Merge commit 'v1.7.0' into jc/checkout-reflog-fix
[git/git.git] / builtin-checkout.c
index cff0179..bc6090d 100644 (file)
@@ -5,6 +5,7 @@
 #include "commit.h"
 #include "tree.h"
 #include "tree-walk.h"
+#include "cache-tree.h"
 #include "unpack-trees.h"
 #include "dir.h"
 #include "run-command.h"
 #include "diff.h"
 #include "revision.h"
 #include "remote.h"
+#include "blob.h"
+#include "xdiff-interface.h"
+#include "ll-merge.h"
+#include "resolve-undo.h"
 
 static const char * const checkout_usage[] = {
        "git checkout [options] <branch>",
@@ -20,26 +25,28 @@ static const char * const checkout_usage[] = {
        NULL,
 };
 
+struct checkout_opts {
+       int quiet;
+       int merge;
+       int force;
+       int writeout_stage;
+       int writeout_error;
+
+       const char *new_branch;
+       int new_branch_log;
+       enum branch_track track;
+};
+
 static int post_checkout_hook(struct commit *old, struct commit *new,
                              int changed)
 {
-       struct child_process proc;
-       const char *name = git_path("hooks/post-checkout");
-       const char *argv[5];
-
-       if (access(name, X_OK) < 0)
-               return 0;
+       return run_hook(NULL, "post-checkout",
+                       sha1_to_hex(old ? old->object.sha1 : null_sha1),
+                       sha1_to_hex(new ? new->object.sha1 : null_sha1),
+                       changed ? "1" : "0", NULL);
+       /* "new" can be NULL when checking out from the index before
+          a commit exists. */
 
-       memset(&proc, 0, sizeof(proc));
-       argv[0] = name;
-       argv[1] = xstrdup(sha1_to_hex(old->object.sha1));
-       argv[2] = xstrdup(sha1_to_hex(new->object.sha1));
-       argv[3] = changed ? "1" : "0";
-       argv[4] = NULL;
-       proc.argv = argv;
-       proc.no_stdin = 1;
-       proc.stdout_to_stderr = 1;
-       return run_command(&proc);
 }
 
 static int update_some(const unsigned char *sha1, const char *base, int baselen,
@@ -48,9 +55,6 @@ static int update_some(const unsigned char *sha1, const char *base, int baselen,
        int len;
        struct cache_entry *ce;
 
-       if (S_ISGITLINK(mode))
-               return 0;
-
        if (S_ISDIR(mode))
                return READ_TREE_RECURSIVE;
 
@@ -76,7 +80,129 @@ static int read_tree_some(struct tree *tree, const char **pathspec)
        return 0;
 }
 
-static int checkout_paths(struct tree *source_tree, const char **pathspec)
+static int skip_same_name(struct cache_entry *ce, int pos)
+{
+       while (++pos < active_nr &&
+              !strcmp(active_cache[pos]->name, ce->name))
+               ; /* skip */
+       return pos;
+}
+
+static int check_stage(int stage, struct cache_entry *ce, int pos)
+{
+       while (pos < active_nr &&
+              !strcmp(active_cache[pos]->name, ce->name)) {
+               if (ce_stage(active_cache[pos]) == stage)
+                       return 0;
+               pos++;
+       }
+       return error("path '%s' does not have %s version",
+                    ce->name,
+                    (stage == 2) ? "our" : "their");
+}
+
+static int check_all_stages(struct cache_entry *ce, int pos)
+{
+       if (ce_stage(ce) != 1 ||
+           active_nr <= pos + 2 ||
+           strcmp(active_cache[pos+1]->name, ce->name) ||
+           ce_stage(active_cache[pos+1]) != 2 ||
+           strcmp(active_cache[pos+2]->name, ce->name) ||
+           ce_stage(active_cache[pos+2]) != 3)
+               return error("path '%s' does not have all three versions",
+                            ce->name);
+       return 0;
+}
+
+static int checkout_stage(int stage, struct cache_entry *ce, int pos,
+                         struct checkout *state)
+{
+       while (pos < active_nr &&
+              !strcmp(active_cache[pos]->name, ce->name)) {
+               if (ce_stage(active_cache[pos]) == stage)
+                       return checkout_entry(active_cache[pos], state, NULL);
+               pos++;
+       }
+       return error("path '%s' does not have %s version",
+                    ce->name,
+                    (stage == 2) ? "our" : "their");
+}
+
+/* NEEDSWORK: share with merge-recursive */
+static void fill_mm(const unsigned char *sha1, mmfile_t *mm)
+{
+       unsigned long size;
+       enum object_type type;
+
+       if (!hashcmp(sha1, null_sha1)) {
+               mm->ptr = xstrdup("");
+               mm->size = 0;
+               return;
+       }
+
+       mm->ptr = read_sha1_file(sha1, &type, &size);
+       if (!mm->ptr || type != OBJ_BLOB)
+               die("unable to read blob object %s", sha1_to_hex(sha1));
+       mm->size = size;
+}
+
+static int checkout_merged(int pos, struct checkout *state)
+{
+       struct cache_entry *ce = active_cache[pos];
+       const char *path = ce->name;
+       mmfile_t ancestor, ours, theirs;
+       int status;
+       unsigned char sha1[20];
+       mmbuffer_t result_buf;
+
+       if (ce_stage(ce) != 1 ||
+           active_nr <= pos + 2 ||
+           strcmp(active_cache[pos+1]->name, path) ||
+           ce_stage(active_cache[pos+1]) != 2 ||
+           strcmp(active_cache[pos+2]->name, path) ||
+           ce_stage(active_cache[pos+2]) != 3)
+               return error("path '%s' does not have all 3 versions", path);
+
+       fill_mm(active_cache[pos]->sha1, &ancestor);
+       fill_mm(active_cache[pos+1]->sha1, &ours);
+       fill_mm(active_cache[pos+2]->sha1, &theirs);
+
+       status = ll_merge(&result_buf, path, &ancestor,
+                         &ours, "ours", &theirs, "theirs", 0);
+       free(ancestor.ptr);
+       free(ours.ptr);
+       free(theirs.ptr);
+       if (status < 0 || !result_buf.ptr) {
+               free(result_buf.ptr);
+               return error("path '%s': cannot merge", path);
+       }
+
+       /*
+        * NEEDSWORK:
+        * There is absolutely no reason to write this as a blob object
+        * and create a phony cache entry just to leak.  This hack is
+        * primarily to get to the write_entry() machinery that massages
+        * the contents to work-tree format and writes out which only
+        * allows it for a cache entry.  The code in write_entry() needs
+        * to be refactored to allow us to feed a <buffer, size, mode>
+        * instead of a cache entry.  Such a refactoring would help
+        * merge_recursive as well (it also writes the merge result to the
+        * object database even when it may contain conflicts).
+        */
+       if (write_sha1_file(result_buf.ptr, result_buf.size,
+                           blob_type, sha1))
+               die("Unable to add merge result for '%s'", path);
+       ce = make_cache_entry(create_ce_mode(active_cache[pos+1]->ce_mode),
+                             sha1,
+                             path, 2, 0);
+       if (!ce)
+               die("make_cache_entry failed for path '%s'", path);
+       status = checkout_entry(ce, state, NULL);
+       return status;
+}
+
+static int checkout_paths(struct tree *source_tree, const char **pathspec,
+                         struct checkout_opts *opts)
 {
        int pos;
        struct checkout state;
@@ -85,12 +211,14 @@ static int checkout_paths(struct tree *source_tree, const char **pathspec)
        int flag;
        struct commit *head;
        int errs = 0;
-
+       int stage = opts->writeout_stage;
+       int merge = opts->merge;
        int newfd;
        struct lock_file *lock_file = xcalloc(1, sizeof(struct lock_file));
 
        newfd = hold_locked_index(lock_file, 1);
-       read_cache();
+       if (read_cache_preload(pathspec) < 0)
+               return error("corrupt index file");
 
        if (source_tree)
                read_tree_some(source_tree, pathspec);
@@ -101,20 +229,54 @@ static int checkout_paths(struct tree *source_tree, const char **pathspec)
 
        for (pos = 0; pos < active_nr; pos++) {
                struct cache_entry *ce = active_cache[pos];
-               pathspec_match(pathspec, ps_matched, ce->name, 0);
+               match_pathspec(pathspec, ce->name, ce_namelen(ce), 0, ps_matched);
        }
 
        if (report_path_error(ps_matched, pathspec, 0))
                return 1;
 
+       /* "checkout -m path" to recreate conflicted state */
+       if (opts->merge)
+               unmerge_cache(pathspec);
+
+       /* Any unmerged paths? */
+       for (pos = 0; pos < active_nr; pos++) {
+               struct cache_entry *ce = active_cache[pos];
+               if (match_pathspec(pathspec, ce->name, ce_namelen(ce), 0, NULL)) {
+                       if (!ce_stage(ce))
+                               continue;
+                       if (opts->force) {
+                               warning("path '%s' is unmerged", ce->name);
+                       } else if (stage) {
+                               errs |= check_stage(stage, ce, pos);
+                       } else if (opts->merge) {
+                               errs |= check_all_stages(ce, pos);
+                       } else {
+                               errs = 1;
+                               error("path '%s' is unmerged", ce->name);
+                       }
+                       pos = skip_same_name(ce, pos) - 1;
+               }
+       }
+       if (errs)
+               return 1;
+
        /* Now we are committed to check them out */
        memset(&state, 0, sizeof(state));
        state.force = 1;
        state.refresh_cache = 1;
        for (pos = 0; pos < active_nr; pos++) {
                struct cache_entry *ce = active_cache[pos];
-               if (pathspec_match(pathspec, NULL, ce->name, 0)) {
-                       errs |= checkout_entry(ce, &state, NULL);
+               if (match_pathspec(pathspec, ce->name, ce_namelen(ce), 0, NULL)) {
+                       if (!ce_stage(ce)) {
+                               errs |= checkout_entry(ce, &state, NULL);
+                               continue;
+                       }
+                       if (stage)
+                               errs |= checkout_stage(stage, ce, pos, &state);
+                       else if (merge)
+                               errs |= checkout_merged(pos, &state);
+                       pos = skip_same_name(ce, pos) - 1;
                }
        }
 
@@ -136,32 +298,23 @@ static void show_local_changes(struct object *head)
        init_revisions(&rev, NULL);
        rev.abbrev = 0;
        rev.diffopt.output_format |= DIFF_FORMAT_NAME_STATUS;
+       if (diff_setup_done(&rev.diffopt) < 0)
+               die("diff_setup_done failed");
        add_pending_object(&rev, head, NULL);
        run_diff_index(&rev, 0);
 }
 
 static void describe_detached_head(char *msg, struct commit *commit)
 {
-       struct strbuf sb;
-       strbuf_init(&sb, 0);
+       struct strbuf sb = STRBUF_INIT;
+       struct pretty_print_context ctx = {0};
        parse_commit(commit);
-       pretty_print_commit(CMIT_FMT_ONELINE, commit, &sb, 0, NULL, NULL, 0, 0);
+       pretty_print_commit(CMIT_FMT_ONELINE, commit, &sb, &ctx);
        fprintf(stderr, "%s %s... %s\n", msg,
                find_unique_abbrev(commit->object.sha1, DEFAULT_ABBREV), sb.buf);
        strbuf_release(&sb);
 }
 
-struct checkout_opts {
-       int quiet;
-       int merge;
-       int force;
-       int writeout_error;
-
-       char *new_branch;
-       int new_branch_log;
-       enum branch_track track;
-};
-
 static int reset_tree(struct tree *tree, struct checkout_opts *o, int worktree)
 {
        struct unpack_trees_options opts;
@@ -203,10 +356,12 @@ struct branch_info {
 
 static void setup_branch_path(struct branch_info *branch)
 {
-       struct strbuf buf;
-       strbuf_init(&buf, 0);
-       strbuf_addstr(&buf, "refs/heads/");
-       strbuf_addstr(&buf, branch->name);
+       struct strbuf buf = STRBUF_INIT;
+
+       strbuf_branchname(&buf, branch->name);
+       if (strcmp(buf.buf, branch->name))
+               branch->name = xstrdup(buf.buf);
+       strbuf_splice(&buf, 0, 0, "refs/heads/", 11);
        branch->path = strbuf_detach(&buf, NULL);
 }
 
@@ -216,8 +371,11 @@ static int merge_working_tree(struct checkout_opts *opts,
        int ret;
        struct lock_file *lock_file = xcalloc(1, sizeof(struct lock_file));
        int newfd = hold_locked_index(lock_file, 1);
-       read_cache();
 
+       if (read_cache_preload(NULL) < 0)
+               return error("corrupt index file");
+
+       resolve_undo_clear();
        if (opts->force) {
                ret = reset_tree(new->commit->tree, opts, 1);
                if (ret)
@@ -242,15 +400,18 @@ static int merge_working_tree(struct checkout_opts *opts,
                }
 
                /* 2-way merge to the new branch */
+               topts.initial_checkout = is_cache_unborn();
                topts.update = 1;
                topts.merge = 1;
-               topts.gently = opts->merge;
+               topts.gently = opts->merge && old->commit;
                topts.verbose_update = !opts->quiet;
                topts.fn = twoway_merge;
                topts.dir = xcalloc(1, sizeof(*topts.dir));
-               topts.dir->show_ignored = 1;
+               topts.dir->flags |= DIR_SHOW_IGNORED;
                topts.dir->exclude_per_dir = ".gitignore";
-               tree = parse_tree_indirect(old->commit->object.sha1);
+               tree = parse_tree_indirect(old->commit ?
+                                          old->commit->object.sha1 :
+                                          (unsigned char *)EMPTY_TREE_SHA1_BIN);
                init_tree_desc(&trees[0], tree->buffer, tree->size);
                tree = parse_tree_indirect(new->commit->object.sha1);
                init_tree_desc(&trees[1], tree->buffer, tree->size);
@@ -264,9 +425,16 @@ static int merge_working_tree(struct checkout_opts *opts,
                         */
                        struct tree *result;
                        struct tree *work;
+                       struct merge_options o;
                        if (!opts->merge)
                                return 1;
-                       parse_commit(old->commit);
+
+                       /*
+                        * Without old->commit, the below is the same as
+                        * the two-tree unpack we already tried and failed.
+                        */
+                       if (!old->commit)
+                               return 1;
 
                        /* Do more real merge */
 
@@ -282,13 +450,17 @@ static int merge_working_tree(struct checkout_opts *opts,
                         */
 
                        add_files_to_cache(NULL, NULL, 0);
-                       work = write_tree_from_memory();
+                       init_merge_options(&o);
+                       o.verbosity = 0;
+                       work = write_tree_from_memory(&o);
 
                        ret = reset_tree(new->commit->tree, opts, 1);
                        if (ret)
                                return ret;
-                       merge_trees(new->commit->tree, work, old->commit->tree,
-                                   new->name, "local", &result);
+                       o.branch1 = new->name;
+                       o.branch2 = "local";
+                       merge_trees(&o, new->commit->tree, work,
+                               old->commit->tree, &result);
                        ret = reset_tree(new->commit->tree, opts, 0);
                        if (ret)
                                return ret;
@@ -299,7 +471,7 @@ static int merge_working_tree(struct checkout_opts *opts,
            commit_locked_index(lock_file))
                die("unable to write new index file");
 
-       if (!opts->force)
+       if (!opts->force && !opts->quiet)
                show_local_changes(&new->commit->object);
 
        return 0;
@@ -320,7 +492,7 @@ static void update_refs_for_switch(struct checkout_opts *opts,
                                   struct branch_info *old,
                                   struct branch_info *new)
 {
-       struct strbuf msg;
+       struct strbuf msg = STRBUF_INIT;
        const char *old_desc;
        if (opts->new_branch) {
                create_branch(old->name, opts->new_branch, new->name, 0,
@@ -329,21 +501,20 @@ static void update_refs_for_switch(struct checkout_opts *opts,
                setup_branch_path(new);
        }
 
-       strbuf_init(&msg, 0);
        old_desc = old->name;
-       if (!old_desc)
+       if (!old_desc && old->commit)
                old_desc = sha1_to_hex(old->commit->object.sha1);
        strbuf_addf(&msg, "checkout: moving from %s to %s",
-                   old_desc, new->name);
+                   old_desc ? old_desc : "(invalid)", new->name);
 
        if (new->path) {
                create_symref("HEAD", new->path, msg.buf);
                if (!opts->quiet) {
                        if (old->path && !strcmp(new->path, old->path))
-                               fprintf(stderr, "Already on \"%s\"\n",
+                               fprintf(stderr, "Already on '%s'\n",
                                        new->name);
                        else
-                               fprintf(stderr, "Switched to%s branch \"%s\"\n",
+                               fprintf(stderr, "Switched to%s branch '%s'\n",
                                        opts->new_branch ? " a new" : "",
                                        new->name);
                }
@@ -352,7 +523,7 @@ static void update_refs_for_switch(struct checkout_opts *opts,
                           REF_NODEREF, DIE_ON_ERR);
                if (!opts->quiet) {
                        if (old->path)
-                               fprintf(stderr, "Note: moving to \"%s\" which isn't a local branch\nIf you want to create a new branch from this checkout, you may do so\n(now or later) by using -b with the checkout command again. Example:\n  git checkout -b <new_branch_name>\n", new->name);
+                               fprintf(stderr, "Note: moving to '%s' which isn't a local branch\nIf you want to create a new branch from this checkout, you may do so\n(now or later) by using -b with the checkout command again. Example:\n  git checkout -b <new_branch_name>\n", new->name);
                        describe_detached_head("HEAD is now at", new->commit);
                }
        }
@@ -387,28 +558,18 @@ static int switch_branches(struct checkout_opts *opts, struct branch_info *new)
                parse_commit(new->commit);
        }
 
-       /*
-        * If the new thing isn't a branch and isn't HEAD and we're
-        * not starting a new branch, and we want messages, and we
-        * weren't on a branch, and we're moving to a new commit,
-        * describe the old commit.
-        */
-       if (!new->path && strcmp(new->name, "HEAD") && !opts->new_branch &&
-           !opts->quiet && !old.path && new->commit != old.commit)
-               describe_detached_head("Previous HEAD position was", old.commit);
-
-       if (!old.commit) {
-               if (!opts->quiet) {
-                       fprintf(stderr, "warning: You appear to be on a branch yet to be born.\n");
-                       fprintf(stderr, "warning: Forcing checkout of %s.\n", new->name);
-               }
-               opts->force = 1;
-       }
-
        ret = merge_working_tree(opts, &old, new);
        if (ret)
                return ret;
 
+       /*
+        * If we were on a detached HEAD, but have now moved to
+        * a new commit, we want to mention the old commit once more
+        * to remind the user that it might be lost.
+        */
+       if (!opts->quiet && !old.path && old.commit && new->commit != old.commit)
+               describe_detached_head("Previous HEAD position was", old.commit);
+
        update_refs_for_switch(opts, &old, new);
 
        ret = post_checkout_hook(old.commit, new->commit, 1);
@@ -416,6 +577,52 @@ static int switch_branches(struct checkout_opts *opts, struct branch_info *new)
        return ret || opts->writeout_error;
 }
 
+static int git_checkout_config(const char *var, const char *value, void *cb)
+{
+       return git_xmerge_config(var, value, cb);
+}
+
+static int interactive_checkout(const char *revision, const char **pathspec,
+                               struct checkout_opts *opts)
+{
+       return run_add_interactive(revision, "--patch=checkout", pathspec);
+}
+
+struct tracking_name_data {
+       const char *name;
+       char *remote;
+       int unique;
+};
+
+static int check_tracking_name(const char *refname, const unsigned char *sha1,
+                              int flags, void *cb_data)
+{
+       struct tracking_name_data *cb = cb_data;
+       const char *slash;
+
+       if (prefixcmp(refname, "refs/remotes/"))
+               return 0;
+       slash = strchr(refname + 13, '/');
+       if (!slash || strcmp(slash + 1, cb->name))
+               return 0;
+       if (cb->remote) {
+               cb->unique = 0;
+               return 0;
+       }
+       cb->remote = xstrdup(refname);
+       return 0;
+}
+
+static const char *unique_tracking_name(const char *name)
+{
+       struct tracking_name_data cb_data = { name, NULL, 1 };
+       for_each_ref(check_tracking_name, &cb_data);
+       if (cb_data.unique)
+               return cb_data.remote;
+       free(cb_data.remote);
+       return NULL;
+}
+
 int cmd_checkout(int argc, const char **argv, const char *prefix)
 {
        struct checkout_opts opts;
@@ -423,14 +630,27 @@ int cmd_checkout(int argc, const char **argv, const char *prefix)
        const char *arg;
        struct branch_info new;
        struct tree *source_tree = NULL;
+       char *conflict_style = NULL;
+       int patch_mode = 0;
+       int dwim_new_local_branch = 1;
        struct option options[] = {
                OPT__QUIET(&opts.quiet),
                OPT_STRING('b', NULL, &opts.new_branch, "new branch", "branch"),
                OPT_BOOLEAN('l', NULL, &opts.new_branch_log, "log for new branch"),
                OPT_SET_INT('t', "track",  &opts.track, "track",
                        BRANCH_TRACK_EXPLICIT),
-               OPT_BOOLEAN('f', NULL, &opts.force, "force"),
-               OPT_BOOLEAN('m', NULL, &opts.merge, "merge"),
+               OPT_SET_INT('2', "ours", &opts.writeout_stage, "stage",
+                           2),
+               OPT_SET_INT('3', "theirs", &opts.writeout_stage, "stage",
+                           3),
+               OPT_BOOLEAN('f', "force", &opts.force, "force"),
+               OPT_BOOLEAN('m', "merge", &opts.merge, "merge"),
+               OPT_STRING(0, "conflict", &conflict_style, "style",
+                          "conflict style (merge or diff3)"),
+               OPT_BOOLEAN('p', "patch", &patch_mode, "select hunks interactively"),
+               { OPTION_BOOLEAN, 0, "guess", &dwim_new_local_branch, NULL,
+                 "second guess 'git checkout no-such-branch'",
+                 PARSE_OPT_NOARG | PARSE_OPT_HIDDEN },
                OPT_END(),
        };
        int has_dash_dash;
@@ -438,15 +658,36 @@ int cmd_checkout(int argc, const char **argv, const char *prefix)
        memset(&opts, 0, sizeof(opts));
        memset(&new, 0, sizeof(new));
 
-       git_config(git_default_config, NULL);
+       git_config(git_checkout_config, NULL);
 
-       opts.track = git_branch_track;
+       opts.track = BRANCH_TRACK_UNSPECIFIED;
 
-       argc = parse_options(argc, argv, options, checkout_usage,
+       argc = parse_options(argc, argv, prefix, options, checkout_usage,
                             PARSE_OPT_KEEP_DASHDASH);
 
-       if (!opts.new_branch && (opts.track != git_branch_track))
-               die("git checkout: --track and --no-track require -b");
+       if (patch_mode && (opts.track > 0 || opts.new_branch
+                          || opts.new_branch_log || opts.merge || opts.force))
+               die ("--patch is incompatible with all other options");
+
+       /* --track without -b should DWIM */
+       if (0 < opts.track && !opts.new_branch) {
+               const char *argv0 = argv[0];
+               if (!argc || !strcmp(argv0, "--"))
+                       die ("--track needs a branch name");
+               if (!prefixcmp(argv0, "refs/"))
+                       argv0 += 5;
+               if (!prefixcmp(argv0, "remotes/"))
+                       argv0 += 8;
+               argv0 = strchr(argv0, '/');
+               if (!argv0 || !argv0[1])
+                       die ("Missing branch name; try -b");
+               opts.new_branch = argv0 + 1;
+       }
+
+       if (conflict_style) {
+               opts.merge = 1; /* implied */
+               git_xmerge_config("merge.conflictstyle", conflict_style, NULL);
+       }
 
        if (opts.force && opts.merge)
                die("git checkout: -f and -m are incompatible");
@@ -464,7 +705,15 @@ int cmd_checkout(int argc, const char **argv, const char *prefix)
         * case 3: git checkout <something> [<paths>]
         *
         *   With no paths, if <something> is a commit, that is to
-        *   switch to the branch or detach HEAD at it.
+        *   switch to the branch or detach HEAD at it.  As a special case,
+        *   if <something> is A...B (missing A or B means HEAD but you can
+        *   omit at most one side), and if there is a unique merge base
+        *   between A and B, A...B names that merge base.
+        *
+        *   With no paths, if <something> is _not_ a commit, no -t nor -b
+        *   was given, and there is a tracking branch whose name is
+        *   <something> in one and only one remote, then this is a short-hand
+        *   to fork local <something> from that remote tracking branch.
         *
         *   Otherwise <something> shall not be ambiguous.
         *   - If it's *only* a reference, treat it like case (1).
@@ -482,21 +731,40 @@ int cmd_checkout(int argc, const char **argv, const char *prefix)
                arg = argv[0];
                has_dash_dash = (argc > 1) && !strcmp(argv[1], "--");
 
-               if (get_sha1(arg, rev)) {
+               if (!strcmp(arg, "-"))
+                       arg = "@{-1}";
+
+               if (get_sha1_mb(arg, rev)) {
                        if (has_dash_dash)          /* case (1) */
                                die("invalid reference: %s", arg);
-                       goto no_reference;          /* case (3 -> 2) */
+                       if (!patch_mode &&
+                           dwim_new_local_branch &&
+                           opts.track == BRANCH_TRACK_UNSPECIFIED &&
+                           !opts.new_branch &&
+                           !check_filename(NULL, arg) &&
+                           argc == 1) {
+                               const char *remote = unique_tracking_name(arg);
+                               if (!remote || get_sha1(remote, rev))
+                                       goto no_reference;
+                               opts.new_branch = arg;
+                               arg = remote;
+                               /* DWIMmed to create local branch */
+                       }
+                       else
+                               goto no_reference;
                }
 
                /* we can't end up being in (2) anymore, eat the argument */
                argv++;
                argc--;
 
+               new.name = arg;
                if ((new.commit = lookup_commit_reference_gently(rev, 1))) {
-                       new.name = arg;
                        setup_branch_path(&new);
-                       if (resolve_ref(new.path, rev, 1, NULL))
-                               new.commit = lookup_commit_reference(rev);
+
+                       if ((check_ref_format(new.path) == CHECK_REF_FORMAT_OK) &&
+                           resolve_ref(new.path, rev, 1, NULL))
+                               ;
                        else
                                new.path = NULL;
                        parse_commit(new.commit);
@@ -523,27 +791,52 @@ int cmd_checkout(int argc, const char **argv, const char *prefix)
        }
 
 no_reference:
+
+       if (opts.track == BRANCH_TRACK_UNSPECIFIED)
+               opts.track = git_branch_track;
+
        if (argc) {
                const char **pathspec = get_pathspec(prefix, argv);
 
                if (!pathspec)
                        die("invalid path specification");
 
+               if (patch_mode)
+                       return interactive_checkout(new.name, pathspec, &opts);
+
                /* Checkout paths */
-               if (opts.new_branch || opts.force || opts.merge) {
+               if (opts.new_branch) {
                        if (argc == 1) {
-                               die("git checkout: updating paths is incompatible with switching branches/forcing\nDid you intend to checkout '%s' which can not be resolved as commit?", argv[0]);
+                               die("git checkout: updating paths is incompatible with switching branches.\nDid you intend to checkout '%s' which can not be resolved as commit?", argv[0]);
                        } else {
-                               die("git checkout: updating paths is incompatible with switching branches/forcing");
+                               die("git checkout: updating paths is incompatible with switching branches.");
                        }
                }
 
-               return checkout_paths(source_tree, pathspec);
+               if (1 < !!opts.writeout_stage + !!opts.force + !!opts.merge)
+                       die("git checkout: --ours/--theirs, --force and --merge are incompatible when\nchecking out of the index.");
+
+               return checkout_paths(source_tree, pathspec, &opts);
+       }
+
+       if (patch_mode)
+               return interactive_checkout(new.name, NULL, &opts);
+
+       if (opts.new_branch) {
+               struct strbuf buf = STRBUF_INIT;
+               if (strbuf_check_branch_ref(&buf, opts.new_branch))
+                       die("git checkout: we do not like '%s' as a branch name.",
+                           opts.new_branch);
+               if (!get_sha1(buf.buf, rev))
+                       die("git checkout: branch %s already exists", opts.new_branch);
+               strbuf_release(&buf);
        }
 
        if (new.name && !new.commit) {
                die("Cannot switch branch to a non-commit.");
        }
+       if (opts.writeout_stage)
+               die("--ours/--theirs is incompatible with switching branches.");
 
        return switch_branches(&opts, &new);
 }