Share Share Plan

Status: Project

Main proponents: Pierre-YvesDavid PulkitGoyal

$/!\$ This is a speculative project and does not represent any firm decisions on future behavior.

Shares do not share some critical pieces of data with their source, leading to various important bugs. We should fix that by adding an exp-sharesafe requirement.

1. Goal

There are currently some important bugs:

* shares do not read the source repository's config, which becomes a large issues for:

hooks
storage/format configuration
behavior impacting config (eg: phase.publishing)
behavior impacting extension

* shares do not read the source repository's requires file. This leads to the share possibly missing important format upgrades from their source.

Not every config or requirement the user will like to share. Hence we will like to make sure following things too:

* A way to specify requires of shared source which are not shared.

This way we can have working directory specific requirements like exp-sparse.

* A way to specify configs for shared source which are not shared.

Shares are used in many various ways and user might not want some config, hooks to be shared. Configs related to wdir specific requirements is one example. Multiple such examples can be though of when you have working directory specific hooks.

The solution would be to introduce a new exp-sharesafe requirement that fix both the config and requirement needs

2. Detailed description

To make sure older version cannot create shares from safe repo, we introduce a new exp-sharesafe requirements. New behavior will be gated behind it.

2.1. requirements

Right now, shares copy the requirements at share time and never read them from the source again. This means shares will lag behind if the source repository is updated. This can have serious consequences (eg: repo corruption, bypassed hooks). To avoid this, the share should use the source requirements as the source of truth. However, some requirements are working copy specific (e.g. sparse). For such requirements, reading them from the source is meaningless and we need to still be able to add them on the share.

The best option seems to move the default location for requirements in .hg/store/requires and to explicitly flag the working copy specific ones. The exp-sharesafe requirement needs to also live in .hg/requires to fend off older clients.

2.2. config

The current behavior prevents hooks and other information to be propagated to shares. This can lead to very serious issues. For this reason, it seems "reasonable" to have shares read the source .hg/hgrc by default when exp-sharesafe requirement is present. There can be cases like config which enables sparse extension that requires non-shared config, a new .hg/nonsharedrc is to be introduced.

3. Roadmap

introduce a exp-sharesafe requirement to test the new code controlled by a format.exp-share-safe config
move appropriate requirements under .hg/store/requires (if exp-sharesafe)
have shares read the source repository .hg/store/requires
introduces a .hg/nonsharedrc read after the .hg/hgrc (with add associated flag for hg config)
get shares to also read .hg/hgrc (if exp-sharesafe)
rename exp-sharesafe and config requirement