debug: tweaks to make these clearer

Author: nedbat

coverage/parser.py

@@ -644,7 +644,7 @@ def __init__(self, text, statements, multiline):
         self.missing_arc_fragments = collections.defaultdict(list)
         self.block_stack = []
 
-        # $set_env.py: COVERAGE_TRACK_ARCS - Trace every arc added while parsing code.
+        # $set_env.py: COVERAGE_TRACK_ARCS - Trace possible arcs added while parsing code.
         self.debug = bool(int(os.environ.get("COVERAGE_TRACK_ARCS", 0)))
 
     def analyze(self):
@@ -664,8 +664,8 @@ def analyze(self):
     def add_arc(self, start, end, smsg=None, emsg=None):
         """Add an arc, including message fragments to use if it is missing."""
         if self.debug:                      # pragma: debugging
-            print(f"\nAdding arc: ({start}, {end}): {smsg!r}, {emsg!r}")
-            print(short_stack(limit=6))
+            print(f"\nAdding possible arc: ({start}, {end}): {smsg!r}, {emsg!r}")
+            print(short_stack(limit=10))
         self.arcs.add((start, end))
 
         if smsg is not None or emsg is not None:

coverage/pytracer.py

@@ -82,13 +82,13 @@ def log(self, marker, *args):
                 id(self),
                 len(self.data_stack),
             ))
-            if 0:
+            if 0:   # if you want thread ids..
                 f.write(".{:x}.{:x}".format(
                     self.thread.ident,
                     self.threading.current_thread().ident,
                 ))
             f.write(" {}".format(" ".join(map(str, args))))
-            if 0:
+            if 0:   # if you want callers..
                 f.write(" | ")
                 stack = " / ".join(
                     (fname or "???").rpartition("/")[-1]
@@ -136,8 +136,7 @@ def _trace(self, frame, event, arg_unused):
             else:
                 self.started_context = False
 
-            # Entering a new frame.  Decide if we should trace
-            # in this file.
+            # Entering a new frame.  Decide if we should trace in this file.
             self._activity = True
             self.data_stack.append(
                 (