help: allow commands to be hidden

This is useful in enterprise environments where some workflows are
discouraged.

Differential Revision: https://phab.mercurial-scm.org/D5076

tests/test-help-hide.t

@@ -0,0 +1,127 b''
+Test hiding some commands (which also happens to hide an entire category).
+
+  $ hg --config help.hidden-command.clone=true \
+  > --config help.hidden-command.init=true help
+  Mercurial Distributed SCM
+  
+  list of commands:
+  
+  Remote repository management:
+  
+   incoming      show new changesets found in source
+   outgoing      show changesets not found in the destination
+   paths         show aliases for remote repositories
+   pull          pull changes from the specified source
+   push          push changes to the specified destination
+   serve         start stand-alone webserver
+  
+  Change creation:
+  
+   commit        commit the specified files or all outstanding changes
+  
+  Change manipulation:
+  
+   backout       reverse effect of earlier changeset
+   graft         copy changes from other branches onto the current branch
+   merge         merge another revision into working directory
+  
+  Change organization:
+  
+   bookmarks     create a new bookmark or list existing bookmarks
+   branch        set or show the current branch name
+   branches      list repository named branches
+   phase         set or show the current phase name
+   tag           add one or more tags for the current or given revision
+   tags          list repository tags
+  
+  File content management:
+  
+   annotate      show changeset information by line for each file
+   cat           output the current or given revision of files
+   copy          mark files as copied for the next commit
+   diff          diff repository (or selected files)
+   grep          search revision history for a pattern in specified files
+  
+  Change navigation:
+  
+   bisect        subdivision search of changesets
+   heads         show branch heads
+   identify      identify the working directory or specified revision
+   log           show revision history of entire repository or files
+  
+  Working directory management:
+  
+   add           add the specified files on the next commit
+   addremove     add all new files, delete all missing files
+   files         list tracked files
+   forget        forget the specified files on the next commit
+   remove        remove the specified files on the next commit
+   rename        rename files; equivalent of copy + remove
+   resolve       redo merges or set/view the merge status of files
+   revert        restore files to their checkout state
+   root          print the root (top) of the current working directory
+   status        show changed files in the working directory
+   summary       summarize working directory state
+   update        update working directory (or switch revisions)
+  
+  Change import/export:
+  
+   archive       create an unversioned archive of a repository revision
+   bundle        create a bundle file
+   export        dump the header and diffs for one or more changesets
+   import        import an ordered set of patches
+   unbundle      apply one or more bundle files
+  
+  Repository maintenance:
+  
+   manifest      output the current or given revision of the project manifest
+   recover       roll back an interrupted transaction
+   verify        verify the integrity of the repository
+  
+  Help:
+  
+   config        show combined config settings from all hgrc files
+   help          show help for a given topic or a help overview
+   version       output version and copyright information
+  
+  additional help topics:
+  
+  Mercurial identifiers:
+  
+   filesets      Specifying File Sets
+   hgignore      Syntax for Mercurial Ignore Files
+   patterns      File Name Patterns
+   revisions     Specifying Revisions
+   urls          URL Paths
+  
+  Mercurial output:
+  
+   color         Colorizing Outputs
+   dates         Date Formats
+   diffs         Diff Formats
+   templating    Template Usage
+  
+  Mercurial configuration:
+  
+   config        Configuration Files
+   environment   Environment Variables
+   extensions    Using Additional Features
+   flags         Command-line flags
+   hgweb         Configuring hgweb
+   merge-tools   Merge Tools
+   pager         Pager Support
+  
+  Concepts:
+  
+   bundlespec    Bundle File Formats
+   glossary      Glossary
+   phases        Working with Phases
+   subrepos      Subrepositories
+  
+  Miscellaneous:
+  
+   deprecated    Deprecated Features
+   internals     Technical implementation topics
+   scripting     Using Mercurial from scripts and automation
+  
+  (use 'hg help -v' to show built-in aliases and global options)

mercurial/configitems.py

@@ -699,6 +699,10 b" coreconfigitem('fsmonitor', 'warn_when_u"
 coreconfigitem('fsmonitor', 'warn_update_file_count',
     default=50000,
 )
+coreconfigitem('help', 'hidden-command\..*',
+    default=False,
+    generic=True,
+)
 coreconfigitem('hooks', '.*',
     default=dynamicdefault,
     generic=True,

mercurial/help.py

@@ -194,6 +194,8 b' def filtercmd(ui, cmd, kw, doc):'
         return True
     if not ui.verbose and doc and any(w in doc for w in _exclkeywords):
         return True
+    if ui.configbool('help', 'hidden-command.%s' % cmd):
+        return True
     return False
 
 def topicmatch(ui, commands, kw):