1 Important notes on Mercurial repository access for Isabelle
2 ===========================================================
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.
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
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.
35 The official Isabelle repository can be cloned like this:
37 hg clone http://isabelle.in.tum.de/repos/isabelle
39 This will create a local directory "isabelle", unless an alternative
40 name is specified. The full repository meta-data and history of
41 changes is in isabelle/.hg; local configuration for this clone can be
42 added to isabelle/.hg/hgrc, but note that hgrc files are never copied
43 by another clone operation!
46 There is also $HOME/.hgrc for per-user Mercurial configuration. The
47 initial configuration should include at least an entry to identify
48 yourself. For example, something like this in /home/wenzelm/.hgrc:
53 Of course, the user identity can be also configured in
54 isabelle/.hg/hgrc on per-repository basis. Failing to specify the
55 username correctly makes the system invent funny machine names that
56 may persist indefinitely in the public flow of changesets.
58 In principle, user names can be chosen freely, but for longterm
59 committers of the Isabelle repository the obvious choice is to keep
60 with the old CVS naming scheme. Others should use their regular "full
61 name"; including an email address is optional.
64 There are other useful configuration to go into $HOME/.hgrc,
65 e.g. defaults for common commands:
70 The next example shows how to install some Mercurial extension:
75 Now the additional glog command will be available.
78 See also the fine documentation for further details, especially the
79 book http://hgbook.red-bean.com/
81 There is also a nice tutorial at http://hginit.com/
84 Shared pull/push access
85 -----------------------
87 The entry point http://isabelle.in.tum.de/repos/isabelle is world
88 readable, both via plain web browsing and the hg client as described
89 above. Anybody can produce a clone, change it arbitrarily, and then
90 use regular mechanisms of Mercurial to report changes upstream, say
91 via e-mail to someone with write access to that file space. It is
92 also quite easy to publish changed clones again on the web, using the
93 adhoc command "hg serve -v", or the hgweb.cgi or hgwebdir.cgi scripts
94 that are included in the Mercurial distribution.
96 The downstream/upstream mode of operation is quite common in the
97 distributed version control community, and works well for occasional
98 changes produced by anybody out there. Of course, upstream
99 maintainers need to review and moderate changes being proposed, before
100 pushing anything onto the official Isabelle repository at TUM.
103 Write access to the Isabelle repository requires an account at TUM,
104 with properly configured ssh access to the local machines
105 (e.g. macbroy20, atbroy100). You also need to be a member of the
106 "isabelle" Unix group.
108 Sharing a locally modified clone then works as follows, using your
109 user name instead of "wenzelm":
111 hg out ssh://wenzelm@atbroy100//home/isabelle-repository/repos/isabelle
113 In fact, the "out" or "outgoing" command performs only a dry run: it
114 displays the changesets that would get published. An actual "push",
115 with a lasting effect on the Isabelle repository, works like this:
117 hg push ssh://wenzelm@atbroy100//home/isabelle-repository/repos/isabelle
120 Default paths for push and pull can be configure in isabelle/.hg/hgrc,
124 default = ssh://wenzelm@atbroy100//home/isabelle-repository/repos/isabelle
126 Now "hg pull" or "hg push" will use that shared file space, unless a
127 different URL is specified explicitly.
129 When cloning a repository, the default path is set to the initial
130 source URL. So we could have cloned via that ssh URL in the first
131 place, to get exactly to the same point:
133 hg clone ssh://wenzelm@atbroy100//home/isabelle-repository/repos/isabelle
139 The main idea of Mercurial is to let individual users produce
140 independent branches of development first, but merge with others
141 frequently. The basic hg merge operation is more general than
142 required for the mode of operation with a shared pull/push area. The
143 hg fetch extension accommodates this case nicely, automating trivial
144 merges and requiring manual intervention for actual conflicts only.
146 The fetch extension can be configured via the user's ~/.hgrc like
155 Note that the potential for merge conflicts can be greatly reduced by
156 doing "hg fetch" before any starting local changes!
162 Old-style centralized version control is occasionally compared to "a
163 library where everybody scribbles into the books". Or seen the other
164 way round, the centralized model discourages individual
165 experimentation (with local branches etc.), because everything is
166 forced to happen on a shared file space. With Mercurial, arbitrary
167 variations on local clones are no problem, but care is required again
168 when publishing changes eventually.
170 The following principles should be kept in mind when producing
171 changesets that might become public at some point.
173 * The author of changes should be properly identified, using
174 ui/username configuration as described above.
176 While Mercurial also provides means for signed changesets, we want
177 to keep things simple and trust that users specify their identity
180 * The history of sources is an integral part of the sources
181 themselves. This means that private experiments and branches
182 should not be published, unless they are really meant to become
183 universally available.
185 Note that exchanging local experiments with some other users can
186 be done directly on peer-to-peer basis, without affecting the
187 central pull/push area.
189 * Log messages are an integral part of the history of sources.
190 Other users will have to look there eventually, to understand why
191 things have been done in a certain way at some point.
193 Mercurial provides nice web presentation of incoming changes with
194 a digest of log entries; this also includes RSS/Atom news feeds.
195 Users should be aware that others will actually read what is
196 written into log messages. There are also add-on browsers,
197 notably hgtk that is part of the TortoiseHg distribution and works
198 for generic Python/GTk platforms.
200 The usual changelog presentation style for the Isabelle repository
201 admits log entries that consist of several lines, but without the
202 special headline that is used in Mercurial projects elsewhere.
203 Since some display styles strip newlines from text, it is
204 advisable to separate lines via punctuation, and not rely on
205 two-dimensional presentation too much.
208 Building a repository version of Isabelle
209 -----------------------------------------
211 Compared to a proper distribution or development snapshot, a
212 repository version of Isabelle lacks textual version identifiers in
213 some sources and scripts, and various components produced by
214 Admin/build are missing. After applying that script with suitable
215 arguments, the regular user instructions for building and running
216 Isabelle from sources apply.
218 Needless to say, the results from the build process must not be added