Halfwidth katakana voiced and semi-voiced sound marks are not treated as...

Halfwidth katakana voiced and semi-voiced sound marks are not treated as combining marks by Terminal. I don't really know why; my only guess is that japanese text should be rendered monospaced (TextEdit does) but when these marks combine they don't become double-width, so things don't line up as you'd expect. The solution is to force them to be base characters. Issue 6048.

sources/NSStringITerm.m

@@ -1507,12 +1507,40 @@ static TECObjectRef CreateTECConverterForUTF8Variants(TextEncodingVariant varian
     if (self.length == 0) {
         return;
     }
+    static dispatch_once_t onceToken;
+    static NSCharacterSet *exceptions;
+    dispatch_once(&onceToken, ^{
+        // These characters are forced to be base characters.
+        exceptions = [[NSCharacterSet characterSetWithCharactersInString:@"\uff9e\uff9f"] retain];
+    });
     CFIndex index = 0;
+    NSInteger minimumLocation = 0;
     NSRange range;
     do {
         CFRange tempRange = CFStringGetRangeOfComposedCharactersAtIndex((CFStringRef)self, index);
+        if (tempRange.location < minimumLocation) {
+            NSInteger diff = minimumLocation - tempRange.location;
+            tempRange.location += diff;
+            if (diff > tempRange.length) {
+                tempRange.length = 0;
+            } else {
+                tempRange.length -= diff;
+            }
+        }
         range = NSMakeRange(tempRange.location, tempRange.length);
         if (range.length > 0) {
+            // CFStringGetRangeOfComposedCharactersAtIndex thinks that U+FF9E and U+FF9F are
+            // combining marks. Terminal.app and the person in issue 6048 disagree. Prevent them
+            // from combining.
+            NSRange rangeOfFirstException = [self rangeOfCharacterFromSet:exceptions
+                                                                  options:NSLiteralSearch
+                                                                    range:range];
+            if (rangeOfFirstException.location != NSNotFound &&
+                rangeOfFirstException.location > range.location) {
+                range.length = rangeOfFirstException.location - range.location;
+                minimumLocation = NSMaxRange(range);
+            }
+
             unichar simple = range.length == 1 ? [self characterAtIndex:range.location] : 0;
             NSString *complexString = range.length == 1 ? nil : [self substringWithRange:range];
             BOOL stop = NO;