fix: bug #1902

Author: nedbat

CHANGES.rst

@@ -23,7 +23,12 @@ upgrading your version of coverage.py.
 Unreleased
 ----------
 
-Nothing yet.
+- Fixed an obscure and mysterious problem on PyPy 3.10 seemingly involving
+  mocks, imports, and trace functions: `issue 1902`_.  To be honest, I don't
+  understand the problem or the solution, but ``git bisect`` helped find it,
+  and now it's fixed.
+
+.. _issue 1902: https://github.com/nedbat/coveragepy/issues/1902
 
 
 .. start-releases

coverage/pytracer.py

@@ -28,6 +28,15 @@
     Tracer,
 )
 
+
+# I don't understand why, but if we use `cast(set[TLineNo], ...)` inside
+# the _trace() function, we get some strange behavior on PyPy 3.10.
+# Assigning these names here and using them below fixes the problem.
+# See https://github.com/nedbat/coveragepy/issues/1902
+set_TLineNo = set[TLineNo]
+set_TArc = set[TArc]
+
+
 # We need the YIELD_VALUE opcode below, in a comparison-friendly form.
 # PYVERSIONS: RESUME is new in Python3.11
 RESUME = dis.opmap.get("RESUME")
@@ -253,9 +262,9 @@ def _trace(
                 flineno: TLineNo = frame.f_lineno
 
                 if self.trace_arcs:
-                    cast(set[TArc], self.cur_file_data).add((self.last_line, flineno))
+                    cast(set_TArc, self.cur_file_data).add((self.last_line, flineno))
                 else:
-                    cast(set[TLineNo], self.cur_file_data).add(flineno)
+                    cast(set_TLineNo, self.cur_file_data).add(flineno)
                 self.last_line = flineno
 
         elif event == "return":
@@ -286,7 +295,7 @@ def _trace(
                         real_return = True
                 if real_return:
                     first = frame.f_code.co_firstlineno
-                    cast(set[TArc], self.cur_file_data).add((self.last_line, -first))
+                    cast(set_TArc, self.cur_file_data).add((self.last_line, -first))
 
             # Leaving this function, pop the filename stack.
             self.cur_file_data, self.cur_file_name, self.last_line, self.started_context = (