also to note that this also don't works:
--

struct A{
    int n;
}
template genA(){
    enum A genA = { n:4 };
}
immutable A b = genA!();

--

but this works:

--

struct A{
    int n;
}
template genA(){
    //works with immutable
    immutable  A genA = { n:4 };
}
immutable A b = genA!();

void main(){
    //ok
    assert(b.n == 4);
}
--

Further reduced test case shows it doesn't need a template.  It's just an enum static initializer problem.
---
struct Move{
   int Dx;
}
enum Move genMove = { Dx:4 };
immutable Move b = genMove;
---

It's happening because static struct initializers with names are not evaluated at compile time. And this is because init.c, StructInitializer::toExpression() doesn't deal with it. BTW -- now that we have struct literals, I'm not sure that we need struct initializers any more. They're a bit annoying, implementation-wise.

--- TEST CASE ---
struct Move{ int Dx; }
immutable Move genMove = { Dx:4};
static assert(genMove.Dx == 4); // not evaluatable at compile time.

PATCH: With the demise of struct initializers, it's not worth fixing properly.
But DsymbolExp::semantic() should check for a null value anyway (it checks in other places in expression.c). This would prevent the segfault.

expression.c line 2306 (svn 267):

	if ((v->storage_class & STCmanifest) && v->init)
	{
	    e = v->init->toExpression();
+  	    if (!e)
+	    {   error("cannot make expression out of initializer for %s", v->toChars());
+		e = new ErrorExp();
+	    }
	    e->semantic(sc);
	    return e;
	}

Changeset 349

fixed dmd 2.040