In 3.10, modules always have firstlineno==1

Author: nedbat

coverage/env.py

@@ -92,6 +92,10 @@ class PYBEHAVIOR(object):
     # PyPy has always omitted statements after return.
     omit_after_return = omit_after_jump or PYPY
 
+    # Modules used to have firstlineno equal to the line number of the first
+    # real line of code.  Now they always start at 1.
+    module_firstline_1 = pep626
+
 # Coverage.py specifics.
 
 # Are we using the C-implemented trace function?

coverage/parser.py

@@ -205,6 +205,12 @@ def _raw_parse(self):
         if not empty:
             self.raw_statements.update(self.byte_parser._find_statements())
 
+        # The first line of modules can lie and say 1 always, even if the first
+        # line of code is later. If so, map 1 to the actual first line of the
+        # module.
+        if env.PYBEHAVIOR.module_firstline_1 and self._multiline:
+            self._multiline[1] = min(self.raw_statements)
+
     def first_line(self, line):
         """Return the first line number of the statement including `line`."""
         if line < 0:
@@ -620,7 +626,9 @@ def _line__List(self, node):
             return node.lineno
 
     def _line__Module(self, node):
-        if node.body:
+        if env.PYBEHAVIOR.module_firstline_1:
+            return 1
+        elif node.body:
             return self.line_for_node(node.body[0])
         else:
             # Empty modules have no line number, they always start at 1.

tests/coveragetest.py

@@ -219,6 +219,11 @@ def check_coverage(
                     self.fail("None of the missing choices matched %r" % missing_formatted)
 
         if arcs is not None:
+            # print("Possible arcs:")
+            # print(" expected:", arcs)
+            # print(" actual:", analysis.arc_possibilities())
+            # print("Executed:")
+            # print(" actual:", sorted(set(analysis.arcs_executed())))
             with self.delayed_assertions():
                 self.assert_equal_arcs(
                     arcs, analysis.arc_possibilities(),

tests/test_arcs.py

@@ -25,14 +25,16 @@ def test_simple_sequence(self):
             b = 3
             """,
             arcz=".1 13 3.")
+        line1 = 1 if env.PYBEHAVIOR.module_firstline_1 else 2
         self.check_coverage("""\
 
             a = 2
             b = 3
 
             c = 5
             """,
-            arcz="-22 23 35 5-2")
+            arcz="-{0}2 23 35 5-{0}".format(line1)
+        )
 
     def test_function_def(self):
         self.check_coverage("""\