help: add "internals" topic

We introduce the "internals" help topic, which renders an index of
available sub-topics. The sub-topics themselves are still not
reachable via the help system.

mercurial/help.py

@@ -161,6 +161,21 b' 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')),
+])
+
+def internalshelp(ui):
+    """Generate the index for the "internals" topic."""
+    lines = []
+    for names, header, doc in internalstable:
+        lines.append(' :%s: %s' % (names[0], header))
+
+    return '\n'.join(lines)
+
 helptable = sorted([
     (["config", "hgrc"], _("Configuration Files"), loaddoc('config')),
     (["dates"], _("Date Formats"), loaddoc('dates')),
@@ -187,6 +202,8 b' helptable = sorted(['
     (["phases"], _("Working with Phases"), loaddoc('phases')),
     (['scripting'], _('Using Mercurial from scripts and automation'),
      loaddoc('scripting')),
+    (['internals'], _("Technical implementation topics"),
+     internalshelp),
 ])
 
 # Map topics to lists of callable taking the current topic help and

tests/test-globalopts.t

@@ -349,6 +349,7 b' Testing -h/--help:'
    glossary      Glossary
    hgignore      Syntax for Mercurial Ignore Files
    hgweb         Configuring hgweb
+   internals     Technical implementation topics
    merge-tools   Merge Tools
    multirevs     Specifying Multiple Revisions
    patterns      File Name Patterns
@@ -431,6 +432,7 b' Testing -h/--help:'
    glossary      Glossary
    hgignore      Syntax for Mercurial Ignore Files
    hgweb         Configuring hgweb
+   internals     Technical implementation topics
    merge-tools   Merge Tools
    multirevs     Specifying Multiple Revisions
    patterns      File Name Patterns

tests/test-help.t

@@ -111,6 +111,7 b' Short help:'
    glossary      Glossary
    hgignore      Syntax for Mercurial Ignore Files
    hgweb         Configuring hgweb
+   internals     Technical implementation topics
    merge-tools   Merge Tools
    multirevs     Specifying Multiple Revisions
    patterns      File Name Patterns
@@ -187,6 +188,7 b' Short help:'
    glossary      Glossary
    hgignore      Syntax for Mercurial Ignore Files
    hgweb         Configuring hgweb
+   internals     Technical implementation topics
    merge-tools   Merge Tools
    multirevs     Specifying Multiple Revisions
    patterns      File Name Patterns
@@ -773,6 +775,7 b' Test that default list of commands omits'
    glossary      Glossary
    hgignore      Syntax for Mercurial Ignore Files
    hgweb         Configuring hgweb
+   internals     Technical implementation topics
    merge-tools   Merge Tools
    multirevs     Specifying Multiple Revisions
    patterns      File Name Patterns
@@ -862,6 +865,14 b' Test list of internal help commands'
   
   (use "hg help -v debug" to show built-in aliases and global options)
 
+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
 
 Test list of commands with command with no help text
 
@@ -1530,6 +1541,13 b' Dish up an empty repo; serve it cold.'
   Configuring hgweb
   </td></tr>
   <tr><td>
+  <a href="/help/internals">
+  internals
+  </a>
+  </td><td>
+  Technical implementation topics
+  </td></tr>
+  <tr><td>
   <a href="/help/merge-tools">
   merge-tools
   </a>

tests/test-hgweb-json.t

@@ -1062,6 +1062,10 b' help/ shows help topics'
         "topic": "hgweb"
       },
       {
+        "summary": "Technical implementation topics",
+        "topic": "internals"
+      },
+      {
         "summary": "Merge Tools",
         "topic": "merge-tools"
       },