1 Important notes on Mercurial repository access for Isabelle
2 ===========================================================
7 Mercurial http://www.selenic.com/mercurial belongs to the current
8 generation of source code management systems that follow the so-called
9 paradigm of "distributed version control". This is a terrific name
10 for plain revision control without the legacy of CVS or SVN. See also
11 http://hginit.com/ for an introduction to the main ideas. The
12 Mercurial book http://hgbook.red-bean.com/ explains many more details.
14 Mercurial offers great flexibility in organizing the flow of changes,
15 both between individual developers and designated pull/push areas that
16 are shared with others. This additional power demands some additional
17 responsibility to maintain a certain development process that fits to
20 Regular Mercurial operations are strictly monotonic, where changeset
21 transactions are only added, but never deleted. There are special
22 tools to manipulate repositories via non-monotonic actions (such as
23 "rollback" or "strip"), but recovering from gross mistakes that have
24 escaped into the public can be hard and embarrassing. It is much
25 easier to inspect and amend changesets routinely before pushing.
27 The effect of the critical "pull" / "push" operations can be tested in
28 a dry run via "incoming" / "outgoing". The "fetch" extension includes
29 useful sanity checks beyond raw "pull" / "update" / "merge". Most
30 other operations are local to the user's repository clone. This gives
31 some freedom for experimentation without affecting anybody else.
33 Mercurial provides nice web presentation of incoming changes with a
34 digest of log entries; this also includes RSS/Atom news feeds. There
35 are add-on history browsers such as "hg view" and TortoiseHg. Unlike
36 the default web view, some of these tools help to inspect the semantic
37 content of non-trivial merge nodes.
43 The official Isabelle repository can be cloned like this:
45 hg clone http://isabelle.in.tum.de/repos/isabelle
47 This will create a local directory "isabelle", unless an alternative
48 name is specified. The full repository meta-data and history of
49 changes is in isabelle/.hg; local configuration for this clone can be
50 added to isabelle/.hg/hgrc, but note that hgrc files are never copied
51 by another clone operation.
54 There is also $HOME/.hgrc for per-user Mercurial configuration. The
55 initial configuration requires at least an entry to identify yourself
61 Isabelle contributors are free to choose either a short "login name"
62 (for accounts at TU Munich) or a "full name" -- with or without mail
63 address. It is important to stick to this choice once and for all.
64 The machine default that Mercurial produces for unspecified
65 [ui]username is not appropriate.
67 Such configuration can be given in $HOME/.hgrc (for each home
68 directory on each machine) or in .hg/hgrc (for each repository clone).
71 Here are some further examples for hgrc. This is how to provide
72 default options for common commands:
77 This is how to configure some extension, which is called "graphlog"
78 and provides the "glog" command:
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 locally, and then use
90 regular mechanisms of Mercurial to report changes upstream, say via
91 mail to someone with write access to that file space. It is also
92 quite easy to publish changed clones again on the web, using the
93 ad-hoc command "hg serve -v", or the hgweb.cgi or hgwebdir.cgi scripts
94 that are included in the Mercurial distribution, and send a "pull
95 request" to someone else. There are also public hosting services for
96 Mercurial repositories.
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. Direct
103 pushes are also reviewed routinely in a post-hoc fashion; everybody
104 hooked on the main repository is called to keep an eye on incoming
105 changes. In any case, changesets need to be understandable, at the
106 time of writing and many years later.
108 Push access to the Isabelle repository requires an account at TUM,
109 with properly configured ssh to the local machines (e.g. macbroy20 ..
110 macbroy29). You also need to be a member of the "isabelle" Unix
113 Sharing a locally modified clone then works as follows, using your
114 user name instead of "wenzelm":
116 hg out ssh://wenzelm@macbroy20//home/isabelle-repository/repos/isabelle
118 In fact, the "out" or "outgoing" command performs only a dry run: it
119 displays the changesets that would get published. An actual "push",
120 with a lasting effect on the Isabelle repository, works like this:
122 hg push ssh://wenzelm@macbroy20//home/isabelle-repository/repos/isabelle
125 Default paths for push and pull can be configured in
126 isabelle/.hg/hgrc, for example:
129 default = ssh://wenzelm@macbroy20//home/isabelle-repository/repos/isabelle
131 Now "hg pull" or "hg push" will use that shared file space, unless a
132 different URL is specified explicitly.
134 When cloning a repository, the default path is set to the initial
135 source URL. So we could have cloned via that ssh URL in the first
136 place, to get exactly to the same point:
138 hg clone ssh://wenzelm@macbroy20//home/isabelle-repository/repos/isabelle
144 The main idea of Mercurial is to let individual users produce
145 independent branches of development first, but merge with others
146 frequently. The basic hg merge operation is more general than
147 required for the mode of operation with a shared pull/push area. The
148 "fetch" extension accommodates this case nicely, automating trivial
149 merges and requiring manual intervention for actual conflicts only.
151 The fetch extension can be configured via $HOME/.hgrc like this:
159 To keep merges semantically trivial and prevent genuine merge
160 conflicts or lost updates, it is essential to observe to following
161 general discipline wrt. the public Isabelle push area:
163 * Before editing, pull or fetch the latest version.
165 * Accumulate private commits for a maximum of 1-3 days.
167 * Start publishing again by pull or fetch, which normally produces
170 * Test the merged result as usual and push back in real time.
172 Piling private changes and public merges longer than 0.5-2 hours is
173 apt to produce some mess when pushing eventually!
179 The following principles should be kept in mind when producing
180 changesets that are meant to be published at some point.
182 * The author of changes needs to be properly identified, using
183 [ui]username configuration as described above.
185 While Mercurial also provides means for signed changesets, we want
186 to keep things simple and trust that users specify their identity
187 correctly (and uniquely).
189 * The history of sources is an integral part of the sources
190 themselves. This means that private experiments and branches
191 should not be published by accident. Named branches are not
192 allowed on the public version. Note that old SVN-style branching
193 is replaced by regular repository clones in Mercurial.
195 Exchanging local experiments with some other users can be done
196 directly on peer-to-peer basis, without affecting the central
199 * Log messages are an integral part of the history of sources.
200 Other people will have to inspect them routinely, to understand
201 why things have been done in a certain way at some point.
203 Authors of log entries should be aware that published changes are
204 actually read. The main point is not to announce novelties, but
205 to describe faithfully what has been done, and provide some clues
206 about the motivation behind it. The main recipient is someone who
207 needs to understand the change in the distant future to isolate
208 problems. Sometimes it is helpful to reference past changes via
209 changeset ids in the log entry.
211 * The standard changelog entry format of the Isabelle repository
212 admits several (vaguely related) items to be rolled into one
213 changeset. Each item is then described on a separate line that
214 may become longer as screen line and is terminated by punctuation.
215 These lines are roughly ordered by importance.
217 This format conforms to established Isabelle tradition. In
218 contrast, the default of Mercurial prefers a single headline
219 followed by a long body text. The reason for that is a somewhat
220 different development model of typical "distributed" projects,
221 where external changes pass through a hierarchy of reviewers and
222 maintainers, until they end up in some authoritative repository.
223 Isabelle changesets can be more spontaneous, growing from the
226 The web style of http://isabelle.in.tum.de/repos/isabelle/
227 accommodates the Isabelle changelog format. Note that multiple
228 lines will sometimes display as a single paragraph in HTML, so
229 some terminating punctuation is required. Do not squeeze multiple
230 items on the same line in the original text!
233 Building a repository version of Isabelle
234 -----------------------------------------
236 Compared to a proper distribution or development snapshot, it is
237 relatively hard to build from the raw repository version. Essential
238 contributing components are missing and need to be reconstructed by
239 running the Admin/build script by hand. Afterwards the main Isabelle
240 system and logic images can be compiled via the toplevel ./build
241 script. Note that the repository lacks some textual version
242 identifiers in the sources and scripts; this implies some changed
243 behavior when processing settings etc.
245 There is no guarantee that the NEWS file is up to date at an arbitrary