Preelaboration

[Simon Wright <simon@pushface.org>]

I (think I) need to eliminate elaboration calls in parts of my Cortex
GNAT Runtime Systems project[1], and I'm left with one that I can't
understand.

(1) what does pragma Preelaborate actually mean? I hoped it would mean
"you don't need to elaborate this package".

(2) If you give Preelaborate, is it a compiler error to generate
elaboration code? (the generated elaboration procedure does nothing).

(3) I find ARM 10.2.1(10)[2] unclear (I got here because the problematic
package body instantiates a generic). Does it mean that the
instantiation won't be preelaborable unless all of 10.1 .. 10.4 are
false? Or does it mean that the compiler will make these assumptions
regardless of actuals?

And, looking at (10.1), would you expect

   generic
      type Item is private with Preelaborable_Initialization;
   package Generic_Queues is

to be legal? GNAT rejects it, 'aspect "Preelaborable_Initialization" not
allowed for formal type declaration'.

[1] https://sourceforge.net/projects/cortex-gnat-rts/
[2] http://www.ada-auth.org/standards/rm12_w_tc1/html/RM-10-2-1.html#p10