documentation: use clearer prepositions

[alt-git.git] / help.c

#include "git-compat-util.h"
#include "config.h"
#include "builtin.h"
#include "exec-cmd.h"
#include "run-command.h"
#include "levenshtein.h"
#include "gettext.h"
#include "help.h"
#include "command-list.h"
#include "string-list.h"
#include "column.h"
#include "version.h"
#include "refs.h"
#include "parse-options.h"
#include "prompt.h"
#include "fsmonitor-ipc.h"

struct category_description {
        uint32_t category;
        const char *desc;
};
static uint32_t common_mask =
        CAT_init | CAT_worktree | CAT_info |
        CAT_history | CAT_remote;
static struct category_description common_categories[] = {
        { CAT_init, N_("start a working area (see also: git help tutorial)") },
        { CAT_worktree, N_("work on the current change (see also: git help everyday)") },
        { CAT_info, N_("examine the history and state (see also: git help revisions)") },
        { CAT_history, N_("grow, mark and tweak your common history") },
        { CAT_remote, N_("collaborate (see also: git help workflows)") },
        { 0, NULL }
};
static struct category_description main_categories[] = {
        { CAT_mainporcelain, N_("Main Porcelain Commands") },
        { CAT_ancillarymanipulators, N_("Ancillary Commands / Manipulators") },
        { CAT_ancillaryinterrogators, N_("Ancillary Commands / Interrogators") },
        { CAT_foreignscminterface, N_("Interacting with Others") },
        { CAT_plumbingmanipulators, N_("Low-level Commands / Manipulators") },
        { CAT_plumbinginterrogators, N_("Low-level Commands / Interrogators") },
        { CAT_synchingrepositories, N_("Low-level Commands / Syncing Repositories") },
        { CAT_purehelpers, N_("Low-level Commands / Internal Helpers") },
        { CAT_userinterfaces, N_("User-facing repository, command and file interfaces") },
        { CAT_developerinterfaces, N_("Developer-facing file formats, protocols and other interfaces") },
        { 0, NULL }
};

static const char *drop_prefix(const char *name, uint32_t category)
{
        const char *new_name;
        const char *prefix;

        switch (category) {
        case CAT_guide:
        case CAT_userinterfaces:
        case CAT_developerinterfaces:
                prefix = "git";
                break;
        default:
                prefix = "git-";
                break;
        }
        if (skip_prefix(name, prefix, &new_name))
                return new_name;

        return name;
}

static void extract_cmds(struct cmdname_help **p_cmds, uint32_t mask)
{
        int i, nr = 0;
        struct cmdname_help *cmds;

        if (ARRAY_SIZE(command_list) == 0)
                BUG("empty command_list[] is a sign of broken generate-cmdlist.sh");

        ALLOC_ARRAY(cmds, ARRAY_SIZE(command_list) + 1);

        for (i = 0; i < ARRAY_SIZE(command_list); i++) {
                const struct cmdname_help *cmd = command_list + i;

                if (!(cmd->category & mask))
                        continue;

                cmds[nr] = *cmd;
                cmds[nr].name = drop_prefix(cmd->name, cmd->category);

                nr++;
        }
        cmds[nr].name = NULL;
        *p_cmds = cmds;
}

static void print_command_list(const struct cmdname_help *cmds,
                               uint32_t mask, int longest)
{
        int i;

        for (i = 0; cmds[i].name; i++) {
                if (cmds[i].category & mask) {
                        size_t len = strlen(cmds[i].name);
                        printf("   %s   ", cmds[i].name);
                        if (longest > len)
                                mput_char(' ', longest - len);
                        puts(_(cmds[i].help));
                }
        }
}

static int cmd_name_cmp(const void *elem1, const void *elem2)
{
        const struct cmdname_help *e1 = elem1;
        const struct cmdname_help *e2 = elem2;

        return strcmp(e1->name, e2->name);
}

static void print_cmd_by_category(const struct category_description *catdesc,
                                  int *longest_p)
{
        struct cmdname_help *cmds;
        int longest = 0;
        int i, nr = 0;
        uint32_t mask = 0;

        for (i = 0; catdesc[i].desc; i++)
                mask |= catdesc[i].category;

        extract_cmds(&cmds, mask);

        for (i = 0; cmds[i].name; i++, nr++) {
                if (longest < strlen(cmds[i].name))
                        longest = strlen(cmds[i].name);
        }
        QSORT(cmds, nr, cmd_name_cmp);

        for (i = 0; catdesc[i].desc; i++) {
                uint32_t mask = catdesc[i].category;
                const char *desc = catdesc[i].desc;

                if (i)
                        putchar('\n');
                puts(_(desc));
                print_command_list(cmds, mask, longest);
        }
        free(cmds);
        if (longest_p)
                *longest_p = longest;
}

void add_cmdname(struct cmdnames *cmds, const char *name, int len)
{
        struct cmdname *ent;
        FLEX_ALLOC_MEM(ent, name, name, len);
        ent->len = len;

        ALLOC_GROW(cmds->names, cmds->cnt + 1, cmds->alloc);
        cmds->names[cmds->cnt++] = ent;
}

static void clean_cmdnames(struct cmdnames *cmds)
{
        int i;
        for (i = 0; i < cmds->cnt; ++i)
                free(cmds->names[i]);
        free(cmds->names);
        cmds->cnt = 0;
        cmds->alloc = 0;
}

static int cmdname_compare(const void *a_, const void *b_)
{
        struct cmdname *a = *(struct cmdname **)a_;
        struct cmdname *b = *(struct cmdname **)b_;
        return strcmp(a->name, b->name);
}

static void uniq(struct cmdnames *cmds)
{
        int i, j;

        if (!cmds->cnt)
                return;

        for (i = j = 1; i < cmds->cnt; i++) {
                if (!strcmp(cmds->names[i]->name, cmds->names[j-1]->name))
                        free(cmds->names[i]);
                else
                        cmds->names[j++] = cmds->names[i];
        }

        cmds->cnt = j;
}

void exclude_cmds(struct cmdnames *cmds, struct cmdnames *excludes)
{
        int ci, cj, ei;
        int cmp;

        ci = cj = ei = 0;
        while (ci < cmds->cnt && ei < excludes->cnt) {
                cmp = strcmp(cmds->names[ci]->name, excludes->names[ei]->name);
                if (cmp < 0)
                        cmds->names[cj++] = cmds->names[ci++];
                else if (cmp == 0) {
                        ei++;
                        free(cmds->names[ci++]);
                } else if (cmp > 0)
                        ei++;
        }

        while (ci < cmds->cnt)
                cmds->names[cj++] = cmds->names[ci++];

        cmds->cnt = cj;
}

static void pretty_print_cmdnames(struct cmdnames *cmds, unsigned int colopts)
{
        struct string_list list = STRING_LIST_INIT_NODUP;
        struct column_options copts;
        int i;

        for (i = 0; i < cmds->cnt; i++)
                string_list_append(&list, cmds->names[i]->name);
        /*
         * always enable column display, we only consult column.*
         * about layout strategy and stuff
         */
        colopts = (colopts & ~COL_ENABLE_MASK) | COL_ENABLED;
        memset(&copts, 0, sizeof(copts));
        copts.indent = "  ";
        copts.padding = 2;
        print_columns(&list, colopts, &copts);
        string_list_clear(&list, 0);
}

static void list_commands_in_dir(struct cmdnames *cmds,
                                         const char *path,
                                         const char *prefix)
{
        DIR *dir = opendir(path);
        struct dirent *de;
        struct strbuf buf = STRBUF_INIT;
        int len;

        if (!dir)
                return;
        if (!prefix)
                prefix = "git-";

        strbuf_addf(&buf, "%s/", path);
        len = buf.len;

        while ((de = readdir(dir)) != NULL) {
                const char *ent;
                size_t entlen;

                if (!skip_prefix(de->d_name, prefix, &ent))
                        continue;

                strbuf_setlen(&buf, len);
                strbuf_addstr(&buf, de->d_name);
                if (!is_executable(buf.buf))
                        continue;

                entlen = strlen(ent);
                strip_suffix(ent, ".exe", &entlen);

                add_cmdname(cmds, ent, entlen);
        }
        closedir(dir);
        strbuf_release(&buf);
}

void load_command_list(const char *prefix,
                struct cmdnames *main_cmds,
                struct cmdnames *other_cmds)
{
        const char *env_path = getenv("PATH");
        const char *exec_path = git_exec_path();

        load_builtin_commands(prefix, main_cmds);

        if (exec_path) {
                list_commands_in_dir(main_cmds, exec_path, prefix);
                QSORT(main_cmds->names, main_cmds->cnt, cmdname_compare);
                uniq(main_cmds);
        }

        if (env_path) {
                char *paths, *path, *colon;
                path = paths = xstrdup(env_path);
                while (1) {
                        if ((colon = strchr(path, PATH_SEP)))
                                *colon = 0;
                        if (!exec_path || strcmp(path, exec_path))
                                list_commands_in_dir(other_cmds, path, prefix);

                        if (!colon)
                                break;
                        path = colon + 1;
                }
                free(paths);

                QSORT(other_cmds->names, other_cmds->cnt, cmdname_compare);
                uniq(other_cmds);
        }
        exclude_cmds(other_cmds, main_cmds);
}

static int get_colopts(const char *var, const char *value,
                       const struct config_context *ctx UNUSED, void *data)
{
        unsigned int *colopts = data;

        if (starts_with(var, "column."))
                return git_column_config(var, value, "help", colopts);

        return 0;
}

void list_commands(struct cmdnames *main_cmds, struct cmdnames *other_cmds)
{
        unsigned int colopts = 0;
        git_config(get_colopts, &colopts);

        if (main_cmds->cnt) {
                const char *exec_path = git_exec_path();
                printf_ln(_("available git commands in '%s'"), exec_path);
                putchar('\n');
                pretty_print_cmdnames(main_cmds, colopts);
                putchar('\n');
        }

        if (other_cmds->cnt) {
                puts(_("git commands available from elsewhere on your $PATH"));
                putchar('\n');
                pretty_print_cmdnames(other_cmds, colopts);
                putchar('\n');
        }
}

void list_common_cmds_help(void)
{
        puts(_("These are common Git commands used in various situations:"));
        putchar('\n');
        print_cmd_by_category(common_categories, NULL);
}

void list_all_main_cmds(struct string_list *list)
{
        struct cmdnames main_cmds, other_cmds;
        int i;

        memset(&main_cmds, 0, sizeof(main_cmds));
        memset(&other_cmds, 0, sizeof(other_cmds));
        load_command_list("git-", &main_cmds, &other_cmds);

        for (i = 0; i < main_cmds.cnt; i++)
                string_list_append(list, main_cmds.names[i]->name);

        clean_cmdnames(&main_cmds);
        clean_cmdnames(&other_cmds);
}

void list_all_other_cmds(struct string_list *list)
{
        struct cmdnames main_cmds, other_cmds;
        int i;

        memset(&main_cmds, 0, sizeof(main_cmds));
        memset(&other_cmds, 0, sizeof(other_cmds));
        load_command_list("git-", &main_cmds, &other_cmds);

        for (i = 0; i < other_cmds.cnt; i++)
                string_list_append(list, other_cmds.names[i]->name);

        clean_cmdnames(&main_cmds);
        clean_cmdnames(&other_cmds);
}

void list_cmds_by_category(struct string_list *list,
                           const char *cat)
{
        int i, n = ARRAY_SIZE(command_list);
        uint32_t cat_id = 0;

        for (i = 0; category_names[i]; i++) {
                if (!strcmp(cat, category_names[i])) {
                        cat_id = 1UL << i;
                        break;
                }
        }
        if (!cat_id)
                die(_("unsupported command listing type '%s'"), cat);

        for (i = 0; i < n; i++) {
                struct cmdname_help *cmd = command_list + i;

                if (!(cmd->category & cat_id))
                        continue;
                string_list_append(list, drop_prefix(cmd->name, cmd->category));
        }
}

void list_cmds_by_config(struct string_list *list)
{
        const char *cmd_list;

        if (git_config_get_string_tmp("completion.commands", &cmd_list))
                return;

        string_list_sort(list);
        string_list_remove_duplicates(list, 0);

        while (*cmd_list) {
                struct strbuf sb = STRBUF_INIT;
                const char *p = strchrnul(cmd_list, ' ');

                strbuf_add(&sb, cmd_list, p - cmd_list);
                if (sb.buf[0] == '-')
                        string_list_remove(list, sb.buf + 1, 0);
                else
                        string_list_insert(list, sb.buf);
                strbuf_release(&sb);
                while (*p == ' ')
                        p++;
                cmd_list = p;
        }
}

void list_guides_help(void)
{
        struct category_description catdesc[] = {
                { CAT_guide, N_("The Git concept guides are:") },
                { 0, NULL }
        };
        print_cmd_by_category(catdesc, NULL);
        putchar('\n');
}

void list_user_interfaces_help(void)
{
        struct category_description catdesc[] = {
                { CAT_userinterfaces, N_("User-facing repository, command and file interfaces:") },
                { 0, NULL }
        };
        print_cmd_by_category(catdesc, NULL);
        putchar('\n');
}

void list_developer_interfaces_help(void)
{
        struct category_description catdesc[] = {
                { CAT_developerinterfaces, N_("File formats, protocols and other developer interfaces:") },
                { 0, NULL }
        };
        print_cmd_by_category(catdesc, NULL);
        putchar('\n');
}

static int get_alias(const char *var, const char *value,
                     const struct config_context *ctx UNUSED, void *data)
{
        struct string_list *list = data;

        if (skip_prefix(var, "alias.", &var))
                string_list_append(list, var)->util = xstrdup(value);

        return 0;
}

static void list_all_cmds_help_external_commands(void)
{
        struct string_list others = STRING_LIST_INIT_DUP;
        int i;

        list_all_other_cmds(&others);
        if (others.nr)
                printf("\n%s\n", _("External commands"));
        for (i = 0; i < others.nr; i++)
                printf("   %s\n", others.items[i].string);
        string_list_clear(&others, 0);
}

static void list_all_cmds_help_aliases(int longest)
{
        struct string_list alias_list = STRING_LIST_INIT_DUP;
        struct cmdname_help *aliases;
        int i;

        git_config(get_alias, &alias_list);
        string_list_sort(&alias_list);

        for (i = 0; i < alias_list.nr; i++) {
                size_t len = strlen(alias_list.items[i].string);
                if (longest < len)
                        longest = len;
        }

        if (alias_list.nr) {
                printf("\n%s\n", _("Command aliases"));
                ALLOC_ARRAY(aliases, alias_list.nr + 1);
                for (i = 0; i < alias_list.nr; i++) {
                        aliases[i].name = alias_list.items[i].string;
                        aliases[i].help = alias_list.items[i].util;
                        aliases[i].category = 1;
                }
                aliases[alias_list.nr].name = NULL;
                print_command_list(aliases, 1, longest);
                free(aliases);
        }
        string_list_clear(&alias_list, 1);
}

void list_all_cmds_help(int show_external_commands, int show_aliases)
{
        int longest;

        puts(_("See 'git help <command>' to read about a specific subcommand"));
        putchar('\n');
        print_cmd_by_category(main_categories, &longest);

        if (show_external_commands)
                list_all_cmds_help_external_commands();
        if (show_aliases)
                list_all_cmds_help_aliases(longest);
}

int is_in_cmdlist(struct cmdnames *c, const char *s)
{
        int i;
        for (i = 0; i < c->cnt; i++)
                if (!strcmp(s, c->names[i]->name))
                        return 1;
        return 0;
}

static int autocorrect;
static struct cmdnames aliases;

#define AUTOCORRECT_PROMPT (-3)
#define AUTOCORRECT_NEVER (-2)
#define AUTOCORRECT_IMMEDIATELY (-1)

static int git_unknown_cmd_config(const char *var, const char *value,
                                  const struct config_context *ctx,
                                  void *cb UNUSED)
{
        const char *p;

        if (!strcmp(var, "help.autocorrect")) {
                if (!value)
                        return config_error_nonbool(var);
                if (!strcmp(value, "never")) {
                        autocorrect = AUTOCORRECT_NEVER;
                } else if (!strcmp(value, "immediate")) {
                        autocorrect = AUTOCORRECT_IMMEDIATELY;
                } else if (!strcmp(value, "prompt")) {
                        autocorrect = AUTOCORRECT_PROMPT;
                } else {
                        int v = git_config_int(var, value, ctx->kvi);
                        autocorrect = (v < 0)
                                ? AUTOCORRECT_IMMEDIATELY : v;
                }
        }
        /* Also use aliases for command lookup */
        if (skip_prefix(var, "alias.", &p))
                add_cmdname(&aliases, p, strlen(p));

        return 0;
}

static int levenshtein_compare(const void *p1, const void *p2)
{
        const struct cmdname *const *c1 = p1, *const *c2 = p2;
        const char *s1 = (*c1)->name, *s2 = (*c2)->name;
        int l1 = (*c1)->len;
        int l2 = (*c2)->len;
        return l1 != l2 ? l1 - l2 : strcmp(s1, s2);
}

static void add_cmd_list(struct cmdnames *cmds, struct cmdnames *old)
{
        int i;
        ALLOC_GROW(cmds->names, cmds->cnt + old->cnt, cmds->alloc);

        for (i = 0; i < old->cnt; i++)
                cmds->names[cmds->cnt++] = old->names[i];
        FREE_AND_NULL(old->names);
        old->cnt = 0;
}

/* An empirically derived magic number */
#define SIMILARITY_FLOOR 7
#define SIMILAR_ENOUGH(x) ((x) < SIMILARITY_FLOOR)

static const char bad_interpreter_advice[] =
        N_("'%s' appears to be a git command, but we were not\n"
        "able to execute it. Maybe git-%s is broken?");

const char *help_unknown_cmd(const char *cmd)
{
        int i, n, best_similarity = 0;
        struct cmdnames main_cmds, other_cmds;
        struct cmdname_help *common_cmds;

        memset(&main_cmds, 0, sizeof(main_cmds));
        memset(&other_cmds, 0, sizeof(other_cmds));
        memset(&aliases, 0, sizeof(aliases));

        read_early_config(git_unknown_cmd_config, NULL);

        /*
         * Disable autocorrection prompt in a non-interactive session
         */
        if ((autocorrect == AUTOCORRECT_PROMPT) && (!isatty(0) || !isatty(2)))
                autocorrect = AUTOCORRECT_NEVER;

        if (autocorrect == AUTOCORRECT_NEVER) {
                fprintf_ln(stderr, _("git: '%s' is not a git command. See 'git --help'."), cmd);
                exit(1);
        }

        load_command_list("git-", &main_cmds, &other_cmds);

        add_cmd_list(&main_cmds, &aliases);
        add_cmd_list(&main_cmds, &other_cmds);
        QSORT(main_cmds.names, main_cmds.cnt, cmdname_compare);
        uniq(&main_cmds);

        extract_cmds(&common_cmds, common_mask);

        /* This abuses cmdname->len for levenshtein distance */
        for (i = 0, n = 0; i < main_cmds.cnt; i++) {
                int cmp = 0; /* avoid compiler stupidity */
                const char *candidate = main_cmds.names[i]->name;

                /*
                 * An exact match means we have the command, but
                 * for some reason exec'ing it gave us ENOENT; probably
                 * it's a bad interpreter in the #! line.
                 */
                if (!strcmp(candidate, cmd))
                        die(_(bad_interpreter_advice), cmd, cmd);

                /* Does the candidate appear in common_cmds list? */
                while (common_cmds[n].name &&
                       (cmp = strcmp(common_cmds[n].name, candidate)) < 0)
                        n++;
                if (common_cmds[n].name && !cmp) {
                        /* Yes, this is one of the common commands */
                        n++; /* use the entry from common_cmds[] */
                        if (starts_with(candidate, cmd)) {
                                /* Give prefix match a very good score */
                                main_cmds.names[i]->len = 0;
                                continue;
                        }
                }

                main_cmds.names[i]->len =
                        levenshtein(cmd, candidate, 0, 2, 1, 3) + 1;
        }
        FREE_AND_NULL(common_cmds);

        QSORT(main_cmds.names, main_cmds.cnt, levenshtein_compare);

        if (!main_cmds.cnt)
                die(_("Uh oh. Your system reports no Git commands at all."));

        /* skip and count prefix matches */
        for (n = 0; n < main_cmds.cnt && !main_cmds.names[n]->len; n++)
                ; /* still counting */

        if (main_cmds.cnt <= n) {
                /* prefix matches with everything? that is too ambiguous */
                best_similarity = SIMILARITY_FLOOR + 1;
        } else {
                /* count all the most similar ones */
                for (best_similarity = main_cmds.names[n++]->len;
                     (n < main_cmds.cnt &&
                      best_similarity == main_cmds.names[n]->len);
                     n++)
                        ; /* still counting */
        }
        if (autocorrect && n == 1 && SIMILAR_ENOUGH(best_similarity)) {
                const char *assumed = main_cmds.names[0]->name;
                main_cmds.names[0] = NULL;
                clean_cmdnames(&main_cmds);
                fprintf_ln(stderr,
                           _("WARNING: You called a Git command named '%s', "
                             "which does not exist."),
                           cmd);
                if (autocorrect == AUTOCORRECT_IMMEDIATELY)
                        fprintf_ln(stderr,
                                   _("Continuing under the assumption that "
                                     "you meant '%s'."),
                                   assumed);
                else if (autocorrect == AUTOCORRECT_PROMPT) {
                        char *answer;
                        struct strbuf msg = STRBUF_INIT;
                        strbuf_addf(&msg, _("Run '%s' instead [y/N]? "), assumed);
                        answer = git_prompt(msg.buf, PROMPT_ECHO);
                        strbuf_release(&msg);
                        if (!(starts_with(answer, "y") ||
                              starts_with(answer, "Y")))
                                exit(1);
                } else {
                        fprintf_ln(stderr,
                                   _("Continuing in %0.1f seconds, "
                                     "assuming that you meant '%s'."),
                                   (float)autocorrect/10.0, assumed);
                        sleep_millisec(autocorrect * 100);
                }
                return assumed;
        }

        fprintf_ln(stderr, _("git: '%s' is not a git command. See 'git --help'."), cmd);

        if (SIMILAR_ENOUGH(best_similarity)) {
                fprintf_ln(stderr,
                           Q_("\nThe most similar command is",
                              "\nThe most similar commands are",
                           n));

                for (i = 0; i < n; i++)
                        fprintf(stderr, "\t%s\n", main_cmds.names[i]->name);
        }

        exit(1);
}

void get_version_info(struct strbuf *buf, int show_build_options)
{
        /*
         * The format of this string should be kept stable for compatibility
         * with external projects that rely on the output of "git version".
         *
         * Always show the version, even if other options are given.
         */
        strbuf_addf(buf, "git version %s\n", git_version_string);

        if (show_build_options) {
                strbuf_addf(buf, "cpu: %s\n", GIT_HOST_CPU);
                if (git_built_from_commit_string[0])
                        strbuf_addf(buf, "built from commit: %s\n",
                               git_built_from_commit_string);
                else
                        strbuf_addstr(buf, "no commit associated with this build\n");
                strbuf_addf(buf, "sizeof-long: %d\n", (int)sizeof(long));
                strbuf_addf(buf, "sizeof-size_t: %d\n", (int)sizeof(size_t));
                strbuf_addf(buf, "shell-path: %s\n", SHELL_PATH);
                /* NEEDSWORK: also save and output GIT-BUILD_OPTIONS? */

                if (fsmonitor_ipc__is_supported())
                        strbuf_addstr(buf, "feature: fsmonitor--daemon\n");
        }
}

int cmd_version(int argc, const char **argv, const char *prefix)
{
        struct strbuf buf = STRBUF_INIT;
        int build_options = 0;
        const char * const usage[] = {
                N_("git version [--build-options]"),
                NULL
        };
        struct option options[] = {
                OPT_BOOL(0, "build-options", &build_options,
                         "also print build options"),
                OPT_END()
        };

        argc = parse_options(argc, argv, prefix, options, usage, 0);

        get_version_info(&buf, build_options);
        printf("%s", buf.buf);

        strbuf_release(&buf);

        return 0;
}

struct similar_ref_cb {
        const char *base_ref;
        struct string_list *similar_refs;
};

static int append_similar_ref(const char *refname,
                              const struct object_id *oid UNUSED,
                              int flags UNUSED, void *cb_data)
{
        struct similar_ref_cb *cb = (struct similar_ref_cb *)(cb_data);
        char *branch = strrchr(refname, '/') + 1;

        /* A remote branch of the same name is deemed similar */
        if (starts_with(refname, "refs/remotes/") &&
            !strcmp(branch, cb->base_ref))
                string_list_append_nodup(cb->similar_refs,
                                         shorten_unambiguous_ref(refname, 1));
        return 0;
}

static struct string_list guess_refs(const char *ref)
{
        struct similar_ref_cb ref_cb;
        struct string_list similar_refs = STRING_LIST_INIT_DUP;

        ref_cb.base_ref = ref;
        ref_cb.similar_refs = &similar_refs;
        for_each_ref(append_similar_ref, &ref_cb);
        return similar_refs;
}

NORETURN void help_unknown_ref(const char *ref, const char *cmd,
                               const char *error)
{
        int i;
        struct string_list suggested_refs = guess_refs(ref);

        fprintf_ln(stderr, _("%s: %s - %s"), cmd, ref, error);

        if (suggested_refs.nr > 0) {
                fprintf_ln(stderr,
                           Q_("\nDid you mean this?",
                              "\nDid you mean one of these?",
                              suggested_refs.nr));
                for (i = 0; i < suggested_refs.nr; i++)
                        fprintf(stderr, "\t%s\n", suggested_refs.items[i].string);
        }

        string_list_clear(&suggested_refs, 0);
        exit(1);
}