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Avoid build.ninja changes due to order of hash table iteration #7900

Merged
merged 3 commits into from
Nov 18, 2020
Merged

Avoid build.ninja changes due to order of hash table iteration #7900

merged 3 commits into from
Nov 18, 2020

Commits on Nov 15, 2020

  1. stabilize sets that are converted to lists 

    The order of elements in sets cannot be relied upon, because the hash
values are randomized by Python.  Whenever sets are converted to lists
we need to keep their order stable, or random changes in the command line
cause ninja to rebuild a lot of files unnecessarily.  To stabilize them,
use either sort or OrderedSet.  Sorting is not always applicable, but it
can be faster because it's done in C and it can produce slightly nicer
output.
    @bonzini
    bonzini committed Nov 15, 2020
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  2. stabilize iteration order for dictionaries 

    The order of keys in dictionaries cannot be relied upon, because the hash
values are randomized by Python.  Whenever we iterate on dictionaries and
meson.build generates a list during the iteration, the different iteration
orders may cause random changes in the command line and cause ninja to
rebuild a lot of files unnecessarily.
    @bonzini
    bonzini committed Nov 15, 2020
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  3. ninjabackend: stabilize order of dependencies and order-only dependen… 

    …cies

These do not go into the command line, and therefore do not matter
for the purpose of avoiding unnecessary rebuilds after meson is
rerun.  However, they complicate the task of finding differences
between build lines across meson reruns.

So take the easy way out and sort everything after | and ||.
With this change, there is absolutely no change in QEMU's 40000-line
build.ninja file after meson is rerun.
    @bonzini
    bonzini committed Nov 15, 2020
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