Обсуждение: Use "?=" operator for a contrib makefile in documentation

On 25.09.25 15:17, Maxim Orlov wrote:
> I think that the Makefile should be written so that variable values,
> specifically, PG_CONFIG, can be given to it from the environment rather
> than the make command line. As a result, using the "?=" operator rather
> than "=" to set a default value to the PG_CONFIG variable appears more
> acceptable.

I think the current text is preferable.  This allows running

make PG_CONFIG=...

so that you can pick a different PostgreSQL installation for a 
particular build.

If you always want to use a particular PostgreSQL installation, then you 
could alter the PATH in the environment.

I don't know that there is a use case of setting only PG_CONFIG in the 
environment that is not covered by these other two approaches.

Peter Eisentraut <peter@eisentraut.org> writes:
> On 25.09.25 15:17, Maxim Orlov wrote:
>> I think that the Makefile should be written so that variable values,
>> specifically, PG_CONFIG, can be given to it from the environment rather
>> than the make command line. As a result, using the "?=" operator rather
>> than "=" to set a default value to the PG_CONFIG variable appears more
>> acceptable.

> I think the current text is preferable.  This allows running
> make PG_CONFIG=...
> so that you can pick a different PostgreSQL installation for a 
> particular build.

AFAICT that would still work with ?=.  Nonetheless, I agree with
Peter that we shouldn't change this advice (much less change all our
Makefiles that do it like that).  The reason is that the gmake manual
advises caution in the use of this feature:

   Thus, by setting the variable 'CFLAGS' in your environment, you can
   cause all C compilations in most makefiles to use the compiler switches
   you prefer.  This is safe for variables with standard or conventional
   meanings because you know that no makefile will use them for other
   things.
   ...
   Other use of variables from the environment is not recommended.  It
   is not wise for makefiles to depend for their functioning on environment
   variables set up outside their control, since this would cause different
   users to get different results from the same makefile.  This is against
   the whole purpose of most makefiles.

(This is in "Variables from the Environment", section 6.10 in the
gmake manual version that I have at hand.)

            regards, tom lane

On 29.09.25 16:00, Tom Lane wrote:
> Peter Eisentraut <peter@eisentraut.org> writes:
>> On 25.09.25 15:17, Maxim Orlov wrote:
>>> I think that the Makefile should be written so that variable values,
>>> specifically, PG_CONFIG, can be given to it from the environment rather
>>> than the make command line. As a result, using the "?=" operator rather
>>> than "=" to set a default value to the PG_CONFIG variable appears more
>>> acceptable.
> 
>> I think the current text is preferable.  This allows running
>> make PG_CONFIG=...
>> so that you can pick a different PostgreSQL installation for a
>> particular build.
> 
> AFAICT that would still work with ?=.  Nonetheless, I agree with
> Peter that we shouldn't change this advice (much less change all our
> Makefiles that do it like that).  The reason is that the gmake manual
> advises caution in the use of this feature:

Yes, that's what I meant.  The current code allows the "postfix" make 
syntax (make PG_CONFIG=...), but it doesn't allow environment variables 
to take effect silently (which also prevents the "prefix" syntax 
(PG_CONFIG=... make), but that's just the way things work).

Hello!

We use common scripts to check various PostgreSQL modules with various 
PostgreSQL major versions. It is easier to set the required PG_CONFIG in 
the enviroment than to change various make commands. In particular, they 
are quite common if we want to build, install or run installcheck in a 
specific directory. The PATH enviroment variable also works, but 
PG_CONFIG is usually sufficient and we want to be sure of that.

On 2025-09-29 15:50, Peter Eisentraut wrote:
> I think the current text is preferable.  This allows running
> 
> make PG_CONFIG=...
> 
> so that you can pick a different PostgreSQL installation for a 
> particular build.
> 
> If you always want to use a particular PostgreSQL installation, then 
> you could alter the PATH in the environment.
> 
> I don't know that there is a use case of setting only PG_CONFIG in the 
> environment that is not covered by these other two approaches.

-- 
Marina Polyakova
Postgres Professional: http://www.postgrespro.com
The Russian Postgres Company