Handle invalid code points

Author: MoonlightSentinel

src/core/internal/dassert.d

@@ -97,12 +97,23 @@ private string miniFormat(V)(const scope ref V v)
     {
         static if (is(V == char))
         {
-            return ['\'', v, '\''];
+            // Avoid invalid code points
+            if (v < 0x7F)
+                return ['\'', v, '\''];
+
+            uint tmp = v;
+            return "cast(char) " ~ miniFormat(tmp);
         }
         else static if (is(V == wchar) || is(V == dchar))
         {
-            import core.internal.utf: toUTF8;
-            return toUTF8(['\'', v, '\'']);
+            import core.internal.utf: isValidDchar, toUTF8;
+
+            // Avoid invalid code points
+            if (isValidDchar(v))
+                return toUTF8(['\'', v, '\'']);
+
+            uint tmp = v;
+            return "cast(" ~ V.stringof ~ ") " ~ miniFormat(tmp);
         }
         else
         {

test/exceptions/src/assert_fail.d

@@ -67,6 +67,11 @@ void testStrings()
     test('A', 'B', "'A' != 'B'");
     test(wchar('❤'), wchar('∑'), "'❤' != '∑'");
     test(dchar('❤'), dchar('∑'), "'❤' != '∑'");
+
+    // Detect invalid code points
+    test(char(255), 'B', "cast(char) 255 != 'B'");
+    test(wchar(0xD888), wchar('∑'), "cast(wchar) 55432 != '∑'");
+    test(dchar(0xDDDD), dchar('∑'), "cast(dchar) 56797 != '∑'");
 }
 
 void testToString()()