element.py: make BST_STRICT_REBUILD part of the cache key

[Cynical-Optimist]

See original merge request on GitLab
In GitLab by [Gitlab user @abderrahimk] on May 4, 2020, 11:13

Description

Add the value of BST_STRICT_REBUILD to the cache key. This prevents confusing situations like #1270.

This merge request, when approved, will close: #1270

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[Cynical-Optimist]

In GitLab by [Gitlab user @juergbi] on May 4, 2020, 11:38

Commented on src/buildstream/element.py line 2051

It might make sense to add this dict key only when BST_STRICT_REBUILD is set to True. This would reduce unnecessary rebuilds for current users of BuildStream master.

[Cynical-Optimist]

In GitLab by [Gitlab user @abderrahimk] on May 4, 2020, 11:41

Commented on src/buildstream/element.py line 2051

That's true, but I noticed that nothing in the current dict is set conditionally. I'm fine with it either way.

[Cynical-Optimist]

In GitLab by [Gitlab user @tristanvb] on May 4, 2020, 12:20

Do we have this same issue with the strict attribute of dependency declarations ?

[Cynical-Optimist]

In GitLab by [Gitlab user @juergbi] on May 4, 2020, 14:20

Yes. This makes we wonder whether it would be clearer to include the weak cache key in the calculation of the strong cache key, preventing this whole issue class. It would mean that the weak cache key and the strong cache key would never match but I don't think this would cause any issues. And it would obviously invalidate all strong cache keys in BuildStream master.