add assert statements following .communicate() to help type checkers

After calling .communicate() on an asyncio.subprocess.Process object,
the attribute returncode gets set to a non-None value. Type checkers are
not able to figure this out.

Fixed by adding an assert to help type checkers out.

Signed-off-by: Olivier Gayot <olivier.gayot@canonical.com>

subiquity/server/runner.py

@@ -78,6 +78,8 @@ class LoggedCommandRunner:
     async def wait(self, proc: asyncio.subprocess.Process) \
             -> subprocess.CompletedProcess:
         stdout, stderr = await proc.communicate()
+        # .communicate() forces returncode to be set to a value
+        assert(proc.returncode is not None)
         if proc.returncode != 0:
             raise subprocess.CalledProcessError(proc.returncode, proc.args)
         else:

subiquitycore/utils.py

@@ -84,6 +84,8 @@ async def arun_command(cmd: List[str], *,
         if stderr is not None:
             stderr = stderr.decode(encoding)
     log.debug("arun_command %s exited with code %s", cmd, proc.returncode)
+    # .communicate() forces returncode to be set to a value
+    assert(proc.returncode is not None)
     if check and proc.returncode != 0:
         raise subprocess.CalledProcessError(proc.returncode, cmd)
     else: