fix: class statements shouldn't be branches. #1449

Revert "refactor: we no longer need to treat 'class' lines specially"

This reverts commit 79f9f45.

CHANGES.rst

@@ -20,6 +20,9 @@ development at the same time, such as 4.5.x and 5.0.
 Unreleased
 ----------
 
+- Starting with coverage.py 6.2, ``class`` statements were marked as a branch.
+  This wasn't right, and has been reverted, fixing `issue 1449`_.
+
 - Packaging is now compliant with `PEP 517`_, closing `issue 1395`_.
 
 - A new debug option ``--debug=pathmap`` shows details of the remapping of
@@ -31,6 +34,7 @@ Unreleased
 .. _bug 50381: https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=50381
 .. _PEP 517: https://peps.python.org/pep-0517/
 .. _issue 1395: https://github.com/nedbat/coveragepy/issues/1395
+.. _issue 1449: https://github.com/nedbat/coveragepy/issues/1449
 
 
 .. _changes_6-4-4:

coverage/parser.py

@@ -67,6 +67,9 @@ def __init__(self, text=None, filename=None, exclude=None):
         # The raw line numbers of excluded lines of code, as marked by pragmas.
         self.raw_excluded = set()
 
+        # The line numbers of class definitions.
+        self.raw_classdefs = set()
+
         # The line numbers of docstring lines.
         self.raw_docstrings = set()
 
@@ -130,6 +133,12 @@ def _raw_parse(self):
                 indent += 1
             elif toktype == token.DEDENT:
                 indent -= 1
+            elif toktype == token.NAME:
+                if ttext == 'class':
+                    # Class definitions look like branches in the bytecode, so
+                    # we need to exclude them.  The simplest way is to note the
+                    # lines with the 'class' keyword.
+                    self.raw_classdefs.add(slineno)
             elif toktype == token.OP:
                 if ttext == ':' and nesting == 0:
                     should_exclude = (elineno in self.raw_excluded) or excluding_decorators
@@ -292,6 +301,12 @@ def exit_counts(self):
                 continue
             exit_counts[l1] += 1
 
+        # Class definitions have one extra exit, so remove one for each:
+        for l in self.raw_classdefs:
+            # Ensure key is there: class definitions can include excluded lines.
+            if l in exit_counts:
+                exit_counts[l] -= 1
+
         return exit_counts
 
     def missing_arc_description(self, start, end, executed_arcs=None):

lab/parser.py

@@ -108,6 +108,8 @@ def one_file(self, options, filename):
                         marks[2] = str(exits)
                     if lineno in pyparser.raw_docstrings:
                         marks[3] = '"'
+                    if lineno in pyparser.raw_classdefs:
+                        marks[3] = 'C'
                     if lineno in pyparser.raw_excluded:
                         marks[4] = 'x'
 

tests/test_lcov.py

@@ -203,10 +203,8 @@ def test_is_it_x(self):
             DA:9,0,FPTWzd68bDx76HN7VHu1wA
             LF:6
             LH:4
-            BRDA:0,0,0,1
-            BRDA:7,0,1,1
-            BRF:2
-            BRH:2
+            BRF:0
+            BRH:0
             end_of_record
             """)
         actual_result = self.get_lcov_report_content()

tests/test_parser.py

@@ -43,7 +43,7 @@ class Bar:
                 pass
             """)
         assert parser.exit_counts() == {
-            2:2, 3:1, 4:2, 5:1, 7:1, 9:2, 10:1
+            2:1, 3:1, 4:2, 5:1, 7:1, 9:1, 10:1
         }
 
     def test_generator_exit_counts(self):
@@ -89,7 +89,7 @@ class Bar:
                     pass
             """)
         assert parser.exit_counts() == {
-            1:1, 2:1, 3:1
+            1:0, 2:1, 3:1
         }
 
     def test_missing_branch_to_excluded_code(self):
@@ -472,7 +472,7 @@ def foo(self, a):
             class Bar:
                 pass
             """
-        counts = { 2:2, 3:1, 4:2, 5:1, 7:1, 9:2, 10:1 }
+        counts = { 2:1, 3:1, 4:2, 5:1, 7:1, 9:1, 10:1 }
         fname = slug + ".py"
         self.make_file(fname, text, newline=newline)
         parser = self.parse_file(fname)