diff-tree: abbreviate merge parent object names with --abbrev --pretty.

When --abbrev is in effect, abbreviate the merge parent names
in prettyprinted output.

Signed-off-by: Junio C Hamano <junkio@cox.net>

commit.c

@@ -426,9 +426,10 @@ static int is_empty_line(const char *line, int len)
 	return !len;
 }
 
-static int add_parent_info(enum cmit_fmt fmt, char *buf, const char *line, int parents)
+static int add_parent_info(enum cmit_fmt fmt, char *buf, const char *line, int parents, int abbrev)
 {
 	int offset = 0;
+	unsigned char sha1[20];
 
 	if (fmt == CMIT_FMT_ONELINE)
 		return offset;
@@ -437,17 +438,25 @@ static int add_parent_info(enum cmit_fmt fmt, char *buf, const char *line, int p
 		break;
 	case 2:
 		/* Go back to the previous line: 40 characters of previous parent, and one '\n' */
-		offset = sprintf(buf, "Merge: %.40s\n", line-41);
+		if (abbrev && !get_sha1_hex(line-41, sha1))
+			offset = sprintf(buf, "Merge: %s\n",
+					 find_unique_abbrev(sha1, abbrev));
+		else
+			offset = sprintf(buf, "Merge: %.40s\n", line-41);
 		/* Fallthrough */
 	default:
 		/* Replace the previous '\n' with a space */
 		buf[offset-1] = ' ';
-		offset += sprintf(buf + offset, "%.40s\n", line+7);
+		if (abbrev && !get_sha1_hex(line+7, sha1))
+			offset += sprintf(buf + offset, "%s\n",
+					 find_unique_abbrev(sha1, abbrev));
+		else
+			offset += sprintf(buf + offset, "%.40s\n", line+7);
 	}
 	return offset;
 }
 
-unsigned long pretty_print_commit(enum cmit_fmt fmt, const char *msg, unsigned long len, char *buf, unsigned long space)
+unsigned long pretty_print_commit(enum cmit_fmt fmt, const char *msg, unsigned long len, char *buf, unsigned long space, int abbrev)
 {
 	int hdr = 1, body = 0;
 	unsigned long offset = 0;
@@ -488,7 +497,7 @@ unsigned long pretty_print_commit(enum cmit_fmt fmt, const char *msg, unsigned l
 			if (!memcmp(line, "parent ", 7)) {
 				if (linelen != 48)
 					die("bad parent line in commit");
-				offset += add_parent_info(fmt, buf + offset, line, ++parents);
+				offset += add_parent_info(fmt, buf + offset, line, ++parents, abbrev);
 			}
 
 			/*

commit.h

@@ -48,7 +48,7 @@ enum cmit_fmt {
 };
 
 extern enum cmit_fmt get_commit_format(const char *arg);
-extern unsigned long pretty_print_commit(enum cmit_fmt fmt, const char *msg, unsigned long len, char *buf, unsigned long space);
+extern unsigned long pretty_print_commit(enum cmit_fmt fmt, const char *msg, unsigned long len, char *buf, unsigned long space, int abbrev);
 
 /** Removes the first commit from a list sorted by date, and adds all
  * of its parents.

diff-tree.c

@@ -84,7 +84,7 @@ static const char *generate_header(const unsigned char *commit_sha1,
 			 diff_unique_abbrev(parent_sha1, abbrev) : "root");
 	offset += pretty_print_commit(commit_format, msg, len,
 				      this_header + offset,
-				      sizeof(this_header) - offset);
+				      sizeof(this_header) - offset, abbrev);
 	return this_header;
 }
 

rev-list.c

@@ -81,7 +81,7 @@ static void show_commit(struct commit *commit)
 
 	if (verbose_header) {
 		static char pretty_header[16384];
-		pretty_print_commit(commit_format, commit->buffer, ~0, pretty_header, sizeof(pretty_header));
+		pretty_print_commit(commit_format, commit->buffer, ~0, pretty_header, sizeof(pretty_header), 0);
 		printf("%s%c", pretty_header, hdr_termination);
 	}
 	fflush(stdout);

show-branch.c

@@ -259,7 +259,7 @@ static void show_one_commit(struct commit *commit, int no_name)
 	struct commit_name *name = commit->object.util;
 	if (commit->object.parsed)
 		pretty_print_commit(CMIT_FMT_ONELINE, commit->buffer, ~0,
-				    pretty, sizeof(pretty));
+				    pretty, sizeof(pretty), 0);
 	else
 		strcpy(pretty, "(unavailable)");
 	if (!strncmp(pretty, "[PATCH] ", 8))