Combine no longer appends by default

Combine used to always load an existing .coverage file. This lead to confusing
results and extra tox-clean steps.  Now the default is to not load the existing
file, though a new --append switch on coverage combine gets you that behavior
if you need it.

This also pointed up an issue with concurrency=multiprocessing, which is that
the child processes automatically used parallel=True, but the parent process
did not.  Now concurrency=multiprocessing implies parallel=True.

1 files changed, 5 insertions, 2 deletions

diff --git a/coverage/cmdline.py b/coverage/cmdline.py
index e2b79fe..9ff39f4 100644
--- a/coverage/cmdline.py
+++ b/coverage/cmdline.py
@@ -274,7 +274,9 @@ CMDS = {
 
     'combine': CmdOptionParser(
         "combine",
-        GLOBAL_ARGS,
+        [
+            Opts.append,
+            ] + GLOBAL_ARGS,
         usage="<path1> <path2> ... <pathN>",
         description=(
             "Combine data from multiple coverage files collected "
@@ -484,7 +486,8 @@ class CoverageScript(object):
             return self.do_run(options, args)
 
         elif options.action == "combine":
-            self.coverage.load()
+            if options.append:
+                self.coverage.load()
             data_dirs = args or None
             self.coverage.combine(data_dirs)
             self.coverage.save()