Fix py-thrift-namespace-clash-check type issue when logging with `-…

…-no-strict` mode (#7864)

### Problem
When running `py-thrift-namespace-clash-check` in Twitter's sandbox with `--no-strict` mode, Pants crashed with the exception:

```
zip_longest argument #1 must support iteration
```

This is because we were trying to log a `NamespaceExtractionError`, and `log()` only understands `Union[str, Tuple[str, str]]`.

### Solution
Fix the issue by using `str()` to get the underlying message.

Also add an assertion to make sure that we don't introduce this issue again. Once we have MyPy set up, we can remove this assertion.

src/python/pants/backend/codegen/thrift/python/py_thrift_namespace_clash_check.py

@@ -6,7 +6,7 @@
 
 import os
 import re
-from builtins import zip
+from builtins import str, zip
 
 from pants.backend.codegen.thrift.python.python_thrift_library import PythonThriftLibrary
 from pants.base.exceptions import TaskError
@@ -101,7 +101,7 @@ def _extract_all_python_namespaces(self, thrift_file_sources_by_target):
       if self.get_options().strict:
         raise error
       else:
-        self.context.log.warn(error)
+        self.context.log.warn(str(error))
     return py_namespaces_by_target
 
   class ClashingNamespaceError(TaskError): pass
@@ -136,7 +136,7 @@ def _determine_clashing_namespaces(self, py_namespaces_by_target):
       if self.get_options().strict:
         raise error
       else:
-        self.context.log.warn(error)
+        self.context.log.warn(str(error))
     return namespaces_by_files
 
   def execute(self):

src/python/pants/reporting/report.py

@@ -6,7 +6,7 @@
 
 import threading
 import time
-from builtins import object
+from builtins import bytes, object, str
 
 
 class ReportingError(Exception):
@@ -100,8 +100,15 @@ def start_workunit(self, workunit):
   def log(self, workunit, level, *msg_elements):
     """Log a message.
 
-    Each element of msg_elements is either a message string or a (message, detail) pair.
+    Each element of msg_elements is either a message or a (message, detail) pair, i.e. of type
+    Union[str, bytes, Tuple[str, str]].
     """
+    # TODO(6742): Once we have enough MyPy coverage, we can rely on MyPy to catch any issues for us,
+    # rather than this runtime check.
+    # TODO(6071): No longer allow bytes once Py2 is removed.
+    assert all(isinstance(element, (str, bytes, tuple)) for element in msg_elements), \
+      "At least one logged message element is not of type " \
+      "Union[str, bytes, Tuple[str, str]]:\n {}".format(msg_elements)
     with self._lock:
       for reporter in self._reporters.values():
         reporter.handle_log(workunit, level, *msg_elements)