Mercurial 7.2rc0 (2025-11-26)

Mercurial 7.2rc0 (2025-11-26)#

/!\ These are the release notes for a release candidate version. Any and all items can be removed or modified before the final release.

This is the first release to support Python 3.14 and likely the last to support Python 3.9.

This release is exceptionally full of changes, and as always a lot of minor changes have been omitted from these release notes.

New Features#

  • Support for Python 3.14

  • Added a closesbranch() template keyword

  • Added support for support --remote-hidden in hg incoming

  • hg clone now supports --no-stream to force opt-out of a streamclone

  • hg strip will optionally accept empty revision sets without bailing out (--permit-empty-revset). This is unconditionally enabled for hg debugstrip

  • Support for ZSTD is improved by falling back to the system package if the vendored module is not available. This change mostly affects pure python installs and helps distributions to use their integrated version by default. The appropriate package has been added as a Python optional dependency to help people who need it.

  • Added a new usage.resources.bandwidth config to tune how aggressive Mercurial is with its bandwidth usage.

Feature moved out of experimental#

dirstate-v2 format (8c912a652c54)#

A better format for storing the working copy information, provides a significant performance boost to hg status performance (and other commands that need that information like commit, purge, etc).

The use of dirstate-v2 can only be recommended when using the Rust extensions, as the Python version is quite slow at most operations (likely slower than dirstate-v1).

See hg help config.format.use-dirstate-v2 for details.

diff.merge configuration (a1c2e0753d1a)#

When set, running hg diff on a merge will show the difference compared to the default merge result instead of the diff against a parent. This is quite useful to spot changes introduced by a merge and how conflicts were resolved.

See hg help config.diff.merge for details.

tracked-hint format (bdd10cd37f6a)#

A small format variant that keeps a small file that helps external automation to detect changes to the set of tracked files.

See hg help config.revlog.reuse-external-delta-compression for details.

Parallel stream clone processing (2cc0954cef52)#

The parallel processing of incoming stream bundles is now enabled by default. See hg help config.worker.parallel-stream-bundle-processing for details.

Performance improvements for existing features#

  • hg purge (aka hg clean) now better leverages the Rust implementation of “status” when available. This provides performance improvement similar to the one provided by the rust status.

  • The computation of deltas when storing a revision (during commit, clone, push, pull, unbundle, …) was significantly sped up in Mercurial 7.2. This was achieved by a mix of reducing the amount of useless work done, improving the algorithms used, and smarter cache usage. All flavors of Mercurial (using the Rust extensions or not) should see a performance improvement, but using the Rust extensions will show a more dramatic improvement (some benchmark move from almost 4 hours to 2 minutes).

    (Here is small set of the involved changesets: 916d5b1db75f, a2cbf3d71a94, 2e8ba3356d7e, 4eb879393c45, 855cfc1c7c42, 2cbc32498a83)

  • The performance of caches related to tags has been improved when using the Rust extensions (f93ba6645f8e, eed40a296a18)

New Experimental Features and Formats#

Narrow-Store’s Shapes#

We are introducing the concept of “shapes” to improve the experience using narrow. Since using narrow implies using a more centralized workflow of version control, clients being dependent on the server for all practical matters of exchanging changes, we want to make this hybrid centralized/distributed world more practical.

The feature is still experimental and actively worked on, but Mercurial 7.2 ships some already usable parts:

  • A new server-side configuration (.hg/store/server-shapes) to define shapes, which are normalized and minimal descriptions of views into a slice of a repository store based on file names

  • A new admin::narrow-server command to get and list important information about these shapes

  • A new admin::narrow-client command to inspect the client state within this workflow

  • hg bundle is now able to generate streaming narrow clonebundles from shapes:

    • Support for non-streaming narrow clonebundles is not implemented yet

    • Each such bundle’s bundlespec contains the fingerprint of the shape it was generated with

    • A client hg can generate the same fingerprint from the narrow patterns passed to clone (--include, --exclude)

    • This makes the client hg filter out bundles that do not have the expected fingerprint

    • Old clients will not receive fingerprinted bundles when listing clonebundles, so backwards compatibility is conserved

    • This process is quite manual still, but is expected to improve in the coming versions

For more detailed information, see hg help shapes.

File Index#

The File Index is a new repository format that supersedes the fncache format. It tracks all file paths ever used within a repository throughout its entire history (excluding the working copy) and is useful for many common commands. The File Index is designed for efficient querying and updating and our benchmarks show significant performance improvements compared to when using the fncache. This is an internal format change that doesn’t affect the availability of any feature.

The introduction of the File Index will also open the door for other datastructures and algorithms to make use of its internal mapping of unique file to unique token, further unlocking a ton of performance down the line. You can learn more about its design by running hg help internals.file-index.

While basic support for the file index is implemented in Python, its use is only recommended when using the Rust extensions for performance reasons.

Revlog delta info#

The delta-info-revlog format variant is a small adjustment to the revlog-v1 format to better keep track of some information to help speed up some operations and improve the internal storage. This is an internal format change that doesn’t affect the availability of any feature.

The new information stored mostly focuses on:

  • Does a file revision contain file rename metadata?

  • Is a stored delta a “standard delta” or a “snapshot” (of any level)?

  • Is the stored delta “small” and which parent is best to find such a “small” delta?

Having this information around has various benefits:

  • We no longer need to manually inspect rename metadata in any case, speeding up various operations. This especially helps the copy tracing used by hg status and hg merge where such checks would add up to ⅓ of the total time.

  • We no longer need to worry about issue6528 on delta-info repositories (especially during exchanges given that changegroup-v4 is used)

  • Having more information about delta quality and “best parent” helps to generate better bundles faster when the stored delta cannot be directly reused.

  • Having more precise snapshot information allows for more advanced heuristics when creating the delta tree used for storage. In particular, it unlocks skipping over redundant deltas in the parents’ chain, using delta folding heuristics. That last part requires the Rust extensions to be enabled.

Consider giving the format a try on large repositories if you experience slow push/pull.

Some of these features are controlled by the following experimental features:

  • storage.revlog.record-delta-quality

  • storage.delta-fold-estimate

Changegroup v4#

A new changegroup format was introduced to carry the new information from delta-info. The format also includes some extra features that help performance overall:

  • explicitly transfer the full revision size to avoid situations where the client has to recompute at unbundle time

  • explicitly carry the “has metadata” information for filelogs to avoid the need to detect issue6528 at unbundle time

  • explicitly carry snapshot and quality information regarding exchanged delta to help the client to take more informed decisions when applying incoming deltas

  • explicitly carry the source delta base information to help the client find a suitable base quicker when receiving a recomputed delta

  • allow the exchange of deltas in their compressed form. This reduces the overall efficiently of compressing the bundle stream, but avoids costs associated with decompressing and recompressing the deltas on the server and the client. This also helps to identify deltas that won’t benefit from being compressed to speedup their application.

This format is not used by default unless the delta-info-revlog format variant is in use. It can be enabled using the experimental.changegroup4 configuration.

The various new features and behaviors associated with it can be controlled using various configuration options:

  • storage.revlog.exchange-compressed-delta

  • storage.revlog.reuse-external-delta-compression

  • storage.revlog.reuse-external-suspicious-delta-parent

Branchmap v3#

The V3 version of the branchmap is a small evolution from the V2 format that has been used. The main difference is that the topological heads are no longer explicitly listed in the cache. This significantly reduces the size the branchmap that has to be read and written to disk and allows for various optimizations when a repository update only affects topological heads on a branch.

In particular, this new branchmap format drastically reduces the cost of named-branch-related computations for large repositories that don’t use the feature.

Further performance improvements are expected with further code changes in later versions (without affecting the format).

That feature is not enabled by default yet, don’t hesitate to give it a try on any repositories with many heads or branches you might have at hand.

Rust Fast Path#

rhg now supports the purge (aka clean) command, for even better performance that combines with the on this command gains previously mentioned.

Bug Fixes#

  • The profiling.output-dir now supports expansion of tilde and shell variables

  • The lfs extension now expands and resolves the blob cache path to an absolute path

  • The availability of the given compression engine is now checked before applying a clonebundle

  • Extensions can now alter the contents of the repo’s default config when using stream clone

  • Support for changing the process name on Linux and MacOS has been restored (useful for chg users)

  • Using RUST_LOG when profiling with py-spy will not display the logs of py-spy itself anymore

  • hgweb now validates that plain filesystem paths exist in --web-conf file instead of raising 500

  • subrepo: fix an error handler in hgsubrepo.matchfileset()

  • largefiles: fix a MergeAction bytes vs str issue for marking a file removed

  • Local access to repositories with pull/incoming and push now honors server.view (note that hg clone in link-mode still does not honour server.view, hg clone --pull does)

Internal API Changes#

The large and ongoing Python typing effort has once again made significant progress. To that end, there was a large import-cycle-breaking series that implied refactoring, new files which may make this merge more difficult for extension maintainers. We’re sorry about that, but typing the Python code is helping us make the codebase a lot clearer and is now catching a lot of bugs during development, including within common third-party extensions like tortoise-hg.

Raw changes are listed here to help with migrating.

  • 54d9dc0c2209 “cleanup: drop compatibility for islocal(<repo-obj>)”

  • f2aa1bb35860 “deprecations: remove support for HGWITHRUSTEXT env var and its usages”

  • f026848bebe4 “deprecations: remove manifest.readfast”

  • e915f96ea1d5 “deprecations: remove manifest.readdelta”

  • ee0a7fa4cdd5 “revlog: enforce the “writable parameter””

  • 592438265fb3 “cleanup: drop the simplestorerepo extension”

  • 4963494bbd3f “bundle2: deprecate bundle2.getrepocaps() for hg 7.3”

  • a49c8fe2c986 “branchmap: drop the repo.branchheads method”

Miscellaneous#

  • contrib: update apache-server Dockerfile to debian:trixie

  • Added --py-installer option to run-tests.py to control how Mercurial is installed before tests

  • Added an --offline option to run-tests.py

  • Documented installation through uv for Rust extensions (see hg help rust)

Following the significant work made in 7.1 in this area, further changes have been made to the way developers can create a local copy of Mercurial for testing. Here are the unedited changes to make it easier to follow for those affected:

  • e2d10987bf26 “make-local: change the venv name”

  • e53ba925c7eb “make-local: add a symbolic link hg-local”

  • 2d69d5a333a6 “make-local: OFFLINE option”