Improved pre-commit hook to automatically remove submodules (#21222)

no issue

# Before
The pre-commit hook would abort the commit if any submodules were staged
for commit, and prompt the user to manually un-stage them and retry the
commit.

# Now
The pre-commit hook automatically un-stages any staged submodules, then
allows the commit to proceed.

# Why?
This was a daily annoyance that caused many common git commands to
abort, and required manual un-staging of the submodules before retrying
the commit:
- `git commit -a`
- `git add . && git commit`
- `git add -A && git commit`

If we ever _do_ need to commit submodules, we can always add them back
and run `git commit --no-verify` to accomplish that (which we would have
needed to do before regardless). This should accomplish the same goal of
not allowing submodules to be committed, but reduce the day to day
friction of making commits in Ghost.

.github/hooks/pre-commit

@@ -25,20 +25,23 @@ MOD_SUBMODULES=$(git diff --cached --name-only --ignore-submodules=none | grep -
 
 echo -e "Checking submodules ${grey}(pre-commit hook)${no_color} "
 
-# If no modified submodules, exit with status code 0, else prompt the
-# user and exit accordingly
+# If no modified submodules, exit with status code 0, else remove them and continue
 if [[ -n "$MOD_SUBMODULES" ]]; then
-    echo "Submodules to be committed:"
-    echo "  (use \"git reset HEAD <file>...\" to unstage)"
-    echo
-
+    echo -e "${grey}Removing submodules from commit...${no_color}"
     for SUB in $MOD_SUBMODULES
     do
-        echo -e "\t${green}modified:\t$SUB${no_color}"
+        git reset --quiet HEAD "$SUB"
+        echo -e "\t${grey}removed:\t$SUB${no_color}"
     done
     echo
-    echo -e "${red}Aborting commit due to submodule update. Please unstage the submodule(s) and commit again.${no_color}"
-    exit 1
+    echo -e "${grey}Submodules removed from commit, continuing...${no_color}"
+
+    # If there are no changes to commit after removing submodules, abort to avoid an empty commit
+    if output=$(git status --porcelain) && [ -z "$output" ]; then
+        echo -e "nothing to commit, working tree clean"
+        exit 1
+    fi
+    exit 0
 else
     echo "No submodules in commit, continuing..."
     exit 0