unknown-words: Suggest merging

When someone creates a PR to a branch with check-spelling and their head
branch doesn't have check-spelling, the metadata update can't happen on
their head branch, so instead the instructions are to update the
metadata branch.

In order to make this make sense and be useful / helpful, the branch
with the updated metadata must be merged into the head branch.

Author: jsoref

unknown-words.sh

@@ -2643,6 +2643,7 @@ spelling_body() {
 
         $B sh
         $err
+        $(generate_merge_instructions "git commit -m 'updating check-spelling metadata' && " "")
         $B
         </details>
         " | strip_lead)"
@@ -2885,6 +2886,18 @@ add_talk_to_bot_message() {
   fi
 }
 
+escape_git_branch() {
+  echo "$1" | perl -pe "s/'/$q$Q$q$Q$q/g"
+}
+
+generate_merge_instructions() {
+  text_before="$1"
+  text_after="$2"
+  if [ -n "$GITHUB_HEAD_REF" ] && [ "$remote_ref" != "$GITHUB_HEAD_REF" ]; then
+    echo "${text_before}git checkout '$(escape_git_branch "$GITHUB_HEAD_REF")' && git merge '$(escape_git_branch "$remote_ref")'${text_after}"
+  fi
+}
+
 generate_sample_commit_help() {
   if [ ! -s "$tokens_file" ]; then
     return
@@ -2939,6 +2952,7 @@ generate_sample_commit_help() {
     echo "git am <<'$delim'"
     cat "$git_apply_commit"
     echo "$delim$n$B$N"
+    generate_merge_instructions "$b" "$b"
     echo 'And `git push` ...'
     echo "</details>$N**OR**$N"
   else