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Upgrade mypy to 2.4.0 and optimize configuration - #79
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- Set `num_workers = "auto"` in [tool.mypy]: parallel checking is no longer experimental in 2.4, and "auto" picks the worker count from the available CPUs (capped at 8). This replaces the CI-only `--num-workers "$(nproc)"` flag, so local `mypy` runs are parallel too. dmypy forces num_workers=0, so `just lint` is unaffected. - Drop `fixed_format_cache = true`: it has been the default since mypy 2.0. - The native parser is now the default; nothing to configure. - No new documented strictness flags or error codes in 2.4 (the new `--check-unreachable` is a hidden flag), so the enable-checks list is unchanged; only the "last updated" marker moves to 2.4. Co-Authored-By: Claude Opus 5.5 <[email protected]> Claude-Session: https://claude.ai/code/session_0188obxQFxxkZRKmsy9fstfd
Reports [[tool.mypy.overrides]] sections that match no checked module, e.g. a stale ignore_missing_imports for a dropped dependency. It is not part of --strict. mypy 2.4 removed the docs caveat that it requires incremental mode to be off; verified it reports with a warm cache, in parallel mode, and under dmypy. Co-Authored-By: Claude Opus 5.5 <[email protected]> Claude-Session: https://claude.ai/code/session_0188obxQFxxkZRKmsy9fstfd
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Please address the comments from this code review:
## Individual Comments
### Comment 1
<location path="project_name/pyproject.toml.jinja" line_range="189" />
<code_context>
files = ["src", "tests"]
mypy_path = "stubs"
-fixed_format_cache = true
+num_workers = "auto"
# set the platform
python_version = "3.{{ python_min }}"
</code_context>
<issue_to_address>
**Pre-commit mypy remains serial**
When local lint is run through `just lint`, `just lint` runs `prek run --all-files`, whose mypy hook passes `--config-file ''` without a `--num-workers` option, so it ignores this setting and checks files serially. That local mypy entry point does not get the parallelism the commit says local runs gain.
Add `--num-workers=auto` to the pre-commit mypy hook if that hook is intended to share the parallelism improvement.
</issue_to_address>Sourcery assessment
Approved.
validate-pyproject (with the schema store) rejects num_workers = "auto": SchemaStore's partial-mypy.json still types num_workers as an integer, so generated projects failed `just lint`. Keep the parallel run in CI via the CLI flag, which accepts "auto" since mypy 2.4, until the schema catches up. Co-Authored-By: Claude Opus 5.5 <[email protected]> Claude-Session: https://claude.ai/code/session_0188obxQFxxkZRKmsy9fstfd
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Oct 5, 2026
#79 moved this to a CI-only `--num-workers auto` flag because validate-pyproject rejects the value: SchemaStore's mypy schema still types num_workers as an integer. Put it back in [tool.mypy], so local `mypy` runs are parallel too, and disable only the mypy schema in the validate-pyproject hook until the schema catches up. Co-authored-by: Claude Opus 5.5 <[email protected]>
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Summary
This PR upgrades mypy from version 2.3.0 to 2.4.0 and optimizes the mypy configuration to leverage the new version's capabilities.
Key Changes
~=2.3.0to~=2.4.0fixed_format_cache = truewithnum_workers = "auto"for better parallel processingwarn_unused_configs = trueto catch unused configuration options--num-workers "$(nproc)"flag from mypy invocation in CI workflow, allowing mypy to use its configurednum_workers = "auto"setting insteadImplementation Details
The
num_workers = "auto"setting allows mypy to automatically determine the optimal number of worker processes based on the system's CPU count, replacing the previous manual cache format configuration. The CI workflow now relies on the pyproject.toml configuration rather than passing command-line arguments, reducing duplication and improving maintainability.https://claude.ai/code/session_0188obxQFxxkZRKmsy9fstfd