Re: Suggestion about best practice with .gpr files

["Björn Lundin" <b.f.lundin@gmail.com>]

Den 2021-06-01 kl. 11:33, skrev Jeffrey R. Carter:
> The compiler knows the dependencies among the units that make up a 
> project, and every compiler I've used has the ability to do a build, 
> recompiling units that need it, so there is no need for an additional 
> tool to do this, as there is with C.

I can tell that you never used Alsys Ada on Aix then.
It would tell you if a file was obsolete - which it became by
* changing it
* compile its spec (if it was a body)
* compile a spec which it directly or indirectly is dependent on


so - just by compiling some spec, you would obsolete another body.
And there was no such thing as recompilation.
So the whole system was built with korn-shell files stating

ada compile file_a_spec.ada
ada compile file_b_spec.ada
ada compile file_c_spec.ada

ada compile file_a_body.ada
ada compile file_b_body.ada
ada compile file_c_body.ada

and if file_a_spec.ada later on did a 'with' on file_b_spec.ada
you would need to change that korn-shell script to read

ada compile file_b_spec.ada
ada compile file_a_spec.ada
ada compile file_c_spec.ada

...

instead


For windows we had Object Ada (7.?)

It would recompile all file if they belonged to the same object libraray.

We have a hierchal structrure so we can compile code (common utilities) 
into a root object librery, and application specific code to children of 
that root

if you did changed in application layer, it would recompile changes in 
that layer - but not in the root layer.

So - we had to have corresponding bat files stating
ada compile file_a_spec.ada
....



So migrating to Gnat was a great relief.
We did use the -i switch of gnatmake and 2000 lines of tcl-glue code
to get the object files where we wanted them; to krep the hierchal 
structure. Worked very well for 15 years, then project files were
good enough to support all our requirements.
We now have basically just a bash-script calling on gprbuild with 15-20 
gprfiles. much simpler.
And the syntax for setting switches is great

we support
AIX 5,6,7
Win 2003,2008,20012,2016,2019  32/64 bit
Linux debain/ubuntu/redhat/centos on intel64 and arm64
and some playing around with
Freeebsd/macp-pc32/mac-intel64

on that we support Oracle/Postgressql/MS-sql-server
And 3 different ways of doing IPC (pipes/sem+shared mem/rabbitMQ)

and 15-20 different flavours of gnat (mostly pro, but also GPL and FSF 
on some platforms)

Sofar we only deliver on gnat pro, but I test with GPL and FSF as well.

So - the scenario handling of gpr file is just great,
the above will give you quite some combinations.
and some code cannot be compiled on all platforms,
like big-endian/little-endian record layouts.

Controlling source-file directories via gpr is much easier than anything 
we had before.

So - yes if you have small projects - fine you don't need project files.
if you have millions of lines of code - then you tend to like them.


-- 
Björn