Fix serde feature compilation problem

crates/red_knot_python_semantic/src/python_platform.rs

@@ -1,13 +1,15 @@
-use serde::{Deserialize, Serialize};
-
 /// The target platform to assume when resolving types.
-#[derive(Debug, Clone, Default, PartialEq, Eq, Deserialize, Serialize)]
-#[serde(rename_all = "kebab-case")]
+#[derive(Debug, Clone, Default, PartialEq, Eq)]
+#[cfg_attr(
+    feature = "serde",
+    derive(serde::Serialize, serde::Deserialize),
+    serde(rename_all = "kebab-case")
+)]
 pub enum PythonPlatform {
     /// Do not make any assumptions about the target platform.
     #[default]
     All,
     /// Assume a target platform like `linux`, `darwin`, `win32`, etc.
-    #[serde(untagged)]
+    #[cfg_attr(feature = "serde", serde(untagged))]
     Individual(String),
 }

crates/red_knot_python_semantic/src/semantic_index/builder.rs

@@ -929,7 +929,7 @@ where
 
                 // We may execute the `else` clause without ever executing the body, so merge in
                 // the pre-loop state before visiting `else`.
-                self.flow_merge(pre_loop);
+                self.flow_merge(pre_loop.clone());
                 self.record_negated_constraint(constraint);
                 self.visit_body(orelse);
 
@@ -940,6 +940,8 @@ where
                 for break_state in break_states {
                     self.flow_merge(break_state);
                 }
+
+                self.reset_visibility_constraints(pre_loop);
             }
             ast::Stmt::With(ast::StmtWith {
                 items,
@@ -1387,6 +1389,8 @@ where
                 range: _,
                 op,
             }) => {
+                let pre_op = self.flow_snapshot();
+
                 let mut snapshots = vec![];
                 let mut constraints = vec![];
 
@@ -1420,6 +1424,8 @@ where
                 for snapshot in snapshots {
                     self.flow_merge(snapshot);
                 }
+
+                self.reset_visibility_constraints(pre_op);
             }
             _ => {
                 walk_expr(self, expr);