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= 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.

== 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

== 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.

=== 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.

=== 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.

== Roadmap ==

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

== See Also ==

 * ShareExtension
 * SharedRepoExtension
 * SharedRepository

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CategoryDeveloper CategoryNewFeatures