debugcommands: move away from line buffered output on binary stream Line buffering on binary file objects is apparently undefined behavior in Python and emits a RuntimeWarning on Python 3.8. See https://bugs.python.org/issue32236. This commit changes the I/O logging file descriptor from line buffered to unbuffered to work around this. I'm no fan of unbuffered I/O for performance reasons. But I don't think it is an issue here given the nature of the code. With this change, test-ssh-proto.t now passes on Python 3.8. Differential Revision: https://phab.mercurial-scm.org/D7948

py3: conditionalize test-lfs-serve-access.t for Python 3.8 This is another case where Python 3.8's traceback printing varies subtly from older Python versions. Again, I'm not sure why. But this is apparently the new behavior. With this change, test-lfs-serve-access.t now passes on Python 3.8! Differential Revision: https://phab.mercurial-scm.org/D7947

py3: add extra traceback line present on Python 3.8 I'm not sure why Python 3.8 is outputting this line. It appears to be a change in behavior of formatting tracebacks on Python 3.8. So let's add it to expected output. With this change, test-hook.t now passes on Python 3.8. Differential Revision: https://phab.mercurial-scm.org/D7946

py3: conditionalize test-flagprocessor.t on Python 3.8 For reasons I don't understand, Python 3.8 is outputting a different lint in the traceback than prior Pythons. The lines in question are: flagutil.addflagprocessor( REVIDX_NOOP, (noopdonothingread, noopdonothing, validatehash,) ) Python <3.8 prints the 2nd line but 3.8 the first line. Perhaps Python changed its traceback logic to always print the first line of a multiple line expression? Whatever the case, with this change, the test now passes on Python 3.8. Differential Revision: https://phab.mercurial-scm.org/D7945

tests: conditionalize test-hightlight.t on pygments version Output changed slightly in pygments 2.5. I thought it was easier to copy the line and add a version check than to add a regular expression because the line has some special characters. I also like tests explicitly calling out where they vary. Differential Revision: https://phab.mercurial-scm.org/D7943

hgdemandimport: apply lazy module loading to sys.meta_path finders Python's `sys.meta_path` finders are the primary objects whose job it is to find a module at import time. When `import` is called, Python iterates objects in this list and calls `o.find_spec(...)` to find a `ModuleSpec` (or None if the module couldn't be found by that finder). If no meta path finder can find a module, import fails. One of the default meta path finders is `PathFinder`. Its job is to import modules from the filesystem and is probably the most important importer. This finder looks at `sys.path` and `sys.path_hooks` to do its job. The `ModuleSpec` returned by `MetaPathImporter.find_spec()` has a `loader` attribute, which defines the concrete module loader to use. `sys.path_hooks` is a hook point for teaching `PathFinder` to instantiate custom loader types. Previously, we injected a custom `sys.path_hook` that told `PathFinder` to wrap the default loaders with a loader that creates a module object that is lazy. This approach worked. But its main limitation was that it only applied to the `PathFinder` meta path importer. There are other meta path importers that are registered. And in the case of PyOxidizer loading modules from memory, `PathFinder` doesn't come into play since PyOxidizer's own meta path importer was handling all imports. This commit changes our approach to lazy module loading by proxying all meta path importers. Specifically, we overload the `find_spec()` method to swap in a wrapped loader on the `ModuleSpec` before it is returned. The end result of this is all meta path importers should be lazy. As much as I would have loved to utilize .__class__ manipulation to achieve this, some meta path importers are implemented in C/Rust in such a way that they cannot be monkeypatched. This is why we use __getattribute__ to define a proxy. Also, this change could theoretically open us up to regressions in meta path importers whose loader is creating module objects which can't be monkeypatched. But I'm not aware of any of these in the wild. So I think we'll be safe. According to hyperfine, this change yields a decent startup time win of 5-6ms: ``` Benchmark #1: ~/.pyenv/versions/3.6.10/bin/python ./hg version Time (mean ± σ): 86.8 ms ± 0.5 ms [User: 78.0 ms, System: 8.7 ms] Range (min … max): 86.0 ms … 89.1 ms 50 runs Time (mean ± σ): 81.1 ms ± 2.7 ms [User: 74.5 ms, System: 6.5 ms] Range (min … max): 77.8 ms … 90.5 ms 50 runs Benchmark #2: ~/.pyenv/versions/3.7.6/bin/python ./hg version Time (mean ± σ): 78.9 ms ± 0.6 ms [User: 70.2 ms, System: 8.7 ms] Range (min … max): 78.1 ms … 81.2 ms 50 runs Time (mean ± σ): 73.4 ms ± 0.6 ms [User: 65.3 ms, System: 8.0 ms] Range (min … max): 72.4 ms … 75.7 ms 50 runs Benchmark #3: ~/.pyenv/versions/3.8.1/bin/python ./hg version Time (mean ± σ): 78.1 ms ± 0.6 ms [User: 70.2 ms, System: 7.9 ms] Range (min … max): 77.4 ms … 80.9 ms 50 runs Time (mean ± σ): 72.1 ms ± 0.4 ms [User: 64.4 ms, System: 7.6 ms] Range (min … max): 71.4 ms … 74.1 ms 50 runs ``` Differential Revision: https://phab.mercurial-scm.org/D7954

hgdemandimport: disable on Python 3.5 The demand importer functionality isn't working at all on Python 3.5. I'm not sure what's wrong. Since it isn't working, let's disable it completely. ``` $ HGRCPATH= hyperfine -w 1 -r 50 -- "~/.pyenv/versions/3.5.9/bin/python ./hg version" \ "HGDEMANDIMPORT=disable ~/.pyenv/versions/3.5.9/bin/python ./hg version" Benchmark #1: ~/.pyenv/versions/3.5.9/bin/python ./hg version Time (mean ± σ): 163.7 ms ± 2.2 ms [User: 148.5 ms, System: 15.7 ms] Range (min … max): 161.0 ms … 170.2 ms 50 runs Benchmark #2: HGDEMANDIMPORT=disable ~/.pyenv/versions/3.5.9/bin/python ./hg version Time (mean ± σ): 164.3 ms ± 1.4 ms [User: 148.2 ms, System: 16.6 ms] Range (min … max): 161.4 ms … 169.8 ms 50 runs ``` Differential Revision: https://phab.mercurial-scm.org/D7953

py3: suppress unraisable exceptions in test-worker.t Python 3.8 calls sys.unraisablehook when an unraisable exception is encountered. The default behavior is to print a warning. test-worker.t was triggering this hook due to a race between a newly forked process exiting and that process's _os.register_at_fork handlers running. I was seeing the stdlib's random module in the stack re-seeding itself. Although there could be other after-fork handlers in the mix. This commit defines sys.unraisablehook to effectively no-op. This suppresses the warning and makes test output on Python 3.8 consistent with prior versions. test-worker.t now passes on Python 3.8. Differential Revision: https://phab.mercurial-scm.org/D7949

rust: add a README In particular to explain how to build any of the rust. It's neither obvious, nor easy to find out, nor easy to determine if you did it right without some documentation. Differential Revision: https://phab.mercurial-scm.org/D7952

rust: move hgcli's README out of the way My understanding is that it's not meant to be used in the current form. Differential Revision: https://phab.mercurial-scm.org/D7951