Fix ClassVar forward reference detection (#1593)

fix: detect ClassVar forward refs

Co-authored-by: Hynek Schlawack <hs@ox.cx>

changelog.d/1593.change.md

diff --git a/changelog.d/1593.change.md b/changelog.d/1593.change.md
new file mode 100644
index 0000000..d3fd8eb
--- /dev/null
+++ b/changelog.d/1593.change.md
@@ -0,0 +1 @@
+Unimported `typing.ClassVar` annotations created as forward references are now detected as class variables.

src/attr/_make.py

diff --git a/src/attr/_make.py b/src/attr/_make.py
index 04104d9..c71e872 100644
--- a/src/attr/_make.py
+++ b/src/attr/_make.py
@@ -297,6 +297,7 @@
     annotations which would put attrs-based classes at a performance
     disadvantage compared to plain old classes.
     """
+    annot = getattr(annot, "__forward_arg__", annot)
     annot = str(annot)
 
     # Annotation can be quoted.

tests/test_annotations.py

diff --git a/tests/test_annotations.py b/tests/test_annotations.py
index e193d4b..de3d105 100644
--- a/tests/test_annotations.py
+++ b/tests/test_annotations.py
@@ -434,6 +434,23 @@
 
         assert_init_annotations(C)
 
+    @pytest.mark.skipif(
+        sys.version_info[:2] < (3, 14),
+        reason="Python 3.14 changed annotation evaluation behavior.",
+    )
+    def test_missing_classvar_import(self, slots):
+        """
+        Unimported ClassVars are recognized as ForwardRefs.
+        """
+
+        @attr.s(auto_attribs=True, slots=slots)
+        class C:
+            cls_var: ClassVar[str]  # noqa: F821
+            value: int = 1
+
+        assert "cls_var" not in attr.fields_dict(C)
+        assert 1 == C().value
+
     def test_keyword_only_auto_attribs(self):
         """
         `kw_only` propagates to attributes defined via `auto_attribs`.
@@ -691,6 +708,7 @@
         "typing.ClassVar",
         "'typing.ClassVar[dict]'",
         "t.ClassVar[int]",
+        typing.ForwardRef("ClassVar[str]"),
     ],
 )
 def test_is_class_var(annot):