[Scons-users] bug: --debug=explain gives wrong message

[Bill Deegan]

Gary,

If any of those bugs matches this exact case, can you add your repro to it?
If not, please file another.

-Bill

On Fri, Oct 15, 2021 at 10:39 AM Gary Oberbrunner <garyo at oberbrunner.com>
wrote:

> You might look at #3684, #2997, #2996 and #2932 and see if they cover
>> any of what you're seeing.
>
>
> Yes, most of those are relevant to my issue. Thanks for the info! I won't
> file a new bug; those cover it. Would love to see your better explain code
> in SCons!
>
> -- Gary
>
> On Fri, Oct 15, 2021 at 1:32 PM Mats Wichmann <mats at wichmann.us> wrote:
>
>>
>> On 10/15/21 10:04, Gary Oberbrunner wrote:
>> > In some cases, --debug=explain gives the wrong message about why a
>> > target is being rebuilt.
>> > Try this:
>> >
>> > === SConstruct:
>> > SConscript('src/SConscript-lictool', variant_dir='Build', duplicate=0)
>> >
>> > === src/SConscript:
>> > import os
>> > tgt=Command('tgt', ['src.txt'], f'echo hi {os.getpid()} > $TARGET')
>> >
>> > === src/src.txt: empty file
>> >
>> > Run "scons --debug=explain" twice. The first time it rebuilds because
>> > tgt doesn't exist, that's correct. The second time, the actual reason
>> it
>> > rebuilds is because the build action changed (it's set up to change
>> > every time you run it), but the message says that "src.txt is a new
>> > dependency" which (a) isn't correct, and (b) isn't the actual reason
>> for
>> > the rebuild.
>> >
>> > The reason appears to be that `explain` in scons/node/__init__.py
>> checks
>> > the Nodes for the old & new dependencies, and somehow the old dep Node
>> > is `src/src.txt` while the new one is `Build/src.txt`. So it spuriously
>> > says that the deps have changed. And a second issue is that in
>> `explain`
>> > once it has printed one kind of reason, it stops looking for other
>> > reasons, so it doesn't print that the build action has also changed.
>> > That's as far as I've tracked it so far.
>>
>> There are several issues on explain, which has the unfortunate
>> characteristic that it does its own computation, rather than using the
>> determination made by the decider.  I had some work in progress on
>> improving the explain logic, but it ended up with some work Bill did and
>> there didn't seem to be an appetite at the time to pursue the approach I
>> had.
>>
>> You might look at #3684, #2997, #2996 and #2932 and see if they cover
>> any of what you're seeing.
>> _______________________________________________
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>>
>
>
> --
> Gary
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