Add combine --keep (#1110)

* Add combine --keep

Related to https://github.com/nedbat/coveragepy/issues/1108

* Fix unit tests

* Fix line too long

* Fix line too long

3 files changed, 18 insertions, 8 deletions

diff --git a/coverage/cmdline.py b/coverage/cmdline.py
index 9c9ae868..11bc5d99 100644
--- a/coverage/cmdline.py
+++ b/coverage/cmdline.py
@@ -31,6 +31,10 @@ class Opts(object):
         '-a', '--append', action='store_true',
         help="Append coverage data to .coverage, otherwise it starts clean each time.",
     )
+    keep = optparse.make_option(
+        '', '--keep', action='store_true',
+        help="Keep combined coverage files, otherwise they are deleted.",
+    )
     branch = optparse.make_option(
         '', '--branch', action='store_true',
         help="Measure branch coverage in addition to statement coverage.",
@@ -215,6 +219,7 @@ class CoverageOptionParser(optparse.OptionParser, object):
             help=None,
             ignore_errors=None,
             include=None,
+            keep=None,
             module=None,
             omit=None,
             contexts=None,
@@ -333,6 +338,7 @@ CMDS = {
         "combine",
         [
             Opts.append,
+            Opts.keep,
             ] + GLOBAL_ARGS,
         usage="[options] <path1> <path2> ... <pathN>",
         description=(
@@ -585,7 +591,7 @@ class CoverageScript(object):
             if options.append:
                 self.coverage.load()
             data_dirs = args or None
-            self.coverage.combine(data_dirs, strict=True)
+            self.coverage.combine(data_dirs, strict=True, keep=bool(options.keep))
             self.coverage.save()
             return OK
 
diff --git a/coverage/control.py b/coverage/control.py
index 8d129bcb..c952afcd 100644
--- a/coverage/control.py
+++ b/coverage/control.py
@@ -659,7 +659,7 @@ class Coverage(object):
         data = self.get_data()
         data.write()
 
-    def combine(self, data_paths=None, strict=False):
+    def combine(self, data_paths=None, strict=False, keep=False):
         """Combine together a number of similarly-named coverage data files.
 
         All coverage data files whose name starts with `data_file` (from the
@@ -674,6 +674,8 @@ class Coverage(object):
         If `strict` is true, then it is an error to attempt to combine when
         there are no data files to combine.
 
+        If `keep` is true, then combined data files won't be deleted.
+
         .. versionadded:: 4.0
             The `data_paths` parameter.
 
@@ -694,7 +696,8 @@ class Coverage(object):
                 for pattern in paths[1:]:
                     aliases.add(pattern, result)
 
-        combine_parallel_data(self._data, aliases=aliases, data_paths=data_paths, strict=strict)
+        combine_parallel_data(self._data,
+                        aliases=aliases, data_paths=data_paths, strict=strict, keep=keep)
 
     def get_data(self):
         """Get the collected data.
diff --git a/coverage/data.py b/coverage/data.py
index 82bf1d41..5dd1dfe3 100644
--- a/coverage/data.py
+++ b/coverage/data.py
@@ -52,7 +52,7 @@ def add_data_to_hash(data, filename, hasher):
     hasher.update(data.file_tracer(filename))
 
 
-def combine_parallel_data(data, aliases=None, data_paths=None, strict=False):
+def combine_parallel_data(data, aliases=None, data_paths=None, strict=False, keep=False):
     """Combine a number of data files together.
 
     Treat `data.filename` as a file prefix, and combine the data from all
@@ -68,7 +68,7 @@ def combine_parallel_data(data, aliases=None, data_paths=None, strict=False):
     If `data_paths` is not provided, then the directory portion of
     `data.filename` is used as the directory to search for data files.
 
-    Every data file found and combined is then deleted from disk. If a file
+    Unless `keep` is True every data file found and combined is then deleted from disk. If a file
     cannot be read, a warning will be issued, and the file will not be
     deleted.
 
@@ -116,9 +116,10 @@ def combine_parallel_data(data, aliases=None, data_paths=None, strict=False):
         else:
             data.update(new_data, aliases=aliases)
             files_combined += 1
-            if data._debug.should('dataio'):
-                data._debug.write("Deleting combined data file %r" % (f,))
-            file_be_gone(f)
+            if not keep:
+                if data._debug.should('dataio'):
+                    data._debug.write("Deleting combined data file %r" % (f,))
+                file_be_gone(f)
 
     if strict and not files_combined:
         raise CoverageException("No usable data files")