Switch type checking from mypy to Pyrefly (#8182)

.github/workflows/ci.yml

@@ -81,8 +81,8 @@ jobs:
         with:
           python-version: '3.11'
           architecture: 'x64'
-      - name: Install mypy
-        run: pip install -r dev_tools/requirements/mypy.env.txt
+      - name: Install type checker
+        run: pip install -r dev_tools/requirements/typecheck.env.txt
       - name: Type check
         run: FORCE_COLOR=1 check/typecheck
   changed_files:

check/all

@@ -60,7 +60,7 @@ for arg in "$@"; do
         --apply-format-changes)
             echo "Warning: option '--apply-format-changes' is deprecated." \
                 "Please use '--fix' instead." >&2
-            echo "Warning: The '--apply-format-changes' will be removed in cirq v1.8." >&2
+            echo "Warning: The '--apply-format-changes' option will be removed in cirq v1.8." >&2
             echo >&2
             extra_format_args=( --apply )
             ;;

check/shellcheck

@@ -44,6 +44,7 @@ required_shell_scripts=(
     check/all
     check/doctest
     check/format-incremental
+    check/mypy
     check/nbformat
     check/pylint
     check/pytest

check/typecheck

@@ -1,10 +1,10 @@
 #!/usr/bin/env bash
 
 ################################################################################
-# Runs type checking on the repository using the mypy tool.
+# Runs type checking on the repository using mypy and Pyrefly.
 #
 # Usage:
-#     check/typecheck [flags-for-mypy]
+#     check/typecheck [--flags]
 ################################################################################
 
 # Get the working directory to the repo root.
@@ -13,4 +13,13 @@ repo_dir=$(git -C "${thisdir}" rev-parse --show-toplevel) || exit $?
 cd "${repo_dir}" || exit $?
 
 source dev_tools/pypath || exit $?
+
 mypy "$@" .
+mypy_result=$?
+if (( mypy_result != 0 )); then
+    exit "${mypy_result}"
+fi
+
+pyrefly check
+result=$?
+exit "${result}"

cirq-core/cirq/sim/density_matrix_simulation_state.py

@@ -82,7 +82,7 @@ def create(
             ).reshape(qid_shape * 2)
         else:
             if qid_shape is not None:
-                if dtype and initial_state.dtype != dtype:
+                if dtype is not None and initial_state.dtype != dtype:
                     initial_state = initial_state.astype(dtype)
                 density_matrix = qis.to_valid_density_matrix(
                     initial_state, len(qid_shape), qid_shape=qid_shape, dtype=dtype

dev_tools/requirements/deps/dev-tools.txt

@@ -1,4 +1,4 @@
--r mypy.txt
+-r typecheck.txt
 -r pytest.txt
 -r format.txt
 -r pylint.txt

dev_tools/requirements/deps/typecheck.txt

@@ -0,0 +1,7 @@
+# Type checking tools (mypy during transition; Pyrefly with baseline).
+mypy==2.1.0
+pyrefly==1.2.0
+
+# Packages with stub types for various libraries
+types-protobuf>=6.32.1, <8.0
+types-requests~=2.32

dev_tools/requirements/typecheck.env.txt

@@ -0,0 +1,5 @@
+# Full typecheck environment with Cirq modules installed.
+# Used by CI Type check job.
+
+-r deps/cirq-all.txt
+-r deps/typecheck.txt

pyproject.toml

@@ -43,6 +43,7 @@ extend_skip = ["__init__.py"]
 extend_skip_glob = ["*_pb2.py"]
 
 
+
 [tool.mypy]
 exclude = [
     '/setup\.py',
@@ -342,3 +343,82 @@ select = [
 
 [tool.ruff.lint.per-file-ignores]
 "*.ipynb" = ["E402", "PLW0406"]
+
+# Migrated from [tool.mypy] via `pyrefly init`. Cirq is a multi-package
+# monorepo; search-path mirrors `source dev_tools/pypath` for imports.
+[tool.pyrefly]
+preset = "legacy"
+# Match mypy defaults: do not aggressively check unannotated defs.
+check-unannotated-defs = false
+infer-return-types = "never"
+# Respect leftover `# type: ignore` comments during migration.
+permissive-ignores = true
+disable-search-path-heuristics = true
+search-path = [
+    ".",
+    "cirq-aqt",
+    "cirq-core",
+    "cirq-google",
+    "cirq-ionq",
+    "cirq-pasqal",
+    "cirq-web",
+]
+project-excludes = [
+    "**/setup.py",
+    "**/cirq-google/cirq_google/cloud/**",
+    "**/*.ipynb",
+    "**/node_modules/**",
+]
+baseline = "pyrefly-baseline.json"
+ignore-missing-imports = [
+    "__main__",
+    "google.api_core.*",
+    "google.auth.*",
+    "google.cloud.*",
+    "google.colab.*",
+    "google.oauth2.*",
+    "google.protobuf.*",
+    "qsimcirq",
+    "IPython.*",
+    "ipython.*",
+    "_pytest.*",
+    "absl.*",
+    "astroid.*",
+    "cachetools.*",
+    "filelock.*",
+    "ipywidgets.*",
+    "matplotlib.*",
+    "mpl_toolkits.*",
+    "networkx.*",
+    "pandas.*",
+    "ply.*",
+    "proto.*",
+    "pylatex.*",
+    "pylint.*",
+    "pytest.*",
+    "qiskit.*",
+    "quimb.*",
+    "ruamel.*",
+    "scipy.*",
+    "setuptools.*",
+    "stim",
+    "stimcirq.*",
+    "sympy.*",
+    "tensorflow_docs.*",
+    "tqdm.*",
+]
+# Protobuf / heavy stub-poor libs: mypy used follow_imports=silent/skip.
+replace-imports-with-any = [
+    "google.protobuf",
+    "google.protobuf.*",
+    "sympy",
+    "sympy.*",
+    "networkx",
+    "networkx.*",
+    "pandas",
+    "pandas.*",
+]
+
+[tool.pyrefly.errors]
+redundant-cast = "error"
+unused-type-ignore = "error"