revsetlang: enable optimization of 'x + y' expression It's been disabled since 4d1e56b29a91, but it can be enabled now as the ordering requirement is resolved at analyze().

repair: use rawvfs when copying extra store files If we use the normal vfs, store encoding will be applied when we .join() the path to be copied. This results in attempting to copy a file that (likely) doesn't exist. Using the rawvfs operates on the raw file path, which is returned by vfs.readdir(). Users at Mozilla are encountering this, as I've instructed them to run `hg debugupgraderepo` to upgrade to generaldelta. While Mercurial shouldn't deposit any files under .hg/store that require encoding, it is possible for e.g. .DS_Store files to be created by the operating system.

tests: add test demonstrating buggy path handling `hg debugupgraderepo` is currently buggy with regards to path handling when copying files in .hg/store/. Specifically, it applies the store filename encoding to paths instead of operating on raw files. This commit adds a test demonstrating the buggy behavior.

repair: iterate store files deterministically An upcoming test will add a 2nd file. Since readdir() is non-deterministic, add a sorted() to make traversal deterministic.

zstd: vendor python-zstandard 0.8.0 Commit 81e1f5bbf1fc54808649562d3ed829730765c540 from https://github.com/indygreg/python-zstandard is imported without modifications (other than removing unwanted files). Updates relevant to Mercurial include: * Support for multi-threaded compression (we can use this for bundle and wire protocol compression). * APIs for batch compression and decompression operations using multiple threads and optimal memory allocation mechanism. (Can be useful for revlog perf improvements.) * A ``BufferWithSegments`` type that models a single memory buffer containing N discrete items of known lengths. This type can be used for very efficient 0-copy data operations. # no-check-commit

commands: update help for "unbundle" Similar to the recent change to "bundle," this command no longer just deals with "changegroup" data.

commands: update help for "bundle" We now have a dedicated help topic to describe bundle specification strings. Let's update `hg bundle`'s documentation to reflect its existence. While I was hear, I also tweaked some wording which I felt was out of date and needed tweaking. Specifically, `hg bundle` no longer just deals with "changegroup" data: it can also generate files that have non-changegroup data.

help: document bundle specifications I softly formalized the concept of a "bundle specification" a while ago when I was working on clone bundles and stream clone bundles and wanted a more robust way to define what exactly is in a bundle file. The concept has existed for a while. Since it is part of the clone bundles feature and exposed to the user via the "-t" argument to `hg bundle`, it is something we need to support for the long haul. After the 4.1 release, I heard a few people comment that they didn't realize you could generate zstd bundles with `hg bundle`. I'm partially to blame for not documenting it in bundle's docstring. Additionally, I added a hacky, experimental feature for controlling the compression level of bundles in 76104a4899ad. As the commit message says, I went with a quick and dirty solution out of time constraints. Furthermore, I wanted to eventually store this configuration in the "bundlespec" so it could be made more flexible. Given: a) bundlespecs are here to stay b) we don't have great documentation over what they are, despite being a user-facing feature c) the list of available compression engines and their behavior isn't exposed d) we need an extensible place to modify behavior of compression engines I want to move forward with formalizing bundlespecs as a user-facing feature. This commit does that by introducing a "bundlespec" help page. Leaning on the just-added compression engine documentation and API, the topic also conveniently lists available compression engines and details about them. This makes features like zstd bundle compression more discoverable. e.g. you can now `hg help -k zstd` and it lists the "bundlespec" topic.

util: document bundle compression An upcoming patch will add support for documenting bundle specifications in more detail. As part of this, we'd like to enumerate available bundle compression formats. In order to do this, we need to provide the help mechanism a dict of names and objects with docstrings. This patch adds docstrings to compengine.bundletype and adds a function for retrieving a dict of them. The code is not yet used.

tests: store ETag when using --headeronly Previously, --headeronly would prevent --twice from working because the ETag wasn't stored when --headeronly was used. This feels like a bug. That feeling is reaffirmed by the fact that this change doesn't regress any tests.