fish-shell/src/wildcard.cpp

/** \file wildcard.c

Fish needs it's own globbing implementation to support
tab-expansion of globbed parameters. Also provides recursive
wildcards using **.

*/

#include "config.h" // IWYU pragma: keep
#include <stdlib.h>
#include <wchar.h>
#include <unistd.h>
#include <sys/stat.h>
#include <dirent.h>
#include <errno.h>
#include <string.h>
#include <set>
#include <assert.h>
#include <stddef.h>
#include <wctype.h>
#include <string>
#include <utility>

#include "fallback.h"
#include "wutil.h"
#include "common.h"
#include "wildcard.h"
#include "complete.h"
#include "reader.h"
#include "expand.h"
#include <map>

/**
   Description for generic executable
*/
#define COMPLETE_EXEC_DESC _( L"Executable" )
/**
   Description for link to executable
*/
#define COMPLETE_EXEC_LINK_DESC _( L"Executable link" )

/**
   Description for regular file
*/
#define COMPLETE_FILE_DESC _( L"File" )
/**
   Description for character device
*/
#define COMPLETE_CHAR_DESC _( L"Character device" )
/**
   Description for block device
*/
#define COMPLETE_BLOCK_DESC _( L"Block device" )
/**
   Description for fifo buffer
*/
#define COMPLETE_FIFO_DESC _( L"Fifo" )
/**
   Description for symlink
*/
#define COMPLETE_SYMLINK_DESC _( L"Symbolic link" )
/**
   Description for symlink
*/
#define COMPLETE_DIRECTORY_SYMLINK_DESC _( L"Symbolic link to directory" )
/**
   Description for Rotten symlink
*/
#define COMPLETE_ROTTEN_SYMLINK_DESC _( L"Rotten symbolic link" )
/**
   Description for symlink loop
*/
#define COMPLETE_LOOP_SYMLINK_DESC _( L"Symbolic link loop" )
/**
   Description for socket files
*/
#define COMPLETE_SOCKET_DESC _( L"Socket" )
/**
   Description for directories
*/
#define COMPLETE_DIRECTORY_DESC _( L"Directory" )

/* Finds an internal (ANY_STRING, etc.) style wildcard, or wcstring::npos */
static size_t wildcard_find(const wchar_t *wc)
{
    for (size_t i=0; wc[i] != L'\0'; i++)
    {
        if (wc[i] == ANY_CHAR || wc[i] == ANY_STRING || wc[i] == ANY_STRING_RECURSIVE)
        {
            return i;
        }
    }
    return wcstring::npos;
}

// Implementation of wildcard_has. Needs to take the length to handle embedded nulls (#1631)
static bool wildcard_has_impl(const wchar_t *str, size_t len, bool internal)
{
    assert(str != NULL);
    const wchar_t *end = str + len;
    if (internal)
    {
        for (; str < end; str++)
        {
            if ((*str == ANY_CHAR) || (*str == ANY_STRING) || (*str == ANY_STRING_RECURSIVE))
                return true;
        }
    }
    else
    {
        wchar_t prev=0;
        for (; str < end; str++)
        {
            if (((*str == L'*') || (*str == L'?')) && (prev != L'\\'))
                return true;
            prev = *str;
        }
    }

    return false;
}

bool wildcard_has(const wchar_t *str, bool internal)
{
    assert(str != NULL);
    return wildcard_has_impl(str, wcslen(str), internal);
}

bool wildcard_has(const wcstring &str, bool internal)
{
    return wildcard_has_impl(str.data(), str.size(), internal);
}


/**
   Check whether the string str matches the wildcard string wc.

   \param str String to be matched.
   \param wc The wildcard.
   \param is_first Whether files beginning with dots should not be matched against wildcards.
*/
static enum fuzzy_match_type_t wildcard_match_internal(const wchar_t *str, const wchar_t *wc, bool leading_dots_fail_to_match, bool is_first, enum fuzzy_match_type_t max_type)
{
    if (*str == 0 && *wc==0)
    {
        /* We're done */
        return fuzzy_match_exact;
    }

    /* Hackish fix for #270 . Prevent wildcards from matching . or .., but we must still allow literal matches. */
    if (leading_dots_fail_to_match && is_first && contains(str, L".", L".."))
    {
        /* The string is '.' or '..'. Return true if the wildcard exactly matches. */
        return wcscmp(str, wc) ? fuzzy_match_none : fuzzy_match_exact;
    }
    
    /* Hackish fuzzy match support */
    if (! wildcard_has(wc, true))
    {
        const string_fuzzy_match_t match = string_fuzzy_match_string(wc, str);
        return (match.type <= max_type ? match.type : fuzzy_match_none);
    }

    if (*wc == ANY_STRING || *wc == ANY_STRING_RECURSIVE)
    {
        /* Ignore hidden file */
        if (leading_dots_fail_to_match && is_first && *str == L'.')
        {
            return fuzzy_match_none;
        }
        
        /* Common case of * at the end. In that case we can early out since we know it will match. */
        if (wc[1] == L'\0')
        {
            return fuzzy_match_exact;
        }

        /* Try all submatches */
        do
        {
            enum fuzzy_match_type_t subresult = wildcard_match_internal(str, wc+1, leading_dots_fail_to_match, false, max_type);
            if (subresult != fuzzy_match_none)
            {
                return subresult;
            }
        } while (*str++ != 0);
        return fuzzy_match_none;
    }
    else if (*str == 0)
    {
        /*
          End of string, but not end of wildcard, and the next wildcard
          element is not a '*', so this is not a match.
        */
        return fuzzy_match_none;
    }
    else if (*wc == ANY_CHAR)
    {
        if (is_first && *str == L'.')
        {
            return fuzzy_match_none;
        }

        return wildcard_match_internal(str+1, wc+1, leading_dots_fail_to_match, false, max_type);
    }
    else if (*wc == *str)
    {
        return wildcard_match_internal(str+1, wc+1, leading_dots_fail_to_match, false, max_type);
    }

    return fuzzy_match_none;
}


/* This does something horrible refactored from an even more horrible function */
static wcstring resolve_description(wcstring *completion, const wchar_t *explicit_desc, wcstring(*desc_func)(const wcstring &))
{
    size_t complete_sep_loc = completion->find(PROG_COMPLETE_SEP);
    if (complete_sep_loc != wcstring::npos)
    {
        /* This completion has an embedded description, do not use the generic description */
        const wcstring description = completion->substr(complete_sep_loc + 1);
        completion->resize(complete_sep_loc);
        return description;
    }
    else
    {
        const wcstring func_result = (desc_func ? desc_func(*completion) : wcstring());
        if (! func_result.empty())
        {
            return func_result;
        }
        else
        {
            return explicit_desc ? explicit_desc : L"";
        }
    }
}

/* A transient parameter pack needed by wildcard_complete.f */
struct wc_complete_pack_t
{
    const wcstring &orig; // the original string, transient
    const wchar_t *desc; // literal description
    wcstring(*desc_func)(const wcstring &); // function for generating descriptions
    expand_flags_t expand_flags;
    wc_complete_pack_t(const wcstring &str) : orig(str) {}
};

/* Weirdly specific and non-reusable helper function that makes its one call site much clearer */
static bool has_prefix_match(const std::vector<completion_t> *comps, size_t first)
{
    if (comps != NULL)
    {
        const size_t after_count = comps->size();
        for (size_t j = first; j < after_count; j++)
        {
            if (comps->at(j).match.type <= fuzzy_match_prefix)
            {
                return true;
            }
        }
    }
    return false;
}

/**
 Matches the string against the wildcard, and if the wildcard is a
 possible completion of the string, the remainder of the string is
 inserted into the out vector.
 
 We ignore ANY_STRING_RECURSIVE here. The consequence is that you cannot
 tab complete ** wildcards. This is historic behavior.
 */
static bool wildcard_complete_internal(const wchar_t *str,
                                       const wchar_t *wc,
                                       const wc_complete_pack_t &params,
                                       complete_flags_t flags,
                                       std::vector<completion_t> *out,
                                       bool is_first_call = false)
{
    assert(str != NULL);
    assert(wc != NULL);
    
    /* Maybe early out for hidden files. We require that the wildcard match these exactly (i.e. a dot); ANY_STRING not allowed */
    if (is_first_call && str[0] == L'.' && wc[0] != L'.')
    {
        return false;
    }
    
    /* Locate the next wildcard character position, e.g. ANY_CHAR or ANY_STRING */
    const size_t next_wc_char_pos = wildcard_find(wc);
    
    /* Maybe we have no more wildcards at all. This includes the empty string. */
    if (next_wc_char_pos == wcstring::npos)
    {
        string_fuzzy_match_t match = string_fuzzy_match_string(wc, str);
        
        /* If we're allowing fuzzy match, any match is OK. Otherwise we require a prefix match. */
        bool match_acceptable;
        if (params.expand_flags & EXPAND_FUZZY_MATCH)
        {
            match_acceptable = match.type != fuzzy_match_none;
        }
        else
        {
            match_acceptable = match_type_shares_prefix(match.type);
        }
        
        if (match_acceptable && out != NULL)
        {
            /* Wildcard complete */
            bool full_replacement = match_type_requires_full_replacement(match.type) || (flags & COMPLETE_REPLACES_TOKEN);
            
            /* If we are not replacing the token, be careful to only store the part of the string after the wildcard */
            assert(!full_replacement || wcslen(wc) <= wcslen(str));
            wcstring out_completion = full_replacement ? params.orig : str + wcslen(wc);
            wcstring out_desc = resolve_description(&out_completion, params.desc, params.desc_func);
            
            /* Note: out_completion may be empty if the completion really is empty, e.g. tab-completing 'foo' when a file 'foo' exists. */
            complete_flags_t local_flags = flags | (full_replacement ? COMPLETE_REPLACES_TOKEN : 0);
            append_completion(out, out_completion, out_desc, local_flags, match);
        }
        return match_acceptable;
    }
    else if (next_wc_char_pos > 0)
    {
        /* Here we have a non-wildcard prefix. Note that we don't do fuzzy matching for stuff before a wildcard, so just do case comparison and then recurse. */
        if (wcsncmp(str, wc, next_wc_char_pos) == 0)
        {
            // Normal match
            return wildcard_complete_internal(str + next_wc_char_pos, wc + next_wc_char_pos, params, flags, out);
        }
        else if (wcsncasecmp(str, wc, next_wc_char_pos) == 0)
        {
            // Case insensitive match
            return wildcard_complete_internal(str + next_wc_char_pos, wc + next_wc_char_pos, params, flags | COMPLETE_REPLACES_TOKEN, out);
        }
        else
        {
            // No match
            return false;
        }
        assert(0 && "Unreachable code reached");
    }
    else
    {
        /* Our first character is a wildcard. */
        assert(next_wc_char_pos == 0);
        switch (wc[0])
        {
            case ANY_CHAR:
            {
                if (str[0] == L'\0')
                {
                    return false;
                }
                else
                {
                    return wildcard_complete_internal(str + 1, wc + 1, params, flags, out);
                }
                break;
            }
                
            case ANY_STRING:
            {
                /* Hackish. If this is the last character of the wildcard, then just complete with the empty string. This fixes cases like "f*<tab>" -> "f*o" */
                if (wc[1] == L'\0')
                {
                    return wildcard_complete_internal(L"", L"", params, flags, out);
                }
                
                /* Try all submatches. #929: if the recursive call gives us a prefix match, just stop. This is sloppy - what we really want to do is say, once we've seen a match of a particular type, ignore all matches of that type further down the string, such that the wildcard produces the "minimal match.". */
                bool has_match = false;
                for (size_t i=0; str[i] != L'\0'; i++)
                {
                    const size_t before_count = out ? out->size() : 0;
                    if (wildcard_complete_internal(str + i, wc + 1, params, flags, out))
                    {
                        /* We found a match */
                        has_match = true;
                        
                        /* If out is NULL, we don't care about the actual matches. If out is not NULL but we have a prefix match, stop there. */
                        if (out == NULL || has_prefix_match(out, before_count))
                        {
                            break;
                        }
                    }
                }
                return has_match;
            }
                
            case ANY_STRING_RECURSIVE:
                /* We don't even try with this one */
                return false;
            
            default:
                assert(0 && "Unreachable code reached");
                return false;
        }
    }
    assert(0 && "Unreachable code reached");
}

bool wildcard_complete(const wcstring &str,
                       const wchar_t *wc,
                       const wchar_t *desc,
                       wcstring(*desc_func)(const wcstring &),
                       std::vector<completion_t> *out,
                       expand_flags_t expand_flags,
                       complete_flags_t flags)
{
    // Note out may be NULL
    assert(wc != NULL);
    wc_complete_pack_t params(str);
    params.desc = desc;
    params.desc_func = desc_func;
    params.expand_flags = expand_flags;
    return wildcard_complete_internal(str.c_str(), wc, params, flags, out, true /* first call */);
}


bool wildcard_match(const wcstring &str, const wcstring &wc, bool leading_dots_fail_to_match)
{
    enum fuzzy_match_type_t match = wildcard_match_internal(str.c_str(), wc.c_str(), leading_dots_fail_to_match, true /* first */, fuzzy_match_exact);
    return match != fuzzy_match_none;
}
        
enum fuzzy_match_type_t wildcard_match_fuzzy(const wcstring &str, const wcstring &wc, bool leading_dots_fail_to_match, enum fuzzy_match_type_t max_type)
{
    return wildcard_match_internal(str.c_str(), wc.c_str(), leading_dots_fail_to_match, true /* first */, max_type);
}

/**
 Obtain a description string for the file specified by the filename.
 
 The returned value is a string constant and should not be free'd.
 
 \param filename The file for which to find a description string
 \param lstat_res The result of calling lstat on the file
 \param lbuf The struct buf output of calling lstat on the file
 \param stat_res The result of calling stat on the file
 \param buf The struct buf output of calling stat on the file
 \param err The errno value after a failed stat call on the file.
 */

static wcstring file_get_desc(const wcstring &filename,
                              int lstat_res,
                              const struct stat &lbuf,
                              int stat_res,
                              struct stat buf,
                              int err)
{
    
    if (!lstat_res)
    {
        if (S_ISLNK(lbuf.st_mode))
        {
            if (!stat_res)
            {
                if (S_ISDIR(buf.st_mode))
                {
                    return COMPLETE_DIRECTORY_SYMLINK_DESC;
                }
                else
                {
                    
                    if (buf.st_mode & (S_IXUSR | S_IXGRP | S_IXOTH))
                    {
                        
                        if (waccess(filename, X_OK) == 0)
                        {
                            /*
                             Weird group permissions and other such
                             issues make it non-trivial to find out
                             if we can actually execute a file using
                             the result from stat. It is much safer
                             to use the access function, since it
                             tells us exactly what we want to know.
                             */
                            return COMPLETE_EXEC_LINK_DESC;
                        }
                    }
                }
                
                return COMPLETE_SYMLINK_DESC;
                
            }
            else
            {
                switch (err)
                {
                    case ENOENT:
                    {
                        return COMPLETE_ROTTEN_SYMLINK_DESC;
                    }
                        
                    case ELOOP:
                    {
                        return COMPLETE_LOOP_SYMLINK_DESC;
                    }
                }
                /*
                 On unknown errors we do nothing. The file will be
                 given the default 'File' description or one based on the suffix.
                 */
            }
            
        }
        else if (S_ISCHR(buf.st_mode))
        {
            return COMPLETE_CHAR_DESC;
        }
        else if (S_ISBLK(buf.st_mode))
        {
            return COMPLETE_BLOCK_DESC;
        }
        else if (S_ISFIFO(buf.st_mode))
        {
            return COMPLETE_FIFO_DESC;
        }
        else if (S_ISSOCK(buf.st_mode))
        {
            return COMPLETE_SOCKET_DESC;
        }
        else if (S_ISDIR(buf.st_mode))
        {
            return COMPLETE_DIRECTORY_DESC;
        }
        else
        {
            if (buf.st_mode & (S_IXUSR | S_IXGRP | S_IXGRP))
            {
                
                if (waccess(filename, X_OK) == 0)
                {
                    /*
                     Weird group permissions and other such issues
                     make it non-trivial to find out if we can
                     actually execute a file using the result from
                     stat. It is much safer to use the access
                     function, since it tells us exactly what we want
                     to know.
                     */
                    return COMPLETE_EXEC_DESC;
                }
            }
        }
    }
    
    return COMPLETE_FILE_DESC ;
}

/** Test if the given file is an executable (if EXECUTABLES_ONLY) or directory (if DIRECTORIES_ONLY).
    If it matches, call wildcard_complete() with some description that we make up.
    Note that the filename came from a readdir() call, so we know it exists.
 */
static bool wildcard_test_flags_then_complete(const wcstring &filepath,
                                              const wcstring &filename,
                                              const wchar_t *wc,
                                              expand_flags_t expand_flags,
                                              std::vector<completion_t> *out)
{
    /* Check if it will match before stat() */
    if (! wildcard_complete(filename, wc, NULL, NULL, NULL, expand_flags, 0))
    {
        return false;
    }

    struct stat lstat_buf = {}, stat_buf = {};
    int stat_res = -1;
    int stat_errno = 0;
    int lstat_res = lwstat(filepath, &lstat_buf);
    if (lstat_res < 0)
    {
        /* lstat failed */
    }
    else
    {
        if (S_ISLNK(lstat_buf.st_mode))
        {
            stat_res = wstat(filepath, &stat_buf);
            
            if (stat_res < 0)
            {
                /*
                 In order to differentiate between e.g. rotten symlinks
                 and symlink loops, we also need to know the error status of wstat.
                 */
                stat_errno = errno;
            }
        }
        else
        {
            stat_buf = lstat_buf;
            stat_res = lstat_res;
        }
    }
    
    const long long file_size = stat_res == 0 ? stat_buf.st_size : 0;
    const bool is_directory = stat_res == 0 && S_ISDIR(stat_buf.st_mode);
    const bool is_executable = stat_res == 0 && S_ISREG(stat_buf.st_mode);
    
    if (expand_flags & DIRECTORIES_ONLY)
    {
        if (!is_directory)
        {
            return false;
        }
    }
    if (expand_flags & EXECUTABLES_ONLY)
    {
        if (!is_executable || waccess(filepath, X_OK) != 0)
        {
            return false;
        }
    }
    
    /* Compute the description */
    bool wants_desc = !(expand_flags & EXPAND_NO_DESCRIPTIONS);
    wcstring desc;
    if (wants_desc)
    {
        desc = file_get_desc(filepath, lstat_res, lstat_buf, stat_res, stat_buf, stat_errno);
        
        if (file_size >= 0)
        {
            if (!desc.empty())
                desc.append(L", ");
            desc.append(format_size(file_size));
        }
    }
    
    /* Append a / if this is a directory */
    if (is_directory)
    {
        return wildcard_complete(filename + L'/', wc, desc.c_str(), NULL, out, expand_flags, COMPLETE_NO_SPACE);
    }
    else
    {
        return wildcard_complete(filename, wc, desc.c_str(), NULL, out, expand_flags, 0);
    }
}

class wildcard_expander_t
{
    /* The original string we are expanding */
    const wcstring original_base;
    
    /* Original wildcard we are expanding. */
    const wchar_t * const original_wildcard;
    
    /* the set of items we have resolved, used to efficiently avoid duplication */
    std::set<wcstring> completion_set;
    
    /* the set of file IDs we have visited, used to avoid symlink loops */
    std::set<file_id_t> visited_files;
    
    /* flags controlling expansion */
    const expand_flags_t flags;
    
    /* resolved items get inserted into here. This is transient of course. */
    std::vector<completion_t> *resolved_completions;
    
    /* whether we have been interrupted */
    bool did_interrupt;
    
    /* whether we have successfully added any completions */
    bool did_add;
    
    /* We are a trailing slash - expand at the end */
    void expand_trailing_slash(const wcstring &base_dir);
    
    /* Given a directory base_dir, which is opened as base_dir_fp, expand an intermediate segment of the wildcard.
       Treat ANY_STRING_RECURSIVE as ANY_STRING.
       wc_segment is the wildcard segment for this directory
       wc_remainder is the wildcard for subdirectories
     */
    void expand_intermediate_segment(const wcstring &base_dir, DIR *base_dir_fp, const wcstring &wc_segment, const wchar_t *wc_remainder);
    
    /* Given a directory base_dir, which is opened as base_dir_fp, expand an intermediate literal segment.
       Use a fuzzy matching algorithm.
     */
    void expand_literal_intermediate_segment_with_fuzz(const wcstring &base_dir, DIR *base_dir_fp, const wcstring &wc_segment, const wchar_t *wc_remainder);
    
    /* Given a directory base_dir, which is opened as base_dir_fp, expand the last segment of the wildcard.
     Treat ANY_STRING_RECURSIVE as ANY_STRING.
     wc is the wildcard segment to use for matching
     wc_remainder is the wildcard for subdirectories
     */
    void expand_last_segment(const wcstring &base_dir, DIR *base_dir_fp, const wcstring &wc);
    
    /* Indicate whether we should cancel wildcard expansion. This latches 'interrupt' */
    bool interrupted()
    {
        if (! did_interrupt)
        {
            did_interrupt = (is_main_thread() ? reader_interrupted() : reader_thread_job_is_stale());
        }
        return did_interrupt;
    }
    
    void add_expansion_result(const wcstring &result)
    {
        /* This function is only for the non-completions case */
        assert(! (this->flags & EXPAND_FOR_COMPLETIONS));
        if (this->completion_set.insert(result).second)
        {
            append_completion(this->resolved_completions, result);
            this->did_add = true;
        }
    }
    
    void try_add_completion_result(const wcstring &filepath, const wcstring &filename, const wcstring &wildcard)
    {
        /* This function is only for the completions case */
        assert(this->flags & EXPAND_FOR_COMPLETIONS);
        size_t before = this->resolved_completions->size();
        if (wildcard_test_flags_then_complete(filepath, filename, wildcard.c_str(), this->flags, this->resolved_completions))
        {
            /* Hack. We added this completion result based on the last component of the wildcard.
               Prepend all prior components of the wildcard to each completion that replaces its token. */
            size_t wc_len = wildcard.size();
            size_t orig_wc_len = wcslen(this->original_wildcard);
            assert(wc_len <= orig_wc_len);
            const wcstring wc_base(this->original_wildcard, orig_wc_len - wc_len);
            
            size_t after = this->resolved_completions->size();
            for (size_t i=before; i < after; i++)
            {
                completion_t &c = this->resolved_completions->at(i);
                c.prepend_token_prefix(wc_base);
                c.prepend_token_prefix(this->original_base);
            }
            this->did_add = true;
        }
    }
    
    /* Helper to resolve an empty base directory */
    static DIR *open_dir(const wcstring &base_dir)
    {
        return wopendir(base_dir.empty() ? L"." : base_dir);
    }
    
public:
    
    wildcard_expander_t(const wcstring &orig_base, const wchar_t *orig_wc, expand_flags_t f, std::vector<completion_t> *r) :
        original_base(orig_base),
        original_wildcard(orig_wc),
        flags(f),
        resolved_completions(r),
        did_interrupt(false),
        did_add(false)
    {
        assert(resolved_completions != NULL);
        
        /* Insert initial completions into our set to avoid duplicates */
        for (std::vector<completion_t>::const_iterator iter = resolved_completions->begin(); iter != resolved_completions->end(); ++iter)
        {
            this->completion_set.insert(iter->completion);
        }
    }
    
    /* Do wildcard expansion. This is recursive. */
    void expand(const wcstring &base_dir, const wchar_t *wc);
    
    int status_code() const
    {
        if (this->did_interrupt)
        {
            return -1;
        }
        else
        {
            return this->did_add ? 1 : 0;
        }
    }
};

void wildcard_expander_t::expand_trailing_slash(const wcstring &base_dir)
{
    if (interrupted())
    {
        return;
    }
    
    if (! (flags & EXPAND_FOR_COMPLETIONS))
    {
        /* Trailing slash and not accepting incomplete, e.g. `echo /tmp/`. Insert this file if it exists. */
        if (waccess(base_dir, F_OK) == 0)
        {
            this->add_expansion_result(base_dir);
        }
    }
    else
    {
        /* Trailing slashes and accepting incomplete, e.g. `echo /tmp/<tab>`. Everything is added. */
        DIR *dir = open_dir(base_dir);
        if (dir)
        {
            wcstring next;
            while (wreaddir(dir, next) && ! interrupted())
            {
                if (! next.empty() && next.at(0) != L'.')
                {
                    this->try_add_completion_result(base_dir + next, next, L"");
                }
            }
            closedir(dir);
        }
    }
}

void wildcard_expander_t::expand_intermediate_segment(const wcstring &base_dir, DIR *base_dir_fp, const wcstring &wc_segment, const wchar_t *wc_remainder)
{
    wcstring name_str;
    while (!interrupted() && wreaddir_for_dirs(base_dir_fp, &name_str))
    {
        /* Note that it's critical we ignore leading dots here, else we may descend into . and .. */
        if (! wildcard_match(name_str, wc_segment, true))
        {
            /* Doesn't match the wildcard for this segment, skip it */
            continue;
        }
        
        wcstring full_path = base_dir + name_str;
        struct stat buf;
        if (0 != wstat(full_path, &buf) || !S_ISDIR(buf.st_mode))
        {
            /* We either can't stat it, or we did but it's not a directory */
            continue;
        }

        const file_id_t file_id = file_id_t::file_id_from_stat(&buf);
        if (!this->visited_files.insert(file_id).second)
        {
            /* Symlink loop! This directory was already visited, so skip it */
            continue;
        }

        /* We made it through. Perform normal wildcard expansion on this new directory, starting at our tail_wc, which includes the ANY_STRING_RECURSIVE guy. */
        full_path.push_back(L'/');
        this->expand(full_path, wc_remainder);

        /* Now remove the visited file. This is for #2414: only directories "beneath" us should be considered visited. */
        this->visited_files.erase(file_id);
    }
}
        
void wildcard_expander_t::expand_literal_intermediate_segment_with_fuzz(const wcstring &base_dir, DIR *base_dir_fp, const wcstring &wc_segment, const wchar_t *wc_remainder)
{
    // This only works with tab completions
    // Ordinary wildcard expansion should never go fuzzy
    wcstring name_str;
    while (!interrupted() && wreaddir_for_dirs(base_dir_fp, &name_str))
    {
        /* Don't bother with . and .. */
        if (contains(name_str, L".", L".."))
        {
            continue;
        }
        
        // Skip cases that don't match or match exactly
        // The match-exactly case was handled directly in expand()
        const string_fuzzy_match_t match = string_fuzzy_match_string(wc_segment, name_str);
        if (match.type == fuzzy_match_none || match.type == fuzzy_match_exact)
        {
            continue;
        }
        
        wcstring new_full_path = base_dir + name_str;
        new_full_path.push_back(L'/');
        struct stat buf;
        if (0 != wstat(new_full_path, &buf) || !S_ISDIR(buf.st_mode))
        {
            /* We either can't stat it, or we did but it's not a directory */
            continue;
        }
        
        // Ok, this directory matches. Recurse to it.
        // Then perform serious surgery on each result!
        // Each result was computed with a prefix of original_wildcard
        // We need to replace our segment of that with our name_str
        // We also have to mark the completion as replacing and fuzzy
        const size_t before = this->resolved_completions->size();
        
        this->expand(new_full_path, wc_remainder);
        const size_t after = this->resolved_completions->size();
        
        assert(before <= after);
        for (size_t i=before; i < after; i++)
        {
            completion_t *c = &this->resolved_completions->at(i);
            // Mark the completion as replacing
            if (!(c->flags & COMPLETE_REPLACES_TOKEN))
            {
                c->flags |= COMPLETE_REPLACES_TOKEN;
                c->prepend_token_prefix(this->original_wildcard);
                c->prepend_token_prefix(this->original_base);
            }
            // Ok, it's now replacing and is prefixed with the segment base, plus our original wildcard
            // Replace our segment with name_str
            // Our segment starts at the length of the original wildcard, minus what we have left to process, minus the length of our segment
            // This logic is way too picky. Need to clean this up.
            // One possibility is to send the "resolved wildcard" along with the actual wildcard
            const size_t original_wildcard_len = wcslen(this->original_wildcard);
            const size_t wc_remainder_len = wcslen(wc_remainder);
            const size_t segment_len = wc_segment.length();
            assert(c->completion.length() >= original_wildcard_len);
            const size_t segment_start = original_wildcard_len + this->original_base.size() - wc_remainder_len - wc_segment.length() - 1; // -1 for the slash after our segment
            assert(segment_start < original_wildcard_len);
            assert(c->completion.substr(segment_start, segment_len) == wc_segment);
            c->completion.replace(segment_start, segment_len, name_str);
            
            // And every match must be made at least as fuzzy as ours
            if (match.compare(c->match) > 0)
            {
                // Our match is fuzzier
                c->match = match;
            }
        }
    }
}

void wildcard_expander_t::expand_last_segment(const wcstring &base_dir, DIR *base_dir_fp, const wcstring &wc)
{
    wcstring name_str;
    while (wreaddir(base_dir_fp, name_str))
    {
        if (flags & EXPAND_FOR_COMPLETIONS)
        {
            this->try_add_completion_result(base_dir + name_str, name_str, wc);
        }
        else
        {
            // Normal wildcard expansion, not for completions
            if (wildcard_match(name_str, wc, true /* skip files with leading dots */))
            {
                this->add_expansion_result(base_dir + name_str);
            }
        }
    }
}

/**
 The real implementation of wildcard expansion is in this
 function. Other functions are just wrappers around this one.
 
 This function traverses the relevant directory tree looking for
 matches, and recurses when needed to handle wildcrards spanning
 multiple components and recursive wildcards.
 
 Because this function calls itself recursively with substrings,
 it's important that the parameters be raw pointers instead of wcstring,
 which would be too expensive to construct for all substrings.
 
 Args:
 base_dir: the "working directory" against which the wildcard is to be resolved
 wc: the wildcard string itself, e.g. foo*bar/baz (where * is acutally ANY_CHAR)
*/
void wildcard_expander_t::expand(const wcstring &base_dir, const wchar_t *wc)
{
    assert(wc != NULL);
    
    if (interrupted())
    {
        return;
    }
    
    /* Get the current segment and compute interesting properties about it. */
    const size_t wc_len = wcslen(wc);
    const wchar_t * const next_slash = wcschr(wc, L'/');
    const bool is_last_segment = (next_slash == NULL);
    const size_t wc_segment_len = next_slash ? next_slash - wc : wc_len;
    const wcstring wc_segment = wcstring(wc, wc_segment_len);
    const bool segment_has_wildcards = wildcard_has(wc_segment, true /* internal, i.e. look for ANY_CHAR instead of ? */);
    
    if (wc_segment.empty())
    {
        /* Handle empty segment */
        assert(! segment_has_wildcards);
        if (is_last_segment)
        {
            this->expand_trailing_slash(base_dir);
        }
        else
        {
            /* Multiple adjacent slashes in the wildcard. Just skip them. */
            this->expand(base_dir, next_slash + 1);
        }
    }
    else if (! segment_has_wildcards && ! is_last_segment)
    {
        /* Literal intermediate match. Note that we may not be able to actually read the directory (#2099) */
        assert(next_slash != NULL);
        const wchar_t *wc_remainder = next_slash;
        while (*wc_remainder == L'/')
        {
            wc_remainder++;
        }
        
        /* This just trumps everything */
        size_t before = this->resolved_completions->size();
        this->expand(base_dir + wc_segment + L'/', wc_remainder);
        
        /* Maybe try a fuzzy match (#94) if nothing was found with the literal match. Respect EXPAND_NO_DIRECTORY_ABBREVIATIONS (#2413). */
        bool allow_fuzzy = (this->flags & (EXPAND_FUZZY_MATCH | EXPAND_NO_FUZZY_DIRECTORIES)) == EXPAND_FUZZY_MATCH;
        if (allow_fuzzy && this->resolved_completions->size() == before)
        {
            assert(this->flags & EXPAND_FOR_COMPLETIONS);
            DIR *base_dir_fd = open_dir(base_dir);
            if (base_dir_fd != NULL)
            {
                this->expand_literal_intermediate_segment_with_fuzz(base_dir, base_dir_fd, wc_segment, wc_remainder);
                closedir(base_dir_fd);
            }
        }
    }
    else
    {
        assert(! wc_segment.empty() && (segment_has_wildcards || is_last_segment));
        DIR *dir = open_dir(base_dir);
        if (dir)
        {
            if (is_last_segment)
            {
                /* Last wildcard segment, nonempty wildcard */
                this->expand_last_segment(base_dir, dir, wc_segment);
            }
            else
            {
                /* Not the last segment, nonempty wildcard */
                assert(next_slash != NULL);
                const wchar_t *wc_remainder = next_slash;
                while (*wc_remainder == L'/')
                {
                    wc_remainder++;
                }
                this->expand_intermediate_segment(base_dir, dir, wc_segment, wc_remainder);
            }
            
            /* Recursive wildcards require special handling */
            size_t asr_idx = wc_segment.find(ANY_STRING_RECURSIVE);
            if (asr_idx != wcstring::npos)
            {
                /* Construct a "head + any" wildcard for matching stuff in this directory, and an "any + tail" wildcard for matching stuff in subdirectories. Note that the ANY_STRING_RECURSIVE character is present in both the head and the tail. */
                const wcstring head_any(wc_segment, 0, asr_idx + 1);
                const wchar_t *any_tail = wc + asr_idx;
                assert(head_any.at(head_any.size() - 1) == ANY_STRING_RECURSIVE);
                assert(any_tail[0] == ANY_STRING_RECURSIVE);

                rewinddir(dir);
                this->expand_intermediate_segment(base_dir, dir, head_any, any_tail);
            }
            closedir(dir);
        }
    }
}


int wildcard_expand_string(const wcstring &wc, const wcstring &base_dir, expand_flags_t flags, std::vector<completion_t> *output)
{
    assert(output != NULL);
    /* Fuzzy matching only if we're doing completions */
    assert((flags & (EXPAND_FUZZY_MATCH | EXPAND_FOR_COMPLETIONS)) != EXPAND_FUZZY_MATCH);
    /* Hackish fix for 1631. We are about to call c_str(), which will produce a string truncated at any embedded nulls. We could fix this by passing around the size, etc. However embedded nulls are never allowed in a filename, so we just check for them and return 0 (no matches) if there is an embedded null. */
    if (wc.find(L'\0') != wcstring::npos)
    {
        return 0;
    }
    
    wildcard_expander_t expander(base_dir, wc.c_str(), flags, output);
    expander.expand(base_dir, wc.c_str());
    return expander.status_code();
}