streamclone: treat volatile file as "fullfile" The nodemap related file might change (or get deleted) during the stream clone in a way incompatible with the streaming process. So we introduce a new flag for this type of file and integrate it with the existing `revlog_type` field recently added to `store.walk` returns. We use that new flat to dispatch such file to the existing mechanism for "atomic replacement" file for the nodemap docket and datafile. This fix the bugs we have been adding tests for. Strictly speaking, the nodemap datafile is happened only a could maybe be used in a slightly more efficient way, however this is good enough for now. Differential Revision: https://phab.mercurial-scm.org/D10481

nodemap: add a test about nodemap "vacuum" during stream clone When the nodemap "vacuum" it generate a new datafile, with a new unique name and delete the old one. This confuse the stream clone code and create the same kind of crash we were seeing in the previous patch. We build a test case where this happens. The next changeset will contains a fix We can also notice that we are, wrongfully exchanging `undo.*` files that the client will not be able to use. This will be dealt with soon. Differential Revision: https://phab.mercurial-scm.org/D10480

nodemap: add a test about racy commit during stream clone That test show that the resulting client nodemap is different from the server one. This happens because the server one transferred a corrupted node map. The data file match the pre-commit content while the docket has post commit content. As the result the nodemap was detected invalid and recomputed. When running without the rust implementation, the code is also generating a new datafile unconditionally, This mean the older file is no longer there are transfer time, resulting in a crash. We will fix this issue later, but we start with writing tests highlighting the issue. Differential Revision: https://phab.mercurial-scm.org/D10479

streamclone: remove sleep based "synchronisation" in tests Sleep based test synchronisation does not work. Variation in machine performance and load can make the two process miss their windows. Instead we migrate to explicit signaling through the file system as other tests file are using. Differential Revision: https://phab.mercurial-scm.org/D10478

testing: add a `write_file` function The function is kinda trivial, but having a simple function avoid silly mistake. Differential Revision: https://phab.mercurial-scm.org/D10477

testing: add a utility function to wait for file create This is similar to `tests/testlib/wait-on-file`, but for the python code Differential Revision: https://phab.mercurial-scm.org/D10476

streamclone: check the errors log in tests Code can be buggy, in that case having error message tend to help. Differential Revision: https://phab.mercurial-scm.org/D10475