From 3b5bd6b481e32bc525566e3b1e37188f35650e34 Mon Sep 17 00:00:00 2001
From: Ned Batchelder <ned@nedbatchelder.com>
Date: Sun, 13 Oct 2024 12:51:56 -0400
Subject: [PATCH] fix: nested context managers shouldn't cause a phantom
 missing branch #1876

---
 CHANGES.rst          |  5 +++++
 coverage/parser.py   | 12 ++++++++++--
 tests/test_parser.py | 18 ++++++++++++++++++
 3 files changed, 33 insertions(+), 2 deletions(-)

diff --git a/CHANGES.rst b/CHANGES.rst
index 594379095..7a8d99ace 100644
--- a/CHANGES.rst
+++ b/CHANGES.rst
@@ -23,10 +23,15 @@ upgrading your version of coverage.py.
 Unreleased
 ----------
 
+- Fix: nested context managers could incorrectly be analyzed to flag a missing
+  branch on the last context manager, as described in `issue 1876`_.  This is
+  now fixed.
+
 - Fix: the missing branch message about not exiting a module had an extra
   "didn't," as described in `issue 1873`_.  This is now fixed.
 
 .. _issue 1873: https://github.com/nedbat/coveragepy/issues/1873
+.. _issue 1876: https://github.com/nedbat/coveragepy/issues/1876
 
 
 .. start-releases
diff --git a/coverage/parser.py b/coverage/parser.py
index cf454eba1..f8efeea20 100644
--- a/coverage/parser.py
+++ b/coverage/parser.py
@@ -315,12 +315,20 @@ def fix_with_jumps(self, arcs: Iterable[TArc]) -> set[TArc]:
         to_add = set()
         for arc in arcs:
             if arc in self._with_jump_fixers:
+                start = arc[0]
+                to_remove.add(arc)
                 start_next, prev_next = self._with_jump_fixers[arc]
+                prev = prev_next[0]
+                while start_next in self._with_jump_fixers:
+                    to_remove.add(start_next)
+                    start_next, prev_next = self._with_jump_fixers[start_next]
+                    to_remove.add(prev_next)
                 if start_next in arcs:
-                    to_add.add(prev_next)
+                    to_add.add((start, prev_next[1]))
                     to_remove.add(arc)
                     to_remove.add(start_next)
-        return (set(arcs) | to_add) - to_remove
+        arcs = (set(arcs) | to_add) - to_remove
+        return arcs
 
     @functools.lru_cache
     def exit_counts(self) -> dict[TLineNo, int]:
diff --git a/tests/test_parser.py b/tests/test_parser.py
index 62649e237..c6f3e6ec9 100644
--- a/tests/test_parser.py
+++ b/tests/test_parser.py
@@ -151,6 +151,24 @@ def bar(self):
         assert expected_arcs == parser.arcs()
         assert expected_exits == parser.exit_counts()
 
+    def test_nested_context_managers(self) -> None:
+        # https://github.com/nedbat/coveragepy/issues/1876
+        parser = self.parse_text("""\
+            a = 1
+            with suppress(ValueError):
+                with suppress(ValueError):
+                    x = 4
+                with suppress(ValueError):
+                    x = 6
+                with suppress(ValueError):
+                    x = 8
+            a = 9
+            """)
+
+        one_nine = set(range(1, 10))
+        assert parser.statements == one_nine
+        assert parser.exit_counts() == dict.fromkeys(one_nine, 1)
+
     def test_module_docstrings(self) -> None:
         parser = self.parse_text("""\
             '''The docstring on line 1'''