[Development] moc output from non-local tool build

[Joerg Bornemann]

On 10/29/21 11:43 AM, Joerg Bornemann wrote:

>>> With https://codereview.qt-project.org/c/qt/qtbase/+/378053 it's now
>>> possible to turn off the package version check and to use moc of a
>>> different Qt version.  This requires that moc stays either compatible or
>>> handles that /version argument outlined elsewhere in this thread.
>>
>> Which is great, and is what I want, but we still need a decision on 
>> how long
>> the compatibility window will be and how we will inform the tools of what
>> version we're asking for.
> 
> A sliding window of two years has been proposed in this thread. Assuming 
> two minor version bumps per year, that's four minor versions. Let's make 
> that an odd number and we get the following
> 
> Proposal 1:
> Qt 6.X should work with host tools of Qt 6.Y, where X-2 <= Y <= X+2
> 
> That's quite some commitment.
> How about
> 
> Proposal 2:
> Qt 6.X should work with host tools of Qt 6.Y, where X-1 <= Y <= X+1
> 
> That gives us less to test, and the sliding window is something like 1.5 
> years.

Any comments on the sliding window size?

Apart from that, after internal discussion I have to lower expectations 
regarding our commitment to this.  I don't see us creating the test 
infra for testing the build of different host/target Qt combinations. As 
such we offer no commitment or support, but we will accept patches that 
improve the situation

As to the question "how we will inform the tools of what version we're 
asking for": one way is to add -compat-version switches to the tools 
that need them.  The downside here is that this needs to be done the day 
before yesterday for all tools that contribute to the build.

Another way would be to load it onto the user to set an environment 
variable QT_TOOL_COMPAT_VERSION or such that is read by tools that need to.


BR,

Joerg