CoverageData.plugin_name() can now return None or '' to differentiate unmeasured, or measured but no plugin.

2 files changed, 67 insertions, 21 deletions

diff --git a/coverage/data.py b/coverage/data.py
index 1c6a283a..f2e528d4 100644
--- a/coverage/data.py
+++ b/coverage/data.py
@@ -118,11 +118,17 @@ class CoverageData(object):
             filename: the name of the file you're interested in.
 
         Returns:
-            str: the name of the plugin that handles this file.  Can be None
-                if no plugin was involved.
+            str: the name of the plugin that handles this file.  If the file
+                was measured, but didn't use a plugin, then "" is returned.
+                If the file was not measured, then None is returned.
 
         """
-        return self._plugins.get(filename)
+        # Because the vast majority of files involve no plugin, we don't store
+        # them explicitly in self._plugins.  Check the measured data instead
+        # to see if it was a known file with no plugin.
+        if filename in (self._arcs or self._lines):
+            return self._plugins.get(filename, "")
+        return None
 
     def read(self, file_obj):
         """Read the coverage data from the given file object.
@@ -226,6 +232,22 @@ class CoverageData(object):
 
         aliases = aliases or PathAliases()
 
+        # _plugins: only have a string, so they have to agree.
+        # Have to do these first, so that our examination of self._arcs and
+        # self._lines won't be confused by data updated from other_data.
+        for filename in other_data.measured_files():
+            other_plugin = other_data.plugin_name(filename)
+            filename = aliases.map(filename)
+            this_plugin = self.plugin_name(filename)
+            if this_plugin is None:
+                self._plugins[filename] = other_plugin
+            elif this_plugin != other_plugin:
+                raise CoverageException(
+                    "Conflicting plugin name for '%s': %r vs %r" % (
+                        filename, this_plugin, other_plugin,
+                    )
+                )
+
         # _lines: merge dicts.
         for filename, file_data in iitems(other_data._lines):
             filename = aliases.map(filename)
@@ -236,21 +258,6 @@ class CoverageData(object):
             filename = aliases.map(filename)
             self._arcs.setdefault(filename, {}).update(file_data)
 
-        # _plugins: only have a string, so they have to agree.
-        for filename, plugin_name in iitems(other_data._plugins):
-            filename = aliases.map(filename)
-            this_plugin = self._plugins.get(filename)
-            # TODO: plugin=None could mean no filename recorded, or it could
-            # mean, handled by Python.  Need to distinguish those cases.
-            if this_plugin is None:
-                self._plugins[filename] = plugin_name
-            elif this_plugin != plugin_name:
-                raise CoverageException(
-                    "Conflicting plugin name for '%s': %s vs %s" % (
-                        filename, this_plugin, plugin_name,
-                    )
-                )
-
     def touch_file(self, filename):
         """Ensure that `filename` appears in the data, empty if needed."""
         (self._arcs or self._lines).setdefault(filename, {})
diff --git a/tests/test_data.py b/tests/test_data.py
index e48724da..08c3a8d5 100644
--- a/tests/test_data.py
+++ b/tests/test_data.py
@@ -152,8 +152,14 @@ class CoverageDataTest(DataTestHelpers, CoverageTest):
 
     def test_plugin_name(self):
         covdata = CoverageData()
+        covdata.add_lines({
+            "p1.foo": dict.fromkeys([1, 2, 3]),
+            "p2.html": dict.fromkeys([10, 11, 12]),
+            "main.py": dict.fromkeys([20]),
+        })
         covdata.add_plugins({"p1.foo": "p1.plugin", "p2.html": "p2.plugin"})
         self.assertEqual(covdata.plugin_name("p1.foo"), "p1.plugin")
+        self.assertEqual(covdata.plugin_name("main.py"), "")
         self.assertIsNone(covdata.plugin_name("p3.not_here"))
 
     def test_update_lines(self):
@@ -204,7 +210,10 @@ class CoverageDataTest(DataTestHelpers, CoverageTest):
             "p2.html": dict.fromkeys([5, 6, 7]),
             "main.py": dict.fromkeys([10, 11, 12]),
         })
-        covdata1.add_plugins({"p1.html": "html.plugin", "p2.html": "html.plugin2"})
+        covdata1.add_plugins({
+            "p1.html": "html.plugin",
+            "p2.html": "html.plugin2",
+        })
 
         covdata2 = CoverageData()
         covdata2.add_lines({
@@ -213,7 +222,11 @@ class CoverageDataTest(DataTestHelpers, CoverageTest):
             "p3.foo": dict.fromkeys([1000, 1001]),
             "main.py": dict.fromkeys([10, 11, 12]),
         })
-        covdata2.add_plugins({"p1.html": "html.plugin", "p3.foo": "foo_plugin"})
+        covdata2.add_plugins({
+            "p1.html": "html.plugin",
+            "p2.html": "html.plugin2",
+            "p3.foo": "foo_plugin",
+        })
 
         covdata3 = CoverageData()
         covdata3.update(covdata1)
@@ -221,7 +234,33 @@ class CoverageDataTest(DataTestHelpers, CoverageTest):
         self.assertEqual(covdata3.plugin_name("p1.html"), "html.plugin")
         self.assertEqual(covdata3.plugin_name("p2.html"), "html.plugin2")
         self.assertEqual(covdata3.plugin_name("p3.foo"), "foo_plugin")
-        self.assertIsNone(covdata3.plugin_name("main.py"))
+        self.assertEqual(covdata3.plugin_name("main.py"), "")
+
+    def test_update_conflicting_plugins(self):
+        covdata1 = CoverageData()
+        covdata1.add_lines({"p1.html": dict.fromkeys([1, 2, 3])})
+        covdata1.add_plugins({"p1.html": "html.plugin"})
+
+        covdata2 = CoverageData()
+        covdata2.add_lines({"p1.html": dict.fromkeys([1, 2, 3])})
+        covdata2.add_plugins({"p1.html": "html.other_plugin"})
+
+        with self.assertRaises(CoverageException):
+            covdata1.update(covdata2)
+
+    def test_update_plugin_vs_no_plugin(self):
+        covdata1 = CoverageData()
+        covdata1.add_lines({"p1.html": dict.fromkeys([1, 2, 3])})
+        covdata1.add_plugins({"p1.html": "html.plugin"})
+
+        covdata2 = CoverageData()
+        covdata2.add_lines({"p1.html": dict.fromkeys([1, 2, 3])})
+
+        with self.assertRaises(CoverageException):
+            covdata1.update(covdata2)
+
+        with self.assertRaises(CoverageException):
+            covdata2.update(covdata1)
 
 
 class CoverageDataTestInTempDir(DataTestHelpers, CoverageTest):