Fix Issue 20757 - checkaction=context prints characters as integers

Author: MoonlightSentinel

src/core/internal/dassert.d

@@ -95,10 +95,22 @@ private string miniFormat(V)(const scope ref V v)
     }
     else static if (__traits(isIntegral, V))
     {
-        enum printfFormat = getPrintfFormat!V;
-        char[20] val;
-        const len = sprintf(&val[0], printfFormat, v);
-        return val.idup[0 .. len];
+        static if (is(V == char))
+        {
+            return ['\'', v, '\''];
+        }
+        else static if (is(V == wchar) || is(V == dchar))
+        {
+            import core.internal.utf: toUTF8;
+            return toUTF8(['\'', v, '\'']);
+        }
+        else
+        {
+            enum printfFormat = getPrintfFormat!V;
+            char[20] val;
+            const len = sprintf(&val[0], printfFormat, v);
+            return val.idup[0 .. len];
+        }
     }
     else static if (__traits(isFloating, V))
     {

test/exceptions/src/assert_fail.d

@@ -63,6 +63,10 @@ void testStrings()
     // https://issues.dlang.org/show_bug.cgi?id=20322
     test("left"w, "right"w, `"left" != "right"`);
     test("left"d, "right"d, `"left" != "right"`);
+
+    test('A', 'B', "'A' != 'B'");
+    test(wchar('❤'), wchar('∑'), "'❤' != '∑'");
+    test(dchar('❤'), dchar('∑'), "'❤' != '∑'");
 }
 
 void testToString()()