README_REPOSITORY
author wenzelm
Sun Nov 30 15:03:47 2008 +0100 (2008-11-30)
changeset 28918 eda3d9976ec7
parent 28917 20f43e0e0958
child 29481 3e8420c1124a
permissions -rw-r--r--
fixed spelling;
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" and "push" fall into this critical
    25 category.  Note that "incoming" / "outgoing" allow to inspect
    26 changesets before exchanging them globally.  Anything else in
    27 Mercurial is local to the user's repository clone (including "commit",
    28 "update", "merge" etc.) and is in fact much simpler and safer to use
    29 than the corresponding operations of CVS or SVN.
    30 
    31 
    32 Initial configuration
    33 =====================
    34 
    35 Always use Mercurial version 1.0 or later, such as 1.0.1 or 1.0.2.
    36 The old 0.9.x versions do not work in a multi-user environment with
    37 shared file spaces.
    38 
    39 
    40 The official Isabelle repository can be cloned like this:
    41 
    42   hg clone http://isabelle.in.tum.de/repos/isabelle
    43 
    44 This will create a local directory "isabelle", unless an alternative
    45 name is specified.  The full repository meta-data and history of
    46 changes is in isabelle/.hg; local configuration for this clone can be
    47 added to isabelle/.hg/hgrc, but note that hgrc files are never copied
    48 by another clone operation!
    49 
    50 
    51 There is also $HOME/.hgrc for per-user Mercurial configuration.  The
    52 initial configuration should include at least an entry to identify
    53 yourself.  For example, something like this in /home/wenzelm/.hgrc:
    54 
    55   [ui]
    56   username = wenzelm
    57 
    58 Of course, the user identity can be also configured in
    59 isabelle/.hg/hgrc on per-repository basis.  Failing to specify the
    60 username correctly makes the system invent funny machine names that
    61 may persist indefinitely in the public flow of changesets.
    62 
    63 In principle, user names can be chosen freely, but for longterm
    64 committers of the Isabelle repository the obvious choice is to keep
    65 with the old CVS naming scheme.
    66 
    67 
    68 There are other useful configuration to go into $HOME/.hgrc,
    69 e.g. defaults for common commands:
    70 
    71   [defaults]
    72   log = -l 10
    73 
    74 The next example shows how to install some Mercurial extension:
    75 
    76   [extensions]
    77   hgext.graphlog =
    78 
    79 Now the additional glog command will be available.
    80 
    81 
    82 See also the fine documentation for further details, especially the
    83 book http://hgbook.red-bean.com/
    84 
    85 
    86 Shared pull/push access
    87 =======================
    88 
    89 The entry point http://isabelle.in.tum.de/repos/isabelle is world
    90 readable, both via plain web browsing and the hg client as described
    91 above.  Anybody can produce a clone, change it arbitrarily, and then
    92 use regular mechanisms of Mercurial to report changes upstream, say
    93 via e-mail to someone with write access to that file space.  It is
    94 also quite easy to publish changed clones again on the web, using the
    95 adhoc command "hg serve -v", or the hgweb.cgi or hgwebdir.cgi scripts
    96 that are included in the Mercurial distribution.
    97 
    98 The downstream/upstream mode of operation is quite common in the
    99 distributed version control community, and works well for occasional
   100 changes produced by anybody out there.  Of course, upstream
   101 maintainers need to review and moderate changes being proposed, before
   102 pushing anything onto the official Isabelle repository at TUM.
   103 
   104 
   105 Write access to the Isabelle repository requires an account at TUM,
   106 with properly configured ssh access to the local machines
   107 (e.g. macbroy20, atbroy100).  You also need to be a member of the
   108 "isabelle" Unix group.
   109 
   110 Sharing a locally modified clone then works as follows, using your
   111 user name instead of "wenzelm":
   112 
   113   hg out ssh://wenzelm@atbroy100//home/isabelle-repository/repos/isabelle
   114 
   115 In fact, the "out" or "outgoing" command performs only a dry run: it
   116 displays the changesets that would get published.  An actual "push",
   117 with a lasting effect on the Isabelle repository, works like this:
   118 
   119   hg push ssh://wenzelm@atbroy100//home/isabelle-repository/repos/isabelle
   120 
   121 
   122 Default paths for push and pull can be configure in isabelle/.hg/hgrc,
   123 for example:
   124 
   125   [paths]
   126   default = ssh://wenzelm@atbroy100//home/isabelle-repository/repos/isabelle
   127 
   128 Now "hg pull" or "hg push" will use that shared file space, unless a
   129 different URL is specified explicitly.
   130 
   131 When cloning a repository, the default path is set to the initial
   132 source URL.  So we could have cloned via that ssh URL in the first
   133 place, to get exactly to the same point:
   134 
   135   hg clone ssh://wenzelm@atbroy100//home/isabelle-repository/repos/isabelle
   136 
   137 
   138 Content discipline
   139 ==================
   140 
   141 Old-style centralized version control is occasionally compared to "a
   142 library where everybody scribbles into the books".  Or seen the other
   143 way round, the centralized model discourages individual
   144 experimentation (with local branches etc.), because everything is
   145 forced to happen on a shared file space.  With Mercurial, arbitrary
   146 variations on local clones are no problem, but care is required again
   147 when publishing changes eventually.
   148 
   149 The following principles should be kept in mind when producing
   150 changesets that might become public at some point.
   151 
   152   * The author of changes should be properly identified, using
   153     ui/username configuration as described above.
   154 
   155     While Mercurial also provides means for signed changesets, we want
   156     to keep things simple and trust that users specify their identity
   157     correctly.
   158 
   159   * The history of sources is an integral part of the sources
   160     themselves.  This means that private experiments and branches
   161     should not be published, unless they are really meant to become
   162     universally available.
   163 
   164     Note that exchanging local experiments with some other users can
   165     be done directly on peer-to-peer basis, without affecting the
   166     central pull/push area.
   167 
   168   * Log messages are an integral part of the history of sources.
   169     Other users will have to look there eventually, to understand why
   170     things have been done in a certain way at some point.
   171 
   172     Mercurial provides nice web presentation of incoming changes with
   173     a digest of log entries; this also includes RSS/Atom news feeds.
   174     Users should be aware that others will actually read what is
   175     written into log messages.
   176 
   177     The usual changelog presentation style for the Isabelle repository
   178     admits log entries that consist of several lines, but without the
   179     special headline that is used in Mercurial projects elsewhere.
   180     Since some display styles strip newlines from text, it is
   181     advisable to separate lines via punctuation, and not rely on
   182     two-dimensional presentation too much.
   183 
   184 
   185 Building Isabelle from the repository version
   186 =============================================
   187 
   188 Compared to a proper distribution or development snapshot, a
   189 repository version of Isabelle lacks textual version identifiers in
   190 some sources and scripts, and various components produced by
   191 Admin/build are missing.  After applying that script with suitable
   192 arguments, the regular user instructions for building and running
   193 Isabelle from sources apply.
   194 
   195 Needless to say, the results from the build process must not be added
   196 to the repository!
   197 
   198 
   199 Makarius 30-Nov-2008