[Development] Proposing CMake as build tool for Qt 6

Konstantin Tokarev annulen at yandex.ru
Mon Jun 17 18:44:33 CEST 2019



17.06.2019, 19:09, "Konstantin Tokarev" <annulen at yandex.ru>:
> 17.06.2019, 18:43, "Thiago Macieira" <thiago.macieira at intel.com>:
>>  On Monday, 17 June 2019 08:16:38 PDT Konstantin Tokarev wrote:
>>>   17.06.2019, 18:15, "Thiago Macieira" <thiago.macieira at intel.com>:
>>>   > On Monday, 17 June 2019 02:52:03 PDT Konstantin Tokarev wrote:
>>>   >> I think that automatic generation of PCH is a bad idea, leading to
>>>   >> wasting
>>>   >> build time.
>>>   >
>>>   > Like we do in Qt today?
>>>
>>>   Yep. Approach of Qt Creator is much better.
>>
>>  Elaborate, please.
>
> Qt Creator uses manually crafted precompiled header files [1,2], which include
> only those headers which are often used across the project. If you pull all public
> headers of used Qt modules into pch like it was a kitchen sink, you spend a lot of
> extra time precompiling stuff which wiould be used once or twice. It also increases
> size of binary representation of PCH, and might make compilation slower because
> compiler now has to do lookups in larger AST.
>
> [1] https://code.qt.io/cgit/qt-creator/qt-creator.git/tree/src/shared/qtcreator_pch.h
> [2] https://code.qt.io/cgit/qt-creator/qt-creator.git/tree/src/shared/qtcreator_gui_pch.h

To put it differently:

Including some header into PCH is an optimization. Including everything into PCH without
proof that each header there is necessary is premature optimization.

-- 
Regards,
Konstantin



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