Re: [PATCH 1/3] revision: complicated pathspecs disable filters

> -->8--
> From 89beb9598daabb19e3c896bbceeb0fc1b9ccc6ca Mon Sep 17 00:00:00 2001
> From: Derrick Stolee <dstolee@microsoft.com>
> Date: Wed, 15 Apr 2020 18:04:25 +0000
> Subject: [PATCH] bloom: compute all Bloom hashes from lowercase
>
> The changed-path Bloom filters currently hash path strings using
> the exact string for the path. This makes it difficult* to use the
> filters when restricting to case-insensitive pathspecs.
>
> * I say "difficult" because it is possible to generate all 2^n
>   options for the case of a path and test them all, but this is
>   a bad idea and should not be done. "Impossible" is an appropriate
>   alternative.
>
> THIS IS A BREAKING CHANGE. Commit-graph files with changed-path
> Bloom filters computed by a previous commit will not be compatible
> with the filters computed in this commit, nor will we get correct
> results when testing across these incompatible versions. Normally,
> this would be a completely unacceptable change, but the filters
> have not been released and hence are still possible to update
> before release.
>
> TODO: If we decide to move in this direction, then the following
> steps should be done (and some of them should be done anyway):
>
> * We need to document the Bloom filter format to specify exactly
>   how we compute the filter data. The details should be careful
>   enough that someone can reproduce the exact file format without
>   looking at the C code.
>
> * That document would include the tolower() transformation that is
>   being done here.