#pragma section-numbers 2

<<Include(A:dev)>>

= Configuration consolidation =

<<TableOfContents>>

'''Status: Project'''

'''Main proponents: DavidDemelier, [[Pierre-Yves David]]'''

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

Make the .hgrc file more unified.

== Goal ==

The goal of this project is to make a clear naming style regarding the .hgrc configuration options.

== Detailed description ==

The current .hgrc configuration options is messed with many different styles:

 * anoption (~ 192 options, many are unreadable)
 * an_option (~ 8 options)
 * an-option (~ 7 options)

Having a unified style makes the code cleaner, better integrated.

In addition, having guideline for sections would be useful. In Mercurial core + bundled extensions we have about 300 configuration options. They are spread across the following sections:

{{{
     34 ui
     28 convert
     27 experimental
     21 web
     20 bugzilla
     19 lists
     13 notify
     10 format
     10 devel
      9 values
      9 profiling
      7 server
      6 smtp
      5 worker
      5 patchbomb
      5 http_proxy
      4 progress
      4 mq
      3 pager
      3 histedit
      3 factotum
      3 eol
      3 email
      2 transplant
      2 share
      2 phases
      2 paths
      2 patch
      2 merge
      2 hostsecurity
      2 gpg
      2 fsmonitor
      2 color
      2 chgserver
      2 bundle
      2 blackbox
      2 acl
      1 win32text
      1 win32mbcs
      1 shelve
      1 perf
      1 keywordset
      1 hook
      1 hgk
      1 fakepatchtime
      1 fakedirstatewritetime
      1 debug
      1 cmdserver
      1 censor
      1 bookmarks
      1 automv
}}}

There are *many* options is the `[ui]` section and many sections with very few config. Gathering related options in the same config section has multiple advantages. The main one is that it puts related options together in the documentation improving discoverability. But at the same time, having too many options in the `[ui]` is burying the important ones under more minor ones.

==== Proposal: use - in config examples ====

While major options can be written in only one word, we should start using hyphens between words.

The actual config looks like this:

{{{
[web]
allowpull = foo
allow_push = bar # yes, for real

[progress]
assume-tty = yes

[worker]
backgroundcloseminfilecount = 12
}}}

Using hyphens, options will be renamed like this:

{{{
[web]
allow-pull = foo
allow-push = bar

[progress]
assume-tty = yes

[worker]
background-close-min-file-count = 12
}}}

Names like '''backgroundcloseminfilecount''', '''graphnodetemplate''', '''mergemarkertemplate''' are actually not readable by humans.

Using the implemented alias support, we can start renaming options to the new convention without any breakage.

{{{
coreconfigitem('web', 'allowpull',
    default=None,
    alias=[('web', 'allow-pull')]
)
}}}

Note: we need to keep the old name as the original section/key configitem.

=== Proposal for sections: central config declaration ===

Currently, config options do not needs to be declared in any special way. You just fetch a value in the code using `ui.config(section, name[, defaultvalue])`.

On top of that, we have `contrib/check-config.py` that runs on the code in the Mercurial repository trying to catch:

 * inconsistent type used in config
 * undocumented config option

The proposal is to have a central declaration of all known config options. That register would contain:

 * section,
 * name,
 * default value,
 * documentation,
 * state: (deprecated, experimental, etc)

==== direct benefit ====

 * an issue devel warning on access to undefined option. Catching bug from minor typo (eg: `ui.config('path',…)` vs `ui.config('paths',…)`)

 * have declaration/documentation checks also runs for out of core extensions,

 * it becomes less error prone to update an option default value,

 * makes it easier for extensions to change default value,

 * makes it easier to discover existing config and section when adding a new options,

==== sub-proposal: config renaming ====

We could have official "config alias". For example, let's say we could rename `ui.clonebundleprefers` to `clonebundle.preference`, we declare the rename in the central repository and on access, if `clonebundle.preference` is undefined, the old name is checked instead (possibly with a transformation).

That would come really handy in regard with experimental option as we could rename them without breaking existing users.

Having such feature would also allow a large cleanup on the existing config options to merge some related section together and to split some minor options out of the `[ui]` section.

In addition, we could also, decide on one form standard for config option "name" (as describe in the earlier part of the document) and rename all existing one to match our pick.

== Roadmap ==

 * (./) write official naming guideline for options
 * (./) implement a central declaration
 * (./) implement alias support
 * {X} migrate documentation and default config to the central declaration
 * {X} devel warning for non-existing/inconsistent access
 * {X} official way for extensions to overwrite default
 * {X} implement config "forwarding"
 * {X} reorganize existing sections,

== SeeAlso ==

 * [[UIGuideline#config]]
 
 * small patch to list all existing options: https://www.mercurial-scm.org/repo/users/marmoute/mercurial/rev/1696f686f616

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CategoryDeveloper CategoryNewFeatures