templater: extract helper to just evaluate template expression A named function can be easily grepped and is probably good for code readability.

templater: do not destructure operands in buildmap() This makes the next patch slightly simpler.

templater: use helper function to get name of non-iterable keyword

pull: remove inadequate use of operations records to update stepdone The 'stepdone' set is design to be a client side mechanism. If the client used some advanced capabilities to request necessary information (changeset, obsmarkers, phases, etc). It marks the steps as done to avoid having a less advanced mechanism issue a duplicated request. So, the "stepdone.add('phases')" should be the result of a client choice, because only the client can know it has requested all it needed to request. In 4a08cf1a2cfe this principle was broken because any phase-heads part sent by the server to the client would declare the phases retrieval complete. Now that there is an official phases related capability and code associated to it. We do not need the change in 4a08cf1a2cfe anymore and we can back it out. This brings back 'stepdone' management for 'phases' in line with the rest of the code (including other phases handing). Here is an example of potential misbehavior that 4a08cf1a2cfe introduced: Imagine a server that pre-computes bundles. The bundles contains a changegroup part and an (advisory) 'phase-heads' part. When a pull occurs, precomputed bundled are reused if available. As the phase part is advisory it can be sent to all clients. However they could be relevant changesets without phase information. Either because they are already common or because they had no precomputed bundle for them yet. If receiving any 'phase-heads' parts disable subsequent phases re-trivial parts, the client will not request phase data for all relevant changesets. For example common changesets will not turn public.

pull: use 'phase-heads' to retrieve phase information A new bundle2 capability 'phases' has been added. If 'heads' is part of the supported value for 'phases', the server supports reading and sending 'phase- heads' bundle2 part. Server is now able to process a 'phases' boolean parameter to 'getbundle'. If 'True', a 'phase-heads' bundle2 part will be included in the bundle with phase information relevant to the whole pulled set. If this method is available the phases listkey namespace will no longer be listed. Beside the more efficient encoding of the data, this new method will greatly improve the phase exchange efficiency for repositories with non-served changesets (obsolete, secret) since we'll no longer send data about the filtered heads. Add a new 'devel.legacy.exchange' config item to allow fallback to the old 'listkey in bundle2' method. Reminder: the pulled set is not just the changesets bundled by the pull. It also contains changeset selected by the "pull specification" on the client side (eg: everything for bare pull). One of the reason why the 'pulled set' is important is to make sure we can move -common- nodes to public.

bundle2: only grab a transaction when 'phase-heads' affect the repository The next patch will use the 'phase-heads' part to exchange phase data relevant to the pulled set. 'handlephases' currently acquires a transaction even in case of no-op pull, which would results in an empty transaction and messing with the existing journal. Pass the transaction fetcher to updatephases so it can fetch it if necessary.

phases: move the binary decoding function in the phases module We move the decoding function near the encoding one in a place where they can be reused in other place (current target, 'exchange.py').