Add wcstolower

Converts a string to lowercase. Eliminates some loops that did this
explicitly.

src/builtin_string.cpp

@@ -625,9 +625,7 @@ class wildcard_matcher_t : public string_matcher_t {
                        io_streams_t &streams)
         : string_matcher_t(opts, streams), wcpattern(parse_util_unescape_wildcards(pattern)) {
         if (opts.ignore_case) {
-            for (size_t i = 0; i < wcpattern.length(); i++) {
-                wcpattern[i] = towlower(wcpattern[i]);
-            }
+            wcpattern = wcstolower(std::move(wcpattern));
         }
         if (opts.entire) {
             if (!wcpattern.empty()) {
@@ -648,11 +646,7 @@ class wildcard_matcher_t : public string_matcher_t {
         bool match;
 
         if (opts.ignore_case) {
-            wcstring s = arg;
-            for (size_t i = 0; i < s.length(); i++) {
-                s[i] = towlower(s[i]);
-            }
-            match = wildcard_match(s, wcpattern, false);
+            match = wildcard_match(wcstolower(arg), wcpattern, false);
         } else {
             match = wildcard_match(arg, wcpattern, false);
         }

src/fish_tests.cpp

@@ -3490,15 +3490,6 @@ static wcstring random_string() {
     return result;
 }
 
-// Helper to lowercase a string.
-static wcstring lower(const wcstring &s) {
-    wcstring result;
-    for (wchar_t c : s) {
-        result.push_back(towlower(c));
-    }
-    return result;
-}
-
 void history_tests_t::test_history() {
     history_search_t searcher;
     say(L"Testing history");
@@ -3531,7 +3522,7 @@ void history_tests_t::test_history() {
 
     // Items matching "alpha", case-insensitive.
     searcher = history_search_t(history, L"AlPhA", HISTORY_SEARCH_TYPE_CONTAINS, nocase);
-    set_expected([](const wcstring &s) { return lower(s).find(L"alpha") != wcstring::npos; });
+    set_expected([](const wcstring &s) { return wcstolower(s).find(L"alpha") != wcstring::npos; });
     test_history_matches(searcher, expected, __LINE__);
 
     // Items matching "et", case-sensitive.
@@ -3557,7 +3548,7 @@ void history_tests_t::test_history() {
 
     // Items exactly matching "alph", case-insensitive.
     searcher = history_search_t(history, L"alph", HISTORY_SEARCH_TYPE_EXACT, nocase);
-    set_expected([](const wcstring &s) { return lower(s) == L"alph"; });
+    set_expected([](const wcstring &s) { return wcstolower(s) == L"alph"; });
     test_history_matches(searcher, expected, __LINE__);
 
     // Test item removal case-sensitive.

src/history.cpp

@@ -553,10 +553,7 @@ bool history_item_t::merge(const history_item_t &item) {
 history_item_t::history_item_t(const wcstring &str, time_t when, history_identifier_t ident)
     : creation_timestamp(when), identifier(ident) {
     contents = trim(str);
-    contents_lower.reserve(contents.size());
-    for (const auto &c : contents) {
-        contents_lower.push_back(towlower(c));
-    }
+    contents_lower = wcstolower(contents);
 }
 
 bool history_item_t::matches_search(const wcstring &term, enum history_search_type_t type,

src/wcstringutil.cpp

@@ -4,6 +4,8 @@
 #include "common.h"
 #include "wcstringutil.h"
 
+#include <wctype.h>
+
 typedef wcstring::size_type size_type;
 
 wcstring_range wcstring_tok(wcstring &str, const wcstring &needle, wcstring_range last) {
@@ -59,3 +61,9 @@ wcstring trim(const wcstring &input, const wchar_t *any_of) {
     wcstring result(input.begin() + begin_offset, end + 1);
     return result;
 }
+
+wcstring wcstolower(wcstring input) {
+    wcstring result = std::move(input);
+    std::transform(result.begin(), result.end(), result.begin(), towlower);
+    return result;
+}

src/wcstringutil.h

@@ -68,4 +68,7 @@ wcstring truncate(const wcstring &input, int max_len,
 wcstring trim(const wcstring &input);
 wcstring trim(const wcstring &input, const wchar_t *any_of);
 
+/// Converts a string to lowercase.
+wcstring wcstolower(wcstring input);
+
 #endif