Bindings: Add ScalarValueString support

Source/wtf/text/StringImpl.cpp

Index: Source/wtf/text/StringImpl.cpp
diff --git a/Source/wtf/text/StringImpl.cpp b/Source/wtf/text/StringImpl.cpp
index 838b6715fcdce7c992b8a90e4fcfaab69c36ac77..b29005523e2d40f46ee94b2741cf4b43bc5babea 100644
--- a/Source/wtf/text/StringImpl.cpp
+++ b/Source/wtf/text/StringImpl.cpp
@@ -1893,6 +1893,120 @@ PassRefPtr<StringImpl> StringImpl::replace(StringImpl* pattern, StringImpl* repl
     return newImpl.release();
 }
 
+bool StringImpl::hasUnmatchedSurrogates() const
+{
+    // By definition, 8-bit strings are confined to the Latin-1 code page and
+    // have no surrogates, matched or otherwise.
+    if (is8Bit())
+        return false;
+
+    const UChar* characters = characters16();
+    const unsigned length = m_length;
+
+    for (unsigned i = 0; i < length; ++i) {
+        UChar c = characters[i];
+        if (c < 0xD800 || c > 0xDFFF) {

[tkent, 2014/06/16 07:51:16]

!U16_IS_SURROGATE(c)

[jsbell, 2014/06/17 21:39:50]

Done - used U16_XXX macros throughout. Also, tightened the
hasUnmatchedSurrogates() function up since the macros are self-documenting.

+            // Non-surrogate
+            continue;
+        }
+        if (0xDC00 <= c && c <= 0xDFFF) {

[tkent, 2014/06/16 07:51:16]

U16_IS_TRAIL(c)

+            // Unmatched trail surrogate.
+            return true;
+        }

[Nils Barth (inactive), 2014/06/16 07:08:28]

Want to add something like:
// Lead surrogate.
// 0xD800 <= c <= 0xDBFF
ASSERT(0xD800 <= c && c <= 0xDBFF):

+        if (i == length - 1) {
+            // Unmatched lead surrogate at EOF.
+            return true;
+        }
+        UChar d = characters[i + 1];
+        if (0xDC00 <= d && d <= 0xDFFF) {

[tkent, 2014/06/16 07:51:16]

U16_IS_TRAIL(d)

+            // Matching trail surrogate.
+            ++i;
+            continue;
+        }
+        // Unmatched lead.
+        return true;
+    }
+    return false;
+}
+
+PassRefPtr<StringImpl> StringImpl::replaceUnmatchedSurrogates()
+{
+    // This roughly implements http://heycam.github.io/webidl/#dfn-obtain-unicode
+    // but the output is still a sequence of 16-bit code units, effectively
+    // re-encoding to UTF-16 after performing the replacements.
+
+    // The concepts of surrogate pairs are explained at:
+    // http://www.unicode.org/versions/Unicode6.2.0/ch03.pdf#G2630
+
+    // Blink-specific optimization to avoid making an unnecessary copy.
+    if (!hasUnmatchedSurrogates())
+        return this;
+    ASSERT(!is8Bit());
+
+    // 1. Let S be the DOMString value.
+    const UChar* s = characters16();
+
+    // 2. Let n be the length of S.
+    const unsigned n = m_length;
+
+    // 3. Initialize i to 0.
+    unsigned i = 0;
+
+    // 4. Initialize U to be an empty sequence of Unicode characters.
+    // (Blink: we just use an array of UTF-16 code units.)
+    UChar* u;
+    RefPtr<StringImpl> newImpl = createUninitialized(n, u);
+
+    // 5. While i < n:
+    while (i < n) {
+        // 1. Let c be the code unit in S at index i.
+        UChar c = s[i];
+        // 2. Depending on the value of c:
+        if (c < 0xD800 || c > 0xDFFF) {
+            // c < 0xD800 or c > 0xDFFF
+            // Append to U the Unicode character with code point c.
+            u[i] = c;
+        } else if (0xDC00 <= c && c <= 0xDFFF) {
+            // 0xDC00 <= c <= 0xDFFF
+            // Append to U a U+FFFD REPLACEMENT CHARACTER.
+            u[i] = Unicode::replacementCharacter;
+        } else {
+            // 0xD800 <= c <= 0xDBFF
+            ASSERT(0xD800 <= c && c <= 0xDBFF);
+            if (i == n - 1) {
+                // 1. If i = n−1, then append to U a U+FFFD REPLACEMENT CHARACTER.
+                u[i] = Unicode::replacementCharacter;
+            } else {
+                // 2. Otherwise, i < n−1:
+                ASSERT(i < n - 1);
+                // ..1. Let d be the code unit in S at index i+1.
+                UChar d = s[i + 1];
+                if (0xDC00 <= d && d <= 0xDFFF) {
+                    // 2. If 0xDC00 ≤ d ≤ 0xDFFF, then:
+                    // ..1. Let a be c & 0x3FF.
+                    // ..2. Let b be d & 0x3FF.
+                    // ..3. Append to U the Unicode character with code point 2^16+2^10*a+b.
+                    // (Blink: Just pass through the UTF-16 code units rather than
+                    // decoding to a Unicode scalar value then re-encoding.)
+                    u[i] = c;
+                    u[i + 1] = d;
+                    // ..4. Set i to i+1.
+                    ++i;
+                } else {
+                    // 3. Otherwise, d < 0xDC00 or d > 0xDFFF. Append to U a U+FFFD REPLACEMENT CHARACTER.
+                    ASSERT(d < 0xD800 || d > 0xDFFF);
+                    u[i] = Unicode::replacementCharacter;
+                }
+            }
+        }
+        // 3. Set i to i+1.
+        ++i;
+    }
+
+    // 6. Return U.
+    return newImpl.release();
+}
+
 PassRefPtr<StringImpl> StringImpl::upconvertedString()
 {
     if (is8Bit())