Handle surrogate cases

docs/design/features/globalization-hybrid-mode.md

@@ -423,8 +423,3 @@ Below function are used from apple native functions:
 - [uppercaseStringWithLocale](https://developer.apple.com/documentation/foundation/nsstring/1413316-uppercasestringwithlocale?language=objc)
 - [lowercaseStringWithLocale](https://developer.apple.com/documentation/foundation/nsstring/1417298-lowercasestringwithlocale?language=objc)
 
-Behavioural changes compared to ICU
-
-   - Final sigma behavior correction:
-
-     ICU-based case change does not respect final-sigma rule, but hybrid does, so "ΒΌΛΟΣ" -> "βόλος", not "βόλοσ".

src/libraries/System.Globalization/tests/System/Globalization/TextInfoTests.cs

@@ -274,9 +274,9 @@ public static IEnumerable<object[]> ToLower_TestData()
                 // we also don't preform.
                 // Greek Capital Letter Sigma (does not case to U+03C2 with "final sigma" rule).
                 yield return new object[] { cultureName, "\u03A3", "\u03C3" };
-                if (PlatformDetection.IsHybridGlobalizationOnBrowser || PlatformDetection.IsHybridGlobalizationOnOSX)
+                if (PlatformDetection.IsHybridGlobalizationOnBrowser)
                 {
-                    // JS and Apple platforms are using "final sigma" rule correctly - it's costly to unify it with ICU's behavior
+                    // JS is using "final sigma" rule correctly - it's costly to unify it with ICU's behavior
                     yield return new object[] { cultureName, "O\u03A3", "o\u03C2" };
                 }
                 else
@@ -405,7 +405,7 @@ public static IEnumerable<object[]> ToUpper_TestData()
                 // es-zed does not case to SS when uppercased.
                 yield return new object[] { cultureName, "\u00DF", "\u00DF" };
                 yield return new object[] { cultureName, "stra\u00DFe", "STRA\u00DFE" };
-                if (!PlatformDetection.IsNlsGlobalization && !PlatformDetection.IsHybridGlobalizationOnOSX)
+                if (!PlatformDetection.IsNlsGlobalization)
                     yield return new object[] { cultureName, "st\uD801\uDC37ra\u00DFe", "ST\uD801\uDC0FRA\u00DFE" };
 
                 // Ligatures do not expand when cased.

src/native/libs/System.Globalization.Native/pal_casing.m

@@ -9,6 +9,47 @@
 
 #if defined(TARGET_OSX) || defined(TARGET_MACCATALYST) || defined(TARGET_IOS) || defined(TARGET_TVOS)
 
+/**
+ * Is this code unit a lead surrogate (U+d800..U+dbff)?
+ * @param c 16-bit code unit
+ * @return true or false
+ */
+#define IS_LEAD(c) (((c)&0xfffffc00) == 0xd800)
+
+/**
+ * Is this code unit a trail surrogate (U+dc00..U+dfff)?
+ * @param c 16-bit code unit
+ * @return true or false
+ */
+#define IS_TRAIL(c) (((c)&0xfffffc00) == 0xdc00)
+
+/**
+ * Get a code point index from a string at a code point boundary offset,
+ * and advance the offset to the next code point boundary.
+ * (Post-incrementing forward iteration.)
+ * "Safe" macro, handles unpaired surrogates and checks for string boundaries.
+ *
+ * The length can be negative for a NUL-terminated string.
+ *
+ * The offset may point to the lead surrogate unit
+ * for a supplementary code point, in which case for casing will be read
+ * the following trail surrogate as well.
+ * If the offset points to a trail surrogate or
+ * to a single, unpaired lead surrogate, then for casing will be read that unpaired surrogate.
+ *
+ * @param s const uint16_t* string
+ * @param i output string offset, must be i<length
+ * @param length string length
+ */
+#define NEXTOFFSET(s, i, length) { \
+    uint16_t c = (s)[(i)++]; \
+    if (IS_LEAD(c)) { \
+        uint16_t __c2; \
+        if ((i) != (length) && IS_TRAIL(__c2 = (s)[(i)])) { \
+            ++(i); \
+        } \
+    } \
+}
 
 /**
  * Append a code point to a string, overwriting 1 or 2 code units.
@@ -61,33 +102,25 @@ int32_t GlobalizationNative_ChangeCaseNative(const uint16_t* localeName, int32_t
         NSString *locName = [NSString stringWithCharacters: localeName length: lNameLength];
         currentLocale = [NSLocale localeWithLocaleIdentifier:locName];
     }
-    NSString *source = [NSString stringWithCharacters: lpSrc length: cwSrcLength];
-    NSString *result = bToUpper ? [source uppercaseStringWithLocale:currentLocale] : [source lowercaseStringWithLocale:currentLocale];
 
     int32_t srcIdx = 0, dstIdx = 0, isError = 0;
     uint16_t dstCodepoint;
-    if (result.length <= cwDstLength)
+    while (srcIdx < cwSrcLength)
     {
-        while (srcIdx < result.length)
+        int32_t startIndex = srcIdx;
+        NEXTOFFSET(lpSrc, srcIdx, cwSrcLength);
+        int32_t srcLength = srcIdx - startIndex;
+        NSString *src = [NSString stringWithCharacters: lpSrc + startIndex length: srcLength];
+        NSString *dst = bToUpper ? [src uppercaseStringWithLocale:currentLocale] : [src lowercaseStringWithLocale:currentLocale];
+        int32_t index = 0;
+        while (index < srcLength)
         {
-            dstCodepoint = [result characterAtIndex:srcIdx++];
-            Append(lpDst, dstIdx, cwDstLength, dstCodepoint, isError);
-            if (isError)
-                return isError;
-        }
-    }
-    else
-    {
-        while (srcIdx < cwSrcLength)
-        {           
-            NSString *src = [NSString stringWithCharacters: lpSrc + srcIdx length: 1];
-            srcIdx++;
-            NSString *dst = bToUpper ? [src uppercaseStringWithLocale:currentLocale] : [src lowercaseStringWithLocale:currentLocale];
-            dstCodepoint = dst.length > 1 ? [src characterAtIndex: 0] : [dst characterAtIndex: 0];
+            dstCodepoint = dst.length > srcLength ? [src characterAtIndex: index] : [dst characterAtIndex: index];
             Append(lpDst, dstIdx, cwDstLength, dstCodepoint, isError);
-            if (isError)
-                return isError;
+            index++;
         }
+        if (isError)
+            return isError;
     }
     return Success;
 }
@@ -101,33 +134,24 @@ int32_t GlobalizationNative_ChangeCaseNative(const uint16_t* localeName, int32_t
 */
 int32_t GlobalizationNative_ChangeCaseInvariantNative(const uint16_t* lpSrc, int32_t cwSrcLength, uint16_t* lpDst, int32_t cwDstLength, int32_t bToUpper)
 {
-    NSString *source = [NSString stringWithCharacters: lpSrc length: cwSrcLength];
-    NSString *result = bToUpper ? source.uppercaseString : source.lowercaseString;
-
     int32_t srcIdx = 0, dstIdx = 0, isError = 0;
     uint16_t dstCodepoint;
-    if (result.length <= cwDstLength)
+    while (srcIdx < cwSrcLength)
     {
-        while (srcIdx < result.length)
+        int32_t startIndex = srcIdx;
+        NEXTOFFSET(lpSrc, srcIdx, cwSrcLength);
+        int32_t srcLength = srcIdx - startIndex;
+        NSString *src = [NSString stringWithCharacters: lpSrc + startIndex length: srcLength];
+        NSString *dst = bToUpper ? src.uppercaseString : src.lowercaseString;
+        int32_t index = 0;
+        while (index < srcLength)
         {
-            dstCodepoint = [result characterAtIndex:srcIdx++];
-            Append(lpDst, dstIdx, cwDstLength, dstCodepoint, isError);
-            if (isError)
-                return isError;
-        }
-    }
-    else
-    {
-        while (srcIdx < cwSrcLength)
-        {           
-            NSString *src = [NSString stringWithCharacters: lpSrc + srcIdx length: 1];
-            srcIdx++;
-            NSString *dst = bToUpper ? src.uppercaseString : src.lowercaseString;
-            dstCodepoint = dst.length > 1 ? [src characterAtIndex: 0] : [dst characterAtIndex: 0];
+            dstCodepoint = dst.length > srcLength ? [src characterAtIndex: index] : [dst characterAtIndex: index];
             Append(lpDst, dstIdx, cwDstLength, dstCodepoint, isError);
-            if (isError)
-                return isError;
+            index++;
         }
+        if (isError)
+            return isError;
     }
     return Success;
 }