Patchwork help: document requirements

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Submitter Gregory Szorc
Date March 13, 2016, 3:16 a.m.
Message ID <e40a0987f6f96703a2c2.1457838963@ubuntu-vm-main>
Download mbox | patch
Permalink /patch/13850/
State Accepted
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Gregory Szorc - March 13, 2016, 3:16 a.m.
# HG changeset patch
# User Gregory Szorc <gregory.szorc@gmail.com>
# Date 1457837467 28800
#      Sat Mar 12 18:51:07 2016 -0800
# Node ID e40a0987f6f96703a2c2ead417757a36e790780e
# Parent  70c2f8a982766b512e9d7f41f2d93fdb92f5481f
help: document requirements

We didn't have unified documentation of the various repository
requirements. This patch changes that.
Katsunori FUJIWARA - March 13, 2016, 2:56 p.m.
At Sat, 12 Mar 2016 19:16:03 -0800,
Gregory Szorc wrote:
> 
> # HG changeset patch
> # User Gregory Szorc <gregory.szorc@gmail.com>
> # Date 1457837467 28800
> #      Sat Mar 12 18:51:07 2016 -0800
> # Node ID e40a0987f6f96703a2c2ead417757a36e790780e
> # Parent  70c2f8a982766b512e9d7f41f2d93fdb92f5481f
> help: document requirements
> 
> We didn't have unified documentation of the various repository
> requirements. This patch changes that.

Does not adding new help file into "help/internals" require changing
GUID "help.internals.guid" in guids.wxi ? (please ignore if I
misunderstand about Windows installer)

BTW, a tool (as a part of check-commit ?) to detect leaking of
required changes for wix files at adding/removing file is needed,
isn't it ? I've seen "newly added help can't be displayed" issue
sometime.


> diff --git a/contrib/wix/help.wxs b/contrib/wix/help.wxs
> --- a/contrib/wix/help.wxs
> +++ b/contrib/wix/help.wxs
> @@ -35,16 +35,17 @@
>            <File Name="templates.txt" />
>            <File Name="urls.txt" />
>          </Component>
>  
>          <Directory Id="help.internaldir" Name="internals">
>            <Component Id="help.internals" Guid="$(var.help.internals.guid)" Win64='$(var.IsX64)'>
>              <File Id="internals.bundles.txt"      Name="bundles.txt" KeyPath="yes" />
>              <File Id="internals.changegroups.txt" Name="changegroups.txt" />
> +            <File Id="internals.requirements.txt" Name="requirements.txt" />
>              <File Id="internals.revlogs.txt"      Name="revlogs.txt" />
>            </Component>
>          </Directory>
>  
>        </Directory>
>      </DirectoryRef>
>    </Fragment>
>  
> diff --git a/mercurial/help.py b/mercurial/help.py
> --- a/mercurial/help.py
> +++ b/mercurial/help.py
> @@ -183,16 +183,18 @@ def loaddoc(topic, subdir=None):
>  
>      return loader
>  
>  internalstable = sorted([
>      (['bundles'], _('container for exchange of repository data'),
>       loaddoc('bundles', subdir='internals')),
>      (['changegroups'], _('representation of revlog data'),
>       loaddoc('changegroups', subdir='internals')),
> +    (['requirements'], _('repository requirements'),
> +     loaddoc('requirements', subdir='internals')),
>      (['revlogs'], _('revision storage mechanism'),
>       loaddoc('revlogs', subdir='internals')),
>  ])
>  
>  def internalshelp(ui):
>      """Generate the index for the "internals" topic."""
>      lines = []
>      for names, header, doc in internalstable:
> diff --git a/mercurial/help/internals/requirements.txt b/mercurial/help/internals/requirements.txt
> new file mode 100644
> --- /dev/null
> +++ b/mercurial/help/internals/requirements.txt
> @@ -0,0 +1,110 @@
> +Requirements
> +============
> +
> +Repositories contain a file (``.hg/requires``) containing a list of
> +features/capabilities that are *required* for clients to interface
> +with the repository. This file has been present in Mercurial since
> +version 0.9.2 (released December 2006).
> +
> +One of the first things clients do when opening a repository is read
> +``.hg/requires`` and verify that all listed requirements are supported,
> +aborting if not. Requirements are therefore a strong mechanism to
> +prevent incompatible clients from reading from unknown repository
> +formats or even corrupting them by writing to them.
> +
> +Extensions may add requirements. When they do this, clients not running
> +an extension will be unable to read from repositories.
> +
> +The following sections describe the requirements defined by the
> +Mercurial core distribution.
> +
> +revlogv1
> +--------
> +
> +When present, revlogs are version 1 (RevlogNG). RevlogNG was introduced
> +in 2006. The ``revlogv1`` requirement has been enabled by default
> +since the ``requires`` file was introduced in Mercurial 0.9.2.
> +
> +If this requirement is not present, version 0 revlogs are assumed.
> +
> +store
> +-----
> +
> +The *store* repository layout should be used.
> +
> +This requirement has been enabled by default since the ``requires`` file
> +was introduced in Mercurial 0.9.2.
> +
> +fncache
> +-------
> +
> +The *fncache* repository layout should be used.
> +
> +The *fncache* layout hash encodes filenames with long paths and
> +encodes reserved filenames.
> +
> +This requirement is enabled by default when the *store* requirement is
> +enabled (which is the default behavior). It was introduced in Mercurial
> +1.1 (released December 2008).
> +
> +shared
> +------
> +
> +Denotes that the store for a repository is shared from another location
> +(defined by the ``.hg/sharedpath`` file).
> +
> +This requirement is set when a repository is created via :hg:`share`.
> +
> +The requirement was added in Mercurial 1.3 (released July 2009).
> +
> +dotencode
> +---------
> +
> +The *dotencode* repository layout should be used.
> +
> +The *dotencode* layout encodes the first period or space in filenames
> +to prevent issues on OS X and Windows.
> +
> +This requirement is enabled by default when the *store* requirement
> +is enabled (which is the default behavior). It was introduced in
> +Mercurial 1.7 (released November 2010).
> +
> +parentdelta
> +-----------
> +
> +Denotes a revlog delta encoding format that was experimental and
> +replaced by *generaldelta*. It should not be seen in the wild because
> +it was never enabled by default.
> +
> +This requirement was added in Mercurial 1.7 and removed in Mercurial
> +1.9.
> +
> +generaldelta
> +------------
> +
> +Revlogs should be created with the *generaldelta* flag enabled. The
> +generaldelta flag will cause deltas to be encoded against a parent
> +revision instead of the previous revision in the revlog.
> +
> +Support for this requirement was added in Mercurial 1.9 (released
> +July 2011). The requirement was disabled on new repositories by
> +default until Mercurial 3.7 (released February 2016).
> +
> +manifestv2
> +----------
> +
> +Denotes that version 2 of manifests are being used.
> +
> +Support for this requirement was added in Mercurial 3.4 (released
> +May 2015). The requirement is currently experimental and is disabled
> +by default.
> +
> +treemanifest
> +------------
> +
> +Denotes that tree manifests are being used. Tree manifests are
> +one manifest per directory (as opposed to a single flat manifest).
> +
> +Support for this requirement was added in Mercurial 3.4 (released
> +August 2015). The requirement is currently experimental and is
> +disabled by default.
> diff --git a/tests/test-help.t b/tests/test-help.t
> --- a/tests/test-help.t
> +++ b/tests/test-help.t
> @@ -870,16 +870,17 @@ Test list of internal help commands
>  internals topic renders index of available sub-topics
>  
>    $ hg help internals
>    Technical implementation topics
>    """""""""""""""""""""""""""""""
>    
>         bundles       container for exchange of repository data
>         changegroups  representation of revlog data
> +       requirements  repository requirements
>         revlogs       revision storage mechanism
>  
>  sub-topics can be accessed
>  
>    $ hg help internals.changegroups
>        Changegroups
>        ============
>    
> @@ -2722,16 +2723,23 @@ Sub-topic indexes rendered properly
>    <tr><td>
>    <a href="/help/internals.changegroups">
>    changegroups
>    </a>
>    </td><td>
>    representation of revlog data
>    </td></tr>
>    <tr><td>
> +  <a href="/help/internals.requirements">
> +  requirements
> +  </a>
> +  </td><td>
> +  repository requirements
> +  </td></tr>
> +  <tr><td>
>    <a href="/help/internals.revlogs">
>    revlogs
>    </a>
>    </td><td>
>    revision storage mechanism
>    </td></tr>
>    
>    
> _______________________________________________
> Mercurial-devel mailing list
> Mercurial-devel@mercurial-scm.org
> https://www.mercurial-scm.org/mailman/listinfo/mercurial-devel

----------------------------------------------------------------------
[FUJIWARA Katsunori]                             foozy@lares.dti.ne.jp
Gregory Szorc - March 13, 2016, 8:08 p.m.
On Sun, Mar 13, 2016 at 7:56 AM, FUJIWARA Katsunori <foozy@lares.dti.ne.jp>
wrote:

> At Sat, 12 Mar 2016 19:16:03 -0800,
> Gregory Szorc wrote:
> >
> > # HG changeset patch
> > # User Gregory Szorc <gregory.szorc@gmail.com>
> > # Date 1457837467 28800
> > #      Sat Mar 12 18:51:07 2016 -0800
> > # Node ID e40a0987f6f96703a2c2ead417757a36e790780e
> > # Parent  70c2f8a982766b512e9d7f41f2d93fdb92f5481f
> > help: document requirements
> >
> > We didn't have unified documentation of the various repository
> > requirements. This patch changes that.
>
> Does not adding new help file into "help/internals" require changing
> GUID "help.internals.guid" in guids.wxi ? (please ignore if I
> misunderstand about Windows installer)
>

I'm not sure. But the history of the wix files seems to indicate that it
does.


>
> BTW, a tool (as a part of check-commit ?) to detect leaking of
> required changes for wix files at adding/removing file is needed,
> isn't it ? I've seen "newly added help can't be displayed" issue
> sometime.
>
>
> > diff --git a/contrib/wix/help.wxs b/contrib/wix/help.wxs
> > --- a/contrib/wix/help.wxs
> > +++ b/contrib/wix/help.wxs
> > @@ -35,16 +35,17 @@
> >            <File Name="templates.txt" />
> >            <File Name="urls.txt" />
> >          </Component>
> >
> >          <Directory Id="help.internaldir" Name="internals">
> >            <Component Id="help.internals"
> Guid="$(var.help.internals.guid)" Win64='$(var.IsX64)'>
> >              <File Id="internals.bundles.txt"      Name="bundles.txt"
> KeyPath="yes" />
> >              <File Id="internals.changegroups.txt"
> Name="changegroups.txt" />
> > +            <File Id="internals.requirements.txt"
> Name="requirements.txt" />
> >              <File Id="internals.revlogs.txt"      Name="revlogs.txt" />
> >            </Component>
> >          </Directory>
> >
> >        </Directory>
> >      </DirectoryRef>
> >    </Fragment>
> >
> > diff --git a/mercurial/help.py b/mercurial/help.py
> > --- a/mercurial/help.py
> > +++ b/mercurial/help.py
> > @@ -183,16 +183,18 @@ def loaddoc(topic, subdir=None):
> >
> >      return loader
> >
> >  internalstable = sorted([
> >      (['bundles'], _('container for exchange of repository data'),
> >       loaddoc('bundles', subdir='internals')),
> >      (['changegroups'], _('representation of revlog data'),
> >       loaddoc('changegroups', subdir='internals')),
> > +    (['requirements'], _('repository requirements'),
> > +     loaddoc('requirements', subdir='internals')),
> >      (['revlogs'], _('revision storage mechanism'),
> >       loaddoc('revlogs', subdir='internals')),
> >  ])
> >
> >  def internalshelp(ui):
> >      """Generate the index for the "internals" topic."""
> >      lines = []
> >      for names, header, doc in internalstable:
> > diff --git a/mercurial/help/internals/requirements.txt
> b/mercurial/help/internals/requirements.txt
> > new file mode 100644
> > --- /dev/null
> > +++ b/mercurial/help/internals/requirements.txt
> > @@ -0,0 +1,110 @@
> > +Requirements
> > +============
> > +
> > +Repositories contain a file (``.hg/requires``) containing a list of
> > +features/capabilities that are *required* for clients to interface
> > +with the repository. This file has been present in Mercurial since
> > +version 0.9.2 (released December 2006).
> > +
> > +One of the first things clients do when opening a repository is read
> > +``.hg/requires`` and verify that all listed requirements are supported,
> > +aborting if not. Requirements are therefore a strong mechanism to
> > +prevent incompatible clients from reading from unknown repository
> > +formats or even corrupting them by writing to them.
> > +
> > +Extensions may add requirements. When they do this, clients not running
> > +an extension will be unable to read from repositories.
> > +
> > +The following sections describe the requirements defined by the
> > +Mercurial core distribution.
> > +
> > +revlogv1
> > +--------
> > +
> > +When present, revlogs are version 1 (RevlogNG). RevlogNG was introduced
> > +in 2006. The ``revlogv1`` requirement has been enabled by default
> > +since the ``requires`` file was introduced in Mercurial 0.9.2.
> > +
> > +If this requirement is not present, version 0 revlogs are assumed.
> > +
> > +store
> > +-----
> > +
> > +The *store* repository layout should be used.
> > +
> > +This requirement has been enabled by default since the ``requires`` file
> > +was introduced in Mercurial 0.9.2.
> > +
> > +fncache
> > +-------
> > +
> > +The *fncache* repository layout should be used.
> > +
> > +The *fncache* layout hash encodes filenames with long paths and
> > +encodes reserved filenames.
> > +
> > +This requirement is enabled by default when the *store* requirement is
> > +enabled (which is the default behavior). It was introduced in Mercurial
> > +1.1 (released December 2008).
> > +
> > +shared
> > +------
> > +
> > +Denotes that the store for a repository is shared from another location
> > +(defined by the ``.hg/sharedpath`` file).
> > +
> > +This requirement is set when a repository is created via :hg:`share`.
> > +
> > +The requirement was added in Mercurial 1.3 (released July 2009).
> > +
> > +dotencode
> > +---------
> > +
> > +The *dotencode* repository layout should be used.
> > +
> > +The *dotencode* layout encodes the first period or space in filenames
> > +to prevent issues on OS X and Windows.
> > +
> > +This requirement is enabled by default when the *store* requirement
> > +is enabled (which is the default behavior). It was introduced in
> > +Mercurial 1.7 (released November 2010).
> > +
> > +parentdelta
> > +-----------
> > +
> > +Denotes a revlog delta encoding format that was experimental and
> > +replaced by *generaldelta*. It should not be seen in the wild because
> > +it was never enabled by default.
> > +
> > +This requirement was added in Mercurial 1.7 and removed in Mercurial
> > +1.9.
> > +
> > +generaldelta
> > +------------
> > +
> > +Revlogs should be created with the *generaldelta* flag enabled. The
> > +generaldelta flag will cause deltas to be encoded against a parent
> > +revision instead of the previous revision in the revlog.
> > +
> > +Support for this requirement was added in Mercurial 1.9 (released
> > +July 2011). The requirement was disabled on new repositories by
> > +default until Mercurial 3.7 (released February 2016).
> > +
> > +manifestv2
> > +----------
> > +
> > +Denotes that version 2 of manifests are being used.
> > +
> > +Support for this requirement was added in Mercurial 3.4 (released
> > +May 2015). The requirement is currently experimental and is disabled
> > +by default.
> > +
> > +treemanifest
> > +------------
> > +
> > +Denotes that tree manifests are being used. Tree manifests are
> > +one manifest per directory (as opposed to a single flat manifest).
> > +
> > +Support for this requirement was added in Mercurial 3.4 (released
> > +August 2015). The requirement is currently experimental and is
> > +disabled by default.
> > diff --git a/tests/test-help.t b/tests/test-help.t
> > --- a/tests/test-help.t
> > +++ b/tests/test-help.t
> > @@ -870,16 +870,17 @@ Test list of internal help commands
> >  internals topic renders index of available sub-topics
> >
> >    $ hg help internals
> >    Technical implementation topics
> >    """""""""""""""""""""""""""""""
> >
> >         bundles       container for exchange of repository data
> >         changegroups  representation of revlog data
> > +       requirements  repository requirements
> >         revlogs       revision storage mechanism
> >
> >  sub-topics can be accessed
> >
> >    $ hg help internals.changegroups
> >        Changegroups
> >        ============
> >
> > @@ -2722,16 +2723,23 @@ Sub-topic indexes rendered properly
> >    <tr><td>
> >    <a href="/help/internals.changegroups">
> >    changegroups
> >    </a>
> >    </td><td>
> >    representation of revlog data
> >    </td></tr>
> >    <tr><td>
> > +  <a href="/help/internals.requirements">
> > +  requirements
> > +  </a>
> > +  </td><td>
> > +  repository requirements
> > +  </td></tr>
> > +  <tr><td>
> >    <a href="/help/internals.revlogs">
> >    revlogs
> >    </a>
> >    </td><td>
> >    revision storage mechanism
> >    </td></tr>
> >
> >
> > _______________________________________________
> > Mercurial-devel mailing list
> > Mercurial-devel@mercurial-scm.org
> > https://www.mercurial-scm.org/mailman/listinfo/mercurial-devel
>
> ----------------------------------------------------------------------
> [FUJIWARA Katsunori]                             foozy@lares.dti.ne.jp
>
Yuya Nishihara - March 14, 2016, 2:45 p.m.
On Sun, 13 Mar 2016 13:08:20 -0700, Gregory Szorc wrote:
> On Sun, Mar 13, 2016 at 7:56 AM, FUJIWARA Katsunori <foozy@lares.dti.ne.jp>
> wrote:
> > At Sat, 12 Mar 2016 19:16:03 -0800,
> > Gregory Szorc wrote:
> > >
> > > # HG changeset patch
> > > # User Gregory Szorc <gregory.szorc@gmail.com>
> > > # Date 1457837467 28800
> > > #      Sat Mar 12 18:51:07 2016 -0800
> > > # Node ID e40a0987f6f96703a2c2ead417757a36e790780e
> > > # Parent  70c2f8a982766b512e9d7f41f2d93fdb92f5481f
> > > help: document requirements
> > >
> > > We didn't have unified documentation of the various repository
> > > requirements. This patch changes that.
> >
> > Does not adding new help file into "help/internals" require changing
> > GUID "help.internals.guid" in guids.wxi ? (please ignore if I
> > misunderstand about Windows installer)
> 
> I'm not sure. But the history of the wix files seems to indicate that it
> does.

(CC+ Steve)

Last time I changed the content of <Component/>, Steve said it wasn't necessary
to change the GUID. So this would be the same.

https://groups.google.com/d/msg/thg-dev/JWw1m-uw4SU/KSeYWwxyCAAJ
Augie Fackler - March 14, 2016, 6:26 p.m.
On Sat, Mar 12, 2016 at 07:16:03PM -0800, Gregory Szorc wrote:
> # HG changeset patch
> # User Gregory Szorc <gregory.szorc@gmail.com>
> # Date 1457837467 28800
> #      Sat Mar 12 18:51:07 2016 -0800
> # Node ID e40a0987f6f96703a2c2ead417757a36e790780e
> # Parent  70c2f8a982766b512e9d7f41f2d93fdb92f5481f
> help: document requirements

Queued this, please send any windows installer business as a follow-up. Thanks!

>
> We didn't have unified documentation of the various repository
> requirements. This patch changes that.
>
> diff --git a/contrib/wix/help.wxs b/contrib/wix/help.wxs
> --- a/contrib/wix/help.wxs
> +++ b/contrib/wix/help.wxs
> @@ -35,16 +35,17 @@
>            <File Name="templates.txt" />
>            <File Name="urls.txt" />
>          </Component>
>
>          <Directory Id="help.internaldir" Name="internals">
>            <Component Id="help.internals" Guid="$(var.help.internals.guid)" Win64='$(var.IsX64)'>
>              <File Id="internals.bundles.txt"      Name="bundles.txt" KeyPath="yes" />
>              <File Id="internals.changegroups.txt" Name="changegroups.txt" />
> +            <File Id="internals.requirements.txt" Name="requirements.txt" />
>              <File Id="internals.revlogs.txt"      Name="revlogs.txt" />
>            </Component>
>          </Directory>
>
>        </Directory>
>      </DirectoryRef>
>    </Fragment>
>
> diff --git a/mercurial/help.py b/mercurial/help.py
> --- a/mercurial/help.py
> +++ b/mercurial/help.py
> @@ -183,16 +183,18 @@ def loaddoc(topic, subdir=None):
>
>      return loader
>
>  internalstable = sorted([
>      (['bundles'], _('container for exchange of repository data'),
>       loaddoc('bundles', subdir='internals')),
>      (['changegroups'], _('representation of revlog data'),
>       loaddoc('changegroups', subdir='internals')),
> +    (['requirements'], _('repository requirements'),
> +     loaddoc('requirements', subdir='internals')),
>      (['revlogs'], _('revision storage mechanism'),
>       loaddoc('revlogs', subdir='internals')),
>  ])
>
>  def internalshelp(ui):
>      """Generate the index for the "internals" topic."""
>      lines = []
>      for names, header, doc in internalstable:
> diff --git a/mercurial/help/internals/requirements.txt b/mercurial/help/internals/requirements.txt
> new file mode 100644
> --- /dev/null
> +++ b/mercurial/help/internals/requirements.txt
> @@ -0,0 +1,110 @@
> +Requirements
> +============
> +
> +Repositories contain a file (``.hg/requires``) containing a list of
> +features/capabilities that are *required* for clients to interface
> +with the repository. This file has been present in Mercurial since
> +version 0.9.2 (released December 2006).
> +
> +One of the first things clients do when opening a repository is read
> +``.hg/requires`` and verify that all listed requirements are supported,
> +aborting if not. Requirements are therefore a strong mechanism to
> +prevent incompatible clients from reading from unknown repository
> +formats or even corrupting them by writing to them.
> +
> +Extensions may add requirements. When they do this, clients not running
> +an extension will be unable to read from repositories.
> +
> +The following sections describe the requirements defined by the
> +Mercurial core distribution.
> +
> +revlogv1
> +--------
> +
> +When present, revlogs are version 1 (RevlogNG). RevlogNG was introduced
> +in 2006. The ``revlogv1`` requirement has been enabled by default
> +since the ``requires`` file was introduced in Mercurial 0.9.2.
> +
> +If this requirement is not present, version 0 revlogs are assumed.
> +
> +store
> +-----
> +
> +The *store* repository layout should be used.
> +
> +This requirement has been enabled by default since the ``requires`` file
> +was introduced in Mercurial 0.9.2.
> +
> +fncache
> +-------
> +
> +The *fncache* repository layout should be used.
> +
> +The *fncache* layout hash encodes filenames with long paths and
> +encodes reserved filenames.
> +
> +This requirement is enabled by default when the *store* requirement is
> +enabled (which is the default behavior). It was introduced in Mercurial
> +1.1 (released December 2008).
> +
> +shared
> +------
> +
> +Denotes that the store for a repository is shared from another location
> +(defined by the ``.hg/sharedpath`` file).
> +
> +This requirement is set when a repository is created via :hg:`share`.
> +
> +The requirement was added in Mercurial 1.3 (released July 2009).
> +
> +dotencode
> +---------
> +
> +The *dotencode* repository layout should be used.
> +
> +The *dotencode* layout encodes the first period or space in filenames
> +to prevent issues on OS X and Windows.
> +
> +This requirement is enabled by default when the *store* requirement
> +is enabled (which is the default behavior). It was introduced in
> +Mercurial 1.7 (released November 2010).
> +
> +parentdelta
> +-----------
> +
> +Denotes a revlog delta encoding format that was experimental and
> +replaced by *generaldelta*. It should not be seen in the wild because
> +it was never enabled by default.
> +
> +This requirement was added in Mercurial 1.7 and removed in Mercurial
> +1.9.
> +
> +generaldelta
> +------------
> +
> +Revlogs should be created with the *generaldelta* flag enabled. The
> +generaldelta flag will cause deltas to be encoded against a parent
> +revision instead of the previous revision in the revlog.
> +
> +Support for this requirement was added in Mercurial 1.9 (released
> +July 2011). The requirement was disabled on new repositories by
> +default until Mercurial 3.7 (released February 2016).
> +
> +manifestv2
> +----------
> +
> +Denotes that version 2 of manifests are being used.
> +
> +Support for this requirement was added in Mercurial 3.4 (released
> +May 2015). The requirement is currently experimental and is disabled
> +by default.
> +
> +treemanifest
> +------------
> +
> +Denotes that tree manifests are being used. Tree manifests are
> +one manifest per directory (as opposed to a single flat manifest).
> +
> +Support for this requirement was added in Mercurial 3.4 (released
> +August 2015). The requirement is currently experimental and is
> +disabled by default.
> diff --git a/tests/test-help.t b/tests/test-help.t
> --- a/tests/test-help.t
> +++ b/tests/test-help.t
> @@ -870,16 +870,17 @@ Test list of internal help commands
>  internals topic renders index of available sub-topics
>
>    $ hg help internals
>    Technical implementation topics
>    """""""""""""""""""""""""""""""
>
>         bundles       container for exchange of repository data
>         changegroups  representation of revlog data
> +       requirements  repository requirements
>         revlogs       revision storage mechanism
>
>  sub-topics can be accessed
>
>    $ hg help internals.changegroups
>        Changegroups
>        ============
>
> @@ -2722,16 +2723,23 @@ Sub-topic indexes rendered properly
>    <tr><td>
>    <a href="/help/internals.changegroups">
>    changegroups
>    </a>
>    </td><td>
>    representation of revlog data
>    </td></tr>
>    <tr><td>
> +  <a href="/help/internals.requirements">
> +  requirements
> +  </a>
> +  </td><td>
> +  repository requirements
> +  </td></tr>
> +  <tr><td>
>    <a href="/help/internals.revlogs">
>    revlogs
>    </a>
>    </td><td>
>    revision storage mechanism
>    </td></tr>
>
>
> _______________________________________________
> Mercurial-devel mailing list
> Mercurial-devel@mercurial-scm.org
> https://www.mercurial-scm.org/mailman/listinfo/mercurial-devel

Patch

diff --git a/contrib/wix/help.wxs b/contrib/wix/help.wxs
--- a/contrib/wix/help.wxs
+++ b/contrib/wix/help.wxs
@@ -35,16 +35,17 @@ 
           <File Name="templates.txt" />
           <File Name="urls.txt" />
         </Component>
 
         <Directory Id="help.internaldir" Name="internals">
           <Component Id="help.internals" Guid="$(var.help.internals.guid)" Win64='$(var.IsX64)'>
             <File Id="internals.bundles.txt"      Name="bundles.txt" KeyPath="yes" />
             <File Id="internals.changegroups.txt" Name="changegroups.txt" />
+            <File Id="internals.requirements.txt" Name="requirements.txt" />
             <File Id="internals.revlogs.txt"      Name="revlogs.txt" />
           </Component>
         </Directory>
 
       </Directory>
     </DirectoryRef>
   </Fragment>
 
diff --git a/mercurial/help.py b/mercurial/help.py
--- a/mercurial/help.py
+++ b/mercurial/help.py
@@ -183,16 +183,18 @@  def loaddoc(topic, subdir=None):
 
     return loader
 
 internalstable = sorted([
     (['bundles'], _('container for exchange of repository data'),
      loaddoc('bundles', subdir='internals')),
     (['changegroups'], _('representation of revlog data'),
      loaddoc('changegroups', subdir='internals')),
+    (['requirements'], _('repository requirements'),
+     loaddoc('requirements', subdir='internals')),
     (['revlogs'], _('revision storage mechanism'),
      loaddoc('revlogs', subdir='internals')),
 ])
 
 def internalshelp(ui):
     """Generate the index for the "internals" topic."""
     lines = []
     for names, header, doc in internalstable:
diff --git a/mercurial/help/internals/requirements.txt b/mercurial/help/internals/requirements.txt
new file mode 100644
--- /dev/null
+++ b/mercurial/help/internals/requirements.txt
@@ -0,0 +1,110 @@ 
+Requirements
+============
+
+Repositories contain a file (``.hg/requires``) containing a list of
+features/capabilities that are *required* for clients to interface
+with the repository. This file has been present in Mercurial since
+version 0.9.2 (released December 2006).
+
+One of the first things clients do when opening a repository is read
+``.hg/requires`` and verify that all listed requirements are supported,
+aborting if not. Requirements are therefore a strong mechanism to
+prevent incompatible clients from reading from unknown repository
+formats or even corrupting them by writing to them.
+
+Extensions may add requirements. When they do this, clients not running
+an extension will be unable to read from repositories.
+
+The following sections describe the requirements defined by the
+Mercurial core distribution.
+
+revlogv1
+--------
+
+When present, revlogs are version 1 (RevlogNG). RevlogNG was introduced
+in 2006. The ``revlogv1`` requirement has been enabled by default
+since the ``requires`` file was introduced in Mercurial 0.9.2.
+
+If this requirement is not present, version 0 revlogs are assumed.
+
+store
+-----
+
+The *store* repository layout should be used.
+
+This requirement has been enabled by default since the ``requires`` file
+was introduced in Mercurial 0.9.2.
+
+fncache
+-------
+
+The *fncache* repository layout should be used.
+
+The *fncache* layout hash encodes filenames with long paths and
+encodes reserved filenames.
+
+This requirement is enabled by default when the *store* requirement is
+enabled (which is the default behavior). It was introduced in Mercurial
+1.1 (released December 2008).
+
+shared
+------
+
+Denotes that the store for a repository is shared from another location
+(defined by the ``.hg/sharedpath`` file).
+
+This requirement is set when a repository is created via :hg:`share`.
+
+The requirement was added in Mercurial 1.3 (released July 2009).
+
+dotencode
+---------
+
+The *dotencode* repository layout should be used.
+
+The *dotencode* layout encodes the first period or space in filenames
+to prevent issues on OS X and Windows.
+
+This requirement is enabled by default when the *store* requirement
+is enabled (which is the default behavior). It was introduced in
+Mercurial 1.7 (released November 2010).
+
+parentdelta
+-----------
+
+Denotes a revlog delta encoding format that was experimental and
+replaced by *generaldelta*. It should not be seen in the wild because
+it was never enabled by default.
+
+This requirement was added in Mercurial 1.7 and removed in Mercurial
+1.9.
+
+generaldelta
+------------
+
+Revlogs should be created with the *generaldelta* flag enabled. The
+generaldelta flag will cause deltas to be encoded against a parent
+revision instead of the previous revision in the revlog.
+
+Support for this requirement was added in Mercurial 1.9 (released
+July 2011). The requirement was disabled on new repositories by
+default until Mercurial 3.7 (released February 2016).
+
+manifestv2
+----------
+
+Denotes that version 2 of manifests are being used.
+
+Support for this requirement was added in Mercurial 3.4 (released
+May 2015). The requirement is currently experimental and is disabled
+by default.
+
+treemanifest
+------------
+
+Denotes that tree manifests are being used. Tree manifests are
+one manifest per directory (as opposed to a single flat manifest).
+
+Support for this requirement was added in Mercurial 3.4 (released
+August 2015). The requirement is currently experimental and is
+disabled by default.
diff --git a/tests/test-help.t b/tests/test-help.t
--- a/tests/test-help.t
+++ b/tests/test-help.t
@@ -870,16 +870,17 @@  Test list of internal help commands
 internals topic renders index of available sub-topics
 
   $ hg help internals
   Technical implementation topics
   """""""""""""""""""""""""""""""
   
        bundles       container for exchange of repository data
        changegroups  representation of revlog data
+       requirements  repository requirements
        revlogs       revision storage mechanism
 
 sub-topics can be accessed
 
   $ hg help internals.changegroups
       Changegroups
       ============
   
@@ -2722,16 +2723,23 @@  Sub-topic indexes rendered properly
   <tr><td>
   <a href="/help/internals.changegroups">
   changegroups
   </a>
   </td><td>
   representation of revlog data
   </td></tr>
   <tr><td>
+  <a href="/help/internals.requirements">
+  requirements
+  </a>
+  </td><td>
+  repository requirements
+  </td></tr>
+  <tr><td>
   <a href="/help/internals.revlogs">
   revlogs
   </a>
   </td><td>
   revision storage mechanism
   </td></tr>