Merge with upstream changes

2 files changed, 23 insertions, 4 deletions

diff --git a/coverage/collector.py b/coverage/collector.py
index 3fdedaad..73a14b93 100644
--- a/coverage/collector.py
+++ b/coverage/collector.py
@@ -1,12 +1,23 @@
 """Raw data collector for Coverage."""
 
-import sys, threading
+import os, sys, threading
 
 try:
     # Use the C extension code when we can, for speed.
     from coverage.tracer import CTracer
 except ImportError:
     # Couldn't import the C extension, maybe it isn't built.
+    if os.getenv('COVERAGE_TEST_TRACER') == 'c':
+        # During testing, we use the COVERAGE_TEST_TRACER env var to indicate
+        # that we've fiddled with the environment to test this fallback code.
+        # If we thought we had a C tracer, but couldn't import it, then exit
+        # quickly and clearly instead of dribbling confusing errors. I'm using
+        # sys.exit here instead of an exception because an exception here
+        # causes all sorts of other noise in unittest.
+        sys.stderr.write(
+            "*** COVERAGE_TEST_TRACER is 'c' but can't import CTracer!\n"
+            )
+        sys.exit(1)
     CTracer = None
 
 
diff --git a/coverage/files.py b/coverage/files.py
index e6dc4aa1..e07c5766 100644
--- a/coverage/files.py
+++ b/coverage/files.py
@@ -207,9 +207,17 @@ class PathAliases(object):
 
 
 def find_python_files(dirname):
-    """Yield all of the importable Python files in `dirname`, recursively."""
-    for dirpath, dirnames, filenames in os.walk(dirname, topdown=True):
-        if '__init__.py' not in filenames:
+    """Yield all of the importable Python files in `dirname`, recursively.
+
+    To be importable, the files have to be in a directory with a __init__.py,
+    except for `dirname` itself, which isn't required to have one.  The
+    assumption is that `dirname` was specified directly, so the user knows
+    best, but subdirectories are checked for a __init__.py to be sure we only
+    find the importable files.
+
+    """
+    for i, (dirpath, dirnames, filenames) in enumerate(os.walk(dirname)):
+        if i > 0 and '__init__.py' not in filenames:
             # If a directory doesn't have __init__.py, then it isn't
             # importable and neither are its files
             del dirnames[:]