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diff --git a/builtin/commit-tree.c b/builtin/commit-tree.c
--- /dev/null
+++ b/builtin/commit-tree.c
@@ -0,0 +1,133 @@
+/*
+ * GIT - The information manager from hell
+ *
+ * Copyright (C) Linus Torvalds, 2005
+ */
+#include "cache.h"
+#include "commit.h"
+#include "tree.h"
+#include "builtin.h"
+#include "utf8.h"
+
+/*
+ * FIXME! Share the code with "write-tree.c"
+ */
+static void check_valid(unsigned char *sha1, enum object_type expect)
+{
+ enum object_type type = sha1_object_info(sha1, NULL);
+ if (type < 0)
+ die("%s is not a valid object", sha1_to_hex(sha1));
+ if (type != expect)
+ die("%s is not a valid '%s' object", sha1_to_hex(sha1),
+ typename(expect));
+}
+
+static const char commit_tree_usage[] = "git commit-tree <sha1> [-p <sha1>]* < changelog";
+
+static void new_parent(struct commit *parent, struct commit_list **parents_p)
+{
+ unsigned char *sha1 = parent->object.sha1;
+ struct commit_list *parents;
+ for (parents = *parents_p; parents; parents = parents->next) {
+ if (parents->item == parent) {
+ error("duplicate parent %s ignored", sha1_to_hex(sha1));
+ return;
+ }
+ parents_p = &parents->next;
+ }
+ commit_list_insert(parent, parents_p);
+}
+
+static const char commit_utf8_warn[] =
+"Warning: commit message does not conform to UTF-8.\n"
+"You may want to amend it after fixing the message, or set the config\n"
+"variable i18n.commitencoding to the encoding your project uses.\n";
+
+int commit_tree(const char *msg, unsigned char *tree,
+ struct commit_list *parents, unsigned char *ret,
+ const char *author)
+{
+ int result;
+ int encoding_is_utf8;
+ struct strbuf buffer;
+
+ check_valid(tree, OBJ_TREE);
+
+ /* Not having i18n.commitencoding is the same as having utf-8 */
+ encoding_is_utf8 = is_encoding_utf8(git_commit_encoding);
+
+ strbuf_init(&buffer, 8192); /* should avoid reallocs for the headers */
+ strbuf_addf(&buffer, "tree %s\n", sha1_to_hex(tree));
+
+ /*
+ * NOTE! This ordering means that the same exact tree merged with a
+ * different order of parents will be a _different_ changeset even
+ * if everything else stays the same.
+ */
+ while (parents) {
+ struct commit_list *next = parents->next;
+ strbuf_addf(&buffer, "parent %s\n",
+ sha1_to_hex(parents->item->object.sha1));
+ free(parents);
+ parents = next;
+ }
+
+ /* Person/date information */
+ if (!author)
+ author = git_author_info(IDENT_ERROR_ON_NO_NAME);
+ strbuf_addf(&buffer, "author %s\n", author);
+ strbuf_addf(&buffer, "committer %s\n", git_committer_info(IDENT_ERROR_ON_NO_NAME));
+ if (!encoding_is_utf8)
+ strbuf_addf(&buffer, "encoding %s\n", git_commit_encoding);
+ strbuf_addch(&buffer, '\n');
+
+ /* And add the comment */
+ strbuf_addstr(&buffer, msg);
+
+ /* And check the encoding */
+ if (encoding_is_utf8 && !is_utf8(buffer.buf))
+ fprintf(stderr, commit_utf8_warn);
+
+ result = write_sha1_file(buffer.buf, buffer.len, commit_type, ret);
+ strbuf_release(&buffer);
+ return result;
+}
+
+int cmd_commit_tree(int argc, const char **argv, const char *prefix)
+{
+ int i;
+ struct commit_list *parents = NULL;
+ unsigned char tree_sha1[20];
+ unsigned char commit_sha1[20];
+ struct strbuf buffer = STRBUF_INIT;
+
+ git_config(git_default_config, NULL);
+
+ if (argc < 2 || !strcmp(argv[1], "-h"))
+ usage(commit_tree_usage);
+ if (get_sha1(argv[1], tree_sha1))
+ die("Not a valid object name %s", argv[1]);
+
+ for (i = 2; i < argc; i += 2) {
+ unsigned char sha1[20];
+ const char *a, *b;
+ a = argv[i]; b = argv[i+1];
+ if (!b || strcmp(a, "-p"))
+ usage(commit_tree_usage);
+
+ if (get_sha1(b, sha1))
+ die("Not a valid object name %s", b);
+ check_valid(sha1, OBJ_COMMIT);
+ new_parent(lookup_commit(sha1), &parents);
+ }
+
+ if (strbuf_read(&buffer, 0, 0) < 0)
+ die_errno("git commit-tree: failed to read");
+
+ if (!commit_tree(buffer.buf, tree_sha1, parents, commit_sha1, NULL)) {
+ printf("%s\n", sha1_to_hex(commit_sha1));
+ return 0;
+ }
+ else
+ return 1;
+}