Switch type checking from mypy to Pyrefly (#8182) by rosspeili · Pull Request #8227 · quantumlib/Cirq

rosspeili · 2026-07-26T14:36:52Z

Switch type checking from mypy to Pyrefly per 8182, also includes the check/typecheck rename/deprecation from 8225, can close once this lands.

Migrated [tool.mypy] with pyrefly init, then set monorepo search-path to match dev_tools/pypath.
Excluded notebooks (and generated cirq_google/cloud) as discussed on 8182.
Mapped mypy’s follow_imports=silent/skip third-party posture to ignore-missing-imports + replace-imports-with-any for sympy/networkx/pandas/protobuf.
Fixed two first-party issues similar to OpenFermion take (dtype is not None, cast before sorted for Qids).
Added check/typecheck, deprecated check/mypy (remove in v1.8), updated CI / check/all / shellcheck / deps / docs.

notes

Left mypy-protobuf / --mypy_out alone (stub generation, not the typechecker CLI).
Some Pyrefly error kinds that are much stricter than Cirq’s old silent-import mypy setup are disabled in [tool.pyrefly.errors] for this migration.

Test plan

pyrefly check → 0 errors locally
black / ruff clean on touched Python
pytest on touched modules
CI Type check job green

Fixes #8182

rosspeili · 2026-07-26T14:40:06Z

Config choices and follow-up

Since pyrefly is stricter than cirq’s previous mypy config (follow_imports=silent on sympy/networkx/pandas/protobuf), after mapping that to replace-imports-with-any, hundreds of first-party diagnostics remained (bad-argument-type, overload/kwargs patterns, etc.) that mypy did not effectively enforce. Per #8182 (“fix or adjust config for low-priority”), those kinds are disabled for now so the tool switch stays green without cirq-wide annotation rewrite.

Same idea as the OpenFermion pyrefly migration (#1433): migrate the checker first, tighten selectively later.

Suggested follow-up unless otherwise advised

Re-enable error kinds one at a time (start with bad-return / missing-attribute).
Fix or narrowly # type: ignore real first-party issues.
Prefer that over expanding replace-imports-with-any.

Happy to open that follow-ups after this lands, or adjust the disable list here if you’d rather tighten in this PR.

@pavoljuhas @mhucka, this also covers #8225’s check/typecheck / deprecate-check/mypy bits.

codecov · 2026-07-26T14:51:13Z

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.59%. Comparing base (cfa8a84) to head (6eccdbc).
⚠️ Report is 11 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #8227      +/-   ##
==========================================
- Coverage   99.59%   99.59%   -0.01%     
==========================================
  Files        1125     1127       +2     
  Lines      103250   103414     +164     
==========================================
+ Hits       102829   102992     +163     
- Misses        421      422       +1

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mhucka · 2026-09-02T17:40:52Z

Discussed in Cirq Cynq 2026-09-02:

We'll try to do this before 1.8.

rosspeili · 2026-09-03T07:29:26Z

@mhucka you want me to rebase and clean up any arising conflicts or you'll do during merge?

pavoljuhas · 2026-09-03T18:51:31Z

@rosspeili - please hold on with the rebase. I will merge the main branch myself.

pavoljuhas

As it is, the PR removes mypy and suppresses most pyrefly errors - effectively leaving the code without type check. Let us loosely follow the advice at https://pyrefly.org/en/docs/migrating-from-mypy/#3-handle-the-new-errors-and-drop-mypy instead, i.e., please restore mypy and keep it active in the CI. For the initial pyrefly config please generate and commit the "pyrefly-baseline.json" file and configure pyrefly to use it as its baseline.

This will enforce pyrefly for any changed code. We can then gradually work on errors suppressed in pyrefly-baseline.json until it is not needed anymore. Once we get there, we can remove mypy and use the pyrefly only.

pavoljuhas · 2026-09-05T04:07:23Z

@@ -1,7 +1,7 @@
 #!/usr/bin/env bash

 ################################################################################
-# Runs mypy on the repository.


Please restore to the main version. We will keep mypy around for the time of transition.

pavoljuhas · 2026-09-05T04:08:51Z

@@ -154,7 +154,10 @@ def __init__(

    @property
    def qubits(self) -> tuple[cirq.Qid, ...]:
-        return cast(tuple['cirq.Qid', ...], tuple(sorted(self.device_graph.vertices)))
+        return cast(


Please revert, this does not make a difference at this point.

pavoljuhas · 2026-09-05T04:15:32Z

@@ -13,4 +13,4 @@ repo_dir=$(git -C "${thisdir}" rev-parse --show-toplevel) || exit $?
 cd "${repo_dir}" || exit $?

 source dev_tools/pypath || exit $?
-mypy "$@" .


Please update to run both mypy and typecheck, for example,

mypy "$@" . && pyrefly check

For now we can ignore the command-line arguments for pyrefly and add them there after dropping mypy.

pavoljuhas · 2026-09-05T04:16:18Z

@@ -0,0 +1,6 @@
+# Type checking tool
+pyrefly==1.2.0


Please add mypy==2.1.0 back here.

pavoljuhas · 2026-09-05T04:16:33Z

@@ -49,6 +49,7 @@ def run(
        'pylint',
        'env',
        'pytest',
+        'pyrefly',


Not necessary, please revert.

pavoljuhas · 2026-09-05T04:22:17Z

@@ -163,12 +163,12 @@ This script uses the `grpcio-tools` package to generate the Python proto API.

 There are a few options for running continuous integration checks, varying from easy and fast to slow and reliable.

-The simplest way to run checks is to invoke `pytest`, `pylint`, or `mypy` for yourself as follows:
+The simplest way to run checks is to invoke `pytest`, `pylint`, or `pyrefly` for yourself as follows:


Please revert this file, for the transition we will use mypy as the main type checker.

pavoljuhas · 2026-09-05T04:23:50Z

-[tool.mypy]
-exclude = [
-    '/setup\.py',
-    'cirq-google/cirq_google/cloud/',


Please restore the mypy section.

pavoljuhas · 2026-09-05T04:41:46Z

+
+# Checks that are much stricter than mypy under Cirq's silent-import setup.
+# Tracked for follow-up tightening after the tool switch.
+[tool.pyrefly.errors]


This would essentially disable typechecking. For consistency with our internal config, please use

redundant-cast = "error" unused-type-ignore = "error"

Instead of disabling most errors, we should generate and commit the "pyrefly-baseline.json" file following the advice at https://pyrefly.org/en/docs/migrating-from-mypy/#3-handle-the-new-errors-and-drop-mypy. When pyrefly checks against the baseline file, it will flag typing errors in any new code. We can then gradually work on fixing the errors in the baseline file so it is eventually not necessary and can be removed. At that point we can drop mypy and use pyrefly only.

pavoljuhas · 2026-09-05T04:53:10Z

+    "**/setup.py",
+    "**/cirq-google/cirq_google/cloud/**",
+    "**/*.ipynb",
+    "**/docs/**",
+    "**/__pycache__/**",
+    "**/.venv/**",
+    "**/venv/**",
+    "**/node_modules/**",


Are all of these needed? Please keep only the patterns which may match some files in the search-path above.

Add check/typecheck, deprecate check/mypy, and wire CI/deps/docs. Migrate config from mypy with monorepo search-path and notebook excludes.

Restore mypy as the primary type checker during the Pyrefly transition. Run both mypy and pyrefly in check/typecheck, commit pyrefly-baseline.json so only new/changed code must satisfy Pyrefly, and revert docs to reference mypy per maintainer feedback.

Fixes check/misc EOF whitespace failure in CI.

Add stim to pyrefly ignore-missing-imports (matching mypy) and baseline entries for numpy typing errors seen in CI on Python 3.11.

rosspeili · 2026-09-06T12:02:50Z

Hey @pavoljuhas, all points addressed the best I could. Will tweak if CI has issues. Let me know how this looks, and any feedback and directional tips more than welcome <3

Drop the ANSI red prefix and EXIT trap; mypy and pyrefly already colorize their own output when FORCE_COLOR is set.

rosspeili · 2026-09-11T10:50:37Z

Good catch @mhucka and yes, that would have turned all mypy/pyrefly output red until exit. Removed in last commit as both tools already colorize their own output via FORCE_COLOR=1.

rosspeili requested a review from a team as a code owner July 26, 2026 14:36

rosspeili requested a review from viathor July 26, 2026 14:36

github-actions Bot added the size: L 250< lines changed <1000 label Jul 26, 2026

mhucka self-assigned this Sep 2, 2026

mhucka added the triage/discuss Needs decision / discussion, bring these up during Cirq Cynque label Sep 2, 2026

mhucka assigned pavoljuhas and unassigned mhucka Sep 2, 2026

mhucka added the priority/before-1.8 Leave for after the Cirq 1.7 release label Sep 2, 2026

pavoljuhas self-requested a review September 3, 2026 18:51

pavoljuhas requested changes Sep 5, 2026

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pavoljuhas reviewed Sep 5, 2026

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rosspeili added 3 commits September 6, 2026 14:47

Switch type checking from mypy to Pyrefly (quantumlib#8182)

487a607

Add check/typecheck, deprecate check/mypy, and wire CI/deps/docs. Migrate config from mypy with monorepo search-path and notebook excludes.

Fix trailing blank line at EOF in pyproject.toml

bcf78d9

rosspeili force-pushed the switch-to-pyrefly-8182 branch from 3476384 to 53ee0cc Compare September 6, 2026 11:54

github-actions Bot added size: XL lines changed >1000 and removed size: L 250< lines changed <1000 labels Sep 6, 2026

rosspeili added 2 commits September 6, 2026 14:56

Add trailing newline to pyrefly-baseline.json

bd9748a

Fixes check/misc EOF whitespace failure in CI.

Fix CI pyrefly failures and baseline EOF

bc21ba5

Add stim to pyrefly ignore-missing-imports (matching mypy) and baseline entries for numpy typing errors seen in CI on Python 3.11.

mhucka requested changes Sep 10, 2026

View reviewed changes

Comment thread check/typecheck Outdated

Remove global red coloring from check/typecheck

6eccdbc

Drop the ANSI red prefix and EXIT trap; mypy and pyrefly already colorize their own output when FORCE_COLOR is set.

mhucka added area/typecheck and removed triage/discuss Needs decision / discussion, bring these up during Cirq Cynque labels Sep 16, 2026

mhucka added the area/devops Involving development tools, procedures, documentation, services, and so on label Sep 16, 2026

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Test plan

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rosspeili commented Jul 26, 2026

Config choices and follow-up

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