Always show something when rendering exceptions (#166)

cleo/ui/exception_trace.py

@@ -252,9 +252,11 @@ def ignore_files_in(self, ignore: str) -> ExceptionTrace:
         return self
 
     def render(self, io: IO | Output, simple: bool = False) -> None:
-        if simple:
+        # If simple rendering wouldn't show anything useful, abandon it.
+        simple_string = str(self._exception) if simple else ""
+        if simple_string:
             io.write_line("")
-            io.write_line(f"<error>{str(self._exception)}</error>")
+            io.write_line(f"<error>{simple_string}</error>")
         else:
             self._render_exception(io, self._exception)
 

tests/ui/test_exception_trace.py

@@ -408,3 +408,34 @@ def test_simple_render_supports_solutions():
     https://example2.com
 """
     assert io.fetch_output() == expected
+
+
+def test_simple_render_aborts_if_no_message():
+    io = BufferedIO()
+
+    with pytest.raises(Exception) as e:
+        raise AssertionError
+
+    trace = ExceptionTrace(e.value)
+
+    trace.render(io, simple=True)
+    lineno = 417
+
+    expected = f"""
+  AssertionError
+
+  
+
+  at {trace._get_relative_file_path(__file__)}:{lineno} in \
+test_simple_render_aborts_if_no_message
+      {lineno - 4}│ def test_simple_render_aborts_if_no_message():
+      {lineno - 3}│     io = BufferedIO()
+      {lineno - 2}│ 
+      {lineno - 1}│     with pytest.raises(Exception) as e:
+    → {lineno + 0}│         raise AssertionError
+      {lineno + 1}│ 
+      {lineno + 2}│     trace = ExceptionTrace(e.value)
+      {lineno + 3}│ 
+      {lineno + 4}│     trace.render(io, simple=True)
+"""  # noqa: W293
+    assert expected == io.fetch_output()