Bug 5722: Critical regression

src/constfold.c

@@ -1372,10 +1372,12 @@ Expression *Cat(Type *type, Expression *e1, Expression *e2)
             int sz = t->size();
 
             dinteger_t v = e->toInteger();
-
-            size_t len = utf_codeLength(sz, v);
+            size_t len = (t->ty == tn->ty) ? 1 : utf_codeLength(sz, v);
             s = mem.malloc((len + 1) * sz);
-            utf_encode(sz, s, v);
+            if (t->ty == tn->ty)
+                memcpy((unsigned char *)s, &v, sz);
+            else
+                utf_encode(sz, s, v);
 
             // Add terminating 0
             memset((unsigned char *)s + len * sz, 0, sz);
@@ -1468,10 +1470,17 @@ Expression *Cat(Type *type, Expression *e1, Expression *e2)
         int sz = es1->sz;
         dinteger_t v = e2->toInteger();
 
-        size_t len = es1->len + utf_codeLength(sz, v);
+        // Is it a concatentation of homogenous types?
+        // (char[] ~ char, wchar[]~wchar, or dchar[]~dchar)
+        bool homoConcat = (sz == t2->size());
+        size_t len = es1->len;
+        len += homoConcat ? 1 : utf_codeLength(sz, v);
         s = mem.malloc((len + 1) * sz);
         memcpy(s, es1->string, es1->len * sz);
-        utf_encode(sz, (unsigned char *)s + (sz * es1->len), v);
+        if (homoConcat)
+            memcpy((unsigned char *)s + (sz * es1->len), &v, sz);
+        else
+            utf_encode(sz, (unsigned char *)s + (sz * es1->len), v);
 
         // Add terminating 0
         memset((unsigned char *)s + len * sz, 0, sz);

src/func.c

@@ -255,6 +255,9 @@ void FuncDeclaration::semantic(Scope *sc)
     if (isAbstract() && !isVirtual())
         error("non-virtual functions cannot be abstract");
 
+    if (isOverride() && !isVirtual())
+        error("cannot override a non-virtual function");
+
     if ((f->isConst() || f->isImmutable()) && !isThis())
         error("without 'this' cannot be const/immutable");
 

test/compilable/interpret3.d

@@ -350,3 +350,10 @@ size_t bug5524(int x, int[] more...)
 }
 
 static assert(bug5524(3) == 10);
+
+// 5722
+
+static assert( ("" ~ "\©"[0]).length == 1 );
+const char[] null5722 = null;
+static assert( (null5722 ~ "\©"[0]).length == 1 );
+static assert( ("\©"[0] ~ null5722).length == 1 );