The following compiles but does not link:

# import std.stdio;
#
# template Bar(Y)
# {
#   void Bar(Y param) {writefln("The parameter was: ", param);}
# }
#
# template Foo(alias X)
# {
#   alias Bar!(typeof(X)) Foo;
# }
#
# void unused()
# {
#   float f;
#   // Uncomment this line and the linker error disappears
#   // Bar!(typeof(f))(f);
# }
#
# void main()
# {
#   float f = 1.2;
#
#   // A really ugly kind of implicit instantiation :-)
#   mixin Foo!(f); Foo(f);
# }

Instantiating the template explicitly (even in another scope in an uncalled function) solves the problem.

Nick