AK: Implement a UTF-16 method to check if a string is ASCII whitespace

Author: https://github.com/trflynn89
Commit: 6c73dff120
Pull-request: https://github.com/LadybirdBrowser/ladybird/pull/5592
Reviewed-by: https://github.com/gmta ✅

AK/Utf16StringBase.h

@@ -156,6 +156,7 @@ public:
 
     [[nodiscard]] ALWAYS_INLINE bool is_empty() const { return length_in_code_units() == 0uz; }
     [[nodiscard]] ALWAYS_INLINE bool is_ascii() const { return utf16_view().is_ascii(); }
+    [[nodiscard]] ALWAYS_INLINE bool is_ascii_whitespace() const { return utf16_view().is_ascii_whitespace(); }
 
     [[nodiscard]] ALWAYS_INLINE size_t length_in_code_units() const
     {

AK/Utf16View.h

@@ -268,8 +268,16 @@ public:
     }
 
     [[nodiscard]] constexpr bool is_empty() const { return length_in_code_units() == 0; }
+
     [[nodiscard]] bool is_ascii() const;
 
+    [[nodiscard]] constexpr bool is_ascii_whitespace() const
+    {
+        if (has_ascii_storage())
+            return all_of(ascii_span(), AK::is_ascii_space);
+        return all_of(utf16_span(), AK::is_ascii_space);
+    }
+
     [[nodiscard]] ALWAYS_INLINE bool validate(AllowLonelySurrogates allow_lonely_surrogates = AllowLonelySurrogates::Yes) const
     {
         size_t valid_code_units = 0;

Tests/AK/TestUtf16View.cpp

@@ -341,6 +341,22 @@ TEST_CASE(is_ascii)
     EXPECT(!u"The quick (“brown”) fox can’t jump 32.3 feet, right?"sv.is_ascii());
 }
 
+TEST_CASE(is_ascii_whitespace)
+{
+    EXPECT(Utf16View {}.is_ascii_whitespace());
+    EXPECT(u" "sv.is_ascii_whitespace());
+    EXPECT(u"\t"sv.is_ascii_whitespace());
+    EXPECT(u"\r"sv.is_ascii_whitespace());
+    EXPECT(u"\n"sv.is_ascii_whitespace());
+    EXPECT(u" \t\r\n\v "sv.is_ascii_whitespace());
+
+    EXPECT(!u"a"sv.is_ascii_whitespace());
+    EXPECT(!u"😀"sv.is_ascii_whitespace());
+    EXPECT(!u"\u00a0"sv.is_ascii_whitespace());
+    EXPECT(!u"\ufeff"sv.is_ascii_whitespace());
+    EXPECT(!u"  \t \u00a0 \ufeff  "sv.is_ascii_whitespace());
+}
+
 TEST_CASE(to_ascii_lowercase)
 {
     EXPECT_EQ(u""sv.to_ascii_lowercase(), u""sv);