Re: [RFC/PATCH 4/4] replace: add --edit option

This allows you to run:

    git replace --edit SHA1

to get dumped in an editor with the contents of the object
for SHA1. The result is then read back in and used as a
"replace" object for SHA1. The writing/reading is
type-aware, so you get to edit "ls-tree" output rather than
the binary tree format.

Signed-off-by: Jeff King <redacted>
---

diff --git a/builtin/replace.c b/builtin/replace.c
index a090302..3ed5f75 100644
--- a/builtin/replace.c
+++ b/builtin/replace.c

@@ -176,6 +177,105 @@ static int replace_object(const char *object_ref, const char *replace_ref, int f
        return replace_object_sha1(object_ref, object, replace_ref, repl, force);
 }

+/*
+ * Read a previously-exported (and possibly edited) object back from "filename",
+ * interpreting it as "type", and writing the result to the object database.
+ * The sha1 of the written object is returned via sha1.
+ */
+static void import_object(unsigned char *sha1, enum object_type type,
+                         const char *filename)
+{
+       int fd;
+
+       fd = open(filename, O_RDONLY);
+       if (fd < 0)
+               die_errno("unable to open %s for reading", filename);
+
+       if (type == OBJ_TREE) {
+               const char *argv[] = { "mktree", NULL };
+               struct child_process cmd = { argv };
+               struct strbuf result = STRBUF_INIT;
+
+               cmd.argv = argv;
+               cmd.git_cmd = 1;
+               cmd.in = fd;
+               cmd.out = -1;
+
+               if (start_command(&cmd))
+                       die("unable to spawn mktree");
+
+               if (strbuf_read(&result, cmd.out, 41) < 0)
+                       die_errno("unable to read from mktree");
+               close(cmd.out);
+
+               if (finish_command(&cmd))
+                       die("mktree reported failure");
+               if (get_sha1_hex(result.buf, sha1) < 0)
+                       die("mktree did not return an object name");