[PATCH 1 of 5] transaction: introduce scope

[Ryan McElroy]

FWIW, I thought this approach was elegant and it would have benefits 
even on systems without good hardlink support.


On 3/1/17 8:48 PM, Jun Wu wrote:
> I'm going to drop this series from patchwork. The new dirstate patches is a
> better fix.
>
> Excerpts from Jun Wu's message of 2017-02-27 09:35:25 -0800:
>> # HG changeset patch
>> # User Jun Wu <quark at fb.com>
>> # Date 1488185788 28800
>> #      Mon Feb 27 00:56:28 2017 -0800
>> # Node ID 5dac612ec9a87553fcd329100846bcb01bae9d80
>> # Parent  b4cb86ab4c719eb615a4308eafd8b1386a511eeb
>> # Available At https://urldefense.proofpoint.com/v2/url?u=https-3A__bitbucket.org_quark-2Dzju_hg-2Ddraft&d=DwIGaQ&c=5VD0RTtNlTh3ycd41b3MUw&r=Jw8rundaE7TbmqBYd1txIQ&m=PUI_VSItx4f9h9UN0MwUI5ZWzNcTzVxIX5kISKO7ndY&s=dpXH9Ao6YM_Ho7SmRBoNsXmlruqUd2Lo6JlEEetKfRI&e=
>> #              hg pull https://urldefense.proofpoint.com/v2/url?u=https-3A__bitbucket.org_quark-2Dzju_hg-2Ddraft&d=DwIGaQ&c=5VD0RTtNlTh3ycd41b3MUw&r=Jw8rundaE7TbmqBYd1txIQ&m=PUI_VSItx4f9h9UN0MwUI5ZWzNcTzVxIX5kISKO7ndY&s=dpXH9Ao6YM_Ho7SmRBoNsXmlruqUd2Lo6JlEEetKfRI&e=   -r 5dac612ec9a8
>> transaction: introduce scope
>>
>> Previously, transaction tries to cover everything: bookmarks, dirstate,
>> phaseroots, and branch. It backs them up unconditionally.
>>
>> That could be inefficient if we still back up the dirstate in a giant repo,
>> where the transaction is only intended to change bookmarks.
>>
>> This patch introduces "scope" to transactions, which is a set of things that
>> the transaction should cover. For bookmark-only update, it could avoid
>> specifying the "dirstate" scope to be more efficient.
>>
>> diff --git a/mercurial/transaction.py b/mercurial/transaction.py
>> --- a/mercurial/transaction.py
>> +++ b/mercurial/transaction.py
>> @@ -102,5 +102,6 @@ def _playback(journal, report, opener, v
>>   class transaction(object):
>>       def __init__(self, report, opener, vfsmap, journalname, undoname=None,
>> -                 after=None, createmode=None, validator=None, releasefn=None):
>> +                 after=None, createmode=None, validator=None, releasefn=None,
>> +                 scope=None):
>>           """Begin a new transaction
>>   
>> @@ -111,4 +112,5 @@ class transaction(object):
>>           * `createmode`: the mode of the journal file that will be created
>>           * `releasefn`: called after releasing (with transaction and result)
>> +        * `scope`: a set-like, nested transaction's scope must be a subset
>>           """
>>           self.count = 1
>> @@ -171,4 +173,7 @@ class transaction(object):
>>           self._abortcallback = {}
>>   
>> +        # a set indicating what's covered
>> +        self._scope = scope or frozenset()
>> +
>>       def __del__(self):
>>           if self.journal:
>> @@ -342,5 +347,10 @@ class transaction(object):
>>   
>>       @active
>> -    def nest(self):
>> +    def nest(self, scope=None):
>> +        scope = scope or frozenset()
>> +        if not scope.issubset(self._scope):
>> +            raise error.ProgrammingError(
>> +                'nested transaction has a superset scope (%s > %s)'
>> +                % (scope, self._scope))
>>           self.count += 1
>>           self.usages += 1
>> @@ -555,4 +565,7 @@ class transaction(object):
>>               self.releasefn(self, False) # notify failure of transaction
>>   
>> +    def scope(self):
>> +        return self._scope
>> +
>>   def rollback(opener, vfsmap, file, report):
>>       """Rolls back the transaction contained in the given file
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