view tests/test-extdata.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

  $ hg init repo
  $ cd repo
  $ for n in 0 1 2 3 4 5 6 7 8 9 10 11; do
  >   echo $n > $n
  >   hg ci -qAm $n
  > done

test revset support

  $ cat <<'EOF' >> .hg/hgrc
  > [extdata]
  > filedata = file:extdata.txt
  > notes = notes.txt
  > shelldata = shell:cat extdata.txt | grep 2
  > emptygrep = shell:cat extdata.txt | grep empty
  > badparse = shell:cat badparse.txt
  > EOF
  $ cat <<'EOF' > extdata.txt
  > 2 another comment on 2
  > 3
  > EOF
  $ cat <<'EOF' > notes.txt
  > f6ed this change is great!
  > e834 this is buggy :(
  > 0625 first post
  > bogusnode gives no error
  > a ambiguous node gives no error
  > EOF

  $ hg log -qr "extdata(filedata)"
  2:f6ed99a58333
  3:9de260b1e88e
  $ hg log -qr "extdata(shelldata)"
  2:f6ed99a58333

test weight of extdata() revset

  $ hg debugrevspec -p optimized "extdata(filedata) & 3"
  * optimized:
  (andsmally
    (func
      (symbol 'extdata')
      (symbol 'filedata'))
    (symbol '3'))
  3

test non-zero exit of shell command

  $ hg log -qr "extdata(emptygrep)"
  abort: extdata command 'cat extdata.txt | grep empty' failed: exited with status 1
  [255]

test bad extdata() revset source

  $ hg log -qr "extdata()"
  hg: parse error: extdata takes at least 1 string argument
  [255]
  $ hg log -qr "extdata(unknown)"
  abort: unknown extdata source 'unknown'
  [255]

test a zero-exiting source that emits garbage to confuse the revset parser

  $ cat > badparse.txt <<'EOF'
  > +---------------------------------------+
  > 9de260b1e88e
  > EOF

It might be nice if this error message mentioned where the bad string
came from (eg line X of extdata source S), but the important thing is
that we don't crash before we can print the parse error.
  $ hg log -qr "extdata(badparse)"
  hg: parse error at 0: not a prefix: +
  (+---------------------------------------+
   ^ here)
  [255]

test template support:

  $ hg log -r:3 -T "{node|short}{if(extdata('notes'), ' # {extdata('notes')}')}\n"
  06254b906311 # first post
  e8342c9a2ed1 # this is buggy :(
  f6ed99a58333 # this change is great!
  9de260b1e88e

test template cache:

  $ hg log -r:3 -T '{rev} "{extdata("notes")}" "{extdata("shelldata")}"\n'
  0 "first post" ""
  1 "this is buggy :(" ""
  2 "this change is great!" "another comment on 2"
  3 "" ""

test bad extdata() template source

  $ hg log -T "{extdata()}\n"
  hg: parse error: extdata expects one argument
  [255]
  $ hg log -T "{extdata('unknown')}\n"
  abort: unknown extdata source 'unknown'
  [255]
  $ hg log -T "{extdata(unknown)}\n"
  hg: parse error: empty data source specified
  (did you mean extdata('unknown')?)
  [255]
  $ hg log -T "{extdata('{unknown}')}\n"
  hg: parse error: empty data source specified
  [255]

we don't fix up relative file URLs, but we do run shell commands in repo root

  $ mkdir sub
  $ cd sub
  $ hg log -qr "extdata(filedata)"
  abort: error: $ENOENT$
  [255]
  $ hg log -qr "extdata(shelldata)"
  2:f6ed99a58333

  $ cd ..