Re: Standard Library Interest?

[tmoran@acm.org]

Some comments from the experience of making the Claw library on
four different Ada compilers:

> - Ada is not a preprocessed language, yet there must be some code
>   tweaks for each environment:
>   - Different pragma Linker_Options depending upon platform (for
>     linker convenience)
>   - Some language constructs don't compile, due to version specific
>     GNAT bugs.
  Sometimes the changes are needed in the package specs, not just
the bodies.  For instance, one version of Gnat required a whole bunch
of stuff to get moved from private to public, with appropriate order
of declaration changes.  On a large library like Claw, it took a lot
of work to find and fix all occurrences.  IIRC we had to use a tool
that parsed the specs and figured out the inheritance pattern and
flagged the problematic cases.  And no, we couldn't use ASIS because
Gnat wouldn't compile, and thus wouldn't produce ASIS databases, for
the relevant packages.

>  Different versions of GNAT have different *.ali file format differences.
  This doesn't directly apply to Claw, since it's distributed as source
code, but there are other changes needed every year when there's a new
Gnat release.  Most recently, they changed the default behavior of
elaboration so we could either tell all users to add -gnatE to their
compile lines, an option unlikely to be greeted with applause, or go
through the entire Claw library inserting specific pragma Elaborate's.
And of course the library and tests must all be recompiled and run with
each vendor's new compiler release.  When there are new bugs, they may be
non-trivial to find and work around, and may require significant knowledge
of the inner workings of the library.  This work is of course proportional
to the number of versions and vendors of Ada compilers.  (Of course if the
vendors supported the Standard Library, they would have done this before
releasing a new compiler version.  :)