README_REPOSITORY
author wenzelm
Sun Nov 30 14:43:29 2008 +0100 (2008-11-30)
changeset 28917 20f43e0e0958
parent 28913 86ed1c86e0ef
child 28918 eda3d9976ec7
permissions -rw-r--r--
tuned;
     1 Important notes on Mercurial repository access for Isabelle
     2 ===========================================================
     3 
     4 Preamble
     5 --------
     6 
     7 Mercurial http://www.selenic.com/mercurial belongs to a new generation
     8 of source code management systems, following the paradigm of
     9 "distributed version control".  Compared to the old centralized model
    10 of CVS or SVN, this gives considerable more power and freedom in
    11 organizing the flow of changes, both between individual developers and
    12 designated pull/push areas that are shared with others.
    13 
    14 More power for the user also means more responsibility!  Due to its
    15 decentralized nature, changesets that have been published once,
    16 e.g. via "push" to a shared repository that is visible on the net,
    17 cannot be easily retracted from the public again.  Regular Mercurial
    18 operations are strictly monotonic, where changset transactions are
    19 only added, but never deleted.  There are special tools to manipulate
    20 individual repositories via non-monotonic actions, but this does not
    21 yet retrieve any changesets that have escaped into the public by
    22 accident.
    23 
    24 Only global operations like "pull" / "push", "unbundle" / "bundle"
    25 etc. fall into this critical category.  Note that "incoming" /
    26 "outgoing" allow to inspect changesets before exchanging them
    27 globally.  Anything else in Mercurial is local to the user's
    28 repository clone (including "commit", "update", "merge" etc.) and is
    29 in fact much simpler and safer to use than the corresponding
    30 operations of CVS or SVN.
    31 
    32 
    33 Initial configuration
    34 =====================
    35 
    36 Always use Mercurial version 1.0 or later, such as 1.0.1 or 1.0.2.
    37 The old 0.9.x versions do not work in a multi-user environment with
    38 shared file spaces.
    39 
    40 
    41 The official Isabelle repository can be cloned like this:
    42 
    43   hg clone http://isabelle.in.tum.de/repos/isabelle
    44 
    45 This will create a local directory "isabelle", unless an alternative
    46 name is specified.  The full repository meta-data and history of
    47 changes is in isabelle/.hg; local configuration for this clone can be
    48 added to isabelle/.hg/hgrc, but note that hgrc files are never copied
    49 by another clone operation!
    50 
    51 
    52 There is also $HOME/.hgrc for per-user Mercurial configuration.  The
    53 initial configuration should include at least an entry to identify
    54 yourself.  For example, something like this in /home/wenzelm/.hgrc:
    55 
    56   [ui]
    57   username = wenzelm
    58 
    59 Of course, the user identity can be also configured in
    60 isabelle/.hg/hgrc on per-repitory basis.  Failing to specify the
    61 username correctly makes the system invent funny machine names that
    62 may persist indefinitely in the public flow of changesets.
    63 
    64 In principle, user names can be chosen freely, but for longterm
    65 committers of the Isabelle repository the obvious choice is to keep
    66 with the old CVS naming scheme.
    67 
    68 
    69 There are other useful configuration to go into $HOME/.hgrc,
    70 e.g. defaults for common commands:
    71 
    72   [defaults]
    73   log = -l 10
    74 
    75 The next example shows how to install some Mercurial extension:
    76 
    77   [extensions]
    78   hgext.graphlog =
    79 
    80 Now the additional glog command will be available.
    81 
    82 
    83 See also the fine documentation for further details, especially the
    84 book http://hgbook.red-bean.com/
    85 
    86 
    87 Shared pull/push access
    88 =======================
    89 
    90 The entry point http://isabelle.in.tum.de/repos/isabelle is world
    91 readable, both via plain web browsing and the hg client as described
    92 above.  Anybody can produce a clone, change it arbitrarily, and then
    93 use regular mechanisms of Mercurial to report changes upstream, say
    94 via e-mail to someone with write access to that file space.  It is
    95 also quite easy to publish changed clones again on the web, using the
    96 adhoc command "hg serve -v", or the hgweb.cgi or hgwebdir.cgi scripts
    97 that are included in the Mercurial distribution.
    98 
    99 The downstream/upstream mode of operation is quite common in the
   100 distributed version control community, and works well for occasional
   101 changes produced by anybody out there.  Of course, upstream
   102 maintainers need to review and moderate changes being proposed, before
   103 pushing anything onto the official Isabelle repository at TUM.
   104 
   105 
   106 Write access to the Isabelle repository requires an account at TUM,
   107 with properly configured ssh access to the local machines
   108 (e.g. macbroy20, atbroy100).  You also need to be a member of the
   109 "isabelle" Unix group.
   110 
   111 Sharing a locally modified clone then works as follows, using your
   112 user name instead of "wenzelm":
   113 
   114   hg out ssh://wenzelm@atbroy100//home/isabelle-repository/repos/isabelle
   115 
   116 In fact, the "out" or "outgoing" command performs only a dry run: it
   117 displays the changesets that would get published.  An actual "push",
   118 with a lasting effect on the Isabelle repository, works like this:
   119 
   120   hg push ssh://wenzelm@atbroy100//home/isabelle-repository/repos/isabelle
   121 
   122 
   123 Default paths for push and pull can be configure in isabelle/.hg/hgrc,
   124 for example:
   125 
   126   [paths]
   127   default = ssh://wenzelm@atbroy100//home/isabelle-repository/repos/isabelle
   128 
   129 Now "hg pull" or "hg push" will use that shared file space, unless a
   130 different URL is specified explicitly.
   131 
   132 When cloning a repository, the default path is set to the initial
   133 source URL.  So we could have cloned via that ssh URL in the first
   134 place, to get exactly to the same point:
   135 
   136   hg clone ssh://wenzelm@atbroy100//home/isabelle-repository/repos/isabelle
   137 
   138 
   139 Content discipline
   140 ==================
   141 
   142 Old-style centralized version control is occasionally compared to "a
   143 library where everybody scribbles into the books".  Or seen the other
   144 way round, the centralized model discourages individual
   145 experimentation (with local branches etc.), because everything is
   146 forced to happen on a shared file space.  With Mercurial, arbitrary
   147 variations on local clones are no problem, but care is required again
   148 when publishing changes eventually.
   149 
   150 The following principles should be kept in mind when producing
   151 changesets that might become public at some point.
   152 
   153   * The author of changes should be properly identified, using
   154     ui/username configuration as described above.
   155 
   156     While Mercurial also provides means for signed changesets, we want
   157     to keep things simple and trust that users specify their identity
   158     correctly.
   159 
   160   * The history of sources is an integral part of the sources
   161     themselves.  This means that private experiments and branches
   162     should not be published, unless they are really meant to become
   163     universally available.
   164 
   165     Note that exchanging local experiments with some other users can
   166     be done directly on peer-to-peer basis, without affecting the
   167     central pull/push area.
   168 
   169   * Log messages are an integral part of the history of sources.
   170     Other users will have to look there eventually, to understand why
   171     things have been done in a certain way at some point.
   172 
   173     Mercurial provides nice web presentation of incoming changes with
   174     a digest of log entries; this also includes RSS/Atom news feeds.
   175     Users should be aware that others will actually read what is
   176     written into log messages.
   177 
   178     The usual changelog presentation style for the Isabelle repository
   179     admits log entries that consist of several lines, but without the
   180     special headline that is used in Mercurial projects elsewhere.
   181     Since some display styles strip newlines from text, it is
   182     advisable to separate lines via punctuation, and not rely on
   183     two-dimensional presentation too much.
   184 
   185 
   186 Building Isabelle from the repository version
   187 =============================================
   188 
   189 Compared to a proper distribution or development snapshot, a
   190 repository version of Isabelle lacks textual version identifiers in
   191 some sources and scripts, and various components produced by
   192 Admin/build are missing.  After applying that script with suitable
   193 arguments, the regular user instructions for building and running
   194 Isabelle from sources apply.
   195 
   196 Needless to say, the results from the build process must not be added
   197 to the repository!
   198 
   199 
   200 Makarius 30-Nov-2008