Merge branch 'pk/rebase-in-c-2-basic'

Rewrite "git rebase" in C.

* pk/rebase-in-c-2-basic:
  builtin rebase: support `git rebase <upstream> <switch-to>`
  builtin rebase: only store fully-qualified refs in `options.head_name`
  builtin rebase: start a new rebase only if none is in progress
  builtin rebase: support --force-rebase
  builtin rebase: try to fast forward when possible
  builtin rebase: require a clean worktree
  builtin rebase: support the `verbose` and `diffstat` options
  builtin rebase: support --quiet
  builtin rebase: handle the pre-rebase hook and --no-verify
  builtin rebase: support `git rebase --onto A...B`
  builtin rebase: support --onto

builtin/rebase.c

@@ -16,6 +16,21 @@
 #include "cache-tree.h"
 #include "unpack-trees.h"
 #include "lockfile.h"
+#include "parse-options.h"
+#include "commit.h"
+#include "diff.h"
+#include "wt-status.h"
+#include "revision.h"
+#include "commit-reach.h"
+
+static char const * const builtin_rebase_usage[] = {
+	N_("git rebase [-i] [options] [--exec <cmd>] [--onto <newbase>] "
+		"[<upstream>] [<branch>]"),
+	N_("git rebase [-i] [options] [--exec <cmd>] [--onto <newbase>] "
+		"--root [<branch>]"),
+	N_("git rebase --continue | --abort | --skip | --edit-todo"),
+	NULL
+};
 
 static GIT_PATH_FUNC(apply_dir, "rebase-apply")
 static GIT_PATH_FUNC(merge_dir, "rebase-merge")
@@ -59,16 +74,32 @@ struct rebase_options {
 	const char *state_dir;
 	struct commit *upstream;
 	const char *upstream_name;
+	const char *upstream_arg;
 	char *head_name;
 	struct object_id orig_head;
 	struct commit *onto;
 	const char *onto_name;
 	const char *revisions;
+	const char *switch_to;
 	int root;
 	struct commit *restrict_revision;
 	int dont_finish_rebase;
+	enum {
+		REBASE_NO_QUIET = 1<<0,
+		REBASE_VERBOSE = 1<<1,
+		REBASE_DIFFSTAT = 1<<2,
+		REBASE_FORCE = 1<<3,
+		REBASE_INTERACTIVE_EXPLICIT = 1<<4,
+	} flags;
+	struct strbuf git_am_opt;
 };
 
+static int is_interactive(struct rebase_options *opts)
+{
+	return opts->type == REBASE_INTERACTIVE ||
+		opts->type == REBASE_PRESERVE_MERGES;
+}
+
 /* Returns the filename prefixed by the state_dir */
 static const char *state_dir_path(const char *filename, struct rebase_options *opts)
 {
@@ -140,13 +171,25 @@ static int run_specific_rebase(struct rebase_options *opts)
 	add_var(&script_snippet, "upstream_name", opts->upstream_name);
 	add_var(&script_snippet, "upstream",
 				 oid_to_hex(&opts->upstream->object.oid));
-	add_var(&script_snippet, "head_name", opts->head_name);
+	add_var(&script_snippet, "head_name",
+		opts->head_name ? opts->head_name : "detached HEAD");
 	add_var(&script_snippet, "orig_head", oid_to_hex(&opts->orig_head));
 	add_var(&script_snippet, "onto", oid_to_hex(&opts->onto->object.oid));
 	add_var(&script_snippet, "onto_name", opts->onto_name);
 	add_var(&script_snippet, "revisions", opts->revisions);
 	add_var(&script_snippet, "restrict_revision", opts->restrict_revision ?
 		oid_to_hex(&opts->restrict_revision->object.oid) : NULL);
+	add_var(&script_snippet, "GIT_QUIET",
+		opts->flags & REBASE_NO_QUIET ? "" : "t");
+	add_var(&script_snippet, "git_am_opt", opts->git_am_opt.buf);
+	add_var(&script_snippet, "verbose",
+		opts->flags & REBASE_VERBOSE ? "t" : "");
+	add_var(&script_snippet, "diffstat",
+		opts->flags & REBASE_DIFFSTAT ? "t" : "");
+	add_var(&script_snippet, "force_rebase",
+		opts->flags & REBASE_FORCE ? "t" : "");
+	if (opts->switch_to)
+		add_var(&script_snippet, "switch_to", opts->switch_to);
 
 	switch (opts->type) {
 	case REBASE_AM:
@@ -213,6 +256,9 @@ static int reset_head(struct object_id *oid, const char *action,
 		*old_orig = NULL, oid_old_orig;
 	int ret = 0;
 
+	if (switch_to_branch && !starts_with(switch_to_branch, "refs/"))
+		BUG("Not a fully qualified branch: '%s'", switch_to_branch);
+
 	if (hold_locked_index(&lock, LOCK_REPORT_ON_ERROR) < 0)
 		return -1;
 
@@ -292,15 +338,98 @@ static int reset_head(struct object_id *oid, const char *action,
 	return ret;
 }
 
+static int rebase_config(const char *var, const char *value, void *data)
+{
+	struct rebase_options *opts = data;
+
+	if (!strcmp(var, "rebase.stat")) {
+		if (git_config_bool(var, value))
+			opts->flags |= REBASE_DIFFSTAT;
+		else
+			opts->flags &= !REBASE_DIFFSTAT;
+		return 0;
+	}
+
+	return git_default_config(var, value, data);
+}
+
+/*
+ * Determines whether the commits in from..to are linear, i.e. contain
+ * no merge commits. This function *expects* `from` to be an ancestor of
+ * `to`.
+ */
+static int is_linear_history(struct commit *from, struct commit *to)
+{
+	while (to && to != from) {
+		parse_commit(to);
+		if (!to->parents)
+			return 1;
+		if (to->parents->next)
+			return 0;
+		to = to->parents->item;
+	}
+	return 1;
+}
+
+static int can_fast_forward(struct commit *onto, struct object_id *head_oid,
+			    struct object_id *merge_base)
+{
+	struct commit *head = lookup_commit(the_repository, head_oid);
+	struct commit_list *merge_bases;
+	int res;
+
+	if (!head)
+		return 0;
+
+	merge_bases = get_merge_bases(onto, head);
+	if (merge_bases && !merge_bases->next) {
+		oidcpy(merge_base, &merge_bases->item->object.oid);
+		res = !oidcmp(merge_base, &onto->object.oid);
+	} else {
+		oidcpy(merge_base, &null_oid);
+		res = 0;
+	}
+	free_commit_list(merge_bases);
+	return res && is_linear_history(onto, head);
+}
+
 int cmd_rebase(int argc, const char **argv, const char *prefix)
 {
 	struct rebase_options options = {
 		.type = REBASE_UNSPECIFIED,
+		.flags = REBASE_NO_QUIET,
+		.git_am_opt = STRBUF_INIT,
 	};
 	const char *branch_name;
-	int ret, flags;
+	int ret, flags, in_progress = 0;
+	int ok_to_skip_pre_rebase = 0;
 	struct strbuf msg = STRBUF_INIT;
 	struct strbuf revisions = STRBUF_INIT;
+	struct strbuf buf = STRBUF_INIT;
+	struct object_id merge_base;
+	struct option builtin_rebase_options[] = {
+		OPT_STRING(0, "onto", &options.onto_name,
+			   N_("revision"),
+			   N_("rebase onto given branch instead of upstream")),
+		OPT_BOOL(0, "no-verify", &ok_to_skip_pre_rebase,
+			 N_("allow pre-rebase hook to run")),
+		OPT_NEGBIT('q', "quiet", &options.flags,
+			   N_("be quiet. implies --no-stat"),
+			   REBASE_NO_QUIET| REBASE_VERBOSE | REBASE_DIFFSTAT),
+		OPT_BIT('v', "verbose", &options.flags,
+			N_("display a diffstat of what changed upstream"),
+			REBASE_NO_QUIET | REBASE_VERBOSE | REBASE_DIFFSTAT),
+		{OPTION_NEGBIT, 'n', "no-stat", &options.flags, NULL,
+			N_("do not show diffstat of what changed upstream"),
+			PARSE_OPT_NOARG, NULL, REBASE_DIFFSTAT },
+		OPT_BIT('f', "force-rebase", &options.flags,
+			N_("cherry-pick all commits, even if unchanged"),
+			REBASE_FORCE),
+		OPT_BIT(0, "no-ff", &options.flags,
+			N_("cherry-pick all commits, even if unchanged"),
+			REBASE_FORCE),
+		OPT_END(),
+	};
 
 	/*
 	 * NEEDSWORK: Once the builtin rebase has been tested enough
@@ -318,13 +447,70 @@ int cmd_rebase(int argc, const char **argv, const char *prefix)
 			BUG("sane_execvp() returned???");
 	}
 
-	if (argc != 2)
-		die(_("Usage: %s <base>"), argv[0]);
+	if (argc == 2 && !strcmp(argv[1], "-h"))
+		usage_with_options(builtin_rebase_usage,
+				   builtin_rebase_options);
+
 	prefix = setup_git_directory();
 	trace_repo_setup(prefix);
 	setup_work_tree();
 
-	git_config(git_default_config, NULL);
+	git_config(rebase_config, &options);
+
+	if (is_directory(apply_dir())) {
+		options.type = REBASE_AM;
+		options.state_dir = apply_dir();
+	} else if (is_directory(merge_dir())) {
+		strbuf_reset(&buf);
+		strbuf_addf(&buf, "%s/rewritten", merge_dir());
+		if (is_directory(buf.buf)) {
+			options.type = REBASE_PRESERVE_MERGES;
+			options.flags |= REBASE_INTERACTIVE_EXPLICIT;
+		} else {
+			strbuf_reset(&buf);
+			strbuf_addf(&buf, "%s/interactive", merge_dir());
+			if(file_exists(buf.buf)) {
+				options.type = REBASE_INTERACTIVE;
+				options.flags |= REBASE_INTERACTIVE_EXPLICIT;
+			} else
+				options.type = REBASE_MERGE;
+		}
+		options.state_dir = merge_dir();
+	}
+
+	if (options.type != REBASE_UNSPECIFIED)
+		in_progress = 1;
+
+	argc = parse_options(argc, argv, prefix,
+			     builtin_rebase_options,
+			     builtin_rebase_usage, 0);
+
+	if (argc > 2)
+		usage_with_options(builtin_rebase_usage,
+				   builtin_rebase_options);
+
+	/* Make sure no rebase is in progress */
+	if (in_progress) {
+		const char *last_slash = strrchr(options.state_dir, '/');
+		const char *state_dir_base =
+			last_slash ? last_slash + 1 : options.state_dir;
+		const char *cmd_live_rebase =
+			"git rebase (--continue | --abort | --skip)";
+		strbuf_reset(&buf);
+		strbuf_addf(&buf, "rm -fr \"%s\"", options.state_dir);
+		die(_("It seems that there is already a %s directory, and\n"
+		      "I wonder if you are in the middle of another rebase.  "
+		      "If that is the\n"
+		      "case, please try\n\t%s\n"
+		      "If that is not the case, please\n\t%s\n"
+		      "and run me again.  I am stopping in case you still "
+		      "have something\n"
+		      "valuable there.\n"),
+		    state_dir_base, cmd_live_rebase, buf.buf);
+	}
+
+	if (!(options.flags & REBASE_NO_QUIET))
+		strbuf_addstr(&options.git_am_opt, " -q");
 
 	switch (options.type) {
 	case REBASE_MERGE:
@@ -343,10 +529,10 @@ int cmd_rebase(int argc, const char **argv, const char *prefix)
 	}
 
 	if (!options.root) {
-		if (argc < 2)
+		if (argc < 1)
 			die("TODO: handle @{upstream}");
 		else {
-			options.upstream_name = argv[1];
+			options.upstream_name = argv[0];
 			argc--;
 			argv++;
 			if (!strcmp(options.upstream_name, "-"))
@@ -355,6 +541,7 @@ int cmd_rebase(int argc, const char **argv, const char *prefix)
 		options.upstream = peel_committish(options.upstream_name);
 		if (!options.upstream)
 			die(_("invalid upstream '%s'"), options.upstream_name);
+		options.upstream_arg = options.upstream_name;
 	} else
 		die("TODO: upstream for --root");
 
@@ -362,7 +549,11 @@ int cmd_rebase(int argc, const char **argv, const char *prefix)
 	if (!options.onto_name)
 		options.onto_name = options.upstream_name;
 	if (strstr(options.onto_name, "...")) {
-		die("TODO");
+		if (get_oid_mb(options.onto_name, &merge_base) < 0)
+			die(_("'%s': need exactly one merge base"),
+			    options.onto_name);
+		options.onto = lookup_commit_or_die(&merge_base,
+						    options.onto_name);
 	} else {
 		options.onto = peel_committish(options.onto_name);
 		if (!options.onto)
@@ -375,11 +566,25 @@ int cmd_rebase(int argc, const char **argv, const char *prefix)
 	 * branch_name -- branch/commit being rebased, or
 	 * 		  HEAD (already detached)
 	 * orig_head -- commit object name of tip of the branch before rebasing
-	 * head_name -- refs/heads/<that-branch> or "detached HEAD"
+	 * head_name -- refs/heads/<that-branch> or NULL (detached HEAD)
 	 */
-	if (argc > 1)
-		 die("TODO: handle switch_to");
-	else {
+	if (argc == 1) {
+		/* Is it "rebase other branchname" or "rebase other commit"? */
+		branch_name = argv[0];
+		options.switch_to = argv[0];
+
+		/* Is it a local branch? */
+		strbuf_reset(&buf);
+		strbuf_addf(&buf, "refs/heads/%s", branch_name);
+		if (!read_ref(buf.buf, &options.orig_head))
+			options.head_name = xstrdup(buf.buf);
+		/* If not is it a valid ref (branch or commit)? */
+		else if (!get_oid(branch_name, &options.orig_head))
+			options.head_name = NULL;
+		else
+			die(_("fatal: no such branch/commit '%s'"),
+			    branch_name);
+	} else if (argc == 0) {
 		/* Do not need to switch branches, we are already on it. */
 		options.head_name =
 			xstrdup_or_null(resolve_ref_unsafe("HEAD", 0, NULL,
@@ -392,13 +597,115 @@ int cmd_rebase(int argc, const char **argv, const char *prefix)
 				branch_name = options.head_name;
 
 		} else {
-			options.head_name = xstrdup("detached HEAD");
+			free(options.head_name);
+			options.head_name = NULL;
 			branch_name = "HEAD";
 		}
 		if (get_oid("HEAD", &options.orig_head))
 			die(_("Could not resolve HEAD to a revision"));
+	} else
+		BUG("unexpected number of arguments left to parse");
+
+	if (read_index(the_repository->index) < 0)
+		die(_("could not read index"));
+
+	if (require_clean_work_tree("rebase",
+				    _("Please commit or stash them."), 1, 1)) {
+		ret = 1;
+		goto cleanup;
 	}
 
+	/*
+	 * Now we are rebasing commits upstream..orig_head (or with --root,
+	 * everything leading up to orig_head) on top of onto.
+	 */
+
+	/*
+	 * Check if we are already based on onto with linear history,
+	 * but this should be done only when upstream and onto are the same
+	 * and if this is not an interactive rebase.
+	 */
+	if (can_fast_forward(options.onto, &options.orig_head, &merge_base) &&
+	    !is_interactive(&options) && !options.restrict_revision &&
+	    !oidcmp(&options.upstream->object.oid, &options.onto->object.oid)) {
+		int flag;
+
+		if (!(options.flags & REBASE_FORCE)) {
+			/* Lazily switch to the target branch if needed... */
+			if (options.switch_to) {
+				struct object_id oid;
+
+				if (get_oid(options.switch_to, &oid) < 0) {
+					ret = !!error(_("could not parse '%s'"),
+						      options.switch_to);
+					goto cleanup;
+				}
+
+				strbuf_reset(&buf);
+				strbuf_addf(&buf, "rebase: checkout %s",
+					    options.switch_to);
+				if (reset_head(&oid, "checkout",
+					       options.head_name, 0) < 0) {
+					ret = !!error(_("could not switch to "
+							"%s"),
+						      options.switch_to);
+					goto cleanup;
+				}
+			}
+
+			if (!(options.flags & REBASE_NO_QUIET))
+				; /* be quiet */
+			else if (!strcmp(branch_name, "HEAD") &&
+				 resolve_ref_unsafe("HEAD", 0, NULL, &flag))
+				puts(_("HEAD is up to date."));
+			else
+				printf(_("Current branch %s is up to date.\n"),
+				       branch_name);
+			ret = !!finish_rebase(&options);
+			goto cleanup;
+		} else if (!(options.flags & REBASE_NO_QUIET))
+			; /* be quiet */
+		else if (!strcmp(branch_name, "HEAD") &&
+			 resolve_ref_unsafe("HEAD", 0, NULL, &flag))
+			puts(_("HEAD is up to date, rebase forced."));
+		else
+			printf(_("Current branch %s is up to date, rebase "
+				 "forced.\n"), branch_name);
+	}
+
+	/* If a hook exists, give it a chance to interrupt*/
+	if (!ok_to_skip_pre_rebase &&
+	    run_hook_le(NULL, "pre-rebase", options.upstream_arg,
+			argc ? argv[0] : NULL, NULL))
+		die(_("The pre-rebase hook refused to rebase."));
+
+	if (options.flags & REBASE_DIFFSTAT) {
+		struct diff_options opts;
+
+		if (options.flags & REBASE_VERBOSE)
+			printf(_("Changes from %s to %s:\n"),
+				oid_to_hex(&merge_base),
+				oid_to_hex(&options.onto->object.oid));
+
+		/* We want color (if set), but no pager */
+		diff_setup(&opts);
+		opts.stat_width = -1; /* use full terminal width */
+		opts.stat_graph_width = -1; /* respect statGraphWidth config */
+		opts.output_format |=
+			DIFF_FORMAT_SUMMARY | DIFF_FORMAT_DIFFSTAT;
+		opts.detect_rename = DIFF_DETECT_RENAME;
+		diff_setup_done(&opts);
+		diff_tree_oid(&merge_base, &options.onto->object.oid,
+			      "", &opts);
+		diffcore_std(&opts);
+		diff_flush(&opts);
+	}
+
+	/* Detach HEAD and reset the tree */
+	if (options.flags & REBASE_NO_QUIET)
+		printf(_("First, rewinding head to replay your work on top of "
+			 "it...\n"));
+
 	strbuf_addf(&msg, "rebase: checkout %s", options.onto_name);
 	if (reset_head(&options.onto->object.oid, "checkout", NULL, 1))
 		die(_("Could not detach HEAD"));
@@ -415,6 +722,7 @@ int cmd_rebase(int argc, const char **argv, const char *prefix)
 
 	ret = !!run_specific_rebase(&options);
 
+cleanup:
 	strbuf_release(&revisions);
 	free(options.head_name);
 	return ret;