fix: metadata journal can rollback incorrectly (#3569)

this commit fixes an issue where multiple writes inside of a checkpoint
lead to journal corruption on rollback. it ensures a call to
`register_update()` when the metadata dict has already been updated
inside of a given checkpoint.

note this does not change any observed functionality in the compiler
because writes to the metadata journal inside for loops only ever happen
to be written once, but it prevents a bug in case we ever add multiple
writes inside of the same checkpoint.

chainsec june review 5.3

---------

Co-authored-by: tserg <8017125+tserg@users.noreply.github.com>

tests/ast/test_metadata_journal.py

@@ -0,0 +1,82 @@
+from vyper.ast.metadata import NodeMetadata
+from vyper.exceptions import VyperException
+
+
+def test_metadata_journal_basic():
+    m = NodeMetadata()
+
+    m["x"] = 1
+    assert m["x"] == 1
+
+
+def test_metadata_journal_commit():
+    m = NodeMetadata()
+
+    with m.enter_typechecker_speculation():
+        m["x"] = 1
+
+    assert m["x"] == 1
+
+
+def test_metadata_journal_exception():
+    m = NodeMetadata()
+
+    m["x"] = 1
+    try:
+        with m.enter_typechecker_speculation():
+            m["x"] = 2
+            m["x"] = 3
+
+            assert m["x"] == 3
+            raise VyperException("dummy exception")
+
+    except VyperException:
+        pass
+
+    # rollback upon exception
+    assert m["x"] == 1
+
+
+def test_metadata_journal_rollback_inner():
+    m = NodeMetadata()
+
+    m["x"] = 1
+    with m.enter_typechecker_speculation():
+        m["x"] = 2
+
+        try:
+            with m.enter_typechecker_speculation():
+                m["x"] = 3
+                m["x"] = 4  # test multiple writes
+
+                assert m["x"] == 4
+                raise VyperException("dummy exception")
+
+        except VyperException:
+            pass
+
+    assert m["x"] == 2
+
+
+def test_metadata_journal_rollback_outer():
+    m = NodeMetadata()
+
+    m["x"] = 1
+    try:
+        with m.enter_typechecker_speculation():
+            m["x"] = 2
+
+            with m.enter_typechecker_speculation():
+                m["x"] = 3
+                m["x"] = 4  # test multiple writes
+
+            assert m["x"] == 4
+
+            m["x"] = 5
+
+            raise VyperException("dummy exception")
+
+    except VyperException:
+        pass
+
+    assert m["x"] == 1

vyper/ast/metadata.py

@@ -17,8 +17,11 @@ def __init__(self):
         self._node_updates: list[dict[tuple[int, str, Any], NodeMetadata]] = []
 
     def register_update(self, metadata, k):
+        KEY = (id(metadata), k)
+        if KEY in self._node_updates[-1]:
+            return
         prev = metadata.get(k, self._NOT_FOUND)
-        self._node_updates[-1][(id(metadata), k)] = (metadata, prev)
+        self._node_updates[-1][KEY] = (metadata, prev)
 
     @contextlib.contextmanager
     def enter(self):