[gentoo-dev] 'Local' USE_EXPAND flags -- aka plugins are not that special

[gentoo-dev] 'Local' USE_EXPAND flags -- aka plugins are not that special

[Michał Górny]

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Hello,

I've did a quick statistic of how often USE_EXPAND flags are used.
In order to obtain the results, I have put all known USE_EXPANDs into
${flags[@]} and then did:

  for a in "${flags[@]}"; do
    echo -n "$a: "
    grep -l IUSE=.*${a}_ */* | xargs qatom | cut -d' ' -f1-2 | sort -u
  | wc -l done | tee /tmp/use-expand.txt

The result was a table of USE_EXPAND flags with counts of how many
*different* packages declare them in IUSE.

The results are:

   package count | n flags
  ---------------+---------
               0 |       3
               1 |      24
               2 |       4
             3-8 |       3
             >10 |      11

As you can see, we have *a lot* of USE_EXPAND variables which are only
used by a *single* package. This feels a lot like people are overusing
USE_EXPANDs in place of local USE flags, just to have them prefixed.
And if you take a look at the detailed list (attached for
completeness), you can see that they really do.

And if anyone wondered why it's wrong -- it's wrong because it's much
like declaring global USE flags for a very specific features which are
not only specific to a single package, but are even defined in a way
that they will *never* be suitable to anything else.

Although most of the cases need to be handled separately
and specifically to a particular flag, a common mistake is to introduce
USE_EXPAND every time plugins or modules are involved.

People, plugins are *not* special. There are regular features, just
packaged in a bit different way.

Let's take an example of a mail client. We have two mail clients, one
tightly integrated and the other plugin-based. Both have optional HTML
message support, the latter in the form of a plugin.

Now, let's assume we have global USE=html (why the heck we don't have
this and instead a dozen of local USE=html, then USE=webkit?!). It is
described as something vague like:

  enable HTML support

If I take this USE=html and see it in a mail client, I add 2+2 and get
that USE=html enables HTML message support. Now, why the heck I am
supposed to find out that the latter mail client instead of this
USE=html uses FOO_PLUGINS=htmlviewer?

This looks like a double crime to me. First of all, it's introducing
a specific, local flag for something that we have a global flag for.
Secondly, it's introducing that local flag in a global manner via
USE_EXPAND.

While we actually avoided having that USE_EXPAND for that specific mail
client, there are other cases which are very similar to this.

We have three HTTP servers which define USE_EXPANDs for their modules.
Each of them uses a completely separate namespace and different names
for the *same* features. We have global USE=cgi yet for apache we have
to use apache2_modules_cgi. People are reinventing USE=ssl like this
as well.

And CURL_SSL is a complete disaster. Does supporting 6 different SSL
backends (what for?!) justify inventing a global USE_EXPAND? Most of
those backends have their local (or even global) flags already. Why do
I have to repeat my preference twice?

People, get some reason! The major point of having global USE flags is
to let user express his preferences *once*. Extensively using
USE_EXPAND as a cheap namespace for local flags forces him to re-state
those preferences for every single affected package (USE_EXPAND set).

-- 
Best regards,
Michał Górny

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abi_x86: 86
alsa_cards: 2
alsa_pcm_plugins: 0
apache2_modules: 1
apache2_mpms: 1
calligra_features: 1
cameras: 1
crosscompile_opts: 11
curl_ssl: 2
dracut_modules: 1
dvb_cards: 1
elibc: 1300
fftools: 1
foo2zjs_devices: 0
gpsd_protocols: 1
grub_platforms: 1
input_devices: 5
kernel: 136
lcd_devices: 2
libreoffice_extensions: 1
linguas: 363
lirc_devices: 1
misdn_cards: 0
monkeyd_plugins: 1
netbeans_modules: 1
nginx_modules_http: 1
nginx_modules_mail: 1
ofed_drivers: 1
office_implementation: 8
openmpi_fabrics: 1
openmpi_ofed_features: 1
openmpi_rm: 1
php_targets: 64
python_single_target: 127
python_targets: 808
qemu_softmmu_targets: 1
qemu_user_targets: 2
ruby_targets: 559
sane_backends: 1
userland: 19
video_cards: 24
vmware_guest: 1
voicemail_storage: 1
xfce_plugins: 3
xtables_addons: 1

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Re: [gentoo-dev] 'Local' USE_EXPAND flags -- aka plugins are not that special

[Samuli Suominen]

On 30/05/13 11:58, Michał Górny wrote:
> Hello,

Only replying in behalf of xfce_plugins. Our policy has been always to + 
enable them by default as they are only used in Xfce specific packages
So setting XFCE_PLUGINS="" is a way to counter effect that policy

This has worked well for us and I don't see a reason to change it, but 
in general I have to agree, I've seen it overused myself too

Re: [gentoo-dev] 'Local' USE_EXPAND flags -- aka plugins are not that special

[Rick "Zero_Chaos" Farina]

-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1

On 05/30/2013 06:26 AM, Samuli Suominen wrote:
> On 30/05/13 11:58, Michał Górny wrote:
>> Hello,
> 
> Only replying in behalf of xfce_plugins. Our policy has been always to +
> enable them by default as they are only used in Xfce specific packages
> So setting XFCE_PLUGINS="" is a way to counter effect that policy
> 
> This has worked well for us and I don't see a reason to change it, but
> in general I have to agree, I've seen it overused myself too
> 
> 
> 
I remember when the use expand was first added for XFCE stuff, nothing
worked on my system for days while I tried to figure out what was wrong
because I was only looking at the regular use flags.

- -- (that's minus minus) on use_expand in general.

- -Zero
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Re: [gentoo-dev] 'Local' USE_EXPAND flags -- aka plugins are not that special

[Samuli Suominen]

On 30/05/13 17:25, Rick "Zero_Chaos" Farina wrote:
> -----BEGIN PGP SIGNED MESSAGE-----
> Hash: SHA1
>
> On 05/30/2013 06:26 AM, Samuli Suominen wrote:
>> On 30/05/13 11:58, Michał Górny wrote:
>>> Hello,
>>
>> Only replying in behalf of xfce_plugins. Our policy has been always to +
>> enable them by default as they are only used in Xfce specific packages
>> So setting XFCE_PLUGINS="" is a way to counter effect that policy
>>
>> This has worked well for us and I don't see a reason to change it, but
>> in general I have to agree, I've seen it overused myself too
>>
>>
>>
> I remember when the use expand was first added for XFCE stuff, nothing
> worked on my system for days while I tried to figure out what was wrong
> because I was only looking at the regular use flags.
>
> - -- (that's minus minus) on use_expand in general.

Well, we didn't + enable them at first by default which caused the confusion
I take responsibility for that mistake

- Samuli