Fix psycopg2

[hamdanal]

Unblocks sbdchd/django-types#74

I did some careful reading of the docs and the C code and some testing in the repl. This hopefully yields a much better quality stubs for psycopg2.

[srittau]

Thanks and I'm sorry for the late review. Looks good to me, a few nits below.

[hamdanal]

Running stubtest for psycopg2 locally fails on my machine because it tries to build it from source and apparently it is missing some dependencies. psycopg2 is special because the compiled wheels exist on PyPI as the psycopg2-binary package. I did this locally to get around this issue:

diff --git a/tests/stubtest_third_party.py b/tests/stubtest_third_party.py
index af393c35f..65241e7be 100755
--- a/tests/stubtest_third_party.py
+++ b/tests/stubtest_third_party.py
@@ -45,7 +45,10 @@ def run_stubtest(
             print_error("fail")
             raise
         dist_extras = ", ".join(stubtest_settings.extras)
-        dist_req = f"{dist_name}[{dist_extras}]=={metadata.version}"
+        pypi_dist_name = dist_name
+        if dist_name == "psycopg2":
+            pypi_dist_name = "psycopg2-binary"  # psycopg2 is named psycopg2-binary on PyPI
+        dist_req = f"{pypi_dist_name}[{dist_extras}]=={metadata.version}"

         # If tool.stubtest.stubtest_requirements exists, run "pip install" on it.
         if stubtest_settings.stubtest_requirements:

I don't know how many packages you have that are in the same situation but installing from wheels would make CI faster and cause less problems while developing. It might not be worth the effort though, I don't know.

[github-actions]

According to mypy_primer, this change has no effect on the checked open source code. 🤖🎉

[andersk]

This needs to be Iterable[Composable], not SupportsIter[Composable]. The difference is that

• seq: Iterable[Composable] means iter(seq): Iterator[Composable] (hence next(iter(seq)): Composable), while
• seq: SupportsIter[Composable] means iter(seq): Composable, which is not an iterator.

• Psycopg2 SQL.join false positive #10715
• Fix psycopg2.sql.SQL.join annotation #10716