Re: Why doesn't merge fail if message has only sign-off?

@@ -748,6 +748,39 @@ static void abort_commit(struct commit_list *remoteheads, const char *err_msg)
 	exit(1);
 }
 
+/*
+ * Find out if the message in the strbuf contains only whitespace and
+ * Signed-off-by lines.
+ *
+ * This function is the "rest_is_space" function of "commit" with the unwanted
+ * parameter removed.
+ */
+static int message_is_empty(struct strbuf *sb)
+{
+	int i, eol;
+	const char *nl;
+
+	/* Check if the rest is just whitespace and Signed-off-by's. */
+	for (i = 0; i < sb->len; i++) {
+		nl = memchr(sb->buf + i, '\n', sb->len - i);
+		if (nl)
+			eol = nl - sb->buf;
+		else
+			eol = sb->len;
+
+		if (strlen(sign_off_header) <= eol - i &&
+		    starts_with(sb->buf + i, sign_off_header)) {
+			i = eol;
+			continue;
+		}
+		while (i < eol)
+			if (!isspace(sb->buf[i++]))
+				return 0;
+	}
+
+	return 1;
+}
+
 static const char merge_editor_comment[] =
 N_("Please enter a commit message to explain why this merge is necessary,\n"
    "especially if it merges an updated upstream into a topic branch.\n"

@@ -772,7 +805,7 @@ static void prepare_to_commit(struct commit_list *remoteheads)
 	}
 	read_merge_msg(&msg);
 	strbuf_stripspace(&msg, 0 < option_edit);
-	if (!msg.len)
+	if (!msg.len || message_is_empty(&msg))
 		abort_commit(remoteheads, _("Empty commit message."));
 	strbuf_release(&merge_msg);
 	strbuf_addbuf(&merge_msg, &msg);

@@ -783,6 +783,7 @@ LIB_OBJS += merge.o
 LIB_OBJS += merge-blobs.o
 LIB_OBJS += merge-recursive.o
 LIB_OBJS += mergesort.o
+LIB_OBJS += message-validator.o
 LIB_OBJS += mru.o
 LIB_OBJS += name-hash.o
 LIB_OBJS += notes.o

@@ -33,6 +33,7 @@
 #include "notes-utils.h"
 #include "mailmap.h"
 #include "sigchain.h"
+#include "message-validator.h"
 
 static const char * const builtin_commit_usage[] = {
 	N_("git commit [<options>] [--] <pathspec>..."),

@@ -979,41 +980,11 @@ static int prepare_to_commit(const char *index_file, const char *prefix,
 	return 1;
 }
 
-static int rest_is_empty(struct strbuf *sb, int start)
-{
-	int i, eol;
-	const char *nl;
-
-	/* Check if the rest is just whitespace and Signed-of-by's. */
-	for (i = start; i < sb->len; i++) {
-		nl = memchr(sb->buf + i, '\n', sb->len - i);
-		if (nl)
-			eol = nl - sb->buf;
-		else
-			eol = sb->len;
-
-		if (strlen(sign_off_header) <= eol - i &&
-		    starts_with(sb->buf + i, sign_off_header)) {
-			i = eol;
-			continue;
-		}
-		while (i < eol)
-			if (!isspace(sb->buf[i++]))
-				return 0;
-	}
-
-	return 1;
-}
-
-/*
- * Find out if the message in the strbuf contains only whitespace and
- * Signed-off-by lines.
- */
-static int message_is_empty(struct strbuf *sb)
+static int is_empty(struct strbuf *sb)
 {
 	if (cleanup_mode == CLEANUP_NONE && sb->len)
 		return 0;
-	return rest_is_empty(sb, 0);
+	return message_is_empty(sb, 0);
 }
 
 /*

@@ -1035,7 +1006,7 @@ static int template_untouched(struct strbuf *sb)
 	if (!skip_prefix(sb->buf, tmpl.buf, &start))
 		start = sb->buf;
 	strbuf_release(&tmpl);
-	return rest_is_empty(sb, start - sb->buf);
+	return message_is_empty(sb, start - sb->buf);
 }
 
 static const char *find_author_by_nickname(const char *name)

@@ -1744,7 +1715,7 @@ int cmd_commit(int argc, const char **argv, const char *prefix)
 		fprintf(stderr, _("Aborting commit; you did not edit the message.\n"));
 		exit(1);
 	}
-	if (message_is_empty(&sb) && !allow_empty_message) {
+	if (is_empty(&sb) && !allow_empty_message) {
 		rollback_index_files();
 		fprintf(stderr, _("Aborting commit due to empty commit message.\n"));
 		exit(1);

@@ -31,6 +31,7 @@
 #include "gpg-interface.h"
 #include "sequencer.h"
 #include "string-list.h"
+#include "message-validator.h"
 
 #define DEFAULT_TWOHEAD (1<<0)
 #define DEFAULT_OCTOPUS (1<<1)

@@ -772,7 +773,7 @@ static void prepare_to_commit(struct commit_list *remoteheads)
 	}
 	read_merge_msg(&msg);
 	strbuf_stripspace(&msg, 0 < option_edit);
-	if (!msg.len)
+	if (!msg.len || message_is_empty(&msg, 0))
 		abort_commit(remoteheads, _("Empty commit message."));
 	strbuf_release(&merge_msg);
 	strbuf_addbuf(&merge_msg, &msg);

@@ -0,0 +1,34 @@
+#include "git-compat-util.h"
+#include "sequencer.h"
+#include "strbuf.h"
+#include "message-validator.h"
+
+/*
+ * Find out if the message in the strbuf contains only whitespace and
+ * Signed-off-by lines.
+ */
+int message_is_empty(struct strbuf *sb, int start)
+{
+	int i, eol;
+	const char *nl;
+
+	/* Check if the rest is just whitespace and Signed-of-by's. */
+	for (i = start; i < sb->len; i++) {
+		nl = memchr(sb->buf + i, '\n', sb->len - i);
+		if (nl)
+			eol = nl - sb->buf;
+		else
+			eol = sb->len;
+
+		if (strlen(sign_off_header) <= eol - i &&
+		    starts_with(sb->buf + i, sign_off_header)) {
+			i = eol;
+			continue;
+		}
+		while (i < eol)
+			if (!isspace(sb->buf[i++]))
+				return 0;
+	}
+
+	return 1;
+}

@@ -0,0 +1,6 @@
+#ifndef MESSAGE_VALIDATOR_H
+#define MESSAGE_VALIDATOR_H
+
+extern int message_is_empty(struct strbuf *sb, int start);
+
+#endif