Re: [FFmpeg-devel] [PATCH] configure: disable vulkan if min version insufficient

[Timo Rothenpieler <timo@rothenpieler.org>]

On 29.09.2023 20:10, Tristan Matthews wrote:
> On Fri, Sep 29, 2023 at 1:37 PM Timo Rothenpieler <timo@rothenpieler.org> wrote:
>>
>> On 29.09.2023 15:52, Tristan Matthews wrote:
>>> Fixes: https://trac.ffmpeg.org/ticket/10596
>>> ---
>>>    configure | 3 ++-
>>>    1 file changed, 2 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/configure b/configure
>>> index 20db1801ed..50ba6f772f 100755
>>> --- a/configure
>>> +++ b/configure
>>> @@ -7154,7 +7154,8 @@ enabled crystalhd && check_lib crystalhd "stdint.h libcrystalhd/libcrystalhd_if.
>>>
>>>    if enabled vulkan; then
>>>        check_pkg_config_header_only vulkan "vulkan >= 1.3.255" "vulkan/vulkan.h" "defined VK_VERSION_1_3" ||
>>> -        check_cpp_condition vulkan "vulkan/vulkan.h" "defined(VK_VERSION_1_4) || (defined(VK_VERSION_1_3) && VK_HEADER_VERSION >= 255)"
>>> +        check_cpp_condition vulkan "vulkan/vulkan.h" "defined(VK_VERSION_1_4) || (defined(VK_VERSION_1_3) && VK_HEADER_VERSION >= 255)" ||
>>> +        warn "Disabling vulkan" && disable vulkan
>>>    fi
>>
>> Doesn't that just always disable vulkan if any of the previous checks
>> succeed? The logic looks weird to me.
> 
> No, it will only disable vulkan if all the previous checks fail as
> this conditional shortcircuits (so to get to here it would have to be
> false || false || false || false || false || warn "Disable vulkan" &&
> disable vulkan). If I hack the version number to match mine (changing
> it to 1.3.239), vulkan won't be disabled (that's why I added the
> warning message) and you'll hit the build breakage I and others are
> hitting currently.

My shell disagrees:

$ function warn() { echo $1; }
$ true || false || warn "Disabling vulkan" && echo DISABLED
DISABLED
$ false || true || warn "Disabling vulkan" && echo DISABLED
DISABLED
$ false || false || warn "Disabling vulkan" && echo DISABLED
Disabling vulkan
DISABLED
$ true || true || warn "Disabling vulkan" && echo DISABLED
DISABLED

No matter the results of the checks, this will always disable Vulkan, 
since the chain before it will always have a positive outcome, so && 
continues.
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