wireproto: add transport specific capabilities in the transport We add a method to the protocol handler interface that allows specific implementations to add their own capabilities. The SSH implementation is a no-op. The HTTP implementation adds the HTTP-specific capabilities. The end result is transport specific capabilities now live in the transport code instead of in some generic function in the wireproto module. Differential Revision: https://phab.mercurial-scm.org/D2512

wireproto: don't expose changegroupsubset capability if not available We just marked the changegroupsubset command as only available to version 1 of the wire transports. There is a capability of the same name of the command that indicates if the command is supported. This commit teaches the capabilities code to conditionally emit that capability depending on whether the command is available for the current transport. Most test output is reordering of capabilities. But the limited tests for version 2 of the SSH protocol do show the capability disappearing. Differential Revision: https://phab.mercurial-scm.org/D2486

wireproto: don't expose legacy commands to version 2 of wire protocol Now that we have the ability to control which transports a wire protocol command is exposed on, let's put it to use. We flag the "branches," "changegroup," and "changegroupsubset" commands as only available on version 1. "branches" was used by the legacy discovery mechanism and was replaced by the "known" and "heads" commands. "changegroup" and "changegroupsubset" were replaced by "getbundle." "between" is also legacy. However, since it is used by the SSH handshake protocol, marking it as legacy is a bit more complicated and will be done in a later commit. Another nuanced issue with this change is that the server-advertised capabilities still list "changegroupsubset" despite the command not being available. This will be addressed in a subsequent commit. Differential Revision: https://phab.mercurial-scm.org/D2485

wireprotoserver: identify requests via version 2 of SSH protocol as such The protocol handler needs to advertise itself as version 2 in order for a future feature to work. Differential Revision: https://phab.mercurial-scm.org/D2484

wireproto: allow wire protocol commands to declare transport support Currently, wire protocol commands are exposed on all transports. Some wire protocol commands are only supported or sensical on some transports. In the future, new wire protocol commands may only be available on new transports and legacy wire protocol commands may not be available to newer transports. This commit introduces a mechanism to allow @wireprotocommand to declare transports for which they should not be available. The mechanism for determining if a wire protocol command is available for a given transport instance has been taught to take this knowledge into account. To help implement this feature, we add a dict to wireprototypes declaring all wire transports and their metadata. There's probably room to refactor the constants used to identify the wire protocols. But that can be in another commit. Differential Revision: https://phab.mercurial-scm.org/D2483

sshpeer: don't read from stderr when that behavior is disabled We previously prevented the creation of doublepipe instances when we're not supposed to automatically read from stderr. However, there were other automatic calls to read from stderr that were undermining this effort. This commit prevents all automatic reads from stderr from occurring when they are supposed to be disabled. Because stderr is no longer being read, we need to call "readavailable" from tests so stderr is read from. Test output changes because stderr is now always (manually) read after stdout. And, since sshpeer no longer automatically tends to stderr, no "remote: " messages are printed. This should fix non-deterministic test output. FWIW, doublepipe automatically reads from stderr when reading from stdout, so I'm not sure some of these calls to self._readerr() are even needed. Differential Revision: https://phab.mercurial-scm.org/D2571