win32: add a method to fetch the available pipe data size This will be used in the next patch to do nonblocking reads from the child process, like on posix platforms. See that for why os.fstat() is insufficient.

dirs._addpath: reinstate use of Py_CLEAR I changed this to an explicit Py_DECREF + set to null in 6f0e6fa9fdd7. This was a silly misunderstanding on my part -- for some reason I thought Py_CLEAR set its argument to null only if its refcount reached 0. Turns out that's not actually the case -- Py_CLEAR is just Py_DECREF + set to null with some additional precautions around destructors that aren't relevant here. The real bug that 6f0e6fa9fdd7 fixed was the fact that we were mutating the string after setting it in the Python dictionary.

exchange: introduce a '_canusebundle2' function This function refactors the logic that decides to use 'bundle2' during an exchange (pull/push). This will help being consistent while transitioning from the experimental protocol to the final frozen version. I do not expect this function to survive on the long run when using 'bundle2' will become a simple capability check. This is also necessary to allow HG2Y support in an extension to ease transition of companies using the experimental protocol in production (yeah...). Such extension will be able to wrap this function to use the experimental protocol in some case.

bundle2: detect bundle2 stream/request on /HG2./ instead of /HG2Y/ To support more bundle2 formats, we need a wider detection of bundle2-family streams. The various places what were explicitly detecting the full magic string are now matching on the first three characters of it.

unbundle20: allow generic dispatch between unbundlers We now take full advantage of the 'getunbundler' function by using a '{version -> unbundler-class}' mapping. This map currently contains a single entry but will make it easy to support more versions from an extension/the future. At some point, this map will probably contain bundler-class information too, in the same fashion the packer map does. However, this is not critically required right now so it will happen by itself when needed. The main target is to allow HG2Y support in an extension to ease transition of companies using the experimental protocol in production (yeah...) But I've no doubt this will be useful when playing with a future HG21.

treemanifest: refactor treemanifest.walk() This refactor is a preparation for an optimization in the next commit. This introduces a recursive element that recurses each submanifest. By using a recursive function, the next commit can avoid walking over some subdirectories altogether.

manifest: move changectx.walk() to manifests The logic of walking a manifest to yield files matching a match object is currently being done by context, not the manifest itself. This moves the walk() function to both manifestdict and treemanifest. This separate implementation will also permit differing, optimized implementations for each manifest.

subrepo: precisely identify the missing subrepo spec file It isn't obvious which file is the problem with deep subrepos, so provide the path. Since the parsing is done with a ctx and not a subrepo object, it isn't possible to display a path from the root subrepo. Therefore, the path shown is relative to cwd. There's no test coverage for the first abort, and I couldn't figure out how to trigger it, but it is changed for consistency.

graft: record intermediate grafts in extras Previously the extra field for a graft only contained the original commit hash. This made it impossible to use graft to copy a commit more than once, because the extras fields did not change after the second graft. The fix is to add an extra.intermediate-source field that records the immediate predecessor to graft. This changes hashes for commits that have been grafted twice, which is why the test was affected.

graft: allow creating sibling grafts Previously it was impossible to graft a commit onto it's own parent (i.e. create a copy of the commit). This is useful when wanting to create a backup of the commit before continuing to amend it. This patch enables that behavior. The change to the histedit test is because histedit uses graft to apply commits. The test in question moves a commit backwards onto an ancestor. Since the graft logic now more explicitly supports this, it knows to simply accept the incoming changes (since they are more recent), instead of prompting.