templater: drop extension point of engine classes (API) I don't think this would ever be used by third-party extensions, as we've heavily changed both the templater internals and the syntax since then. The main reason of removing this API is that I want to move the parsing function from the engine to the templater class so that we can peek keywords and functions used in a user template. This change also removes reference cycle between the templater and the engine.

templater: make it clearer that parsing doesn't cause recursion Only compileexp() may recurse into _load().

templater: mark most attributes as private

setdiscovery: use progress helper Differential Revision: https://phab.mercurial-scm.org/D3770

streamclone: use progress helper Differential Revision: https://phab.mercurial-scm.org/D3769

similar: use progress helper Note that a functional change here is that we now show the progress position *before* we start working on the item. This is consistent with how we do it elsewhere. Differential Revision: https://phab.mercurial-scm.org/D3768

remove: use progress helper Differential Revision: https://phab.mercurial-scm.org/D3767

changegroup: use progress helper in apply() (API) Differential Revision: https://phab.mercurial-scm.org/D3766

progress: create helper class for incrementing progress When using ui.progress(), there's a clear pattern that is followed: * Pass the same topic and unit * Usually pass the same total * Call with pos=None to close the progress bar * Often keep track of the current position and increment it This patch creates a simple helper class for this. I'll probably make it implement the context manager protocol later (calling update(None) on __exit__). Progress is used in low-level modules like changegroup, so I also exposed it via a method on the ui object. Perhaps the class itself should also live in ui.py? This patch also makes merge.oy use it to show that it works. Differential Revision: https://phab.mercurial-scm.org/D3765

extensions: use context manger for open()