Switch type-checking from pyright to ty

DEVELOPMENT.md

@@ -45,7 +45,7 @@ uv run poe test-conformance
 We use:
 
 - **ruff** for linting and formatting
-- **pyright** for type checking
+- **ty** for type checking
 - **pytest** for testing
 
 The project follows strict type checking and formatting standards.

README.md

@@ -398,7 +398,7 @@ service YourService {
 
 ## Development
 
-We use `ruff` for linting and formatting, `pyright` for type checking, and `tombi` for TOML linting and formatting.
+We use `ruff` for linting and formatting, `ty` for type checking, and `tombi` for TOML linting and formatting.
 
 We rely on the conformance test suit (in
 [./conformance](./conformance)) to verify behavior.

conformance/test/_util.py

@@ -28,7 +28,7 @@ def maybe_patch_args_with_debug(args: list[str]) -> list[str]:
     # This invokes internal methods from bundles provided by the IDE
     # and may not always work.
     try:
-        from pydevd import (  # pyright:ignore[reportMissingImports] - provided by IDE  # noqa: PLC0415
+        from pydevd import (  # ty: ignore[unresolved-import] - provided by IDE  # noqa: PLC0415
             _pydev_bundle,
         )
 

conformance/test/test_client.py

@@ -6,8 +6,7 @@
 from typing import TYPE_CHECKING
 
 import pytest
-
-from ._util import VERSION_CONFORMANCE, coverage_env, maybe_patch_args_with_debug
+from _util import VERSION_CONFORMANCE, coverage_env, maybe_patch_args_with_debug
 
 if TYPE_CHECKING:
     from coverage import Coverage

conformance/test/test_server.py

@@ -7,8 +7,7 @@
 from typing import TYPE_CHECKING
 
 import pytest
-
-from ._util import VERSION_CONFORMANCE, coverage_env, maybe_patch_args_with_debug
+from _util import VERSION_CONFORMANCE, coverage_env, maybe_patch_args_with_debug
 
 if TYPE_CHECKING:
     from coverage import Coverage

example/example/eliza_service_sync.py

@@ -67,4 +67,4 @@ def health_check():
 
 eliza_app = ElizaServiceWSGIApplication(DemoElizaServiceSync())
 
-app.wsgi_app = DispatcherMiddleware(app.wsgi_app, {eliza_app.path: eliza_app})
+app.wsgi_app = DispatcherMiddleware(app.wsgi_app, {eliza_app.path: eliza_app})  # ty: ignore[invalid-assignment]

poe_tasks.toml

@@ -95,7 +95,7 @@ cmd = "tombi lint"
 
 [tasks.lint-types]
 help = "Apply type checking to Python files"
-cmd = "pyright"
+cmd = "ty check ."
 
 [tasks.test]
 help = "Run unit tests"

pyproject.toml

@@ -47,10 +47,12 @@ dev = [
   "gunicorn==25.3.0",
   "hypercorn==0.18.0",
   "poethepoet==0.45.0",
-  "pyright[nodejs]==1.1.409",
   "pyvoy==0.3.0",
   "ruff==0.15.12",
   "tombi==0.10.2",
+  "ty==0.0.34",
+  "types-grpcio==1.0.0.20260408",
+  "types-protobuf==7.34.1.20260503",
   "typing_extensions==4.15.0",
   "uvicorn==0.46.0",
   "zstandard==0.25.0",
@@ -79,30 +81,6 @@ docs = ["mkdocstrings-python==2.0.3", "zensical==0.0.39"]
 requires = ["uv_build>=0.11.0,<0.12.0"]
 build-backend = "uv_build"
 
-[tool.pyright]
-exclude = [
-  # Defaults.
-  "**/node_modules",
-  "**/__pycache__",
-  "**/.*",
-  ".venv",
-
-  # Recent versions of typeshed fail on 5.x gencode.
-  # https://github.com/python/typeshed/pull/15677
-  "**/*_pb.py",
-
-  # Recent versions of typeshed have improved typing of functions that then expose
-  # type errors for accessing
-  "**/*_pb2.py",
-
-  # GRPC python files don't typecheck on their own.
-  # See https://github.com/grpc/grpc/issues/39555
-  "**/*_pb2_grpc.py",
-
-  # TODO: Work out the import issues to allow it to work.
-  "conformance/**",
-]
-
 [tool.pytest]
 # Turn all warnings into errors
 filterwarnings = ["error"]
@@ -250,6 +228,19 @@ typing-extensions = false
 required-imports = ["from __future__ import annotations"]
 split-on-trailing-comma = false
 
+[tool.ty.src]
+exclude = [
+  # gRPC generated code references `grpc.experimental`, which is not exposed by the
+  # `grpc` package's public API. See https://github.com/grpc/grpc/issues/39555.
+  "**/*_pb2_grpc.py",
+]
+
+[tool.ty.environment]
+# Conformance test files import generated code as `from gen.connectrpc...` and
+# sibling modules like `_util`/`_cov_embed`. Pytest and the launched server/client
+# subprocesses put `conformance/test/` on sys.path; teach ty to do the same.
+extra-paths = ["conformance/test"]
+
 [tool.uv]
 constraint-dependencies = [
   "coverage==7.13.2",

src/connectrpc/_asyncio_timeout.py

@@ -119,8 +119,8 @@ async def __aexit__(
                     raise TimeoutError from exc_val
                 if exc_val is not None:
                     self._insert_timeout_error(exc_val)
-                    if _HAX_EXCEPTION_GROUP and isinstance(exc_val, ExceptionGroup):  # pyright: ignore[reportUndefinedVariable] # noqa: F821
-                        for exc in exc_val.exceptions:  # pyright: ignore[reportAttributeAccessIssue]
+                    if _HAX_EXCEPTION_GROUP and isinstance(exc_val, ExceptionGroup):  # noqa: F821
+                        for exc in exc_val.exceptions:
                             self._insert_timeout_error(exc)
         elif self._state is _State.ENTERED:
             self._state = _State.EXITED

src/connectrpc/_client_async.py

@@ -11,7 +11,6 @@
 from pyqwest import Headers as HTTPHeaders
 
 from . import _client_shared
-from ._asyncio_timeout import timeout as asyncio_timeout
 from ._codec import proto_binary_codec
 from ._compression import IdentityCompression, _gzip, resolve_compressions
 from ._interceptor_async import (
@@ -31,9 +30,7 @@
 from .protocol import ProtocolType
 
 try:
-    from asyncio import (
-        timeout as asyncio_timeout,  # pyright: ignore[reportAttributeAccessIssue]
-    )
+    from asyncio import timeout as asyncio_timeout  # ty: ignore[unresolved-import]
 except ImportError:
     from ._asyncio_timeout import timeout as asyncio_timeout
 

src/connectrpc/_codec.py

@@ -33,7 +33,7 @@ def decode(self, data: bytes | bytearray, message: U) -> U:
 
 
 class ProtoBinaryCodec(Codec[Message, V]):
-    """Codec for Protocol bytes | bytearrays binary format."""
+    """Codec for the Protocol Buffers binary format."""
 
     def name(self) -> str:
         return "proto"
@@ -42,12 +42,16 @@ def encode(self, message: Message) -> bytes:
         return message.SerializeToString()
 
     def decode(self, data: bytes | bytearray, message: V) -> V:
-        message.ParseFromString(data)  # pyright: ignore[reportArgumentType] - type is incorrect
+        # ParseFromString accepts the buffer protocol at runtime, but typeshed
+        # declares only `bytes`. Skipping the conversion avoids a copy on the
+        # streaming decode path (see _envelope.py). Tracked upstream in
+        # https://github.com/python/typeshed/issues/9006.
+        message.ParseFromString(data)  # ty: ignore[invalid-argument-type]
         return message
 
 
 class ProtoJSONCodec(Codec[Message, V]):
-    """Codec for Protocol bytes | bytearrays JSON format."""
+    """Codec for the Protocol Buffers JSON format."""
 
     def __init__(self, name: str = "json") -> None:
         self._name = name
@@ -59,13 +63,16 @@ def encode(self, message: Message) -> bytes:
         return MessageToJson(message).encode()
 
     def decode(self, data: bytes | bytearray, message: V) -> V:
-        MessageFromJson(data, message)  # pyright: ignore[reportArgumentType] - type is incorrect
+        # google.protobuf.json_format.Parse accepts the buffer protocol at
+        # runtime, but typeshed declares only `bytes | str`. See
+        # ProtoBinaryCodec.decode for the upstream tracking issue.
+        MessageFromJson(data, message)  # ty: ignore[invalid-argument-type]
         return message
 
 
 _proto_binary_codec = ProtoBinaryCodec()
 _proto_json_codec = ProtoJSONCodec()
-_default_codecs = [_proto_binary_codec, _proto_json_codec]
+_default_codecs: list[Codec] = [_proto_binary_codec, _proto_json_codec]
 
 
 def get_default_codecs() -> list[Codec]:

src/connectrpc/_headers.py

@@ -9,6 +9,7 @@
     Sequence,
     ValuesView,
 )
+from typing import cast
 
 
 class Headers(MutableMapping[str, str]):
@@ -28,6 +29,10 @@ def __init__(
     ) -> None:
         self._extra = None
         if isinstance(items, Mapping):
+            # ty does not preserve type parameters when narrowing a union via
+            # `isinstance(x, Mapping)`, so we re-assert `Mapping[str, str]`.
+            # See https://github.com/astral-sh/ty/issues/456.
+            items = cast("Mapping[str, str]", items)
             self._store = {k.lower(): v for k, v in items.items()}
         else:
             self._store = {}

src/connectrpc/_protocol_grpc.py

@@ -181,7 +181,7 @@ def end(self, user_trailers: Headers, error: ConnectWireError | None) -> Headers
 
 
 class GRPCWebEnvelopeWriter(GRPCEnvelopeWriter):
-    def end(self, user_trailers: Headers, error: ConnectWireError | None) -> bytes:  # pyright: ignore[reportIncompatibleMethodOverride]
+    def end(self, user_trailers: Headers, error: ConnectWireError | None) -> bytes:  # ty: ignore[invalid-method-override]
         trailers = super().end(user_trailers, error)
         data = "".join(f"{k}: {v}\r\n" for k, v in trailers.allitems()).encode()
         if self._compression: