hook: have a generic hook for transaction opening

We are adding generic hooking for all transactions. We do not really have any
useful information to include when opening the transaction but this is a
useful time to allow a hook anyway. We better let people abort transaction before
they happen than after multiple seconds/minutes of processing.

mercurial/help/config.txt

@@ -808,6 +808,11 b' variables it is passed are listed with n'
   changeset to tag is in ``$HG_NODE``. Name of tag is in ``$HG_TAG``. Tag is
   local if ``$HG_LOCAL=1``, in repository if ``$HG_LOCAL=0``.
 
+``pretxnopen``
+  Run before any new repository transaction is open. The reason for the
+  transaction will be in ``$HG_TXNNAME``. A non-zero status will
+  prevent the transaction from being opened.
+
 ``pretxnchangegroup``
   Run after a changegroup has been added via push, pull or unbundle,
   but before the transaction has been committed. Changegroup is

mercurial/localrepo.py

@@ -909,6 +909,8 b' class localrepository(object):'
                 _("abandoned transaction found"),
                 hint=_("run 'hg recover' to clean up transaction"))
 
+        self.hook('pretxnopen', throw=True, txnname=desc)
+
         self._writejournal(desc)
         renames = [(vfs, x, undoname(x)) for vfs, x in self._journalfiles()]
         rp = report and report or self.ui.warn

tests/test-hook.t

@@ -12,11 +12,13 b' commit hooks can see env vars'
   > pre-identify = python "$TESTDIR/printenv.py" pre-identify 1
   > pre-cat = python "$TESTDIR/printenv.py" pre-cat
   > post-cat = python "$TESTDIR/printenv.py" post-cat
+  > pretxnopen = sh -c "HG_LOCAL= HG_TAG= python \"$TESTDIR/printenv.py\" pretxnopen"
   > EOF
   $ echo a > a
   $ hg add a
   $ hg commit -m a
   precommit hook: HG_PARENT1=0000000000000000000000000000000000000000
+  pretxnopen hook: HG_TXNNAME=commit
   pretxncommit hook: HG_NODE=cb9a9f314b8b07ba71012fcdbc544b5a4d82ff5b HG_PARENT1=0000000000000000000000000000000000000000 HG_PENDING=$TESTTMP/a
   0:cb9a9f314b8b
   commit hook: HG_NODE=cb9a9f314b8b07ba71012fcdbc544b5a4d82ff5b HG_PARENT1=0000000000000000000000000000000000000000
@@ -42,6 +44,7 b' pretxncommit and commit hooks can see bo'
   $ echo b >> a
   $ hg commit -m a1 -d "1 0"
   precommit hook: HG_PARENT1=cb9a9f314b8b07ba71012fcdbc544b5a4d82ff5b
+  pretxnopen hook: HG_TXNNAME=commit
   pretxncommit hook: HG_NODE=ab228980c14deea8b9555d91c9581127383e40fd HG_PARENT1=cb9a9f314b8b07ba71012fcdbc544b5a4d82ff5b HG_PENDING=$TESTTMP/a
   1:ab228980c14d
   commit hook: HG_NODE=ab228980c14deea8b9555d91c9581127383e40fd HG_PARENT1=cb9a9f314b8b07ba71012fcdbc544b5a4d82ff5b
@@ -52,6 +55,7 b' pretxncommit and commit hooks can see bo'
   $ hg add b
   $ hg commit -m b -d '1 0'
   precommit hook: HG_PARENT1=cb9a9f314b8b07ba71012fcdbc544b5a4d82ff5b
+  pretxnopen hook: HG_TXNNAME=commit
   pretxncommit hook: HG_NODE=ee9deb46ab31e4cc3310f3cf0c3d668e4d8fffc2 HG_PARENT1=cb9a9f314b8b07ba71012fcdbc544b5a4d82ff5b HG_PENDING=$TESTTMP/a
   2:ee9deb46ab31
   commit hook: HG_NODE=ee9deb46ab31e4cc3310f3cf0c3d668e4d8fffc2 HG_PARENT1=cb9a9f314b8b07ba71012fcdbc544b5a4d82ff5b
@@ -62,6 +66,7 b' pretxncommit and commit hooks can see bo'
   (branch merge, don't forget to commit)
   $ hg commit -m merge -d '2 0'
   precommit hook: HG_PARENT1=ee9deb46ab31e4cc3310f3cf0c3d668e4d8fffc2 HG_PARENT2=ab228980c14deea8b9555d91c9581127383e40fd
+  pretxnopen hook: HG_TXNNAME=commit
   pretxncommit hook: HG_NODE=07f3376c1e655977439df2a814e3cc14b27abac2 HG_PARENT1=ee9deb46ab31e4cc3310f3cf0c3d668e4d8fffc2 HG_PARENT2=ab228980c14deea8b9555d91c9581127383e40fd HG_PENDING=$TESTTMP/a
   3:07f3376c1e65
   commit hook: HG_NODE=07f3376c1e655977439df2a814e3cc14b27abac2 HG_PARENT1=ee9deb46ab31e4cc3310f3cf0c3d668e4d8fffc2 HG_PARENT2=ab228980c14deea8b9555d91c9581127383e40fd
@@ -103,6 +108,7 b' tag hooks can see env vars'
   $ hg tag -d '3 0' a
   pretag hook: HG_LOCAL=0 HG_NODE=07f3376c1e655977439df2a814e3cc14b27abac2 HG_TAG=a
   precommit hook: HG_PARENT1=07f3376c1e655977439df2a814e3cc14b27abac2
+  pretxnopen hook: HG_TXNNAME=commit
   pretxncommit hook: HG_NODE=539e4b31b6dc99b3cfbaa6b53cbc1c1f9a1e3a10 HG_PARENT1=07f3376c1e655977439df2a814e3cc14b27abac2 HG_PENDING=$TESTTMP/a
   4:539e4b31b6dc
   tag hook: HG_LOCAL=0 HG_NODE=07f3376c1e655977439df2a814e3cc14b27abac2 HG_TAG=a
@@ -137,6 +143,7 b' more there after'
   4:539e4b31b6dc
   $ hg commit -m 'fail' -d '4 0'
   precommit hook: HG_PARENT1=539e4b31b6dc99b3cfbaa6b53cbc1c1f9a1e3a10
+  pretxnopen hook: HG_TXNNAME=commit
   pretxncommit hook: HG_NODE=6f611f8018c10e827fee6bd2bc807f937e761567 HG_PARENT1=539e4b31b6dc99b3cfbaa6b53cbc1c1f9a1e3a10 HG_PENDING=$TESTTMP/a
   5:6f611f8018c1
   5:6f611f8018c1
@@ -198,6 +205,7 b' pushkey hook'
   pushing to ../a
   searching for changes
   no changes found
+  pretxnopen hook: HG_TXNNAME=bookmarks
   pushkey hook: HG_KEY=foo HG_NAMESPACE=bookmarks HG_NEW=0000000000000000000000000000000000000000 HG_RET=1
   exporting bookmark foo
   [1]