view tests/test-identify.t @ 44118:f81c17ec303c

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

#require serve

#if no-outer-repo

no repo

  $ hg id
  abort: there is no Mercurial repository here (.hg not found)
  [255]

#endif

create repo

  $ hg init test
  $ cd test
  $ echo a > a
  $ hg ci -Ama
  adding a

basic id usage

  $ hg id
  cb9a9f314b8b tip
  $ hg id --debug
  cb9a9f314b8b07ba71012fcdbc544b5a4d82ff5b tip
  $ hg id -q
  cb9a9f314b8b
  $ hg id -v
  cb9a9f314b8b tip

with options

  $ hg id -r.
  cb9a9f314b8b tip
  $ hg id -n
  0
  $ hg id -t
  tip
  $ hg id -b
  default
  $ hg id -i
  cb9a9f314b8b
  $ hg id -n -t -b -i
  cb9a9f314b8b 0 default tip
  $ hg id -Tjson
  [
   {
    "bookmarks": [],
    "branch": "default",
    "dirty": "",
    "id": "cb9a9f314b8b07ba71012fcdbc544b5a4d82ff5b",
    "node": "ffffffffffffffffffffffffffffffffffffffff",
    "parents": ["cb9a9f314b8b07ba71012fcdbc544b5a4d82ff5b"],
    "tags": ["tip"]
   }
  ]

test template keywords and functions which require changectx:

  $ hg id -T '{rev} {node|shortest}\n'
  2147483647 ffff
  $ hg id -T '{parents % "{rev} {node|shortest} {desc}\n"}'
  0 cb9a a
  $ hg id -T '{parents}\n'
  cb9a9f314b8b07ba71012fcdbc544b5a4d82ff5b

test nested template: '{tags}'/'{node}' constants shouldn't override the
default keywords, but '{id}' persists because there's no default keyword
for '{id}' (issue5612)

  $ hg id -T '{tags}\n'
  tip
  $ hg id -T '{revset("null:.") % "{rev}:{node|short} {tags} {id|short}\n"}'
  -1:000000000000  cb9a9f314b8b
  0:cb9a9f314b8b tip cb9a9f314b8b

with modifications

  $ echo b > a
  $ hg id -n -t -b -i
  cb9a9f314b8b+ 0+ default tip
  $ hg id -Tjson
  [
   {
    "bookmarks": [],
    "branch": "default",
    "dirty": "+",
    "id": "cb9a9f314b8b07ba71012fcdbc544b5a4d82ff5b+",
    "node": "ffffffffffffffffffffffffffffffffffffffff",
    "parents": ["cb9a9f314b8b07ba71012fcdbc544b5a4d82ff5b"],
    "tags": ["tip"]
   }
  ]

other local repo

  $ cd ..
  $ hg -R test id
  cb9a9f314b8b+ tip
#if no-outer-repo
  $ hg id test
  cb9a9f314b8b+ tip
#endif

with remote http repo

  $ cd test
  $ hg serve -p $HGPORT1 -d --pid-file=hg.pid
  $ cat hg.pid >> $DAEMON_PIDS
  $ hg id http://localhost:$HGPORT1/
  cb9a9f314b8b

remote with rev number?

  $ hg id -n http://localhost:$HGPORT1/
  abort: can't query remote revision number, branch, or tags
  [255]

remote with tags?

  $ hg id -t http://localhost:$HGPORT1/
  abort: can't query remote revision number, branch, or tags
  [255]

remote with branch?

  $ hg id -b http://localhost:$HGPORT1/
  abort: can't query remote revision number, branch, or tags
  [255]

test bookmark support

  $ hg bookmark Y
  $ hg bookmark Z
  $ hg bookmarks
     Y                         0:cb9a9f314b8b
   * Z                         0:cb9a9f314b8b
  $ hg id
  cb9a9f314b8b+ tip Y/Z
  $ hg id --bookmarks
  Y Z

test remote identify with bookmarks

  $ hg id http://localhost:$HGPORT1/
  cb9a9f314b8b Y/Z
  $ hg id --bookmarks http://localhost:$HGPORT1/
  Y Z
  $ hg id -r . http://localhost:$HGPORT1/
  cb9a9f314b8b Y/Z
  $ hg id --bookmarks -r . http://localhost:$HGPORT1/
  Y Z

test invalid lookup

  $ hg id -r noNoNO http://localhost:$HGPORT1/
  abort: unknown revision 'noNoNO'!
  [255]

Make sure we do not obscure unknown requires file entries (issue2649)

  $ echo fake >> .hg/requires
  $ hg id
  abort: repository requires features unknown to this Mercurial: fake!
  (see https://mercurial-scm.org/wiki/MissingRequirement for more information)
  [255]

  $ cd ..
#if no-outer-repo
  $ hg id test
  abort: repository requires features unknown to this Mercurial: fake!
  (see https://mercurial-scm.org/wiki/MissingRequirement for more information)
  [255]
#endif