random slow down

[stevenh]

Bug Report

Using a basic check on the command line for a package I'm developing which has a bunch of dependencies mypy can be quick or or very slow ranging from 2s to over 40s, with seemingly no rhyme or reason to it. Even consecutive runs without touching the code can exhibit the slowdown.

To Reproduce

Hard to create a reproduction as it seems to be totally random

~/code/projectX$ time mypy src/ tests/
Success: no issues found in 78 source files

real    0m6.214s
user    0m4.533s
sys     0m0.863s
~/code/projectX$ time mypy src/ tests/
Success: no issues found in 78 source files

real    0m42.895s
user    0m37.618s
sys     0m3.718s

Expected Behavior

I would expect the time to run to be relatively constant when little to no changes made.

Actual Behavior

Random slow down even when the code hasn't been touched.

~/code/projectX$ time mypy src/ tests/
Success: no issues found in 78 source files

real    0m6.214s
user    0m4.533s
sys     0m0.863s
~/code/projectX$time mypy src/ tests/
Success: no issues found in 78 source files

real    0m2.638s
user    0m2.138s
sys     0m0.496s
~/code/projectX$time mypy src/ tests/
Success: no issues found in 78 source files

real    0m2.740s
user    0m2.169s
sys     0m0.568s
~/code/projectX$ time mypy src/ tests/
Success: no issues found in 78 source files

real    0m2.985s
user    0m2.314s
sys     0m0.596s
~/code/projectX$ time mypy src/ tests/
Success: no issues found in 78 source files

real    0m42.895s
user    0m37.618s
sys     0m3.718s

Your Environment

• Mypy version used:

mypy --version
mypy 1.16.0 (compiled: yes)

• Mypy command-line flags: none
• Mypy configuration options from mypy.ini (and other config files):

[tool.mypy]
strict = true
mypy_path = ["typing"]
exclude = '.*/data$'

[[tool.mypy.overrides]]
module = [
  "advertools",
  "datasets",
  "evaluate",
  "crawl4ai.*"
]
ignore_missing_imports = true

• Python version used:
  python --version
  Python 3.12.9
• Hardware:
  MacBook Pro - Apple M3 Max running Sequoia 15.5

[stevenh]

Running with --verbose shows a potential smoking gun, on a slow run it reports that metadata missing or abandoned for a bunch of packages e.g.

LOG:  Metadata not found for enum
LOG:  Parsing .venv/lib/python3.12/site-packages/mypy/typeshed/stdlib/enum.pyi (enum)
LOG:  Metadata fresh for json: file .venv/lib/python3.12/site-packages/mypy/typeshed/stdlib/json/__init__.pyi

vs

LOG:  Metadata fresh for enum: file .venv/lib/python3.12/site-packages/mypy/typeshed/stdlib/enum.pyi

This is repeated for a load of modules and then I see:

LOG:  Loaded graph with 7862 nodes (0.916 sec)
LOG:  Found 2295 SCCs; largest has 2878 nodes
LOG:  Processing SCC of size 58 (zipimport zipfile._path zipfile typing_extensions typing types sys._monitoring sys subprocess sre_parse sre_constants sre_compile resource re posixpath pathlib os.path os io importlib.resources.abc importlib.resources._common importlib.resources importlib.readers importlib.metadata._meta importlib.metadata importlib.machinery importlib.abc importlib._bootstrap_external importlib._bootstrap importlib._abc importlib genericpath enum email.policy email.message email.header email.errors email.contentmanager email.charset email._policybase email dataclasses contextlib collections.abc collections codecs ast abc _typeshed.importlib _typeshed _sitebuiltins _io _frozen_importlib_external _frozen_importlib _collections_abc _codecs _ast builtins) as inherently stale
LOG:  Writing zipimport .venv/lib/python3.12/site-packages/mypy/typeshed/stdlib/zipimport.pyi zipimport.meta.json zipimport.data.json
LOG:  Cached module zipimport has changed interface
LOG:  Writing zipfile._path .venv/lib/python3.12/site-packages/mypy/typeshed/stdlib/zipfile/_path/__init__.pyi zipfile/_path/__init__.meta.json zipfile/_path/__init__.data.json
LOG:  Cached module zipfile._path has changed interface
LOG:  Writing zipfile .venv/lib/python3.12/site-packages/mypy/typeshed/stdlib/zipfile/__init__.pyi zipfile/__init__.meta.json zipfile/__init__.data.json
LOG:  Cached module zipfile has changed interface
....
LOG:  No fresh SCCs left in queue
LOG:  Build finished in 39.933 seconds with 7862 modules, and 0 errors
Success: no issues found in 78 source files

vs:

LOG:  Loaded graph with 7862 nodes (0.682 sec)
LOG:  Found 2295 SCCs; largest has 2878 nodes
LOG:  Processing 812 queued fresh SCCs
LOG:  Processing SCC singleton (streamlit.proto.RootContainer_pb2) as stale due to changed suppression (google)
...
LOG:  176 fresh SCCs (4331 nodes) left in queue (and will remain unprocessed)
LOG:  Build finished in 2.518 seconds with 3531 modules, and 0 errors
Success: no issues found in 78 source files

So it seems its rebuilding lots for no discernible reason, these were back to back checks with no changes.

[stevenh]

I think I might have found the reason, the VS Code Mypy Type Checker extension ships with 1.15.0 and I have 1.16.0 installed so the cli and VS Code versions are constantly fighting, resulting in them destroying the cache.

Setting: "mypy-type-checker.importStrategy": "fromEnvironment" should solve, the default is useBundled.

[stevenh]

Not see it happen sync syncing the two environments so closing as a local environment issue.