Re: changing tests/qtest/meson.build causes unnecessary rebuilding

[Philippe Mathieu-Daudé]

Hi Peter,

On 1/21/21 2:12 PM, Paolo Bonzini wrote:
> On 21/01/21 12:56, Peter Maydell wrote:
>> $ make -C build/arm-clang/ -j8
>> make: Entering directory
>> '/home/petmay01/linaro/qemu-from-laptop/qemu/build/arm-clang'
>> [1/23] Generating qemu-version.h with a meson_exe.py custom command
>> make: Leaving directory
>> '/home/petmay01/linaro/qemu-from-laptop/qemu/build/arm-clang'
>> $ touch tests/qtest/meson.build
>> $ make -C build/arm-clang/ -j8
>> make: Entering directory
>> '/home/petmay01/linaro/qemu-from-laptop/qemu/build/arm-clang'
>> /usr/bin/ninja  build.ninja && touch build.ninja.stamp
>> [0/1] Regenerating build files.
>> The Meson build system
>> [...]
>>
>> It then goes on to rebuild hundreds or thousands of files, most of
>> which are not even in tests/. (Oddly, the exact set of files recompiled
>> seems to vary from run to run.)
>>
>> Forcing a full rebuild of all of QEMU seems rather excessive when
>> the change was likely "add a new test case"...
> 
> This is "avoid build.ninja changes due to order of hash table iteration"
> (https://github.com/mesonbuild/meson/pull/7900/).  I think Meson 0.57
> (with the fix) should be out soon, hopefully before 6.0.
> 
> Alternatively you can try to bug your distro to include the patches,
> they are pretty safe.

Possible kludge rebuilding meson locally:

Paolo's #7900 got merged in commit 1c582a9de:
("Merge pull request #7900 from bonzini/stabilize-hash"),
so a possible kludge is to build and install meson in your
$HOME/.local/bin/ directory with pip as:

  $ python3 -m pip install --user \
      git+https://github.com/mesonbuild/meson.git@1c582a9de

Then either update your $PATH or use:

  $ ./configure --meson=$HOME/.local/bin/meson ...

Regards,

Phil.