README_REPOSITORY
author nipkow
Wed Aug 26 19:54:19 2009 +0200 (2009-08-26)
changeset 32416 4ea7648b6ae2
parent 32361 141e5151b918
child 35567 309e75c58af2
permissions -rw-r--r--
merged
     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 versions from the 1.0 or 1.1 branch, or later.
    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.  Others should use their regular "full
    66 name"; including an email address is optional.
    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 Simplified merges
   140 -----------------
   141 
   142 The main idea of Mercurial is to let individual users produce
   143 independent branches of development first, but merge with others
   144 frequently.  The basic hg merge operation is more general than
   145 required for the mode of operation with a shared pull/push area.  The
   146 hg fetch extension accommodates this case nicely, automating trivial
   147 merges and requiring manual intervention for actual conflicts only.
   148 
   149 The fetch extension can be configured via the user's ~/.hgrc like
   150 this:
   151 
   152   [extensions]
   153   hgext.fetch =
   154 
   155   [defaults]
   156   fetch = -m "merged"
   157 
   158 Note that the potential for merge conflicts can be greatly reduced by
   159 doing "hg fetch" before any starting local changes!
   160 
   161 
   162 Content discipline
   163 ------------------
   164 
   165 Old-style centralized version control is occasionally compared to "a
   166 library where everybody scribbles into the books".  Or seen the other
   167 way round, the centralized model discourages individual
   168 experimentation (with local branches etc.), because everything is
   169 forced to happen on a shared file space.  With Mercurial, arbitrary
   170 variations on local clones are no problem, but care is required again
   171 when publishing changes eventually.
   172 
   173 The following principles should be kept in mind when producing
   174 changesets that might become public at some point.
   175 
   176   * The author of changes should be properly identified, using
   177     ui/username configuration as described above.
   178 
   179     While Mercurial also provides means for signed changesets, we want
   180     to keep things simple and trust that users specify their identity
   181     correctly.
   182 
   183   * The history of sources is an integral part of the sources
   184     themselves.  This means that private experiments and branches
   185     should not be published, unless they are really meant to become
   186     universally available.
   187 
   188     Note that exchanging local experiments with some other users can
   189     be done directly on peer-to-peer basis, without affecting the
   190     central pull/push area.
   191 
   192   * Log messages are an integral part of the history of sources.
   193     Other users will have to look there eventually, to understand why
   194     things have been done in a certain way at some point.
   195 
   196     Mercurial provides nice web presentation of incoming changes with
   197     a digest of log entries; this also includes RSS/Atom news feeds.
   198     Users should be aware that others will actually read what is
   199     written into log messages.  There are also add-on browsers,
   200     notably hgtk that is part of the TortoiseHg distribution and works
   201     for generic Python/GTk platforms.
   202 
   203     The usual changelog presentation style for the Isabelle repository
   204     admits log entries that consist of several lines, but without the
   205     special headline that is used in Mercurial projects elsewhere.
   206     Since some display styles strip newlines from text, it is
   207     advisable to separate lines via punctuation, and not rely on
   208     two-dimensional presentation too much.
   209 
   210 
   211 Building a repository version of Isabelle
   212 -----------------------------------------
   213 
   214 Compared to a proper distribution or development snapshot, a
   215 repository version of Isabelle lacks textual version identifiers in
   216 some sources and scripts, and various components produced by
   217 Admin/build are missing.  After applying that script with suitable
   218 arguments, the regular user instructions for building and running
   219 Isabelle from sources apply.
   220 
   221 Needless to say, the results from the build process must not be added
   222 to the repository!