#22752 regression in 2.29.0 when running `pants check` on a large repository Issue created by cburroughs When trying to run

pants check ::

in an internal Python repository I get 75 inscrutable mypy errors that were not present before. I use

mypy.install_from_resolve

so this is unrelated to the specific version of mypy. The exact errors seem to vary in a 'spooky' way based on which targets I

check

. From

git bisect

I've narrowed this down to da7cba5 (#22578). Prior to that change we would generate

__run.sh

scripts that look like:

-env -i MYPYPATH=$'my:source:roots' MYPY_FORCE_COLOR=1 MYPY_FORCE_TERMINAL_WIDTH=642092230765939 PEX_EXTRA_SYS_PATH=$'my:source_roots' TERM=ansi ./__mypy_runner.sh

But with that change the command instead has

PEX_EXTRA_SYS_PATH=''

. This is presumably due to:

diff --git a/src/python/pants/backend/python/typecheck/mypy/rules.py b/src/python/pants/backend/python/typecheck/mypy/rules.py
index 0c31d1f6d8..449bf0d47a 100644
--- a/src/python/pants/backend/python/typecheck/mypy/rules.py
+++ b/src/python/pants/backend/python/typecheck/mypy/rules.py
@@ -4,7 +4,6 @@
 from __future__ import annotations
 
 import dataclasses
-import itertools
 from collections.abc import Iterable
 from dataclasses import dataclass
 from hashlib import sha256
@@ -336,12 +335,9 @@ async def mypy_typecheck_partition(
         )
     )
 
-    all_used_source_roots = sorted(
-        set(itertools.chain(first_party_plugins.source_roots, closure_sources.source_roots))
-    )
     env = {
-        "PEX_EXTRA_SYS_PATH": ":".join(all_used_source_roots),
-        "MYPYPATH": ":".join(all_used_source_roots),
+        "PEX_EXTRA_SYS_PATH": ":".join(first_party_plugins.source_roots),
+        "MYPYPATH": ":".join(closure_sources.source_roots),
         # Always emit colors to improve cache hit rates, the results are post-processed to match the
         # global setting
         "MYPY_FORCE_COLOR": "1",

Possible Slack Thread Breadcrumb: https://pantsbuild.slack.com/archives/C046T6T9U/p1661627014305049 I am uncertain why

pantsbuild/pants

itself is unaffected. Perhaps generated protocal buffers are part of the puzzle? pantsbuild/pants