Merge branch 'cc/replace-edit'

"git replace" learns a new "--edit" option.

* cc/replace-edit:
  Documentation: replace: describe new --edit option
  replace: add --edit to usage string
  replace: add tests for --edit
  replace: die early if replace ref already exists
  replace: refactor checking ref validity
  replace: make sure --edit results in a different object
  replace: add --edit option
  replace: factor object resolution out of replace_object
  replace: use OPT_CMDMODE to handle modes
  replace: refactor command-mode determination

3 files changed, 222 insertions, 46 deletions

diff --git a/Documentation/git-replace.txt b/Documentation/git-replace.txt
index 0a02f70657..61461b9f33 100644
--- a/Documentation/git-replace.txt
+++ b/Documentation/git-replace.txt
@@ -9,6 +9,7 @@ SYNOPSIS
 --------
 [verse]
 'git replace' [-f] <object> <replacement>
+'git replace' [-f] --edit <object>
 'git replace' -d <object>...
 'git replace' [--format=<format>] [-l [<pattern>]]
 
@@ -63,6 +64,15 @@ OPTIONS
 --delete::
 	Delete existing replace refs for the given objects.
 
+--edit <object>::
+	Edit an object's content interactively. The existing content
+	for <object> is pretty-printed into a temporary file, an
+	editor is launched on the file, and the result is parsed to
+	create a new object of the same type as <object>. A
+	replacement ref is then created to replace <object> with the
+	newly created object. See linkgit:git-var[1] for details about
+	how the editor will be chosen.
+
 -l <pattern>::
 --list <pattern>::
 	List replace refs for objects that match the given pattern (or
@@ -92,7 +102,9 @@ CREATING REPLACEMENT OBJECTS
 
 linkgit:git-filter-branch[1], linkgit:git-hash-object[1] and
 linkgit:git-rebase[1], among other git commands, can be used to create
-replacement objects from existing objects.
+replacement objects from existing objects. The `--edit` option can
+also be used with 'git replace' to create a replacement object by
+editing an existing object.
 
 If you want to replace many blobs, trees or commits that are part of a
 string of commits, you may just want to create a replacement string of
@@ -117,6 +129,8 @@ linkgit:git-filter-branch[1]
 linkgit:git-rebase[1]
 linkgit:git-tag[1]
 linkgit:git-branch[1]
+linkgit:git-commit[1]
+linkgit:git-var[1]
 linkgit:git[1]
 
 GIT
diff --git a/builtin/replace.c b/builtin/replace.c
index b62420a01a..1bb491d3c4 100644
--- a/builtin/replace.c
+++ b/builtin/replace.c
@@ -12,9 +12,11 @@
 #include "builtin.h"
 #include "refs.h"
 #include "parse-options.h"
+#include "run-command.h"
 
 static const char * const git_replace_usage[] = {
 	N_("git replace [-f] <object> <replacement>"),
+	N_("git replace [-f] --edit <object>"),
 	N_("git replace -d <object>..."),
 	N_("git replace [--format=<format>] [-l [<pattern>]]"),
 	NULL
@@ -123,26 +125,36 @@ static int delete_replace_ref(const char *name, const char *ref,
 	return 0;
 }
 
-static int replace_object(const char *object_ref, const char *replace_ref,
-			  int force)
+static void check_ref_valid(unsigned char object[20],
+			    unsigned char prev[20],
+			    char *ref,
+			    int ref_size,
+			    int force)
 {
-	unsigned char object[20], prev[20], repl[20];
-	enum object_type obj_type, repl_type;
-	char ref[PATH_MAX];
-	struct ref_lock *lock;
-
-	if (get_sha1(object_ref, object))
-		die("Failed to resolve '%s' as a valid ref.", object_ref);
-	if (get_sha1(replace_ref, repl))
-		die("Failed to resolve '%s' as a valid ref.", replace_ref);
-
-	if (snprintf(ref, sizeof(ref),
+	if (snprintf(ref, ref_size,
 		     "refs/replace/%s",
-		     sha1_to_hex(object)) > sizeof(ref) - 1)
+		     sha1_to_hex(object)) > ref_size - 1)
 		die("replace ref name too long: %.*s...", 50, ref);
 	if (check_refname_format(ref, 0))
 		die("'%s' is not a valid ref name.", ref);
 
+	if (read_ref(ref, prev))
+		hashclr(prev);
+	else if (!force)
+		die("replace ref '%s' already exists", ref);
+}
+
+static int replace_object_sha1(const char *object_ref,
+			       unsigned char object[20],
+			       const char *replace_ref,
+			       unsigned char repl[20],
+			       int force)
+{
+	unsigned char prev[20];
+	enum object_type obj_type, repl_type;
+	char ref[PATH_MAX];
+	struct ref_lock *lock;
+
 	obj_type = sha1_object_info(object, NULL);
 	repl_type = sha1_object_info(repl, NULL);
 	if (!force && obj_type != repl_type)
@@ -152,10 +164,7 @@ static int replace_object(const char *object_ref, const char *replace_ref,
 		    object_ref, typename(obj_type),
 		    replace_ref, typename(repl_type));
 
-	if (read_ref(ref, prev))
-		hashclr(prev);
-	else if (!force)
-		die("replace ref '%s' already exists", ref);
+	check_ref_valid(object, prev, ref, sizeof(ref), force);
 
 	lock = lock_any_ref_for_update(ref, prev, 0, NULL);
 	if (!lock)
@@ -166,13 +175,140 @@ static int replace_object(const char *object_ref, const char *replace_ref,
 	return 0;
 }
 
+static int replace_object(const char *object_ref, const char *replace_ref, int force)
+{
+	unsigned char object[20], repl[20];
+
+	if (get_sha1(object_ref, object))
+		die("Failed to resolve '%s' as a valid ref.", object_ref);
+	if (get_sha1(replace_ref, repl))
+		die("Failed to resolve '%s' as a valid ref.", replace_ref);
+
+	return replace_object_sha1(object_ref, object, replace_ref, repl, force);
+}
+
+/*
+ * Write the contents of the object named by "sha1" to the file "filename",
+ * pretty-printed for human editing based on its type.
+ */
+static void export_object(const unsigned char *sha1, const char *filename)
+{
+	const char *argv[] = { "--no-replace-objects", "cat-file", "-p", NULL, NULL };
+	struct child_process cmd = { argv };
+	int fd;
+
+	fd = open(filename, O_WRONLY | O_CREAT | O_TRUNC, 0666);
+	if (fd < 0)
+		die_errno("unable to open %s for writing", filename);
+
+	argv[3] = sha1_to_hex(sha1);
+	cmd.git_cmd = 1;
+	cmd.out = fd;
+
+	if (run_command(&cmd))
+		die("cat-file reported failure");
+
+	close(fd);
+}
+
+/*
+ * 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");
+
+		strbuf_release(&result);
+	} else {
+		struct stat st;
+		int flags = HASH_FORMAT_CHECK | HASH_WRITE_OBJECT;
+
+		if (fstat(fd, &st) < 0)
+			die_errno("unable to fstat %s", filename);
+		if (index_fd(sha1, fd, &st, type, NULL, flags) < 0)
+			die("unable to write object to database");
+		/* index_fd close()s fd for us */
+	}
+
+	/*
+	 * No need to close(fd) here; both run-command and index-fd
+	 * will have done it for us.
+	 */
+}
+
+static int edit_and_replace(const char *object_ref, int force)
+{
+	char *tmpfile = git_pathdup("REPLACE_EDITOBJ");
+	enum object_type type;
+	unsigned char old[20], new[20], prev[20];
+	char ref[PATH_MAX];
+
+	if (get_sha1(object_ref, old) < 0)
+		die("Not a valid object name: '%s'", object_ref);
+
+	type = sha1_object_info(old, NULL);
+	if (type < 0)
+		die("unable to get object type for %s", sha1_to_hex(old));
+
+	check_ref_valid(old, prev, ref, sizeof(ref), force);
+
+	export_object(old, tmpfile);
+	if (launch_editor(tmpfile, NULL, NULL) < 0)
+		die("editing object file failed");
+	import_object(new, type, tmpfile);
+
+	free(tmpfile);
+
+	if (!hashcmp(old, new))
+		return error("new object is the same as the old one: '%s'", sha1_to_hex(old));
+
+	return replace_object_sha1(object_ref, old, "replacement", new, force);
+}
+
 int cmd_replace(int argc, const char **argv, const char *prefix)
 {
-	int list = 0, delete = 0, force = 0;
+	int force = 0;
 	const char *format = NULL;
+	enum {
+		MODE_UNSPECIFIED = 0,
+		MODE_LIST,
+		MODE_DELETE,
+		MODE_EDIT,
+		MODE_REPLACE
+	} cmdmode = MODE_UNSPECIFIED;
 	struct option options[] = {
-		OPT_BOOL('l', "list", &list, N_("list replace refs")),
-		OPT_BOOL('d', "delete", &delete, N_("delete replace refs")),
+		OPT_CMDMODE('l', "list", &cmdmode, N_("list replace refs"), MODE_LIST),
+		OPT_CMDMODE('d', "delete", &cmdmode, N_("delete replace refs"), MODE_DELETE),
+		OPT_CMDMODE('e', "edit", &cmdmode, N_("edit existing object"), MODE_EDIT),
 		OPT_BOOL('f', "force", &force, N_("replace the ref if it exists")),
 		OPT_STRING(0, "format", &format, N_("format"), N_("use this format")),
 		OPT_END()
@@ -182,44 +318,43 @@ int cmd_replace(int argc, const char **argv, const char *prefix)
 
 	argc = parse_options(argc, argv, prefix, options, git_replace_usage, 0);
 
-	if (list && delete)
-		usage_msg_opt("-l and -d cannot be used together",
-			      git_replace_usage, options);
+	if (!cmdmode)
+		cmdmode = argc ? MODE_REPLACE : MODE_LIST;
 
-	if (format && delete)
-		usage_msg_opt("--format and -d cannot be used together",
+	if (format && cmdmode != MODE_LIST)
+		usage_msg_opt("--format cannot be used when not listing",
 			      git_replace_usage, options);
 
-	if (force && (list || delete))
-		usage_msg_opt("-f cannot be used with -d or -l",
+	if (force && cmdmode != MODE_REPLACE && cmdmode != MODE_EDIT)
+		usage_msg_opt("-f only makes sense when writing a replacement",
 			      git_replace_usage, options);
 
-	/* Delete refs */
-	if (delete) {
+	switch (cmdmode) {
+	case MODE_DELETE:
 		if (argc < 1)
 			usage_msg_opt("-d needs at least one argument",
 				      git_replace_usage, options);
 		return for_each_replace_name(argv, delete_replace_ref);
-	}
 
-	/* Replace object */
-	if (!list && argc) {
+	case MODE_REPLACE:
 		if (argc != 2)
 			usage_msg_opt("bad number of arguments",
 				      git_replace_usage, options);
-		if (format)
-			usage_msg_opt("--format cannot be used when not listing",
-				      git_replace_usage, options);
 		return replace_object(argv[0], argv[1], force);
-	}
 
-	/* List refs, even if "list" is not set */
-	if (argc > 1)
-		usage_msg_opt("only one pattern can be given with -l",
-			      git_replace_usage, options);
-	if (force)
-		usage_msg_opt("-f needs some arguments",
-			      git_replace_usage, options);
+	case MODE_EDIT:
+		if (argc != 1)
+			usage_msg_opt("-e needs exactly one argument",
+				      git_replace_usage, options);
+		return edit_and_replace(argv[0], force);
+
+	case MODE_LIST:
+		if (argc > 1)
+			usage_msg_opt("only one pattern can be given with -l",
+				      git_replace_usage, options);
+		return list_replace_refs(argv[0], format);
 
-	return list_replace_refs(argv[0], format);
+	default:
+		die("BUG: invalid cmdmode %d", (int)cmdmode);
+	}
 }
diff --git a/t/t6050-replace.sh b/t/t6050-replace.sh
index 719a11673b..68b3cb26d9 100755
--- a/t/t6050-replace.sh
+++ b/t/t6050-replace.sh
@@ -318,6 +318,33 @@ test_expect_success 'test --format long' '
 	test_cmp expected actual
 '
 
+test_expect_success 'setup a fake editor' '
+	write_script fakeeditor <<-\EOF
+		sed -e "s/A U Thor/A fake Thor/" "$1" >"$1.new"
+		mv "$1.new" "$1"
+	EOF
+'
+
+test_expect_success '--edit with and without already replaced object' '
+	test_must_fail env GIT_EDITOR=./fakeeditor git replace --edit "$PARA3" &&
+	GIT_EDITOR=./fakeeditor git replace --force --edit "$PARA3" &&
+	git replace -l | grep "$PARA3" &&
+	git cat-file commit "$PARA3" | grep "A fake Thor" &&
+	git replace -d "$PARA3" &&
+	GIT_EDITOR=./fakeeditor git replace --edit "$PARA3" &&
+	git replace -l | grep "$PARA3" &&
+	git cat-file commit "$PARA3" | grep "A fake Thor"
+'
+
+test_expect_success '--edit and change nothing or command failed' '
+	git replace -d "$PARA3" &&
+	test_must_fail env GIT_EDITOR=true git replace --edit "$PARA3" &&
+	test_must_fail env GIT_EDITOR="./fakeeditor;false" git replace --edit "$PARA3" &&
+	GIT_EDITOR=./fakeeditor git replace --edit "$PARA3" &&
+	git replace -l | grep "$PARA3" &&
+	git cat-file commit "$PARA3" | grep "A fake Thor"
+'
+
 test_expect_success 'replace ref cleanup' '
 	test -n "$(git replace)" &&
 	git replace -d $(git replace) &&