Merge branch 'mg/killed-merge' into maint

Killing "git merge --edit" before the editor returns control left
the repository in a state with MERGE_MSG but without MERGE_HEAD,
which incorrectly tells the subsequent "git commit" that there was
a squash merge in progress.  This has been fixed.

* mg/killed-merge:
  merge: save merge state earlier
  merge: split write_merge_state in two
  merge: clarify call chain
  Documentation/git-merge: explain --continue

Documentation/git-merge.txt

@@ -280,7 +280,10 @@ After seeing a conflict, you can do two things:
 
  * Resolve the conflicts.  Git will mark the conflicts in
    the working tree.  Edit the files into shape and
-   'git add' them to the index.  Use 'git commit' to seal the deal.
+   'git add' them to the index.  Use 'git commit' or
+   'git merge --continue' to seal the deal. The latter command
+   checks whether there is a (interrupted) merge in progress
+   before calling 'git commit'.
 
 You can work through the conflict with a number of tools:
 

builtin/merge.c

@@ -756,13 +756,17 @@ N_("Please enter a commit message to explain why this merge is necessary,\n"
    "Lines starting with '%c' will be ignored, and an empty message aborts\n"
    "the commit.\n");
 
+static void write_merge_heads(struct commit_list *);
 static void prepare_to_commit(struct commit_list *remoteheads)
 {
 	struct strbuf msg = STRBUF_INIT;
 	strbuf_addbuf(&msg, &merge_msg);
 	strbuf_addch(&msg, '\n');
+	if (squash)
+		BUG("the control must not reach here under --squash");
 	if (0 < option_edit)
 		strbuf_commented_addf(&msg, _(merge_editor_comment), comment_line_char);
+	write_merge_heads(remoteheads);
 	write_file_buf(git_path_merge_msg(), msg.buf, msg.len);
 	if (run_commit_hook(0 < option_edit, get_index_file(), "prepare-commit-msg",
 			    git_path_merge_msg(), "merge", NULL))
@@ -904,7 +908,7 @@ static int setup_with_upstream(const char ***argv)
 	return i;
 }
 
-static void write_merge_state(struct commit_list *remoteheads)
+static void write_merge_heads(struct commit_list *remoteheads)
 {
 	struct commit_list *j;
 	struct strbuf buf = STRBUF_INIT;
@@ -920,8 +924,6 @@ static void write_merge_state(struct commit_list *remoteheads)
 		strbuf_addf(&buf, "%s\n", oid_to_hex(oid));
 	}
 	write_file_buf(git_path_merge_head(), buf.buf, buf.len);
-	strbuf_addch(&merge_msg, '\n');
-	write_file_buf(git_path_merge_msg(), merge_msg.buf, merge_msg.len);
 
 	strbuf_reset(&buf);
 	if (fast_forward == FF_NO)
@@ -929,6 +931,13 @@ static void write_merge_state(struct commit_list *remoteheads)
 	write_file_buf(git_path_merge_mode(), buf.buf, buf.len);
 }
 
+static void write_merge_state(struct commit_list *remoteheads)
+{
+	write_merge_heads(remoteheads);
+	strbuf_addch(&merge_msg, '\n');
+	write_file_buf(git_path_merge_msg(), merge_msg.buf, merge_msg.len);
+}
+
 static int default_edit_option(void)
 {
 	static const char name[] = "GIT_MERGE_AUTOEDIT";

t/t7600-merge.sh

@@ -774,4 +774,19 @@ test_expect_success 'merge can be completed with --continue' '
 	verify_parents $c0 $c1
 '
 
+write_script .git/FAKE_EDITOR <<EOF
+# kill -TERM command added below.
+EOF
+
+test_expect_success EXECKEEPSPID 'killed merge can be completed with --continue' '
+	git reset --hard c0 &&
+	! "$SHELL_PATH" -c '\''
+	  echo kill -TERM $$ >> .git/FAKE_EDITOR
+	  GIT_EDITOR=.git/FAKE_EDITOR
+	  export GIT_EDITOR
+	  exec git merge --no-ff --edit c1'\'' &&
+	git merge --continue &&
+	verify_parents $c0 $c1
+'
+
 test_done