RHEL and CentOS specific Requires in spec file

[Ron Olson]

Hey all-

I got a bug report about installing Swift on RHEL 8 where nothing 
provides binutils-gold. I _think_ this will fix it:

```
%if 0%{?el8}
Requires:       binutils
%else
Requires:       binutils-gold
%endif
```
But was hoping for some confirmation about this being the right way to 
handle this situation.

Thanks!

Ron

[Neal Gompa]

On Tue, May 10, 2022 at 11:01 AM Ron Olson  wrote:
> Hey all-
>
> I got a bug report about installing Swift on RHEL 8 where nothing provides binutils-gold. I think this will fix it:
>
> %if 0%{?el8}
> Requires:       binutils
> %else
> Requires:       binutils-gold
> %endif
>
> But was hoping for some confirmation about this being the right way to handle this situation.

It works, but is binutils-gold available in RHEL at all? If not, you
probably want to swap to 0%{?rhel} instead.

[Ron Olson]

No, it’s not available in RHEL nor in CentOS 8 and Stream 8; if I used the rhel tag would that include those?

On 10 May 2022, at 10:24, Neal Gompa wrote:
> On Tue, May 10, 2022 at 11:01 AM Ron Olson  wrote:
> > Hey all-
> >
> > I got a bug report about installing Swift on RHEL 8 where nothing provides binutils-gold. I think this will fix it:
> >
> > %if 0%{?el8}
> > Requires:       binutils
> > %else
> > Requires:       binutils-gold
> > %endif
> >
> > But was hoping for some confirmation about this being the right way to handle this situation.
>
> It works, but is binutils-gold available in RHEL at all? If not, you
> probably want to swap to 0%{?rhel} instead.
>
> -- 
> 真実はいつも一つ！/ Always, there's only one truth!
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[Neal Gompa]

On Tue, May 10, 2022 at 11:42 AM Ron Olson  wrote:
> No, it’s not available in RHEL nor in CentOS 8 and Stream 8; if I used the rhel tag would that include those?

Either is fine. %rhel and %el8 are both defined for all EL8 platforms.
Using %rhel is mostly useful if you want to handle multiple versions
of RHEL.

[Vitaly Zaitsev]

On 10/05/2022 17:01, Ron Olson wrote:
> |%if 0%{?el8}|

Better fix:

%if 0%{?rhel} && 0%{?rhel} == 8
...
%else
...
%endif

[Ben Beasley]

Could you please elaborate on why this form is better? I would have 
thought they were more or less equivalent, but it’s very possible that 
there is some non-obvious difference I don’t know about.

At minimum, “%if 0%{?rhel} && 0%{?rhel} == 8” is exactly equivalent to 
“%if 0%{?rhel} == 8”.

– Ben

On 5/10/22 11:53, Vitaly Zaitsev via devel wrote:
> On 10/05/2022 17:01, Ron Olson wrote:
> > |%if 0%{?el8}|
>
> Better fix:
>
> %if 0%{?rhel} && 0%{?rhel} == 8
> ...
> %else
> ...
> %endif

[Vitaly Zaitsev]

On 10/05/2022 18:00, Ben Beasley wrote:
> Could you please elaborate on why this form is better?

For building on RHEL without EPEL being enabled.
> At minimum, “%if 0%{?rhel} && 0%{?rhel} == 8” is exactly equivalent to 
> “%if 0%{?rhel} == 8”.

Double checks are preferable, because "%if 0%{?rhel} < X" can easily 
break things.

For example, on Fedora the %{?rhel} macro is not defined, so the 
condition 0%{?rhel} < 9 will be true because 0 is less than 9.

[Nico Kadel-Garcia]

On Tue, May 10, 2022 at 12:28 PM Vitaly Zaitsev via devel
 wrote:
> On 10/05/2022 18:00, Ben Beasley wrote:
> > Could you please elaborate on why this form is better?
>
> For building on RHEL without EPEL being enabled.
> > At minimum, “%if 0%{?rhel} && 0%{?rhel} == 8” is exactly equivalent to
> > “%if 0%{?rhel} == 8”.
>
> Double checks are preferable, because "%if 0%{?rhel} < X" can easily
> break things.
>
> For example, on Fedora the %{?rhel} macro is not defined, so the
> condition 0%{?rhel} < 9 will be true because 0 is less than 9.

So what? If you're checking:

%if 0%{?rhel} == 8

There's no need for the double check. If you were looking for RHEL <
8, yeah, it could make sense

%if 0%{?rhel} && 0%{?rhel} < 8

[Vitaly Zaitsev]

On 11/05/2022 00:17, Nico Kadel-Garcia wrote:
> %if 0%{?rhel} == 8

"0%{?rhel} == X" or "0%{?rhel} > 8" are okay, but "0%{?rhel} < X" will 
break some things on non-RHEL/EPEL distributions, including Fedora.

Sometimes maintainers forget this behavior after changing the release 
version in a condition. That's why double checks are always preferable.