AK: Add trim methods to Utf16String that skip allocation when not needed

If the string does not begin with any of the provided code units, we do
not need to create a new string.

AK/Utf16String.h

@@ -199,6 +199,29 @@ public:
         return view.replace(needle, replacement, replace_mode);
     }
 
+    ALWAYS_INLINE Utf16String trim(Utf16View const& code_units, TrimMode mode = TrimMode::Both) const
+    {
+        if (is_empty())
+            return {};
+
+        bool needs_trimming = false;
+
+        if (mode == TrimMode::Left || mode == TrimMode::Both)
+            needs_trimming |= code_units.contains(code_unit_at(0));
+        if (mode == TrimMode::Right || mode == TrimMode::Both)
+            needs_trimming |= code_units.contains(code_unit_at(length_in_code_units() - 1));
+
+        if (!needs_trimming)
+            return *this;
+
+        return Utf16String::from_utf16_without_validation(utf16_view().trim(code_units, mode));
+    }
+
+    ALWAYS_INLINE Utf16String trim_ascii_whitespace(TrimMode mode = TrimMode::Both) const
+    {
+        return trim(" \n\t\v\f\r"sv, mode);
+    }
+
     ALWAYS_INLINE Utf16String escape_html_entities() const { return utf16_view().escape_html_entities(); }
 
 private:

AK/Utf16View.h

@@ -477,8 +477,7 @@ public:
 
     [[nodiscard]] constexpr Utf16View trim_ascii_whitespace(TrimMode mode = TrimMode::Both) const
     {
-        static constexpr Utf16View white_space { u" \n\t\v\f\r", 6uz };
-        return trim(white_space, mode);
+        return trim(" \n\t\v\f\r"sv, mode);
     }
 
     constexpr Optional<size_t> find_code_unit_offset(char16_t needle, size_t start_offset = 0) const

Libraries/LibWeb/HTML/HTMLInputElement.cpp

@@ -1644,8 +1644,7 @@ Utf16String HTMLInputElement::value_sanitization_algorithm(Utf16String const& va
     };
 
     auto strip_newlines_and_trim = [&]() {
-        auto value_without_newlines = strip_newlines();
-        return Utf16String::from_utf16_without_validation(value_without_newlines.utf16_view().trim(Infra::ASCII_WHITESPACE));
+        return strip_newlines().trim(Infra::ASCII_WHITESPACE);
     };
 
     // https://html.spec.whatwg.org/multipage/input.html#text-(type=text)-state-and-search-state-(type=search):value-sanitization-algorithm

Libraries/LibWeb/Infra/Strings.cpp

@@ -105,7 +105,7 @@ Utf16String strip_and_collapse_whitespace(Utf16String const& string)
     }
 
     // ...and then remove any leading and trailing ASCII whitespace from that string.
-    return Utf16String::from_utf16(builder.utf16_string_view().trim(Infra::ASCII_WHITESPACE));
+    return builder.to_utf16_string().trim(Infra::ASCII_WHITESPACE);
 }
 
 // https://infra.spec.whatwg.org/#code-unit-prefix

Tests/AK/TestUtf16String.cpp

@@ -913,6 +913,64 @@ TEST_CASE(to_casefold)
     EXPECT_EQ(result, u"\u03B1\u0342\u03B9"sv);
 }
 
+TEST_CASE(trim)
+{
+    auto expect_same_string = [](Utf16String const& string, Utf16String const& result) {
+        EXPECT_EQ(string, result);
+
+        VERIFY(string.has_ascii_storage() == result.has_ascii_storage());
+        auto string_view = string.utf16_view();
+        auto result_view = result.utf16_view();
+
+        if (string.has_ascii_storage())
+            EXPECT_EQ(string_view.ascii_span().data(), result_view.ascii_span().data());
+        else
+            EXPECT_EQ(string_view.utf16_span().data(), result_view.utf16_span().data());
+    };
+
+    Utf16View whitespace { u" "sv };
+    {
+        auto string = u"looooong word"_utf16;
+        expect_same_string(string, string.trim(whitespace, TrimMode::Both));
+        expect_same_string(string, string.trim(whitespace, TrimMode::Left));
+        expect_same_string(string, string.trim(whitespace, TrimMode::Right));
+    }
+    {
+        auto string = u"   looooong word"_utf16;
+        EXPECT_EQ(string.trim(whitespace, TrimMode::Both), u"looooong word"sv);
+        EXPECT_EQ(string.trim(whitespace, TrimMode::Left), u"looooong word"sv);
+        expect_same_string(string, string.trim(whitespace, TrimMode::Right));
+    }
+    {
+        auto string = u"looooong word   "_utf16;
+        EXPECT_EQ(string.trim(whitespace, TrimMode::Both), u"looooong word"sv);
+        expect_same_string(string, string.trim(whitespace, TrimMode::Left));
+        EXPECT_EQ(string.trim(whitespace, TrimMode::Right), u"looooong word"sv);
+    }
+    {
+        auto string = u"   looooong word   "_utf16;
+        EXPECT_EQ(string.trim(whitespace, TrimMode::Both), u"looooong word"sv);
+        EXPECT_EQ(string.trim(whitespace, TrimMode::Left), u"looooong word   "sv);
+        EXPECT_EQ(string.trim(whitespace, TrimMode::Right), u"   looooong word"sv);
+    }
+    {
+        auto string = u"   \u180E   "_utf16;
+        EXPECT_EQ(string.trim(whitespace, TrimMode::Both), u"\u180E"sv);
+        EXPECT_EQ(string.trim(whitespace, TrimMode::Left), u"\u180E   "sv);
+        EXPECT_EQ(string.trim(whitespace, TrimMode::Right), u"   \u180E"sv);
+    }
+    {
+        auto string = u"😀wfh😀"_utf16;
+        EXPECT_EQ(string.trim(u"😀"sv, TrimMode::Both), u"wfh"sv);
+        EXPECT_EQ(string.trim(u"😀"sv, TrimMode::Left), u"wfh😀"sv);
+        EXPECT_EQ(string.trim(u"😀"sv, TrimMode::Right), u"😀wfh"sv);
+
+        expect_same_string(string, string.trim(whitespace, TrimMode::Both));
+        expect_same_string(string, string.trim(whitespace, TrimMode::Left));
+        expect_same_string(string, string.trim(whitespace, TrimMode::Right));
+    }
+}
+
 TEST_CASE(copy_operations)
 {
     auto test = [](Utf16String const& string1) {