debug: add more tracingnedbat/5.5x

This helps us diagnose problems where 5.5 worked and 6.x doesn't.

1 files changed, 6 insertions, 0 deletions

diff --git a/coverage/inorout.py b/coverage/inorout.py
index fbd1a95e..42a40586 100644
--- a/coverage/inorout.py
+++ b/coverage/inorout.py
@@ -389,6 +389,12 @@ class InOrOut(object):
                     msg = "Already imported a file that will be measured: {}".format(filename)
                     self.warn(msg, slug="already-imported")
                     warned.add(filename)
+                elif self.debug and self.debug.should('trace'):
+                    self.debug.write(
+                        "Didn't trace already imported file {!r}: {}".format(
+                            disp.original_filename, disp.reason
+                        )
+                    )
 
     def warn_unimported_source(self):
         """Warn about source packages that were of interest, but never traced."""