revlog: move decompress() from module to revlog class (API) Upcoming patches will convert revlogs to use the compression engine APIs to perform all things compression. The yet-to-be-introduced APIs support a persistent "compressor" object so the same object can be reused for multiple compression operations, leading to better performance. In addition, compression engines like zstd may wish to tweak compression engine state based on the revlog (e.g. per-revlog compression dictionaries). A global and shared decompress() function will shortly no longer make much sense. So, we move decompress() to be a method of the revlog class. It joins compress() there. On the mozilla-unified repo, we can measure the impact of this change on reading performance: $ hg perfrevlogchunks -c ! chunk ! wall 1.932573 comb 1.930000 user 1.900000 sys 0.030000 (best of 6) ! wall 1.955183 comb 1.960000 user 1.930000 sys 0.030000 (best of 6) ! chunk batch ! wall 1.787879 comb 1.780000 user 1.770000 sys 0.010000 (best of 6 ! wall 1.774444 comb 1.770000 user 1.750000 sys 0.020000 (best of 6) "chunk" appeared to become slower but "chunk batch" got faster. Upon further examination by running both sets multiple times, the numbers appear to converge across all runs. This tells me that there is no perceived performance impact to this refactor.

revlog: make compressed size comparisons consistent revlog.compress() compares the compressed size to the input size and throws away the compressed data if it is larger than the input. This is the correct thing to do, as storing compressed data that is larger than the input takes up more storage space and makes reading slower. However, the comparison was implemented inconsistently. For the streaming compression mode, we threw away the result if it was greater than or equal to the input size. But for the one-shot compression, we threw away the compression only if it was greater than the input size! This patch changes the comparison for the simple case so it is consistent with the streaming case. As a few tests demonstrate, this adds 1 byte to some revlog entries. This is because of an added 'u' header on the chunk. It seems somewhat wrong to increase the revlog size here. However, IMO the cost of 1 byte in storage is insignificant compared to the performance gains of avoiding decompression. This patch should invite questions around the heuristic for throwing away compressed data. For example, I'd argue we should be more liberal about rejecting compressed data, additionally doing so where the number of bytes saved fails to reach a threshold. But we can have this discussion another time.

similar: rename local variable to not collide with previous Future patches will move the score function to the module level, so let's not shadow that.

patch: add label for coloring the index extended header Just like the summary says, this will colorize the: index 3d3ba4b65e11..57274a0f46b2 100644 line in the diff output.

patch: add index line for diff output This helps highlighting in third-party diff coloring (which assumes git output) and maintains pedantic correctness with diff --git. Tests will be added at the end of the series.

patch: add config knob for displaying the index header This config knob can take an integer between 0 and 40 or a keyword ('none', 'short', 'full') to control the length of hash to output. It will display diffs with the git index header as such, diff --git a/mercurial/mdiff.py b/mercurial/mdiff.py index 112edf7..d6b52c5 100644 We'll put this in the experimental section for now.

bisect: refer directly to bisect() revset predicate in help We have specific syntax for displaying the help text for a particular revset predicate, so let's refer directly to the bisect() revset in the verbose bisect help. It seems likely that the user doesn't care about other revsets at that point, so they will probably not miss the text about the other revset predicates.

tests: use "hg help revisions.<predicate>" instead of grepping We have specific syntax for displaying the help text for a particular revset predicate, so use that instead of grepping through the full output.

help: remove now-redundant pointer to revsets help "hg help revisions" and "hg help revsets" now point to the same text, so drop the revsets reference.

help: eliminate duplicate text for revset string patterns There's no reason to duplicate this so many times, and it's likely an instance will be missed if support for a new pattern is added and documented. The stringmatcher is mostly used by revsets, though it is also used for the 'tag' related templates, and namespace filtering in the journal extension. So maybe there's a better place to document it. `hg help patterns` seems inappropriate, because that is all file pattern matching. While here, indicate how to perform case insensitive regex searches.