4/bin/awk ]; then
-		# Solaris AWK is just too broken
-		AWK=/usr/xpg4/bin/awk
-	fi
-
-	# Get core.commentChar from git config or use default symbol
-	commentChar=`git config --get core.commentChar`
-	commentChar=${commentChar:-#}
-
-	# How this works:
-	# - parse the commit message as (textLine+ blankLine*)*
-	# - assume textLine+ to be a footer until proven otherwise
-	# - exception: the first block is not footer (as it is the title)
-	# - read textLine+ into a variable
-	# - then count blankLines
-	# - once the next textLine appears, print textLine+ blankLine* as these
-	#   aren't footer
-	# - in END, the last textLine+ block is available for footer parsing
-	$AWK '
-	BEGIN {
-		# while we start with the assumption that textLine+
-		# is a footer, the first block is not.
-		isFooter = 0
-		footerComment = 0
-		blankLines = 0
-	}
-
-	# Skip lines starting with commentChar without any spaces before it.
-	/^'"$commentChar"'/ { next }
-
-	# Skip the line starting with the diff command and everything after it,
-	# up to the end of the file, assuming it is only patch data.
-	# If more than one line before the diff was empty, strip all but one.
-	/^diff --git / {
-		blankLines = 0
-		while (getline) { }
-		next
-	}
-
-	# Count blank lines outside footer comments
-	/^$/ && (footerComment == 0) {
-		blankLines++
-		next
-	}
-
-	# Catch footer comment
-	/^\[[a-zA-Z0-9-]+:/ && (isFooter == 1) {
-		footerComment = 1
-	}
-
-	/]$/ && (footerComment == 1) {
-		footerComment = 2
-	}
-
-	# We have a non-blank line after blank lines. Handle this.
-	(blankLines > 0) {
-		print lines
-		for (i = 0; i < blankLines; i++) {
-			print ""
-		}
-
-		lines = ""
-		blankLines = 0
-		isFooter = 1
-		footerComment = 0
-	}
-
-	# Detect that the current block is not the footer
-	(footerComment == 0) && (!/^\[?[a-zA-Z0-9-]+:/ || /^[a-zA-Z0-9-]+:\/\//) {
-		isFooter = 0
-	}
-
-	{
-		# We need this information about the current last comment line
-		if (footerComment == 2) {
-			footerComment = 0
-		}
-		if (lines != "") {
-			lines = lines "\n";
-		}
-		lines = lines $0
-	}
-
-	# Footer handling:
-	# If the last block is considered a footer, splice in the Change-Id at the
-	# right place.
-	# Look for the right place to inject Change-Id by considering
-	# CHANGE_ID_AFTER. Keys listed in it (case insensitive) come first,
-	# then Change-Id, then everything else (eg. Signed-off-by:).
-	#
-	# Otherwise just print the last block, a new line and the Change-Id as a
-	# block of its own.
-	END {
-		unprinted = 1
-		if (isFooter == 0) {
-			print lines "\n"
-			lines = ""
-		}
-		changeIdAfter = "^(" tolower("'"$CHANGE_ID_AFTER"'") "):"
-		numlines = split(lines, footer, "\n")
-		for (line = 1; line <= numlines; line++) {
-			if (unprinted && match(tolower(footer[line]), changeIdAfter) != 1) {
-				unprinted = 0
-				print "Change-Id: I'"$id"'"
-			}
-			print footer[line]
-		}
-		if (unprinted) {
-			print "Change-Id: I'"$id"'"
-		}
-	}' "$MSG" > "$T" && mv "$T" "$MSG" || rm -f "$T"
-}
-_gen_ChangeIdInput() {
-	echo "tree `git write-tree`"
-	if parent=`git rev-parse "HEAD^0" 2>/dev/null`
-	then
-		echo "parent $parent"
-	fi
-	echo "author `git var GIT_AUTHOR_IDENT`"
-	echo "committer `git var GIT_COMMITTER_IDENT`"
-	echo
-	printf '%s' "$clean_message"
-}
-_gen_ChangeId() {
-	_gen_ChangeIdInput |
-	git hash-object -t commit --stdin
-}
-
 
-add_ChangeId
+# avoid [[ which is not POSIX sh.
+if test "$#" != 1 ; then
+  echo "$0 requires an argument."
+  exit 1
+fi
+
+if test ! -f "$1" ; then
+  echo "file does not exist: $1"
+  exit 1
+fi
+
+# Do not create a change id if requested
+if test "false" = "`git config --bool --get gerrit.createChangeId`" ; then
+  exit 0
+fi
+
+# $RANDOM will be undefined if not using bash, so don't use set -u
+random=$( (whoami ; hostname ; date; cat $1 ; echo $RANDOM) | git hash-object --stdin)
+dest="$1.tmp.${random}"
+
+trap 'rm -f "${dest}"' EXIT
+
+if ! git stripspace --strip-comments < "$1" > "${dest}" ; then
+   echo "cannot strip comments from $1"
+   exit 1
+fi
+
+if test ! -s "${dest}" ; then
+  echo "file is empty: $1"
+  exit 1
+fi
+
+# Avoid the --in-place option which only appeared in Git 2.8
+# Avoid the --if-exists option which only appeared in Git 2.15
+if ! git -c trailer.ifexists=doNothing interpret-trailers \
+      --trailer "Change-Id: I${random}" < "$1" > "${dest}" ; then
+  echo "cannot insert change-id line in $1"
+  exit 1
+fi
+
+if ! mv "${dest}" "$1" ; then
+  echo "cannot mv ${dest} to $1"
+  exit 1
+fi