LibC: Implement wcslcpy

Author: https://github.com/BertalanD
Commit: https://github.com/SerenityOS/serenity/commit/13e6d9d71a5
Pull-request: https://github.com/SerenityOS/serenity/pull/9378
Reviewed-by: https://github.com/ADKaster ✅
Reviewed-by: https://github.com/itamar8910
Reviewed-by: https://github.com/linusg ✅
Reviewed-by: https://github.com/nico
Reviewed-by: https://github.com/timschumi

Tests/LibC/TestWchar.cpp

@@ -414,3 +414,28 @@ TEST_CASE(mbsrtowcs)
     EXPECT_EQ(buf[2], L'\0');
     EXPECT_EQ(src, nullptr);
 }
+
+TEST_CASE(wcslcpy)
+{
+    auto buf = static_cast<wchar_t*>(malloc(8 * sizeof(wchar_t)));
+    if (!buf) {
+        FAIL("Could not allocate space for copy target");
+        return;
+    }
+
+    size_t ret;
+
+    // If buffer is long enough, a straight-forward string copy is performed.
+    ret = wcslcpy(buf, L"abc", 8);
+    EXPECT_EQ(ret, 3ul);
+    EXPECT_EQ(wmemcmp(L"abc", buf, 4), 0);
+
+    // If buffer is (supposedly) too small, the string will be truncated.
+    ret = wcslcpy(buf, L"1234", 4);
+    EXPECT_EQ(ret, 4ul);
+    EXPECT_EQ(wmemcmp(L"123", buf, 4), 0);
+
+    // If the buffer is null, the length of the input is returned.
+    ret = wcslcpy(nullptr, L"abc", 0);
+    EXPECT_EQ(ret, 3ul);
+}

Userland/Libraries/LibC/wchar.cpp

@@ -69,6 +69,18 @@ wchar_t* wcsncpy(wchar_t* dest, const wchar_t* src, size_t num)
     return original_dest;
 }
 
+size_t wcslcpy(wchar_t* dest, const wchar_t* src, size_t n)
+{
+    size_t i;
+    for (i = 0; i + 1 < n && src[i] != L'\0'; ++i)
+        dest[i] = src[i];
+    if (n)
+        dest[i] = L'\0';
+    for (; src[i] != L'\0'; ++i)
+        ; // Determine the length of src, don't copy.
+    return i;
+}
+
 int wcscmp(const wchar_t* s1, const wchar_t* s2)
 {
     while (*s1 == *s2++)

Userland/Libraries/LibC/wchar.h

@@ -29,6 +29,7 @@ struct tm;
 size_t wcslen(const wchar_t*);
 wchar_t* wcscpy(wchar_t*, const wchar_t*);
 wchar_t* wcsncpy(wchar_t*, const wchar_t*, size_t);
+__attribute__((warn_unused_result)) size_t wcslcpy(wchar_t*, const wchar_t*, size_t);
 int wcscmp(const wchar_t*, const wchar_t*);
 int wcsncmp(const wchar_t*, const wchar_t*, size_t);
 wchar_t* wcschr(const wchar_t*, int);