Temporary: Make sure no in parameter would be passed by ref with -preview=in

Author: kinke

src/dmd/typesem.d

@@ -1500,6 +1500,19 @@ extern(C++) Type typeSemantic(Type type, const ref Loc loc, Scope* sc)
                     if (!isPOD || target.preferPassByRef(t))
                         fparam.storageClass |= STC.ref_;
                 }
+                version (all)
+                {
+                    if (!global.params.previewIn && (fparam.storageClass & (STC.in_ | STC.ref_)) == STC.in_)
+                    {
+                        auto ts = t.baseElemOf().isTypeStruct();
+                        const isPOD = !ts || ts.sym.isPOD();
+                        if (!isPOD || target.preferPassByRef(t))
+                        {
+                            .error(loc, "`in` parameter `%s` would be passed by reference with -preview=in", fparam.toChars());
+                            errors = true;
+                        }
+                    }
+                }
             }
 
             // Now that we completed semantic for the argument types,