Re: [BUG] git diff-tree --stdin doesn't accept two trees

@@ -14,20 +14,10 @@ static int diff_tree_commit_sha1(const unsigned char *sha1)
 	return log_tree_commit(&log_tree_opt, commit);
 }
 
-static int diff_tree_stdin(char *line)
+/* Diff one or more commits. */
+static int stdin_diff_commit(struct commit *commit, char *line, int len)
 {
-	int len = strlen(line);
 	unsigned char sha1[20];
-	struct commit *commit;
-
-	if (!len || line[len-1] != '\n')
-		return -1;
-	line[len-1] = 0;
-	if (get_sha1_hex(line, sha1))
-		return -1;
-	commit = lookup_commit(sha1);
-	if (!commit || parse_commit(commit))
-		return -1;
 	if (isspace(line[40]) && !get_sha1_hex(line+41, sha1)) {
 		/* Graft the fake parents locally to the commit */
 		int pos = 41;

@@ -52,6 +42,23 @@ static int diff_tree_stdin(char *line)
 	return log_tree_commit(&log_tree_opt, commit);
 }
 
+static int diff_tree_stdin(char *line)
+{
+	int len = strlen(line);
+	unsigned char sha1[20];
+	struct commit *commit;
+
+	if (!len || line[len-1] != '\n')
+		return -1;
+	line[len-1] = 0;
+	if (get_sha1_hex(line, sha1))
+		return -1;
+	commit = lookup_commit(sha1);
+	if (!commit || parse_commit(commit))
+		return -1;
+	return stdin_diff_commit(commit, line, len);
+}
+
 static const char diff_tree_usage[] =
 "git diff-tree [--stdin] [-m] [-c] [--cc] [-s] [-v] [--pretty] [-t] [-r] [--root] "
 "[<common diff options>] <tree-ish> [<tree-ish>] [<path>...]\n"

@@ -169,6 +169,20 @@ test_expect_success \
      cmp -s .test-a .test-recursive-AB'
 
 test_expect_success \
+    'diff-tree --stdin of known trees.' \
+    'echo $tree_A $tree_B | git diff-tree --stdin > .test-a &&
+     echo $tree_A $tree_B > .test-plain-ABx &&
+     cat .test-plain-AB >> .test-plain-ABx &&
+     cmp -s .test-a .test-plain-ABx'
+
+test_expect_success \
+    'diff-tree --stdin of known trees.' \
+    'echo $tree_A $tree_B | git diff-tree -r --stdin > .test-a &&
+     echo $tree_A $tree_B > .test-recursive-ABx &&
+     cat .test-recursive-AB >> .test-recursive-ABx &&
+     cmp -s .test-a .test-recursive-ABx'
+
+test_expect_success \
     'diff-cache O with A in cache' \
     'git read-tree $tree_A &&
      git diff-index --cached $tree_O >.test-a &&

@@ -49,13 +49,17 @@ include::diff-options.txt[]
 --stdin::
 	When '--stdin' is specified, the command does not take
 	<tree-ish> arguments from the command line.  Instead, it
-	reads either one <commit> or a list of <commit>
-	separated with a single space from its standard input.
+	reads lines containing either two <tree>, one <commit>, or a
+	list of <commit> from its standard input.  (Use a single space
+	as separator.)
 +
-When a single commit is given on one line of such input, it compares
-the commit with its parents.  The following flags further affects its
-behavior.  The remaining commits, when given, are used as if they are
+When two trees are given, it compares the first tree with the second.
+When a single commit is given, it compares the commit with its
+parents.  The remaining commits, when given, are used as if they are
 parents of the first commit.
++
+The following flags further affects the behavior when comparing
+commits (but not trees).
 
 -m::
 	By default, 'git-diff-tree --stdin' does not show

@@ -42,21 +42,48 @@ static int stdin_diff_commit(struct commit *commit, char *line, int len)
 	return log_tree_commit(&log_tree_opt, commit);
 }
 
+/* Diff two trees. */
+static int stdin_diff_trees(struct tree *tree1, char *line, int len)
+{
+	unsigned char sha1[20];
+	struct tree *tree2;
+	if (len != 82 || !isspace(line[40]) || get_sha1_hex(line + 41, sha1)) {
+		error("Need precisely two trees, separated by one space");
+		return -1;
+	}
+	tree2 = lookup_tree(sha1);
+	if (!tree2 || parse_tree(tree2))
+		return -1;
+	printf("%s %s\n", sha1_to_hex(tree1->object.sha1),
+			  sha1_to_hex(tree2->object.sha1));
+	diff_tree_sha1(tree1->object.sha1, tree2->object.sha1,
+		       "", &log_tree_opt.diffopt);
+	log_tree_diff_flush(&log_tree_opt);
+	return 0;
+}
+
 static int diff_tree_stdin(char *line)
 {
 	int len = strlen(line);
 	unsigned char sha1[20];
-	struct commit *commit;
+	struct object *obj;
 
 	if (!len || line[len-1] != '\n')
 		return -1;
 	line[len-1] = 0;
 	if (get_sha1_hex(line, sha1))
 		return -1;
-	commit = lookup_commit(sha1);
-	if (!commit || parse_commit(commit))
+	obj = lookup_object(sha1);
+	obj = obj ? obj : parse_object(sha1);
+	if (!obj)
 		return -1;
-	return stdin_diff_commit(commit, line, len);
+	if (obj->type == OBJ_COMMIT)
+		return stdin_diff_commit((struct commit *)obj, line, len);
+	if (obj->type == OBJ_TREE)
+		return stdin_diff_trees((struct tree *)obj, line, len);
+	error("Object %s is a %s, not a commit or tree",
+	      sha1_to_hex(sha1), typename(obj->type));
+	return -1;
 }
 
 static const char diff_tree_usage[] =