git-hooks/pre-commit: Allow merging deps2submodules changes from upstream

build/git-hooks/pre-commit

 #!/bin/sh
 
-submods=$(git diff-index --cached --ignore-submodules=dirty HEAD | grep -e '^:160000' -e '^:...... 160000' | xargs)
+submodule_diff() {
+  if test -n "$2"; then
+    git diff-tree -r --ignore-submodules=dirty "$1" "$2" | grep -e '^:160000' -e '^:...... 160000' | xargs
+  else
+    git diff-index --cached --ignore-submodules=dirty "$1" | grep -e '^:160000' -e '^:...... 160000' | xargs
+  fi
+}
+
+if git rev-parse --verify --quiet --no-revs MERGE_HEAD; then
+  merge_base=$(git merge-base HEAD MERGE_HEAD)
+  if test -z "$(submodule_diff $merge_base HEAD)"; then
+    # Most up-to-date submodules are in MERGE_HEAD.
+    head_ref=MERGE_HEAD
+  else
+    # Most up-to-date submodules are in HEAD.
+    head_ref=HEAD
+  fi
+else
+  # No merge in progress. Submodules must match HEAD.
+  head_ref=HEAD
+fi
+
+submods=$(submodule_diff $head_ref)
 if test "$submods"; then
   echo "You are trying to commit changes to the following submodules:" 1>&2
   echo 1>&2
   echo $submods | cut -d ' ' -f 6 | sed 's/^/  /g' 1>&2
   cat <<EOF 1>&2
 
 Submodule commits are not allowed.  Please run:
 
   git status --ignore-submodules=dirty
 
 and/or:
 
   git diff-index --cached --ignore-submodules=dirty HEAD
 
 ... to see what's in your index.
 
 If you're really and truly trying to roll the version of a submodule, you should
 commit the new version to DEPS, instead.
 EOF
   exit 1
 fi
 
-if [ -n "$(git ls-files .gitmodules)" ] &&
-   [ -n "$(git diff-index --cached HEAD .gitmodules)" ]; then
+gitmodules_diff() {
+  git diff-index --cached "$1" .gitmodules
+}
+
+if test "$(git ls-files .gitmodules)" -a "$(gitmodules_diff $head_ref)"; then

[Ami GONE FROM CHROMIUM, 2014/04/04 18:07:13]

This change undid the benefit of r257470 because
test "$(/bin/false)" -a "$(echo foo >&2)"
doesn't short-circuit before running the second command, whereas
[ "$(/bin/false)" ] && [ "$(echo foo >&2)" ]
does short-circuit.

Was there any reason to make the change from [ to test other than aesthetics? 
(any objection to me flipping it back?)

[spang, 2014/04/04 18:14:02]

My bad.
There's no intentional change here, since it was always "test".

Your CL changed it to [[, and then it changed to [.

   cat <<EOF 1>&2
 You are trying to commit a change to .gitmodules.  That is not allowed.
 To make changes to submodule names/paths, edit DEPS.
 EOF
   exit 1
 fi
 
 exit 0