[broken] Support TypeQual(TypeSeq)

compiler/src/dmd/mtype.d

@@ -4558,6 +4558,46 @@
     {
         v.visit(this);
     }
+
+    override final Type makeConst()
+    {
+        if (mcache && mcache.cto)
+        {
+            assert(mcache.cto.isConst());
+            return mcache.cto;
+        }
+        TypeTuple t = cast(TypeTuple) Type.makeConst();
+        if (arguments)
+        {
+            t.arguments = new Parameters(arguments.length);
+            foreach (i, ref arg; *t.arguments)
+            {
+                auto tsrc = (*arguments)[i].type;
+                arg = new Parameter(Loc.initial, 0, tsrc.addSTC(STC.const_), null, null, null);
+            }
+        }
+        return t;
+    }
+
+    override final Type makeImmutable()
+    {
+        if (mcache && mcache.ito)
+        {
+            assert(mcache.ito.isImmutable());
+            return mcache.ito;
+        }
+        TypeTuple t = cast(TypeTuple) Type.makeImmutable();
+        if (arguments)
+        {
+            t.arguments = new Parameters(arguments.length);
+            foreach (i, ref arg; *t.arguments)
+            {
+                auto tsrc = (*arguments)[i].type;
+                arg = new Parameter(Loc.initial, 0, tsrc.immutableOf(), null, null, null);
+            }
+        }
+        return t;
+    }
 }
 
 /***********************************************************

compiler/test/compilable/type_seq_qual.d

@@ -0,0 +1,16 @@
+alias AliasSeq(Args...) = Args;
+
+immutable(AliasSeq!(int, float)) c;
+immutable AliasSeq!(int, float) d;
+static assert(is(typeof(c) == typeof(d)));
+
+alias TS = AliasSeq!(int, float);
+static assert(is(typeof(c) == immutable TS));
+static assert(is(immutable(TS)[0] == immutable int));
+
+static assert(is(const(TS) == const TS));
+static assert(is(const(AliasSeq!(int, float))[0] == const int)); // OK
+static assert(is(const(TS)[0] == const int)); // fails
+
+alias CT = const(TS);
+static assert(is(CT[0] == const int));