From 6705a2efc6af31fb509559be2e253447c6a4e533 Mon Sep 17 00:00:00 2001
From: ridiculousfish <corydoras@ridiculousfish.com>
Date: Wed, 15 Jan 2020 13:16:43 -0800
Subject: [PATCH] Migrate a bunch of code out of common.h

Put it into wcstringutil, path, or a new file null_terminated_array.
---
 CMakeLists.txt                |   2 +-
 src/builtin_argparse.cpp      |   1 +
 src/builtin_complete.cpp      |   1 +
 src/builtin_functions.cpp     |   1 +
 src/builtin_printf.cpp        |   1 +
 src/builtin_set.cpp           |   1 +
 src/common.cpp                | 218 +---------------------------------
 src/common.h                  | 174 ---------------------------
 src/complete.cpp              |   1 +
 src/env.h                     |   1 +
 src/exec.cpp                  |   1 +
 src/fish.cpp                  |   1 +
 src/flog.cpp                  |   1 +
 src/flog.h                    |   1 +
 src/future_feature_flags.cpp  |   2 +
 src/highlight.cpp             |   1 +
 src/null_terminated_array.cpp |  73 ++++++++++++
 src/null_terminated_array.h   |  87 ++++++++++++++
 src/output.cpp                |   1 +
 src/path.cpp                  |  18 +++
 src/path.h                    |   3 +
 src/screen.h                  |   1 +
 src/wcstringutil.cpp          | 129 +++++++++++++++++++-
 src/wcstringutil.h            |  97 +++++++++++++++
 src/wildcard.cpp              |   2 +
 25 files changed, 425 insertions(+), 394 deletions(-)
 create mode 100644 src/null_terminated_array.cpp
 create mode 100644 src/null_terminated_array.h

diff --git a/CMakeLists.txt b/CMakeLists.txt
index 46cf4cad8..ee3834c70 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -117,7 +117,7 @@ SET(FISH_SRCS
     src/signal.cpp src/tinyexpr.cpp src/tnode.cpp src/tokenizer.cpp src/utf8.cpp src/util.cpp
     src/wcstringutil.cpp src/wgetopt.cpp src/wildcard.cpp src/wutil.cpp
     src/future_feature_flags.cpp src/redirection.cpp src/topic_monitor.cpp
-    src/flog.cpp src/trace.cpp src/timer.cpp
+    src/flog.cpp src/trace.cpp src/timer.cpp src/null_terminated_array.cpp
 )
 
 # Header files are just globbed.
diff --git a/src/builtin_argparse.cpp b/src/builtin_argparse.cpp
index 3f3c1c43f..0483e79c3 100644
--- a/src/builtin_argparse.cpp
+++ b/src/builtin_argparse.cpp
@@ -23,6 +23,7 @@
 #include "fallback.h"  // IWYU pragma: keep
 #include "io.h"
 #include "parser.h"
+#include "wcstringutil.h"
 #include "wgetopt.h"  // IWYU pragma: keep
 #include "wutil.h"    // IWYU pragma: keep
 
diff --git a/src/builtin_complete.cpp b/src/builtin_complete.cpp
index cbcd7f96a..3e2372826 100644
--- a/src/builtin_complete.cpp
+++ b/src/builtin_complete.cpp
@@ -19,6 +19,7 @@
 #include "parse_util.h"
 #include "parser.h"
 #include "reader.h"
+#include "wcstringutil.h"
 #include "wgetopt.h"
 #include "wutil.h"  // IWYU pragma: keep
 
diff --git a/src/builtin_functions.cpp b/src/builtin_functions.cpp
index c3f5404c0..c1d936351 100644
--- a/src/builtin_functions.cpp
+++ b/src/builtin_functions.cpp
@@ -26,6 +26,7 @@
 #include "parser_keywords.h"
 #include "proc.h"
 #include "signal.h"
+#include "wcstringutil.h"
 #include "wgetopt.h"
 #include "wutil.h"  // IWYU pragma: keep
 
diff --git a/src/builtin_printf.cpp b/src/builtin_printf.cpp
index e8a208b12..bda9d974b 100644
--- a/src/builtin_printf.cpp
+++ b/src/builtin_printf.cpp
@@ -66,6 +66,7 @@
 #include "builtin.h"
 #include "common.h"
 #include "io.h"
+#include "wcstringutil.h"
 #include "wutil.h"  // IWYU pragma: keep
 
 class parser_t;
diff --git a/src/builtin_set.cpp b/src/builtin_set.cpp
index 06af7b60b..d6082ef2b 100644
--- a/src/builtin_set.cpp
+++ b/src/builtin_set.cpp
@@ -25,6 +25,7 @@
 #include "io.h"
 #include "parser.h"
 #include "proc.h"
+#include "wcstringutil.h"
 #include "wgetopt.h"
 #include "wutil.h"  // IWYU pragma: keep
 
diff --git a/src/common.cpp b/src/common.cpp
index 6e43badc4..3fd2da590 100644
--- a/src/common.cpp
+++ b/src/common.cpp
@@ -48,7 +48,6 @@
 
 #include <algorithm>
 #include <atomic>
-#include <locale>
 #include <memory>  // IWYU pragma: keep
 #include <type_traits>
 
@@ -63,6 +62,7 @@
 #include "parser.h"
 #include "proc.h"
 #include "signal.h"
+#include "wcstringutil.h"
 #include "wildcard.h"
 #include "wutil.h"  // IWYU pragma: keep
 
@@ -1870,62 +1870,6 @@ int common_get_width() { return get_current_winsize().ws_col; }
 
 int common_get_height() { return get_current_winsize().ws_row; }
 
-bool string_prefixes_string(const wchar_t *proposed_prefix, const wcstring &value) {
-    return string_prefixes_string(proposed_prefix, value.c_str());
-}
-
-bool string_prefixes_string(const wcstring &proposed_prefix, const wcstring &value) {
-    size_t prefix_size = proposed_prefix.size();
-    return prefix_size <= value.size() && value.compare(0, prefix_size, proposed_prefix) == 0;
-}
-
-bool string_prefixes_string(const wchar_t *proposed_prefix, const wchar_t *value) {
-    for (size_t idx = 0; proposed_prefix[idx] != L'\0'; idx++) {
-        // Note if the prefix is longer than value, then we will compare a nonzero prefix character
-        // against a zero value character, and so we'll return false;
-        if (proposed_prefix[idx] != value[idx]) return false;
-    }
-    // We must have that proposed_prefix[idx] == L'\0', so we have a prefix match.
-    return true;
-}
-
-bool string_prefixes_string(const char *proposed_prefix, const std::string &value) {
-    return string_prefixes_string(proposed_prefix, value.c_str());
-}
-
-bool string_prefixes_string(const char *proposed_prefix, const char *value) {
-    for (size_t idx = 0; proposed_prefix[idx] != L'\0'; idx++) {
-        if (proposed_prefix[idx] != value[idx]) return false;
-    }
-    return true;
-}
-
-bool string_prefixes_string_case_insensitive(const wcstring &proposed_prefix,
-                                             const wcstring &value) {
-    size_t prefix_size = proposed_prefix.size();
-    return prefix_size <= value.size() &&
-           wcsncasecmp(proposed_prefix.c_str(), value.c_str(), prefix_size) == 0;
-}
-
-bool string_suffixes_string(const wcstring &proposed_suffix, const wcstring &value) {
-    size_t suffix_size = proposed_suffix.size();
-    return suffix_size <= value.size() &&
-           value.compare(value.size() - suffix_size, suffix_size, proposed_suffix) == 0;
-}
-
-bool string_suffixes_string(const wchar_t *proposed_suffix, const wcstring &value) {
-    size_t suffix_size = std::wcslen(proposed_suffix);
-    return suffix_size <= value.size() &&
-           value.compare(value.size() - suffix_size, suffix_size, proposed_suffix) == 0;
-}
-
-bool string_suffixes_string_case_insensitive(const wcstring &proposed_suffix,
-                                             const wcstring &value) {
-    size_t suffix_size = proposed_suffix.size();
-    return suffix_size <= value.size() && wcsncasecmp(value.c_str() + (value.size() - suffix_size),
-                                                      proposed_suffix.c_str(), suffix_size) == 0;
-}
-
 /// Returns true if seq, represented as a subsequence, is contained within string.
 static bool subsequence_in_string(const wcstring &seq, const wcstring &str) {
     // Impossible if seq is larger than string.
@@ -2021,74 +1965,6 @@ int string_fuzzy_match_t::compare(const string_fuzzy_match_t &rhs) const {
     return 0;  // equal
 }
 
-template <bool Fuzzy, typename T>
-size_t ifind_impl(const T &haystack, const T &needle) {
-    using char_t = typename T::value_type;
-    std::locale locale;
-
-    auto ieq = [&locale](char_t c1, char_t c2) {
-        if (c1 == c2 || std::toupper(c1, locale) == std::toupper(c2, locale)) return true;
-
-        // In fuzzy matching treat treat `-` and `_` as equal (#3584).
-        if (Fuzzy) {
-            if ((c1 == '-' || c1 == '_') && (c2 == '-' || c2 == '_')) return true;
-        }
-        return false;
-    };
-
-    auto result = std::search(haystack.begin(), haystack.end(), needle.begin(), needle.end(), ieq);
-    if (result != haystack.end()) {
-        return result - haystack.begin();
-    }
-    return T::npos;
-}
-
-size_t ifind(const wcstring &haystack, const wcstring &needle, bool fuzzy) {
-    return fuzzy ? ifind_impl<true>(haystack, needle) : ifind_impl<false>(haystack, needle);
-}
-
-size_t ifind(const std::string &haystack, const std::string &needle, bool fuzzy) {
-    return fuzzy ? ifind_impl<true>(haystack, needle) : ifind_impl<false>(haystack, needle);
-}
-
-wcstring_list_t split_string(const wcstring &val, wchar_t sep) {
-    wcstring_list_t out;
-    size_t pos = 0, end = val.size();
-    while (pos <= end) {
-        size_t next_pos = val.find(sep, pos);
-        if (next_pos == wcstring::npos) {
-            next_pos = end;
-        }
-        out.emplace_back(val, pos, next_pos - pos);
-        pos = next_pos + 1;  // skip the separator, or skip past the end
-    }
-    return out;
-}
-
-wcstring join_strings(const wcstring_list_t &vals, wchar_t sep) {
-    if (vals.empty()) return wcstring{};
-
-    // Reserve the size we will need.
-    // count-1 separators, plus the length of all strings.
-    size_t size = vals.size() - 1;
-    for (const wcstring &s : vals) {
-        size += s.size();
-    }
-
-    // Construct the string.
-    wcstring result;
-    result.reserve(size);
-    bool first = true;
-    for (const wcstring &s : vals) {
-        if (!first) {
-            result.push_back(sep);
-        }
-        result.append(s);
-        first = false;
-    }
-    return result;
-}
-
 int create_directory(const wcstring &d) {
     bool ok = false;
     struct stat buf;
@@ -2212,23 +2088,6 @@ double timef() {
 
 void exit_without_destructors(int code) { _exit(code); }
 
-/// Helper function to convert from a null_terminated_array_t<wchar_t> to a
-/// null_terminated_array_t<char_t>.
-void convert_wide_array_to_narrow(const null_terminated_array_t<wchar_t> &wide_arr,
-                                  null_terminated_array_t<char> *output) {
-    const wchar_t *const *arr = wide_arr.get();
-    if (!arr) {
-        output->clear();
-        return;
-    }
-
-    std::vector<std::string> list;
-    for (size_t i = 0; arr[i]; i++) {
-        list.push_back(wcs2string(arr[i]));
-    }
-    output->set(list);
-}
-
 void autoclose_fd_t::close() {
     if (fd_ < 0) return;
     if (::close(fd_) == -1) {
@@ -2237,24 +2096,6 @@ void autoclose_fd_t::close() {
     fd_ = -1;
 }
 
-void append_path_component(wcstring &path, const wcstring &component) {
-    if (path.empty() || component.empty()) {
-        path.append(component);
-    } else {
-        size_t path_len = path.size();
-        bool path_slash = path.at(path_len - 1) == L'/';
-        bool comp_slash = component.at(0) == L'/';
-        if (!path_slash && !comp_slash) {
-            // Need a slash
-            path.push_back(L'/');
-        } else if (path_slash && comp_slash) {
-            // Too many slashes.
-            path.erase(path_len - 1, 1);
-        }
-        path.append(component);
-    }
-}
-
 extern "C" {
 [[gnu::noinline]] void debug_thread_error(void) {
     // Wait for a SIGINT. We can't use sigsuspend() because the signal may be delivered on another
@@ -2335,63 +2176,6 @@ void assert_is_locked(void *vmutex, const char *who, const char *caller) {
     }
 }
 
-template <typename CharType_t>
-static CharType_t **make_null_terminated_array_helper(
-    const std::vector<std::basic_string<CharType_t> > &argv) {
-    size_t count = argv.size();
-
-    // We allocate everything in one giant block. First compute how much space we need.
-    // N + 1 pointers.
-    size_t pointers_allocation_len = (count + 1) * sizeof(CharType_t *);
-
-    // In the very unlikely event that CharType_t has stricter alignment requirements than does a
-    // pointer, round us up to the size of a CharType_t.
-    pointers_allocation_len += sizeof(CharType_t) - 1;
-    pointers_allocation_len -= pointers_allocation_len % sizeof(CharType_t);
-
-    // N null terminated strings.
-    size_t strings_allocation_len = 0;
-    for (size_t i = 0; i < count; i++) {
-        // The size of the string, plus a null terminator.
-        strings_allocation_len += (argv.at(i).size() + 1) * sizeof(CharType_t);
-    }
-
-    // Now allocate their sum.
-    unsigned char *base =
-        static_cast<unsigned char *>(malloc(pointers_allocation_len + strings_allocation_len));
-    if (!base) return nullptr;
-
-    // Divvy it up into the pointers and strings.
-    CharType_t **pointers = reinterpret_cast<CharType_t **>(base);
-    CharType_t *strings = reinterpret_cast<CharType_t *>(base + pointers_allocation_len);
-
-    // Start copying.
-    for (size_t i = 0; i < count; i++) {
-        const std::basic_string<CharType_t> &str = argv.at(i);
-        *pointers++ = strings;  // store the current string pointer into self
-        strings = std::copy(str.begin(), str.end(), strings);  // copy the string into strings
-        *strings++ = (CharType_t)(0);  // each string needs a null terminator
-    }
-    *pointers++ = nullptr;  // array of pointers needs a null terminator
-
-    // Make sure we know what we're doing.
-    assert((unsigned char *)pointers - base == (std::ptrdiff_t)pointers_allocation_len);
-    assert((unsigned char *)strings - (unsigned char *)pointers ==
-           (std::ptrdiff_t)strings_allocation_len);
-    assert((unsigned char *)strings - base ==
-           (std::ptrdiff_t)(pointers_allocation_len + strings_allocation_len));
-
-    return reinterpret_cast<CharType_t **>(base);
-}
-
-wchar_t **make_null_terminated_array(const wcstring_list_t &lst) {
-    return make_null_terminated_array_helper(lst);
-}
-
-char **make_null_terminated_array(const std::vector<std::string> &lst) {
-    return make_null_terminated_array_helper(lst);
-}
-
 /// Test if the specified character is in a range that fish uses interally to store special tokens.
 ///
 /// NOTE: This is used when tokenizing the input. It is also used when reading input, before
diff --git a/src/common.h b/src/common.h
index d3d1939d3..988d5b55b 100644
--- a/src/common.h
+++ b/src/common.h
@@ -287,69 +287,6 @@ char *wcs2str(const wchar_t *in);
 char *wcs2str(const wcstring &in);
 std::string wcs2string(const wcstring &input);
 
-/// Test if a string prefixes another. Returns true if a is a prefix of b.
-bool string_prefixes_string(const wcstring &proposed_prefix, const wcstring &value);
-bool string_prefixes_string(const wchar_t *proposed_prefix, const wcstring &value);
-bool string_prefixes_string(const wchar_t *proposed_prefix, const wchar_t *value);
-bool string_prefixes_string(const char *proposed_prefix, const std::string &value);
-bool string_prefixes_string(const char *proposed_prefix, const char *value);
-
-/// Test if a string is a suffix of another.
-bool string_suffixes_string(const wcstring &proposed_suffix, const wcstring &value);
-bool string_suffixes_string(const wchar_t *proposed_suffix, const wcstring &value);
-bool string_suffixes_string_case_insensitive(const wcstring &proposed_suffix,
-                                             const wcstring &value);
-
-/// Test if a string prefixes another without regard to case. Returns true if a is a prefix of b.
-bool string_prefixes_string_case_insensitive(const wcstring &proposed_prefix,
-                                             const wcstring &value);
-
-/// Case-insensitive string search, modeled after std::string::find().
-/// \param fuzzy indicates this is being used for fuzzy matching and case insensitivity is
-/// expanded to include symbolic characters (#3584).
-/// \return the offset of the first case-insensitive matching instance of `needle` within
-/// `haystack`, or `string::npos()` if no results were found.
-size_t ifind(const wcstring &haystack, const wcstring &needle, bool fuzzy = false);
-size_t ifind(const std::string &haystack, const std::string &needle, bool fuzzy = false);
-
-/// Split a string by a separator character.
-wcstring_list_t split_string(const wcstring &val, wchar_t sep);
-
-/// Join a list of strings by a separator character.
-wcstring join_strings(const wcstring_list_t &vals, wchar_t sep);
-
-/// Support for iterating over a newline-separated string.
-template <typename Collection>
-class line_iterator_t {
-    // Storage for each line.
-    Collection storage;
-
-    // The collection we're iterating. Note we hold this by reference.
-    const Collection &coll;
-
-    // The current location in the iteration.
-    typename Collection::const_iterator current;
-
-   public:
-    /// Construct from a collection (presumably std::string or std::wcstring).
-    line_iterator_t(const Collection &coll) : coll(coll), current(coll.cbegin()) {}
-
-    /// Access the storage in which the last line was stored.
-    const Collection &line() const { return storage; }
-
-    /// Advances to the next line. \return true on success, false if we have exhausted the string.
-    bool next() {
-        if (current == coll.end()) return false;
-        auto newline_or_end = std::find(current, coll.cend(), '\n');
-        storage.assign(current, newline_or_end);
-        current = newline_or_end;
-
-        // Skip the newline.
-        if (current != coll.cend()) ++current;
-        return true;
-    }
-};
-
 enum fuzzy_match_type_t {
     // We match the string exactly: FOOBAR matches FOOBAR.
     fuzzy_match_exact = 0,
@@ -483,114 +420,6 @@ void format_ullong_safe(wchar_t buff[64], unsigned long long val);
 /// "Narrows" a wide character string. This just grabs any ASCII characters and trunactes.
 void narrow_string_safe(char buff[64], const wchar_t *s);
 
-inline wcstring to_string(long x) {
-    wchar_t buff[64];
-    format_long_safe(buff, x);
-    return wcstring(buff);
-}
-
-inline wcstring to_string(unsigned long long x) {
-    wchar_t buff[64];
-    format_ullong_safe(buff, x);
-    return wcstring(buff);
-}
-
-inline wcstring to_string(int x) { return to_string(static_cast<long>(x)); }
-
-inline wcstring to_string(size_t x) { return to_string(static_cast<unsigned long long>(x)); }
-
-inline bool bool_from_string(const std::string &x) {
-    if (x.empty()) return false;
-    switch (x.front()) {
-        case 'Y':
-        case 'T':
-        case 'y':
-        case 't':
-        case '1':
-            return true;
-        default:
-            return false;
-    }
-}
-
-inline bool bool_from_string(const wcstring &x) {
-    return !x.empty() && std::wcschr(L"YTyt1", x.at(0));
-}
-
-wchar_t **make_null_terminated_array(const wcstring_list_t &lst);
-char **make_null_terminated_array(const std::vector<std::string> &lst);
-
-// Helper class for managing a null-terminated array of null-terminated strings (of some char type).
-template <typename CharType_t>
-class null_terminated_array_t {
-    CharType_t **array{nullptr};
-
-    // No assignment or copying.
-    void operator=(null_terminated_array_t rhs) = delete;
-    null_terminated_array_t(const null_terminated_array_t &) = delete;
-
-    typedef std::vector<std::basic_string<CharType_t>> string_list_t;
-
-    size_t size() const {
-        size_t len = 0;
-        if (array != nullptr) {
-            while (array[len] != nullptr) {
-                len++;
-            }
-        }
-        return len;
-    }
-
-    void free(void) {
-        ::free((void *)array);
-        array = nullptr;
-    }
-
-   public:
-    null_terminated_array_t() = default;
-
-    explicit null_terminated_array_t(const string_list_t &argv)
-        : array(make_null_terminated_array(argv)) {}
-
-    ~null_terminated_array_t() { this->free(); }
-
-    null_terminated_array_t(null_terminated_array_t &&rhs) : array(rhs.array) {
-        rhs.array = nullptr;
-    }
-
-    null_terminated_array_t operator=(null_terminated_array_t &&rhs) {
-        free();
-        array = rhs.array;
-        rhs.array = nullptr;
-    }
-
-    void set(const string_list_t &argv) {
-        this->free();
-        this->array = make_null_terminated_array(argv);
-    }
-
-    /// Convert from a null terminated list to a vector of strings.
-    static string_list_t to_list(const CharType_t *const *arr) {
-        string_list_t result;
-        for (const auto *cursor = arr; cursor && *cursor; cursor++) {
-            result.push_back(*cursor);
-        }
-        return result;
-    }
-
-    /// Instance method.
-    string_list_t to_list() const { return to_list(array); }
-
-    const CharType_t *const *get() const { return array; }
-    CharType_t **get() { return array; }
-
-    void clear() { this->free(); }
-};
-
-// Helper function to convert from a null_terminated_array_t<wchar_t> to a
-// null_terminated_array_t<char_t>.
-void convert_wide_array_to_narrow(const null_terminated_array_t<wchar_t> &arr,
-                                  null_terminated_array_t<char> *output);
 typedef std::lock_guard<std::mutex> scoped_lock;
 typedef std::lock_guard<std::recursive_mutex> scoped_rlock;
 
@@ -736,9 +565,6 @@ class autoclose_fd_t {
     ~autoclose_fd_t() { close(); }
 };
 
-/// Appends a path component, with a / if necessary.
-void append_path_component(wcstring &path, const wcstring &component);
-
 wcstring format_string(const wchar_t *format, ...);
 wcstring vformat_string(const wchar_t *format, va_list va_orig);
 void append_format(wcstring &str, const wchar_t *format, ...);
diff --git a/src/complete.cpp b/src/complete.cpp
index d496dc689..038becaba 100644
--- a/src/complete.cpp
+++ b/src/complete.cpp
@@ -47,6 +47,7 @@
 #include "reader.h"
 #include "tnode.h"
 #include "util.h"
+#include "wcstringutil.h"
 #include "wildcard.h"
 #include "wutil.h"  // IWYU pragma: keep
 
diff --git a/src/env.h b/src/env.h
index b33a5e143..4b0b6421f 100644
--- a/src/env.h
+++ b/src/env.h
@@ -12,6 +12,7 @@
 
 #include "common.h"
 #include "maybe.h"
+#include "null_terminated_array.h"
 
 extern size_t read_byte_limit;
 extern bool curses_initialized;
diff --git a/src/exec.cpp b/src/exec.cpp
index 953b8bc2d..0841c7fdd 100644
--- a/src/exec.cpp
+++ b/src/exec.cpp
@@ -36,6 +36,7 @@
 #include "function.h"
 #include "io.h"
 #include "iothread.h"
+#include "null_terminated_array.h"
 #include "parse_tree.h"
 #include "parser.h"
 #include "path.h"
diff --git a/src/fish.cpp b/src/fish.cpp
index f9d7e2f38..57573a25d 100644
--- a/src/fish.cpp
+++ b/src/fish.cpp
@@ -55,6 +55,7 @@ Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA
 #include "proc.h"
 #include "reader.h"
 #include "signal.h"
+#include "wcstringutil.h"
 #include "wutil.h"  // IWYU pragma: keep
 
 // container to hold the options specified within the command line
diff --git a/src/flog.cpp b/src/flog.cpp
index 477a295dd..5686fb487 100644
--- a/src/flog.cpp
+++ b/src/flog.cpp
@@ -9,6 +9,7 @@
 #include "enum_set.h"
 #include "global_safety.h"
 #include "parse_util.h"
+#include "wcstringutil.h"
 #include "wildcard.h"
 
 namespace flog_details {
diff --git a/src/flog.h b/src/flog.h
index 29677935f..9c478fe28 100644
--- a/src/flog.h
+++ b/src/flog.h
@@ -11,6 +11,7 @@
 #include <utility>
 
 #include "global_safety.h"
+#include "wcstringutil.h"
 
 using wcstring = std::wstring;
 using wcstring_list_t = std::vector<wcstring>;
diff --git a/src/future_feature_flags.cpp b/src/future_feature_flags.cpp
index fd90cd5eb..b50ea03e3 100644
--- a/src/future_feature_flags.cpp
+++ b/src/future_feature_flags.cpp
@@ -4,6 +4,8 @@
 
 #include <cwchar>
 
+#include "wcstringutil.h"
+
 /// The set of features applying to this instance.
 static features_t global_features;
 
diff --git a/src/highlight.cpp b/src/highlight.cpp
index a4a230797..102648ecf 100644
--- a/src/highlight.cpp
+++ b/src/highlight.cpp
@@ -32,6 +32,7 @@
 #include "path.h"
 #include "tnode.h"
 #include "tokenizer.h"
+#include "wcstringutil.h"
 #include "wildcard.h"
 #include "wutil.h"  // IWYU pragma: keep
 
diff --git a/src/null_terminated_array.cpp b/src/null_terminated_array.cpp
new file mode 100644
index 000000000..368584d7f
--- /dev/null
+++ b/src/null_terminated_array.cpp
@@ -0,0 +1,73 @@
+#include "null_terminated_array.h"
+
+template <typename CharT>
+static CharT **make_null_terminated_array_helper(
+    const std::vector<std::basic_string<CharT> > &argv) {
+    size_t count = argv.size();
+
+    // We allocate everything in one giant block. First compute how much space we need.
+    // N + 1 pointers.
+    size_t pointers_allocation_len = (count + 1) * sizeof(CharT *);
+
+    // In the very unlikely event that CharT has stricter alignment requirements than does a
+    // pointer, round us up to the size of a CharT.
+    pointers_allocation_len += sizeof(CharT) - 1;
+    pointers_allocation_len -= pointers_allocation_len % sizeof(CharT);
+
+    // N null terminated strings.
+    size_t strings_allocation_len = 0;
+    for (size_t i = 0; i < count; i++) {
+        // The size of the string, plus a null terminator.
+        strings_allocation_len += (argv.at(i).size() + 1) * sizeof(CharT);
+    }
+
+    // Now allocate their sum.
+    unsigned char *base =
+        static_cast<unsigned char *>(malloc(pointers_allocation_len + strings_allocation_len));
+    if (!base) return nullptr;
+
+    // Divvy it up into the pointers and strings.
+    CharT **pointers = reinterpret_cast<CharT **>(base);
+    CharT *strings = reinterpret_cast<CharT *>(base + pointers_allocation_len);
+
+    // Start copying.
+    for (size_t i = 0; i < count; i++) {
+        const std::basic_string<CharT> &str = argv.at(i);
+        *pointers++ = strings;  // store the current string pointer into self
+        strings = std::copy(str.begin(), str.end(), strings);  // copy the string into strings
+        *strings++ = (CharT)(0);  // each string needs a null terminator
+    }
+    *pointers++ = nullptr;  // array of pointers needs a null terminator
+
+    // Make sure we know what we're doing.
+    assert((unsigned char *)pointers - base == (std::ptrdiff_t)pointers_allocation_len);
+    assert((unsigned char *)strings - (unsigned char *)pointers ==
+           (std::ptrdiff_t)strings_allocation_len);
+    assert((unsigned char *)strings - base ==
+           (std::ptrdiff_t)(pointers_allocation_len + strings_allocation_len));
+
+    return reinterpret_cast<CharT **>(base);
+}
+
+wchar_t **make_null_terminated_array(const wcstring_list_t &lst) {
+    return make_null_terminated_array_helper(lst);
+}
+
+char **make_null_terminated_array(const std::vector<std::string> &lst) {
+    return make_null_terminated_array_helper(lst);
+}
+
+void convert_wide_array_to_narrow(const null_terminated_array_t<wchar_t> &wide_arr,
+                                  null_terminated_array_t<char> *output) {
+    const wchar_t *const *arr = wide_arr.get();
+    if (!arr) {
+        output->clear();
+        return;
+    }
+
+    std::vector<std::string> list;
+    for (size_t i = 0; arr[i]; i++) {
+        list.push_back(wcs2string(arr[i]));
+    }
+    output->set(list);
+}
diff --git a/src/null_terminated_array.h b/src/null_terminated_array.h
new file mode 100644
index 000000000..59950be75
--- /dev/null
+++ b/src/null_terminated_array.h
@@ -0,0 +1,87 @@
+// Support for null-terminated arrays like char**.
+#ifndef FISH_NULL_TERMINATED_ARRAY_H
+#define FISH_NULL_TERMINATED_ARRAY_H
+
+#include "config.h"  // IWYU pragma: keep
+
+#include <string>
+#include <vector>
+
+#include "common.h"
+
+wchar_t **make_null_terminated_array(const wcstring_list_t &lst);
+char **make_null_terminated_array(const std::vector<std::string> &lst);
+
+// Helper class for managing a null-terminated array of null-terminated strings (of some char type).
+template <typename CharT>
+class null_terminated_array_t {
+    using string_list_t = std::vector<std::basic_string<CharT>>;
+
+    CharT **array{nullptr};
+
+    // No assignment or copying.
+    void operator=(null_terminated_array_t rhs) = delete;
+    null_terminated_array_t(const null_terminated_array_t &) = delete;
+
+    size_t size() const {
+        size_t len = 0;
+        if (array != nullptr) {
+            while (array[len] != nullptr) {
+                len++;
+            }
+        }
+        return len;
+    }
+
+    void free(void) {
+        ::free((void *)array);
+        array = nullptr;
+    }
+
+   public:
+    null_terminated_array_t() = default;
+
+    explicit null_terminated_array_t(const string_list_t &argv)
+        : array(make_null_terminated_array(argv)) {}
+
+    ~null_terminated_array_t() { this->free(); }
+
+    null_terminated_array_t(null_terminated_array_t &&rhs) : array(rhs.array) {
+        rhs.array = nullptr;
+    }
+
+    null_terminated_array_t operator=(null_terminated_array_t &&rhs) {
+        free();
+        array = rhs.array;
+        rhs.array = nullptr;
+    }
+
+    void set(const string_list_t &argv) {
+        this->free();
+        this->array = make_null_terminated_array(argv);
+    }
+
+    /// Convert from a null terminated list to a vector of strings.
+    static string_list_t to_list(const CharT *const *arr) {
+        string_list_t result;
+        for (const auto *cursor = arr; cursor && *cursor; cursor++) {
+            result.push_back(*cursor);
+        }
+        return result;
+    }
+
+    /// Instance method.
+    string_list_t to_list() const { return to_list(array); }
+
+    const CharT *const *get() const { return array; }
+    CharT **get() { return array; }
+
+    void clear() { this->free(); }
+};
+
+// Helper function to convert from a null_terminated_array_t<wchar_t> to a
+// null_terminated_array_t<char_t>.
+void convert_wide_array_to_narrow(const null_terminated_array_t<wchar_t> &arr,
+                                  null_terminated_array_t<char> *output);
+
+#endif  // FISH_NULL_TERMINATED_ARRAY_H
diff --git a/src/output.cpp b/src/output.cpp
index 69ce26297..501d3ecd3 100644
--- a/src/output.cpp
+++ b/src/output.cpp
@@ -30,6 +30,7 @@
 #include "fallback.h"  // IWYU pragma: keep
 #include "flog.h"
 #include "output.h"
+#include "wcstringutil.h"
 #include "wutil.h"  // IWYU pragma: keep
 
 /// Whether term256 and term24bit are supported.
diff --git a/src/path.cpp b/src/path.cpp
index 976103df2..3e2995103 100644
--- a/src/path.cpp
+++ b/src/path.cpp
@@ -442,3 +442,21 @@ bool paths_are_same_file(const wcstring &path1, const wcstring &path2) {
 
     return false;
 }
+
+void append_path_component(wcstring &path, const wcstring &component) {
+    if (path.empty() || component.empty()) {
+        path.append(component);
+    } else {
+        size_t path_len = path.size();
+        bool path_slash = path.at(path_len - 1) == L'/';
+        bool comp_slash = component.at(0) == L'/';
+        if (!path_slash && !comp_slash) {
+            // Need a slash
+            path.push_back(L'/');
+        } else if (path_slash && comp_slash) {
+            // Too many slashes.
+            path.erase(path_len - 1, 1);
+        }
+        path.append(component);
+    }
+}
diff --git a/src/path.h b/src/path.h
index 1bf64cb4b..475be6100 100644
--- a/src/path.h
+++ b/src/path.h
@@ -86,4 +86,7 @@ bool paths_are_same_file(const wcstring &path1, const wcstring &path2);
 /// directory. This operates on unescaped paths only (so a ~ means a literal ~).
 wcstring path_apply_working_directory(const wcstring &path, const wcstring &working_directory);
 
+/// Appends a path component, with a / if necessary.
+void append_path_component(wcstring &path, const wcstring &component);
+
 #endif
diff --git a/src/screen.h b/src/screen.h
index d4f3e277c..0394845ef 100644
--- a/src/screen.h
+++ b/src/screen.h
@@ -24,6 +24,7 @@
 
 #include "common.h"
 #include "highlight.h"
+#include "wcstringutil.h"
 
 class page_rendering_t;
 
diff --git a/src/wcstringutil.cpp b/src/wcstringutil.cpp
index f5a5658ae..9a75132c2 100644
--- a/src/wcstringutil.cpp
+++ b/src/wcstringutil.cpp
@@ -5,11 +5,12 @@
 
 #include <wctype.h>
 
+#include <locale>
+
 #include "common.h"
 
-using size_type = wcstring::size_type;
-
 wcstring_range wcstring_tok(wcstring &str, const wcstring &needle, wcstring_range last) {
+    using size_type = wcstring::size_type;
     size_type pos = last.second == wcstring::npos ? wcstring::npos : last.first;
     if (pos != wcstring::npos && last.second != wcstring::npos) pos += last.second;
     if (pos != wcstring::npos && pos != 0) ++pos;
@@ -71,3 +72,127 @@ wcstring wcstolower(wcstring input) {
     std::transform(result.begin(), result.end(), result.begin(), towlower);
     return result;
 }
+
+bool string_prefixes_string(const wchar_t *proposed_prefix, const wcstring &value) {
+    return string_prefixes_string(proposed_prefix, value.c_str());
+}
+
+bool string_prefixes_string(const wcstring &proposed_prefix, const wcstring &value) {
+    size_t prefix_size = proposed_prefix.size();
+    return prefix_size <= value.size() && value.compare(0, prefix_size, proposed_prefix) == 0;
+}
+
+bool string_prefixes_string(const wchar_t *proposed_prefix, const wchar_t *value) {
+    for (size_t idx = 0; proposed_prefix[idx] != L'\0'; idx++) {
+        // Note if the prefix is longer than value, then we will compare a nonzero prefix character
+        // against a zero value character, and so we'll return false;
+        if (proposed_prefix[idx] != value[idx]) return false;
+    }
+    // We must have that proposed_prefix[idx] == L'\0', so we have a prefix match.
+    return true;
+}
+
+bool string_prefixes_string(const char *proposed_prefix, const std::string &value) {
+    return string_prefixes_string(proposed_prefix, value.c_str());
+}
+
+bool string_prefixes_string(const char *proposed_prefix, const char *value) {
+    for (size_t idx = 0; proposed_prefix[idx] != L'\0'; idx++) {
+        if (proposed_prefix[idx] != value[idx]) return false;
+    }
+    return true;
+}
+
+bool string_prefixes_string_case_insensitive(const wcstring &proposed_prefix,
+                                             const wcstring &value) {
+    size_t prefix_size = proposed_prefix.size();
+    return prefix_size <= value.size() &&
+           wcsncasecmp(proposed_prefix.c_str(), value.c_str(), prefix_size) == 0;
+}
+
+bool string_suffixes_string(const wcstring &proposed_suffix, const wcstring &value) {
+    size_t suffix_size = proposed_suffix.size();
+    return suffix_size <= value.size() &&
+           value.compare(value.size() - suffix_size, suffix_size, proposed_suffix) == 0;
+}
+
+bool string_suffixes_string(const wchar_t *proposed_suffix, const wcstring &value) {
+    size_t suffix_size = std::wcslen(proposed_suffix);
+    return suffix_size <= value.size() &&
+           value.compare(value.size() - suffix_size, suffix_size, proposed_suffix) == 0;
+}
+
+bool string_suffixes_string_case_insensitive(const wcstring &proposed_suffix,
+                                             const wcstring &value) {
+    size_t suffix_size = proposed_suffix.size();
+    return suffix_size <= value.size() && wcsncasecmp(value.c_str() + (value.size() - suffix_size),
+                                                      proposed_suffix.c_str(), suffix_size) == 0;
+}
+
+template <bool Fuzzy, typename T>
+size_t ifind_impl(const T &haystack, const T &needle) {
+    using char_t = typename T::value_type;
+    std::locale locale;
+
+    auto ieq = [&locale](char_t c1, char_t c2) {
+        if (c1 == c2 || std::toupper(c1, locale) == std::toupper(c2, locale)) return true;
+
+        // In fuzzy matching treat treat `-` and `_` as equal (#3584).
+        if (Fuzzy) {
+            if ((c1 == '-' || c1 == '_') && (c2 == '-' || c2 == '_')) return true;
+        }
+        return false;
+    };
+
+    auto result = std::search(haystack.begin(), haystack.end(), needle.begin(), needle.end(), ieq);
+    if (result != haystack.end()) {
+        return result - haystack.begin();
+    }
+    return T::npos;
+}
+
+size_t ifind(const wcstring &haystack, const wcstring &needle, bool fuzzy) {
+    return fuzzy ? ifind_impl<true>(haystack, needle) : ifind_impl<false>(haystack, needle);
+}
+
+size_t ifind(const std::string &haystack, const std::string &needle, bool fuzzy) {
+    return fuzzy ? ifind_impl<true>(haystack, needle) : ifind_impl<false>(haystack, needle);
+}
+
+wcstring_list_t split_string(const wcstring &val, wchar_t sep) {
+    wcstring_list_t out;
+    size_t pos = 0, end = val.size();
+    while (pos <= end) {
+        size_t next_pos = val.find(sep, pos);
+        if (next_pos == wcstring::npos) {
+            next_pos = end;
+        }
+        out.emplace_back(val, pos, next_pos - pos);
+        pos = next_pos + 1;  // skip the separator, or skip past the end
+    }
+    return out;
+}
+
+wcstring join_strings(const wcstring_list_t &vals, wchar_t sep) {
+    if (vals.empty()) return wcstring{};
+
+    // Reserve the size we will need.
+    // count-1 separators, plus the length of all strings.
+    size_t size = vals.size() - 1;
+    for (const wcstring &s : vals) {
+        size += s.size();
+    }
+
+    // Construct the string.
+    wcstring result;
+    result.reserve(size);
+    bool first = true;
+    for (const wcstring &s : vals) {
+        if (!first) {
+            result.push_back(sep);
+        }
+        result.append(s);
+        first = false;
+    }
+    return result;
+}
diff --git a/src/wcstringutil.h b/src/wcstringutil.h
index 54ce9ba2a..e18e6cee5 100644
--- a/src/wcstringutil.h
+++ b/src/wcstringutil.h
@@ -8,6 +8,71 @@
 
 #include "common.h"
 
+/// Test if a string prefixes another. Returns true if a is a prefix of b.
+bool string_prefixes_string(const wcstring &proposed_prefix, const wcstring &value);
+bool string_prefixes_string(const wchar_t *proposed_prefix, const wcstring &value);
+bool string_prefixes_string(const wchar_t *proposed_prefix, const wchar_t *value);
+bool string_prefixes_string(const char *proposed_prefix, const std::string &value);
+bool string_prefixes_string(const char *proposed_prefix, const char *value);
+
+/// Test if a string is a suffix of another.
+bool string_suffixes_string(const wcstring &proposed_suffix, const wcstring &value);
+bool string_suffixes_string(const wchar_t *proposed_suffix, const wcstring &value);
+bool string_suffixes_string_case_insensitive(const wcstring &proposed_suffix,
+                                             const wcstring &value);
+
+/// Test if a string prefixes another without regard to case. Returns true if a is a prefix of b.
+bool string_prefixes_string_case_insensitive(const wcstring &proposed_prefix,
+                                             const wcstring &value);
+
+/// Case-insensitive string search, modeled after std::string::find().
+/// \param fuzzy indicates this is being used for fuzzy matching and case insensitivity is
+/// expanded to include symbolic characters (#3584).
+/// \return the offset of the first case-insensitive matching instance of `needle` within
+/// `haystack`, or `string::npos()` if no results were found.
+size_t ifind(const wcstring &haystack, const wcstring &needle, bool fuzzy = false);
+size_t ifind(const std::string &haystack, const std::string &needle, bool fuzzy = false);
+
+/// Split a string by a separator character.
+wcstring_list_t split_string(const wcstring &val, wchar_t sep);
+
+/// Join a list of strings by a separator character.
+wcstring join_strings(const wcstring_list_t &vals, wchar_t sep);
+
+inline wcstring to_string(long x) {
+    wchar_t buff[64];
+    format_long_safe(buff, x);
+    return wcstring(buff);
+}
+
+inline wcstring to_string(unsigned long long x) {
+    wchar_t buff[64];
+    format_ullong_safe(buff, x);
+    return wcstring(buff);
+}
+
+inline wcstring to_string(int x) { return to_string(static_cast<long>(x)); }
+
+inline wcstring to_string(size_t x) { return to_string(static_cast<unsigned long long>(x)); }
+
+inline bool bool_from_string(const std::string &x) {
+    if (x.empty()) return false;
+    switch (x.front()) {
+        case 'Y':
+        case 'T':
+        case 'y':
+        case 't':
+        case '1':
+            return true;
+        default:
+            return false;
+    }
+}
+
+inline bool bool_from_string(const wcstring &x) {
+    return !x.empty() && std::wcschr(L"YTyt1", x.at(0));
+}
+
 /// @typedef wcstring_range represents a range in a wcstring.
 /// The first element is the location, the second is the count.
 typedef std::pair<wcstring::size_type, wcstring::size_type> wcstring_range;
@@ -71,4 +136,36 @@ wcstring trim(wcstring input, const wchar_t *any_of);
 /// Converts a string to lowercase.
 wcstring wcstolower(wcstring input);
 
+/// Support for iterating over a newline-separated string.
+template <typename Collection>
+class line_iterator_t {
+    // Storage for each line.
+    Collection storage;
+
+    // The collection we're iterating. Note we hold this by reference.
+    const Collection &coll;
+
+    // The current location in the iteration.
+    typename Collection::const_iterator current;
+
+   public:
+    /// Construct from a collection (presumably std::string or std::wcstring).
+    line_iterator_t(const Collection &coll) : coll(coll), current(coll.cbegin()) {}
+
+    /// Access the storage in which the last line was stored.
+    const Collection &line() const { return storage; }
+
+    /// Advances to the next line. \return true on success, false if we have exhausted the string.
+    bool next() {
+        if (current == coll.end()) return false;
+        auto newline_or_end = std::find(current, coll.cend(), '\n');
+        storage.assign(current, newline_or_end);
+        current = newline_or_end;
+
+        // Skip the newline.
+        if (current != coll.cend()) ++current;
+        return true;
+    }
+};
+
 #endif
diff --git a/src/wildcard.cpp b/src/wildcard.cpp
index 692342bc6..d3c7ad12b 100644
--- a/src/wildcard.cpp
+++ b/src/wildcard.cpp
@@ -22,7 +22,9 @@
 #include "expand.h"
 #include "fallback.h"  // IWYU pragma: keep
 #include "future_feature_flags.h"
+#include "path.h"
 #include "reader.h"
+#include "wcstringutil.h"
 #include "wutil.h"  // IWYU pragma: keep
 
 /// Description for generic executable.