stash: convert branch to builtin
[gitweb.git] / builtin / checkout.c
index c54c78df547c8c66377f023730958f7a95d3aea1..acdafc6e4c4d104aadcbe7492a8045e16e83ba50 100644 (file)
@@ -4,6 +4,7 @@
 #include "lockfile.h"
 #include "parse-options.h"
 #include "refs.h"
+#include "object-store.h"
 #include "commit.h"
 #include "tree.h"
 #include "tree-walk.h"
@@ -22,6 +23,9 @@
 #include "resolve-undo.h"
 #include "submodule-config.h"
 #include "submodule.h"
+#include "advice.h"
+
+static int checkout_optimize_new_branch;
 
 static const char * const checkout_usage[] = {
        N_("git checkout [<options>] <branch>"),
@@ -40,6 +44,10 @@ struct checkout_opts {
        int ignore_skipworktree;
        int ignore_other_worktrees;
        int show_progress;
+       /*
+        * If new checkout options are added, skip_merge_working_tree
+        * should be updated accordingly.
+        */
 
        const char *new_branch;
        const char *new_branch_force;
@@ -54,19 +62,19 @@ struct checkout_opts {
        struct tree *source_tree;
 };
 
-static int post_checkout_hook(struct commit *old, struct commit *new,
+static int post_checkout_hook(struct commit *old_commit, struct commit *new_commit,
                              int changed)
 {
        return run_hook_le(NULL, "post-checkout",
-                          oid_to_hex(old ? &old->object.oid : &null_oid),
-                          oid_to_hex(new ? &new->object.oid : &null_oid),
+                          oid_to_hex(old_commit ? &old_commit->object.oid : &null_oid),
+                          oid_to_hex(new_commit ? &new_commit->object.oid : &null_oid),
                           changed ? "1" : "0", NULL);
-       /* "new" can be NULL when checking out from the index before
+       /* "new_commit" can be NULL when checking out from the index before
           a commit exists. */
 
 }
 
-static int update_some(const unsigned char *sha1, struct strbuf *base,
+static int update_some(const struct object_id *oid, struct strbuf *base,
                const char *pathname, unsigned mode, int stage, void *context)
 {
        int len;
@@ -77,8 +85,8 @@ static int update_some(const unsigned char *sha1, struct strbuf *base,
                return READ_TREE_RECURSIVE;
 
        len = base->len + strlen(pathname);
-       ce = xcalloc(1, cache_entry_size(len));
-       hashcpy(ce->oid.hash, sha1);
+       ce = make_empty_cache_entry(&the_index, len);
+       oidcpy(&ce->oid, oid);
        memcpy(ce->name, base->buf, base->len);
        memcpy(ce->name + base->len, pathname, len - base->len);
        ce->ce_flags = create_ce_flags(0) | CE_UPDATE;
@@ -94,9 +102,9 @@ static int update_some(const unsigned char *sha1, struct strbuf *base,
        if (pos >= 0) {
                struct cache_entry *old = active_cache[pos];
                if (ce->ce_mode == old->ce_mode &&
-                   !oidcmp(&ce->oid, &old->oid)) {
+                   oideq(&ce->oid, &old->oid)) {
                        old->ce_flags |= CE_UPDATE;
-                       free(ce);
+                       discard_cache_entry(ce);
                        return 0;
                }
        }
@@ -206,7 +214,8 @@ static int checkout_merged(int pos, const struct checkout *state)
         * merge.renormalize set, too
         */
        status = ll_merge(&result_buf, path, &ancestor, "base",
-                         &ours, "ours", &theirs, "theirs", NULL);
+                         &ours, "ours", &theirs, "theirs",
+                         state->istate, NULL);
        free(ancestor.ptr);
        free(ours.ptr);
        free(theirs.ptr);
@@ -227,15 +236,14 @@ static int checkout_merged(int pos, const struct checkout *state)
         * (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, oid.hash))
+       if (write_object_file(result_buf.ptr, result_buf.size, blob_type, &oid))
                die(_("Unable to add merge result for '%s'"), path);
        free(result_buf.ptr);
-       ce = make_cache_entry(mode, oid.hash, path, 2, 0);
+       ce = make_transient_cache_entry(mode, &oid, path, 2);
        if (!ce)
                die(_("make_cache_entry failed for path '%s'"), path);
        status = checkout_entry(ce, state, NULL);
-       free(ce);
+       discard_cache_entry(ce);
        return status;
 }
 
@@ -317,7 +325,7 @@ static int checkout_paths(const struct checkout_opts *opts,
                 * match_pathspec() for _all_ entries when
                 * opts->source_tree != NULL.
                 */
-               if (ce_path_match(ce, &opts->pathspec, ps_matched))
+               if (ce_path_match(&the_index, ce, &opts->pathspec, ps_matched))
                        ce->ce_flags |= CE_MATCHED;
        }
 
@@ -379,7 +387,7 @@ static int checkout_paths(const struct checkout_opts *opts,
                die(_("unable to write new index file"));
 
        read_ref_full("HEAD", 0, &rev, NULL);
-       head = lookup_commit_reference_gently(&rev, 1);
+       head = lookup_commit_reference_gently(the_repository, &rev, 1);
 
        errs |= post_checkout_hook(head, head, 0);
        return errs;
@@ -390,7 +398,7 @@ static void show_local_changes(struct object *head,
 {
        struct rev_info rev;
        /* I think we want full paths, even if we're in a subdirectory. */
-       init_revisions(&rev, NULL);
+       repo_init_revisions(the_repository, &rev, NULL);
        rev.diffopt.flags = opts->flags;
        rev.diffopt.output_format |= DIFF_FORMAT_NAME_STATUS;
        diff_setup_done(&rev.diffopt);
@@ -406,10 +414,10 @@ static void describe_detached_head(const char *msg, struct commit *commit)
                pp_commit_easy(CMIT_FMT_ONELINE, commit, &sb);
        if (print_sha1_ellipsis()) {
                fprintf(stderr, "%s %s... %s\n", msg,
-                       find_unique_abbrev(commit->object.oid.hash, DEFAULT_ABBREV), sb.buf);
+                       find_unique_abbrev(&commit->object.oid, DEFAULT_ABBREV), sb.buf);
        } else {
                fprintf(stderr, "%s %s %s\n", msg,
-                       find_unique_abbrev(commit->object.oid.hash, DEFAULT_ABBREV), sb.buf);
+                       find_unique_abbrev(&commit->object.oid, DEFAULT_ABBREV), sb.buf);
        }
        strbuf_release(&sb);
 }
@@ -471,9 +479,102 @@ static void setup_branch_path(struct branch_info *branch)
        branch->path = strbuf_detach(&buf, NULL);
 }
 
+/*
+ * Skip merging the trees, updating the index and working directory if and
+ * only if we are creating a new branch via "git checkout -b <new_branch>."
+ */
+static int skip_merge_working_tree(const struct checkout_opts *opts,
+       const struct branch_info *old_branch_info,
+       const struct branch_info *new_branch_info)
+{
+       /*
+        * Do the merge if sparse checkout is on and the user has not opted in
+        * to the optimized behavior
+        */
+       if (core_apply_sparse_checkout && !checkout_optimize_new_branch)
+               return 0;
+
+       /*
+        * We must do the merge if we are actually moving to a new commit.
+        */
+       if (!old_branch_info->commit || !new_branch_info->commit ||
+               !oideq(&old_branch_info->commit->object.oid,
+                      &new_branch_info->commit->object.oid))
+               return 0;
+
+       /*
+        * opts->patch_mode cannot be used with switching branches so is
+        * not tested here
+        */
+
+       /*
+        * opts->quiet only impacts output so doesn't require a merge
+        */
+
+       /*
+        * Honor the explicit request for a three-way merge or to throw away
+        * local changes
+        */
+       if (opts->merge || opts->force)
+               return 0;
+
+       /*
+        * --detach is documented as "updating the index and the files in the
+        * working tree" but this optimization skips those steps so fall through
+        * to the regular code path.
+        */
+       if (opts->force_detach)
+               return 0;
+
+       /*
+        * opts->writeout_stage cannot be used with switching branches so is
+        * not tested here
+        */
+
+       /*
+        * Honor the explicit ignore requests
+        */
+       if (!opts->overwrite_ignore || opts->ignore_skipworktree ||
+               opts->ignore_other_worktrees)
+               return 0;
+
+       /*
+        * opts->show_progress only impacts output so doesn't require a merge
+        */
+
+       /*
+        * If we aren't creating a new branch any changes or updates will
+        * happen in the existing branch.  Since that could only be updating
+        * the index and working directory, we don't want to skip those steps
+        * or we've defeated any purpose in running the command.
+        */
+       if (!opts->new_branch)
+               return 0;
+
+       /*
+        * new_branch_force is defined to "create/reset and checkout a branch"
+        * so needs to go through the merge to do the reset
+        */
+       if (opts->new_branch_force)
+               return 0;
+
+       /*
+        * A new orphaned branch requrires the index and the working tree to be
+        * adjusted to <start_point>
+        */
+       if (opts->new_orphan_branch)
+               return 0;
+
+       /*
+        * Remaining variables are not checkout options but used to track state
+        */
+
+       return 1;
+}
+
 static int merge_working_tree(const struct checkout_opts *opts,
-                             struct branch_info *old,
-                             struct branch_info *new,
+                             struct branch_info *old_branch_info,
+                             struct branch_info *new_branch_info,
                              int *writeout_error)
 {
        int ret;
@@ -485,7 +586,8 @@ static int merge_working_tree(const struct checkout_opts *opts,
 
        resolve_undo_clear();
        if (opts->force) {
-               ret = reset_tree(new->commit->tree, opts, 1, writeout_error);
+               ret = reset_tree(get_commit_tree(new_branch_info->commit),
+                                opts, 1, writeout_error);
                if (ret)
                        return ret;
        } else {
@@ -511,7 +613,7 @@ static int merge_working_tree(const struct checkout_opts *opts,
                topts.initial_checkout = is_cache_unborn();
                topts.update = 1;
                topts.merge = 1;
-               topts.gently = opts->merge && old->commit;
+               topts.gently = opts->merge && old_branch_info->commit;
                topts.verbose_update = opts->show_progress;
                topts.fn = twoway_merge;
                if (opts->overwrite_ignore) {
@@ -519,14 +621,15 @@ static int merge_working_tree(const struct checkout_opts *opts,
                        topts.dir->flags |= DIR_SHOW_IGNORED;
                        setup_standard_excludes(topts.dir);
                }
-               tree = parse_tree_indirect(old->commit ?
-                                          &old->commit->object.oid :
+               tree = parse_tree_indirect(old_branch_info->commit ?
+                                          &old_branch_info->commit->object.oid :
                                           the_hash_algo->empty_tree);
                init_tree_desc(&trees[0], tree->buffer, tree->size);
-               tree = parse_tree_indirect(&new->commit->object.oid);
+               tree = parse_tree_indirect(&new_branch_info->commit->object.oid);
                init_tree_desc(&trees[1], tree->buffer, tree->size);
 
                ret = unpack_trees(2, trees, &topts);
+               clear_unpack_trees_porcelain(&topts);
                if (ret == -1) {
                        /*
                         * Unpack couldn't do a trivial merge; either
@@ -540,10 +643,10 @@ static int merge_working_tree(const struct checkout_opts *opts,
                                return 1;
 
                        /*
-                        * Without old->commit, the below is the same as
+                        * Without old_branch_info->commit, the below is the same as
                         * the two-tree unpack we already tried and failed.
                         */
-                       if (!old->commit)
+                       if (!old_branch_info->commit)
                                return 1;
 
                        /* Do more real merge */
@@ -571,18 +674,23 @@ static int merge_working_tree(const struct checkout_opts *opts,
                        o.verbosity = 0;
                        work = write_tree_from_memory(&o);
 
-                       ret = reset_tree(new->commit->tree, opts, 1,
+                       ret = reset_tree(get_commit_tree(new_branch_info->commit),
+                                        opts, 1,
                                         writeout_error);
                        if (ret)
                                return ret;
-                       o.ancestor = old->name;
-                       o.branch1 = new->name;
+                       o.ancestor = old_branch_info->name;
+                       o.branch1 = new_branch_info->name;
                        o.branch2 = "local";
-                       ret = merge_trees(&o, new->commit->tree, work,
-                               old->commit->tree, &result);
+                       ret = merge_trees(&o,
+                                         get_commit_tree(new_branch_info->commit),
+                                         work,
+                                         get_commit_tree(old_branch_info->commit),
+                                         &result);
                        if (ret < 0)
                                exit(128);
-                       ret = reset_tree(new->commit->tree, opts, 0,
+                       ret = reset_tree(get_commit_tree(new_branch_info->commit),
+                                        opts, 0,
                                         writeout_error);
                        strbuf_release(&o.obuf);
                        if (ret)
@@ -600,25 +708,25 @@ static int merge_working_tree(const struct checkout_opts *opts,
                die(_("unable to write new index file"));
 
        if (!opts->force && !opts->quiet)
-               show_local_changes(&new->commit->object, &opts->diff_options);
+               show_local_changes(&new_branch_info->commit->object, &opts->diff_options);
 
        return 0;
 }
 
-static void report_tracking(struct branch_info *new)
+static void report_tracking(struct branch_info *new_branch_info)
 {
        struct strbuf sb = STRBUF_INIT;
-       struct branch *branch = branch_get(new->name);
+       struct branch *branch = branch_get(new_branch_info->name);
 
-       if (!format_tracking_info(branch, &sb))
+       if (!format_tracking_info(branch, &sb, AHEAD_BEHIND_FULL))
                return;
        fputs(sb.buf, stdout);
        strbuf_release(&sb);
 }
 
 static void update_refs_for_switch(const struct checkout_opts *opts,
-                                  struct branch_info *old,
-                                  struct branch_info *new)
+                                  struct branch_info *old_branch_info,
+                                  struct branch_info *new_branch_info)
 {
        struct strbuf msg = STRBUF_INIT;
        const char *old_desc, *reflog_msg;
@@ -645,69 +753,69 @@ static void update_refs_for_switch(const struct checkout_opts *opts,
                        free(refname);
                }
                else
-                       create_branch(opts->new_branch, new->name,
+                       create_branch(opts->new_branch, new_branch_info->name,
                                      opts->new_branch_force ? 1 : 0,
                                      opts->new_branch_force ? 1 : 0,
                                      opts->new_branch_log,
                                      opts->quiet,
                                      opts->track);
-               new->name = opts->new_branch;
-               setup_branch_path(new);
+               new_branch_info->name = opts->new_branch;
+               setup_branch_path(new_branch_info);
        }
 
-       old_desc = old->name;
-       if (!old_desc && old->commit)
-               old_desc = oid_to_hex(&old->commit->object.oid);
+       old_desc = old_branch_info->name;
+       if (!old_desc && old_branch_info->commit)
+               old_desc = oid_to_hex(&old_branch_info->commit->object.oid);
 
        reflog_msg = getenv("GIT_REFLOG_ACTION");
        if (!reflog_msg)
                strbuf_addf(&msg, "checkout: moving from %s to %s",
-                       old_desc ? old_desc : "(invalid)", new->name);
+                       old_desc ? old_desc : "(invalid)", new_branch_info->name);
        else
                strbuf_insert(&msg, 0, reflog_msg, strlen(reflog_msg));
 
-       if (!strcmp(new->name, "HEAD") && !new->path && !opts->force_detach) {
+       if (!strcmp(new_branch_info->name, "HEAD") && !new_branch_info->path && !opts->force_detach) {
                /* Nothing to do. */
-       } else if (opts->force_detach || !new->path) {  /* No longer on any branch. */
-               update_ref(msg.buf, "HEAD", &new->commit->object.oid, NULL,
+       } else if (opts->force_detach || !new_branch_info->path) {      /* No longer on any branch. */
+               update_ref(msg.buf, "HEAD", &new_branch_info->commit->object.oid, NULL,
                           REF_NO_DEREF, UPDATE_REFS_DIE_ON_ERR);
                if (!opts->quiet) {
-                       if (old->path &&
+                       if (old_branch_info->path &&
                            advice_detached_head && !opts->force_detach)
-                               detach_advice(new->name);
-                       describe_detached_head(_("HEAD is now at"), new->commit);
+                               detach_advice(new_branch_info->name);
+                       describe_detached_head(_("HEAD is now at"), new_branch_info->commit);
                }
-       } else if (new->path) { /* Switch branches. */
-               if (create_symref("HEAD", new->path, msg.buf) < 0)
+       } else if (new_branch_info->path) {     /* Switch branches. */
+               if (create_symref("HEAD", new_branch_info->path, msg.buf) < 0)
                        die(_("unable to update HEAD"));
                if (!opts->quiet) {
-                       if (old->path && !strcmp(new->path, old->path)) {
+                       if (old_branch_info->path && !strcmp(new_branch_info->path, old_branch_info->path)) {
                                if (opts->new_branch_force)
                                        fprintf(stderr, _("Reset branch '%s'\n"),
-                                               new->name);
+                                               new_branch_info->name);
                                else
                                        fprintf(stderr, _("Already on '%s'\n"),
-                                               new->name);
+                                               new_branch_info->name);
                        } else if (opts->new_branch) {
                                if (opts->branch_exists)
-                                       fprintf(stderr, _("Switched to and reset branch '%s'\n"), new->name);
+                                       fprintf(stderr, _("Switched to and reset branch '%s'\n"), new_branch_info->name);
                                else
-                                       fprintf(stderr, _("Switched to a new branch '%s'\n"), new->name);
+                                       fprintf(stderr, _("Switched to a new branch '%s'\n"), new_branch_info->name);
                        } else {
                                fprintf(stderr, _("Switched to branch '%s'\n"),
-                                       new->name);
+                                       new_branch_info->name);
                        }
                }
-               if (old->path && old->name) {
-                       if (!ref_exists(old->path) && reflog_exists(old->path))
-                               delete_reflog(old->path);
+               if (old_branch_info->path && old_branch_info->name) {
+                       if (!ref_exists(old_branch_info->path) && reflog_exists(old_branch_info->path))
+                               delete_reflog(old_branch_info->path);
                }
        }
        remove_branch_state();
        strbuf_release(&msg);
        if (!opts->quiet &&
-           (new->path || (!opts->force_detach && !strcmp(new->name, "HEAD"))))
-               report_tracking(new);
+           (new_branch_info->path || (!opts->force_detach && !strcmp(new_branch_info->name, "HEAD"))))
+               report_tracking(new_branch_info);
 }
 
 static int add_pending_uninteresting_ref(const char *refname,
@@ -721,7 +829,7 @@ static int add_pending_uninteresting_ref(const char *refname,
 static void describe_one_orphan(struct strbuf *sb, struct commit *commit)
 {
        strbuf_addstr(sb, "  ");
-       strbuf_add_unique_abbrev(sb, commit->object.oid.hash, DEFAULT_ABBREV);
+       strbuf_add_unique_abbrev(sb, &commit->object.oid, DEFAULT_ABBREV);
        strbuf_addch(sb, ' ');
        if (!parse_commit(commit))
                pp_commit_easy(CMIT_FMT_ONELINE, commit, sb);
@@ -779,7 +887,7 @@ static void suggest_reattach(struct commit *commit, struct rev_info *revs)
                        " git branch <new-branch-name> %s\n\n",
                        /* Give ngettext() the count */
                        lost),
-                       find_unique_abbrev(commit->object.oid.hash, DEFAULT_ABBREV));
+                       find_unique_abbrev(&commit->object.oid, DEFAULT_ABBREV));
 }
 
 /*
@@ -787,75 +895,89 @@ static void suggest_reattach(struct commit *commit, struct rev_info *revs)
  * HEAD.  If it is not reachable from any ref, this is the last chance
  * for the user to do so without resorting to reflog.
  */
-static void orphaned_commit_warning(struct commit *old, struct commit *new)
+static void orphaned_commit_warning(struct commit *old_commit, struct commit *new_commit)
 {
        struct rev_info revs;
-       struct object *object = &old->object;
+       struct object *object = &old_commit->object;
 
-       init_revisions(&revs, NULL);
+       repo_init_revisions(the_repository, &revs, NULL);
        setup_revisions(0, NULL, &revs, NULL);
 
        object->flags &= ~UNINTERESTING;
        add_pending_object(&revs, object, oid_to_hex(&object->oid));
 
        for_each_ref(add_pending_uninteresting_ref, &revs);
-       add_pending_oid(&revs, "HEAD", &new->object.oid, UNINTERESTING);
+       add_pending_oid(&revs, "HEAD", &new_commit->object.oid, UNINTERESTING);
 
        if (prepare_revision_walk(&revs))
                die(_("internal error in revision walk"));
-       if (!(old->object.flags & UNINTERESTING))
-               suggest_reattach(old, &revs);
+       if (!(old_commit->object.flags & UNINTERESTING))
+               suggest_reattach(old_commit, &revs);
        else
-               describe_detached_head(_("Previous HEAD position was"), old);
+               describe_detached_head(_("Previous HEAD position was"), old_commit);
 
        /* Clean up objects used, as they will be reused. */
        clear_commit_marks_all(ALL_REV_FLAGS);
 }
 
 static int switch_branches(const struct checkout_opts *opts,
-                          struct branch_info *new)
+                          struct branch_info *new_branch_info)
 {
        int ret = 0;
-       struct branch_info old;
+       struct branch_info old_branch_info;
        void *path_to_free;
        struct object_id rev;
        int flag, writeout_error = 0;
-       memset(&old, 0, sizeof(old));
-       old.path = path_to_free = resolve_refdup("HEAD", 0, &rev, &flag);
-       if (old.path)
-               old.commit = lookup_commit_reference_gently(&rev, 1);
+       memset(&old_branch_info, 0, sizeof(old_branch_info));
+       old_branch_info.path = path_to_free = resolve_refdup("HEAD", 0, &rev, &flag);
+       if (old_branch_info.path)
+               old_branch_info.commit = lookup_commit_reference_gently(the_repository, &rev, 1);
        if (!(flag & REF_ISSYMREF))
-               old.path = NULL;
+               old_branch_info.path = NULL;
 
-       if (old.path)
-               skip_prefix(old.path, "refs/heads/", &old.name);
+       if (old_branch_info.path)
+               skip_prefix(old_branch_info.path, "refs/heads/", &old_branch_info.name);
 
-       if (!new->name) {
-               new->name = "HEAD";
-               new->commit = old.commit;
-               if (!new->commit)
+       if (!new_branch_info->name) {
+               new_branch_info->name = "HEAD";
+               new_branch_info->commit = old_branch_info.commit;
+               if (!new_branch_info->commit)
                        die(_("You are on a branch yet to be born"));
-               parse_commit_or_die(new->commit);
+               parse_commit_or_die(new_branch_info->commit);
        }
 
-       ret = merge_working_tree(opts, &old, new, &writeout_error);
-       if (ret) {
-               free(path_to_free);
-               return ret;
+       /* optimize the "checkout -b <new_branch> path */
+       if (skip_merge_working_tree(opts, &old_branch_info, new_branch_info)) {
+               if (!checkout_optimize_new_branch && !opts->quiet) {
+                       if (read_cache_preload(NULL) < 0)
+                               return error(_("index file corrupt"));
+                       show_local_changes(&new_branch_info->commit->object, &opts->diff_options);
+               }
+       } else {
+               ret = merge_working_tree(opts, &old_branch_info, new_branch_info, &writeout_error);
+               if (ret) {
+                       free(path_to_free);
+                       return ret;
+               }
        }
 
-       if (!opts->quiet && !old.path && old.commit && new->commit != old.commit)
-               orphaned_commit_warning(old.commit, new->commit);
+       if (!opts->quiet && !old_branch_info.path && old_branch_info.commit && new_branch_info->commit != old_branch_info.commit)
+               orphaned_commit_warning(old_branch_info.commit, new_branch_info->commit);
 
-       update_refs_for_switch(opts, &old, new);
+       update_refs_for_switch(opts, &old_branch_info, new_branch_info);
 
-       ret = post_checkout_hook(old.commit, new->commit, 1);
+       ret = post_checkout_hook(old_branch_info.commit, new_branch_info->commit, 1);
        free(path_to_free);
        return ret || writeout_error;
 }
 
 static int git_checkout_config(const char *var, const char *value, void *cb)
 {
+       if (!strcmp(var, "checkout.optimizenewbranch")) {
+               checkout_optimize_new_branch = git_config_bool(var, value);
+               return 0;
+       }
+
        if (!strcmp(var, "diff.ignoresubmodules")) {
                struct checkout_opts *opts = cb;
                handle_ignore_submodules_arg(&opts->diff_options, value);
@@ -870,9 +992,10 @@ static int git_checkout_config(const char *var, const char *value, void *cb)
 
 static int parse_branchname_arg(int argc, const char **argv,
                                int dwim_new_local_branch_ok,
-                               struct branch_info *new,
+                               struct branch_info *new_branch_info,
                                struct checkout_opts *opts,
-                               struct object_id *rev)
+                               struct object_id *rev,
+                               int *dwim_remotes_matched)
 {
        struct tree **source_tree = &opts->source_tree;
        const char **new_branch = &opts->new_branch;
@@ -904,8 +1027,10 @@ static int parse_branchname_arg(int argc, const char **argv,
         *   (b) If <something> is _not_ a commit, either "--" is present
         *       or <something> is not a path, no -t or -b was given, and
         *       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.
+        *       in one and only one remote (or if the branch exists on the
+        *       remote named in checkout.defaultRemote), then this is a
+        *       short-hand to fork local <something> from that
+        *       remote-tracking branch.
         *
         *   (c) Otherwise, if "--" is present, treat it like case (1).
         *
@@ -966,7 +1091,8 @@ static int parse_branchname_arg(int argc, const char **argv,
                        recover_with_dwim = 0;
 
                if (recover_with_dwim) {
-                       const char *remote = unique_tracking_name(arg, rev);
+                       const char *remote = unique_tracking_name(arg, rev,
+                                                                 dwim_remotes_matched);
                        if (remote) {
                                *new_branch = arg;
                                arg = remote;
@@ -988,22 +1114,22 @@ static int parse_branchname_arg(int argc, const char **argv,
        argv++;
        argc--;
 
-       new->name = arg;
-       setup_branch_path(new);
+       new_branch_info->name = arg;
+       setup_branch_path(new_branch_info);
 
-       if (!check_refname_format(new->path, 0) &&
-           !read_ref(new->path, &branch_rev))
+       if (!check_refname_format(new_branch_info->path, 0) &&
+           !read_ref(new_branch_info->path, &branch_rev))
                oidcpy(rev, &branch_rev);
        else
-               new->path = NULL; /* not an existing branch */
+               new_branch_info->path = NULL; /* not an existing branch */
 
-       new->commit = lookup_commit_reference_gently(rev, 1);
-       if (!new->commit) {
+       new_branch_info->commit = lookup_commit_reference_gently(the_repository, rev, 1);
+       if (!new_branch_info->commit) {
                /* not a commit */
                *source_tree = parse_tree_indirect(rev);
        } else {
-               parse_commit_or_die(new->commit);
-               *source_tree = new->commit->tree;
+               parse_commit_or_die(new_branch_info->commit);
+               *source_tree = get_commit_tree(new_branch_info->commit);
        }
 
        if (!*source_tree)                   /* case (1): want a tree */
@@ -1043,7 +1169,7 @@ static int switch_unborn_to_new_branch(const struct checkout_opts *opts)
 }
 
 static int checkout_branch(struct checkout_opts *opts,
-                          struct branch_info *new)
+                          struct branch_info *new_branch_info)
 {
        if (opts->pathspec.nr)
                die(_("paths cannot be used with switching branches"));
@@ -1072,21 +1198,21 @@ static int checkout_branch(struct checkout_opts *opts,
        } else if (opts->track == BRANCH_TRACK_UNSPECIFIED)
                opts->track = git_branch_track;
 
-       if (new->name && !new->commit)
+       if (new_branch_info->name && !new_branch_info->commit)
                die(_("Cannot switch branch to a non-commit '%s'"),
-                   new->name);
+                   new_branch_info->name);
 
-       if (new->path && !opts->force_detach && !opts->new_branch &&
+       if (new_branch_info->path && !opts->force_detach && !opts->new_branch &&
            !opts->ignore_other_worktrees) {
                int flag;
                char *head_ref = resolve_refdup("HEAD", 0, NULL, &flag);
                if (head_ref &&
-                   (!(flag & REF_ISSYMREF) || strcmp(head_ref, new->path)))
-                       die_if_checked_out(new->path, 1);
+                   (!(flag & REF_ISSYMREF) || strcmp(head_ref, new_branch_info->path)))
+                       die_if_checked_out(new_branch_info->path, 1);
                free(head_ref);
        }
 
-       if (!new->commit && opts->new_branch) {
+       if (!new_branch_info->commit && opts->new_branch) {
                struct object_id rev;
                int flag;
 
@@ -1094,15 +1220,16 @@ static int checkout_branch(struct checkout_opts *opts,
                    (flag & REF_ISSYMREF) && is_null_oid(&rev))
                        return switch_unborn_to_new_branch(opts);
        }
-       return switch_branches(opts, new);
+       return switch_branches(opts, new_branch_info);
 }
 
 int cmd_checkout(int argc, const char **argv, const char *prefix)
 {
        struct checkout_opts opts;
-       struct branch_info new;
+       struct branch_info new_branch_info;
        char *conflict_style = NULL;
        int dwim_new_local_branch = 1;
+       int dwim_remotes_matched = 0;
        struct option options[] = {
                OPT__QUIET(&opts.quiet, N_("suppress progress reporting")),
                OPT_STRING('b', NULL, &opts.new_branch, N_("branch"),
@@ -1114,13 +1241,18 @@ int cmd_checkout(int argc, const char **argv, const char *prefix)
                OPT_SET_INT('t', "track",  &opts.track, N_("set upstream info for new branch"),
                        BRANCH_TRACK_EXPLICIT),
                OPT_STRING(0, "orphan", &opts.new_orphan_branch, N_("new-branch"), N_("new unparented branch")),
-               OPT_SET_INT('2', "ours", &opts.writeout_stage, N_("checkout our version for unmerged files"),
-                           2),
-               OPT_SET_INT('3', "theirs", &opts.writeout_stage, N_("checkout their version for unmerged files"),
-                           3),
-               OPT__FORCE(&opts.force, N_("force checkout (throw away local modifications)")),
+               OPT_SET_INT_F('2', "ours", &opts.writeout_stage,
+                             N_("checkout our version for unmerged files"),
+                             2, PARSE_OPT_NONEG),
+               OPT_SET_INT_F('3', "theirs", &opts.writeout_stage,
+                             N_("checkout their version for unmerged files"),
+                             3, PARSE_OPT_NONEG),
+               OPT__FORCE(&opts.force, N_("force checkout (throw away local modifications)"),
+                          PARSE_OPT_NOCOMPLETE),
                OPT_BOOL('m', "merge", &opts.merge, N_("perform a 3-way merge with the new branch")),
-               OPT_BOOL(0, "overwrite-ignore", &opts.overwrite_ignore, N_("update ignored files (default)")),
+               OPT_BOOL_F(0, "overwrite-ignore", &opts.overwrite_ignore,
+                          N_("update ignored files (default)"),
+                          PARSE_OPT_NOCOMPLETE),
                OPT_STRING(0, "conflict", &conflict_style, N_("style"),
                           N_("conflict style (merge or diff3)")),
                OPT_BOOL('p', "patch", &opts.patch_mode, N_("select hunks interactively")),
@@ -1138,7 +1270,7 @@ int cmd_checkout(int argc, const char **argv, const char *prefix)
        };
 
        memset(&opts, 0, sizeof(opts));
-       memset(&new, 0, sizeof(new));
+       memset(&new_branch_info, 0, sizeof(new_branch_info));
        opts.overwrite_ignore = 1;
        opts.prefix = prefix;
        opts.show_progress = -1;
@@ -1180,12 +1312,12 @@ int cmd_checkout(int argc, const char **argv, const char *prefix)
        if (opts.track != BRANCH_TRACK_UNSPECIFIED && !opts.new_branch) {
                const char *argv0 = argv[0];
                if (!argc || !strcmp(argv0, "--"))
-                       die (_("--track needs a branch name"));
+                       die(_("--track needs a branch name"));
                skip_prefix(argv0, "refs/", &argv0);
                skip_prefix(argv0, "remotes/", &argv0);
                argv0 = strchr(argv0, '/');
                if (!argv0 || !argv0[1])
-                       die (_("Missing branch name; try -b"));
+                       die(_("missing branch name; try -b"));
                opts.new_branch = argv0 + 1;
        }
 
@@ -1210,7 +1342,8 @@ int cmd_checkout(int argc, const char **argv, const char *prefix)
                        opts.track == BRANCH_TRACK_UNSPECIFIED &&
                        !opts.new_branch;
                int n = parse_branchname_arg(argc, argv, dwim_ok,
-                                            &new, &opts, &rev);
+                                            &new_branch_info, &opts, &rev,
+                                            &dwim_remotes_matched);
                argv += n;
                argc -= n;
        }
@@ -1252,8 +1385,26 @@ int cmd_checkout(int argc, const char **argv, const char *prefix)
        }
 
        UNLEAK(opts);
-       if (opts.patch_mode || opts.pathspec.nr)
-               return checkout_paths(&opts, new.name);
-       else
-               return checkout_branch(&opts, &new);
+       if (opts.patch_mode || opts.pathspec.nr) {
+               int ret = checkout_paths(&opts, new_branch_info.name);
+               if (ret && dwim_remotes_matched > 1 &&
+                   advice_checkout_ambiguous_remote_branch_name)
+                       advise(_("'%s' matched more than one remote tracking branch.\n"
+                                "We found %d remotes with a reference that matched. So we fell back\n"
+                                "on trying to resolve the argument as a path, but failed there too!\n"
+                                "\n"
+                                "If you meant to check out a remote tracking branch on, e.g. 'origin',\n"
+                                "you can do so by fully qualifying the name with the --track option:\n"
+                                "\n"
+                                "    git checkout --track origin/<name>\n"
+                                "\n"
+                                "If you'd like to always have checkouts of an ambiguous <name> prefer\n"
+                                "one remote, e.g. the 'origin' remote, consider setting\n"
+                                "checkout.defaultRemote=origin in your config."),
+                              argv[0],
+                              dwim_remotes_matched);
+               return ret;
+       } else {
+               return checkout_branch(&opts, &new_branch_info);
+       }
 }