Fix pylint regression with invalid format strings (#2496)

Catch exceptions when calling string.format

(cherry picked from commit 04f4f3f)

Author: ericvergnaud

ChangeLog

@@ -13,6 +13,9 @@ What's New in astroid 3.3.1?
 ============================
 Release date: TBA
 
+* Fix a crash introduced in 3.3.0 involving invalid format strings.
+
+  Closes #2492
 
 
 What's New in astroid 3.3.0?

astroid/nodes/node_classes.py

@@ -4687,19 +4687,24 @@ def _infer(
                     uninferable_already_generated = True
                 continue
             for value in self.value.infer(context, **kwargs):
-                if not isinstance(value, Const):
-                    if not uninferable_already_generated:
-                        yield util.Uninferable
-                        uninferable_already_generated = True
-                    continue
-                formatted = format(value.value, format_spec.value)
-                yield Const(
-                    formatted,
-                    lineno=self.lineno,
-                    col_offset=self.col_offset,
-                    end_lineno=self.end_lineno,
-                    end_col_offset=self.end_col_offset,
-                )
+                if isinstance(value, Const):
+                    try:
+                        formatted = format(value.value, format_spec.value)
+                        yield Const(
+                            formatted,
+                            lineno=self.lineno,
+                            col_offset=self.col_offset,
+                            end_lineno=self.end_lineno,
+                            end_col_offset=self.end_col_offset,
+                        )
+                        continue
+                    except (ValueError, TypeError):
+                        # happens when format_spec.value is invalid
+                        pass  # fall through
+                if not uninferable_already_generated:
+                    yield util.Uninferable
+                    uninferable_already_generated = True
+                continue
 
 
 MISSING_VALUE = "{MISSING_VALUE}"

tests/test_inference.py

@@ -666,21 +666,6 @@ def test_fstring_inference(self) -> None:
         self.assertIsInstance(value_node, Const)
         self.assertEqual(value_node.value, "Hello John!")
 
-    def test_formatted_fstring_inference(self) -> None:
-        code = """
-            width = 10
-            precision = 4
-            value = 12.34567
-            result = f"result: {value:{width}.{precision}}!"
-            """
-        ast = parse(code, __name__)
-        node = ast["result"]
-        inferred = node.inferred()
-        self.assertEqual(len(inferred), 1)
-        value_node = inferred[0]
-        self.assertIsInstance(value_node, Const)
-        self.assertEqual(value_node.value, "result:      12.35!")
-
     def test_float_complex_ambiguity(self) -> None:
         code = '''
             def no_conjugate_member(magic_flag):  #@
@@ -5517,6 +5502,51 @@ class instance(object):
         self.assertIsInstance(inferred, Instance)
 
 
+@pytest.mark.parametrize(
+    "code, result",
+    [
+        # regular f-string
+        (
+            """width = 10
+precision = 4
+value = 12.34567
+result = f"result: {value:{width}.{precision}}!"
+""",
+            "result:      12.35!",
+        ),
+        # unsupported format
+        (
+            """width = None
+precision = 4
+value = 12.34567
+result = f"result: {value:{width}.{precision}}!"
+""",
+            None,
+        ),
+        # unsupported value
+        (
+            """width = 10
+precision = 4
+value = None
+result = f"result: {value:{width}.{precision}}!"
+""",
+            None,
+        ),
+    ],
+)
+def test_formatted_fstring_inference(code, result) -> None:
+    ast = parse(code, __name__)
+    node = ast["result"]
+    inferred = node.inferred()
+    assert len(inferred) == 1
+    value_node = inferred[0]
+    if result is None:
+        assert value_node is util.Uninferable
+    else:
+        assert isinstance(value_node, Const)
+        assert value_node.value == result
+
+
 def test_augassign_recursion() -> None:
     """Make sure inference doesn't throw a RecursionError.