Write the arcs to the data file.

3 files changed, 38 insertions, 4 deletions

diff --git a/coverage/collector.py b/coverage/collector.py
index 4aec4700..aadbab77 100644
--- a/coverage/collector.py
+++ b/coverage/collector.py
@@ -248,4 +248,4 @@ class Collector:
         if self.branch:
             return self.data
         else:
-            return []
+            return {}
diff --git a/coverage/data.py b/coverage/data.py
index b61adcd6..1744a7fb 100644
--- a/coverage/data.py
+++ b/coverage/data.py
@@ -16,7 +16,8 @@ class CoverageData:
           executed:
             { 'file1': [17,23,45],  'file2': [1,2,3], ... }
     
-        * arcs: TODO
+        * arcs: a dict mapping filenames to sorted lists of line number pairs:
+            { 'file1': [(17,23), (17,25), (25,26)], ... }
 
     """
     
@@ -93,6 +94,12 @@ class CoverageData:
             [(f, sorted(lmap.keys())) for f, lmap in self.lines.items()]
             )
 
+    def arc_data(self):
+        """Return the map from filenames to lists of line number pairs."""
+        return dict(
+            [(f, sorted(amap.keys())) for f, amap in self.arcs.items()]
+            )
+        
     def write_file(self, filename):
         """Write the coverage data to `filename`."""
 
@@ -100,7 +107,8 @@ class CoverageData:
         data = {}
 
         data['lines'] = self.line_data()
-
+        data['arcs'] = self.arc_data()
+        
         if self.collector:
             data['collector'] = self.collector
 
@@ -129,7 +137,12 @@ class CoverageData:
                 # Unpack the 'lines' item.
                 lines = dict([
                     (f, dict.fromkeys(linenos, None))
-                        for f, linenos in data['lines'].items()
+                        for f, linenos in data.get('lines', {}).items()
+                    ])
+                # Unpack the 'arcs' item.
+                arcs = dict([
+                    (f, dict.fromkeys(arcpairs, None))
+                        for f, arcpairs in data.get('arcs', {}).items()
                     ])
         except Exception:
             pass
diff --git a/test/test_data.py b/test/test_data.py
index 12dd80aa..b6bc978a 100644
--- a/test/test_data.py
+++ b/test/test_data.py
@@ -19,6 +19,9 @@ DATA_2 = { 'a.py': {1:None, 5:None}, 'c.py': {17:None} }
 SUMMARY_1_2 = { 'a.py':3, 'b.py':1, 'c.py':1 }
 EXECED_FILES_1_2 = [ 'a.py', 'b.py', 'c.py' ]
 
+ARC_DATA_3 = { 'x.py': {(1,2):None, (2,3):None}, 'y.py': {(17,23):None} }
+X_PY_ARCS_3 = [(1,2), (2,3)]
+Y_PY_ARCS_3 = [(17,23)]
 
 class DataTest(CoverageTest):
     """Test cases for coverage.data."""
@@ -92,3 +95,21 @@ class DataTest(CoverageTest):
         self.assert_equal_sets(lines.keys(), EXECED_FILES_1)
         self.assert_equal_sets(lines['a.py'], A_PY_LINES_1)
         self.assert_equal_sets(lines['b.py'], B_PY_LINES_1)
+        self.assert_equal_sets(data['arcs'].keys(), [])
+        
+    def test_file_format_with_arcs(self):
+        # Write with CoverageData, then read the pickle explicitly.
+        covdata = CoverageData()
+        covdata.add_arc_data(ARC_DATA_3)
+        covdata.write()
+        
+        fdata = open(".coverage", 'rb')
+        try:
+            data = pickle.load(fdata)
+        finally:
+            fdata.close()
+        
+        self.assert_equal_sets(data['lines'].keys(), [])
+        arcs = data['arcs']
+        self.assert_equal_sets(arcs['x.py'], X_PY_ARCS_3)
+        self.assert_equal_sets(arcs['y.py'], Y_PY_ARCS_3)