Bug 24482 – Recursive alias out of order fails to compile with a misleading error message.

`issue.d`: struct Array(E) {} struct Enum(T...) {T t;} alias NodeArray = Array!Node; struct Object {NodeArray values;} alias Node = Enum!(Object); void main() {} `dmd issue.d` fails and gives the following messages. issue.d(3): Error: template instance `Array!Node` recursive template expansion issue.d(5): Error: template instance `issue.Enum!(Object)` error instantiating Moving `NodeArray` below `Object` or `Node` suppresses the issue.

slightly minimized ``` struct Array(E) {} struct Enum(T) {T t;} // <-- here T size is not known yet alias NodeArray = Array!(Enum!(Object)); struct Object {NodeArray values;} ``` IMO the error message is correct, for example ``` struct Array(E) {} struct Enum(T) {T t;} alias NodeArray = Array!(Enum!(Object*)); struct Object {NodeArray values;} ``` compiles. However that's a typical case of "how forward references are handled in D" is under-specified.

Moving decls does not solve anything, just try ``` struct Array(E) { E e;} struct Enum(T) {T t;} struct Object {NodeArray values;} alias NodeArray = Array!Node; alias Node = Enum!(Object); ``` The point is that at some point you must know the size of a member. When the member is a pointer you can guess the size without knowing the actual pointee type size. Might be zero, might be 3 Billions, but in fine it's a pointer so let's see that later ;)

Right; and an actual array would store an `E[]` or an `E*`. When `e`'s type is one of those, the program compiles.

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