Re: [gentoo-user] Re: USE flag question (not total newbie)

[Alan McKinnon <alan.mckinnon@gmail.com>]

On 29/11/2016 04:15, Ian Zimmerman wrote:
> On 2016-11-29 01:55, Stroller wrote:
> 
>>> [ebuild   R   ] dev-db/sqlitebrowser-3.8.0  USE="-qt5 {-test} (-qt4%*)" 
>>>
>>> Does this mean the package will be rebuilt without any qt support at
>>> all?  Why?
>>
>> No, I believe it means that the _option_ to enable or disable qt4 has
>> been removed.
> 
> Well - notice the 'R'.  So the package (or at least the version, see
> below) has not been changed since last time.
> 
>> It could be that the package is always compiled with qt4, or that it's
>> always disabled, or that `make` detects it automatically.  The best
>> things to look at are the ebuild and the changelog.
> 
> There is no changelog for this package :-(
> 
> In the ebuild, the only occurrence of the string "qt4" is:
> 
> src_prepare() {
>         # https://github.com/qingfengxia/qhexedit still bundled
>         # x11-libs/qscintilla[qt4?,qt5?] still bundled
>         #                     ^^^^
>         find libs/{antlr-2.7.7,qcustomplot-source} -delete || die
>         cmake-utils_src_prepare
> }
> 
> I don't think this is responsible for the emerge output.
> 
> Is it possible for the ebuild to change (in particular, for USE flags to
> be removed) without a change in version number?
> 

Yes.

It's quite common to have a change in an ebuild that makes no difference
at all to the files on disk if it's already emerged. Bumping the version
in that case forces a rebuild everywhere to give exactly the same result
= not good.

If the package is not already merged on a given machine, then a new
install simply does what it should.

Suppose you had a situation where a package had qt4 in USE but because
of the way it works it's not actually possible to install it without
qt4. Merging it with USE=qt4 would always proceed, and with USE=-qt4
would always error out (you can get to this state gradually over time)

In that case, removing the flag entirely from USE would make zero
difference where the package is already installed, so no version bump is
needed.

All this depends on the judgement of the ebuild maintainer

-- 
Alan McKinnon
alan.mckinnon@gmail.com