ParamSpec for @st.composite annotations

[Zac-HD]

MVP version of #3212; st.functions() is going to be harder thanks to longstanding mypy issues.

[Zac-HD]

Sadly, it looks like mypy support just isn't there yet:

=================================== FAILURES ===================================
________________________ test_mypy_passes_on_hypothesis ________________________
Traceback (most recent call last):
  File "/home/runner/work/hypothesis/hypothesis/whole-repo-tests/test_type_hints.py", line 20, in test_mypy_passes_on_hypothesis
    pip_tool("mypy", PYTHON_SRC)
  File "/home/runner/work/hypothesis/hypothesis/tooling/src/hypothesistooling/scripts.py", line 69, in pip_tool
    sys.exit(r)
SystemExit: 1
----------------------------- Captured stdout call -----------------------------
mypy /home/runner/work/hypothesis/hypothesis/hypothesis-python/src
hypothesis-python/src/hypothesis/strategies/_internal/core.py:1501: error: The first argument to Callable must be a list of types or "..."
hypothesis-python/src/hypothesis/strategies/_internal/core.py:1502: error: The first argument to Callable must be a list of types or "..."
Found 2 errors in 1 file (checked 100 source files)
_________________________ test_composite_type_tracing __________________________
Traceback (most recent call last):
  File "/home/runner/work/hypothesis/hypothesis/whole-repo-tests/test_type_hints.py", line 155, in test_composite_type_tracing
    assert got == "def (x: int) -> int"
AssertionError: assert 'Any' == 'def (x: int) -> int'
  - def (x: int) -> int
  + Any

Let's revisit in a few months, or when the changelog suggests this might have changed.

[rsokl]

😭

[gjoseph92]

Yeah, seems like MyPy doesn't support Concatenate yet: python/mypy#11833, http://mypy-lang.blogspot.com/2021/12/mypy-0930-released.html#:~:text=Note%20that%20typing.Concatenate%20and%20some%20other%20use%20cases%20are%20still%20not%20supported.

However, other typecheckers (pyright, i.e. VSCode) do, and this annotation would improve the autocomplete experience a lot for Hypothesis users using language servers that do support it. I'm curious what policy (if any) you have on these new typing features; it is part of the spec and supported by typing-extensions, even if one particular type checker doesn't handle it yet.

[Zac-HD]

Generally we're happy to adopt as soon as that's possible without breaking things; which in this case requires basic support in mypy - it doesn't need to be checked, but erroring out is unacceptable 😕

Hopefully we can revisit this soon!