Check for empty format specs (#2574)

(cherry picked from commit a679550)

Author: nickdrozd

ChangeLog

@@ -17,6 +17,11 @@ Release date: TBA
 
   Refs https://github.com/pylint-dev/pylint/pull/9932#issuecomment-2364985551
 
+* Fix a crash from inferring empty format specs.
+
+  Closes pylint-dev/pylint#9945
+
+
 What's New in astroid 3.3.3?
 ============================
 Release date: 2024-09-20

astroid/nodes/node_classes.py

@@ -4779,6 +4779,9 @@ def _infer(
     def _infer_from_values(
         cls, nodes: list[NodeNG], context: InferenceContext | None = None, **kwargs: Any
     ) -> Generator[InferenceResult, None, InferenceErrorInfo | None]:
+        if not nodes:
+            yield
+            return
         if len(nodes) == 1:
             yield from nodes[0]._infer(context, **kwargs)
             return

tests/test_inference.py

@@ -7380,3 +7380,11 @@ def test_sys_argv_uninferable() -> None:
     sys_argv_value = list(a._infer())
     assert len(sys_argv_value) == 1
     assert sys_argv_value[0] is Uninferable
+
+
+def test_empty_format_spec() -> None:
+    """Regression test for https://github.com/pylint-dev/pylint/issues/9945."""
+    node = extract_node('f"{x:}"')
+    assert isinstance(node, nodes.JoinedStr)
+
+    assert list(node.infer()) == [util.Uninferable]