chore(python): better static typing for debuglink and emulator

[no changelog]

python/src/trezorlib/_internal/emulator.py

@@ -72,7 +72,8 @@ class Emulator:
         else:
             self.logfile = self.profile_dir / "trezor.log"
 
-        self.client: Optional[TrezorClientDebugLink] = None
+        # Using `client` property instead to assert `not None`
+        self._client: Optional[TrezorClientDebugLink] = None
         self.process: Optional[subprocess.Popen] = None
 
         self.port = 21324
@@ -81,6 +82,16 @@ class Emulator:
         self.auto_interact = auto_interact
         self.extra_args = list(extra_args)
 
+    @property
+    def client(self) -> TrezorClientDebugLink:
+        """So that type-checkers do not see `client` as `Optional`.
+
+        (it is not None between `start()` and `stop()` calls)
+        """
+        if self._client is None:
+            raise RuntimeError
+        return self._client
+
     def make_args(self) -> List[str]:
         return []
 
@@ -162,14 +173,15 @@ class Emulator:
         (self.profile_dir / "trezor.port").write_text(str(self.port) + "\n")
 
         transport = self._get_transport()
-        self.client = TrezorClientDebugLink(transport, auto_interact=self.auto_interact)
-
-        self.client.open()
+        self._client = TrezorClientDebugLink(
+            transport, auto_interact=self.auto_interact
+        )
+        self._client.open()
 
     def stop(self) -> None:
-        if self.client:
-            self.client.close()
-        self.client = None
+        if self._client:
+            self._client.close()
+        self._client = None
 
         if self.process:
             LOG.info("Terminating emulator...")

python/src/trezorlib/debuglink.py

@@ -36,9 +36,11 @@ from typing import (
     Tuple,
     Type,
     Union,
+    overload,
 )
 
 from mnemonic import Mnemonic
+from typing_extensions import Literal
 
 from . import mapping, messages, protobuf
 from .client import TrezorClient
@@ -296,6 +298,17 @@ class DebugLink:
 
         return None
 
+    # Type overloads make sure that when we supply `wait=True` into `click()`,
+    # it will always return `LayoutContent` and we do not need to assert `is not None`.
+
+    @overload
+    def click(self, click: Tuple[int, int]) -> None:
+        ...
+
+    @overload
+    def click(self, click: Tuple[int, int], wait: Literal[True]) -> LayoutContent:
+        ...
+
     def click(
         self, click: Tuple[int, int], wait: bool = False
     ) -> Optional[LayoutContent]: