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 browsers, notably hgtk that is part of the TortoiseHg
36 distribution and works for generic Python/GTk platforms. The
37 alternative "view" utility helps to inspect the semantic content of
44 The official Isabelle repository can be cloned like this:
46 hg clone http://isabelle.in.tum.de/repos/isabelle
48 This will create a local directory "isabelle", unless an alternative
49 name is specified. The full repository meta-data and history of
50 changes is in isabelle/.hg; local configuration for this clone can be
51 added to isabelle/.hg/hgrc, but note that hgrc files are never copied
52 by another clone operation.
55 There is also $HOME/.hgrc for per-user Mercurial configuration. The
56 initial configuration requires at least an entry to identify yourself
62 Isabelle contributors are free to choose either a short "login name"
63 (for accounts at TU Munich) or a "full name" -- with or without mail
64 address. It is important to stick to this choice once and for all.
65 The machine default that Mercurial produces for unspecified
66 [ui]username is not appropriate.
68 Such configuration can be given in $HOME/.hgrc (for each home
69 directory on each machine) or in .hg/hgrc (for each repository clone).
72 Here are some further examples for hgrc. This is how to provide
73 default options for common commands:
78 This is how to configure some extension, which is called "graphlog"
79 and provides the "glog" command:
85 Shared pull/push access
86 -----------------------
88 The entry point http://isabelle.in.tum.de/repos/isabelle is world
89 readable, both via plain web browsing and the hg client as described
90 above. Anybody can produce a clone, change it locally, and then use
91 regular mechanisms of Mercurial to report changes upstream, say via
92 mail to someone with write access to that file space. It is also
93 quite easy to publish changed clones again on the web, using the
94 ad-hoc command "hg serve -v", or the hgweb.cgi or hgwebdir.cgi scripts
95 that are included in the Mercurial distribution, and send a "pull
96 request" to someone else. There are also public hosting services for
97 Mercurial repositories.
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. Direct
104 pushes are also reviewed routinely in a post-hoc fashion; everybody
105 hooked on the main repository is called to keep an eye on incoming
106 changes. In any case, changesets need to be understandable, at the
107 time of writing and many years later.
109 Push access to the Isabelle repository requires an account at TUM,
110 with properly configured ssh to the local machines (e.g. macbroy20,
111 atbroy100). You also need to be a member of the "isabelle" Unix
114 Sharing a locally modified clone then works as follows, using your
115 user name instead of "wenzelm":
117 hg out ssh://wenzelm@atbroy100//home/isabelle-repository/repos/isabelle
119 In fact, the "out" or "outgoing" command performs only a dry run: it
120 displays the changesets that would get published. An actual "push",
121 with a lasting effect on the Isabelle repository, works like this:
123 hg push ssh://wenzelm@atbroy100//home/isabelle-repository/repos/isabelle
126 Default paths for push and pull can be configured in
127 isabelle/.hg/hgrc, for example:
130 default = ssh://wenzelm@atbroy100//home/isabelle-repository/repos/isabelle
132 Now "hg pull" or "hg push" will use that shared file space, unless a
133 different URL is specified explicitly.
135 When cloning a repository, the default path is set to the initial
136 source URL. So we could have cloned via that ssh URL in the first
137 place, to get exactly to the same point:
139 hg clone ssh://wenzelm@atbroy100//home/isabelle-repository/repos/isabelle
145 The main idea of Mercurial is to let individual users produce
146 independent branches of development first, but merge with others
147 frequently. The basic hg merge operation is more general than
148 required for the mode of operation with a shared pull/push area. The
149 "fetch" extension accommodates this case nicely, automating trivial
150 merges and requiring manual intervention for actual conflicts only.
152 The fetch extension can be configured via $HOME/.hgrc like this:
160 To keep merges semantically trivial and prevent genuine merge
161 conflicts or lost updates, it is essential to observe to following
162 general discipline wrt. the public Isabelle push area:
164 * Before editing, pull or fetch the latest version.
166 * Accumulate private commits for a maximum of 1-3 days.
168 * Start publishing again by pull or fetch, which normally produces
171 * Test the merged result as usual and push back in real time.
173 Piling private changes and public merges longer than 0.5-2 hours is
174 apt to produce some mess when pushing eventually!
180 The following principles should be kept in mind when producing
181 changesets that are meant to be published at some point.
183 * The author of changes needs to be properly identified, using
184 [ui]username configuration as described above.
186 While Mercurial also provides means for signed changesets, we want
187 to keep things simple and trust that users specify their identity
188 correctly (and uniquely).
190 * The history of sources is an integral part of the sources
191 themselves. This means that private experiments and branches
192 should not be published by accident. Named branches are not
193 allowed on the public version. Note that old SVN-style branching
194 is replaced by regular repository clones in Mercurial.
196 Exchanging local experiments with some other users can be done
197 directly on peer-to-peer basis, without affecting the central
200 * Log messages are an integral part of the history of sources.
201 Other people will have to inspect them routinely, to understand
202 why things have been done in a certain way at some point.
204 Authors of log entries should be aware that published changes are
205 actually read. The main point is not to announce novelties, but
206 to describe faithfully what has been done, and provide some clues
207 about the motivation behind it. The main recipient is someone who
208 needs to understand the change in the distant future to isolate
209 problems. Sometimes it is helpful to reference past changes via
210 changeset ids in the log entry.
212 * The standard changelog entry format of the Isabelle repository
213 admits several (vaguely related) items to be rolled into one
214 changeset. Each item is then described on a separate line that
215 may become longer as screen line and is terminated by punctuation.
216 These lines are roughly ordered by importance.
218 This format conforms to established Isabelle tradition. In
219 contrast, the default of Mercurial prefers a single headline
220 followed by a long body text. The reason for that is a somewhat
221 different development model of typical "distributed" projects,
222 where external changes pass through a hierarchy of reviewers and
223 maintainers, until they end up in some authoritative repository.
224 Isabelle changesets can be more spontaneous, growing from the
227 The web style of http://isabelle.in.tum.de/repos/isabelle/
228 accommodates the Isabelle changelog format. Note that multiple
229 lines will sometimes display as a single paragraph in HTML, so
230 some terminating punctuation is required. Do not squeeze multiple
231 items on the same line in the original text!
234 Building a repository version of Isabelle
235 -----------------------------------------
237 Compared to a proper distribution or development snapshot, it is
238 relatively hard to build from the raw repository version. Essential
239 contributing components are missing and need to be reconstructed by
240 running the Admin/build script by hand. Afterwards the main Isabelle
241 system and logic images can be compiled via the toplevel ./build
242 script. Note that the repository lacks some textual version
243 identifiers in the sources and scripts; this implies some changed
244 behavior when processing settings etc.
246 There is no guarantee that the NEWS file is up to date at an arbitrary