fix: unbound-name after assignment to singleton attribute ; unexpected unbound-name error on second walrus conditional assignment for same variable

pyrefly/lib/binding/scope.rs

@@ -2510,8 +2510,11 @@ impl<'a> BindingsBuilder<'a> {
         let mut flow_infos = merge_item.branches;
         // Track the number of branch values before adding base (for LoopDefinitelyRuns)
         let n_branch_flow_infos = flow_infos.len();
-        // Track if base has a value for this name (for LoopDefinitelyRuns init check)
-        let base_has_value = merge_item.base.as_ref().is_some_and(|b| b.value.is_some());
+        // Track if base has a binding for this name (value or narrow) for loop init checks.
+        let base_has_binding = merge_item
+            .base
+            .as_ref()
+            .is_some_and(|base| base.value.is_some() || base.narrow.is_some());
         // If this is a loop, we want to use the current default in any phis we produce,
         // and the base flow is part of the merge for type inference purposes.
         let loop_prior = if merge_style.is_loop()
@@ -2552,11 +2555,9 @@ impl<'a> BindingsBuilder<'a> {
         let mut value_idxs = SmallSet::with_capacity(flow_infos.len());
         let mut branch_idxs = SmallSet::with_capacity(flow_infos.len());
         let mut styles = Vec::with_capacity(flow_infos.len());
-        let mut n_values = 0;
         for flow_info in flow_infos.into_iter() {
             let branch_idx = flow_info.idx();
             if let Some(v) = flow_info.value {
-                n_values += 1;
                 if v.idx == phi_idx {
                     continue;
                 }
@@ -2568,13 +2569,21 @@ impl<'a> BindingsBuilder<'a> {
             }
             branch_idxs.insert(branch_idx);
         }
+        let is_name_exists_in_all_branch_flow = match merge_style {
+            MergeStyle::Loop => n_branch_flow_infos == n_branches.saturating_sub(1),
+            _ => n_branch_flow_infos == n_branches,
+        };
         // For LoopDefinitelyRuns, a name is always defined if:
-        // - It was defined before the loop (base_has_value), OR
-        // - It's defined in all loop body branches (since the loop definitely runs at least once)
-        // For regular loops and other merges, a name is always defined if it's in all branches.
+        // - It was defined before the loop (base_has_binding), OR
+        // - It's defined in all loop body branches (since the loop definitely runs at least once).
+        // For Loop, the name must exist in the base flow and in all loop body branches.
+        // For BoolOp, avoid propagating uninitialized styles across the merge.
+        // For other merges, a name is always defined if it appears in every branch flow.
         let this_name_always_defined = match merge_style {
-            MergeStyle::LoopDefinitelyRuns => base_has_value || n_branch_flow_infos == n_branches,
-            _ => n_values == n_branches,
+            MergeStyle::Loop => base_has_binding && is_name_exists_in_all_branch_flow,
+            MergeStyle::LoopDefinitelyRuns => base_has_binding || is_name_exists_in_all_branch_flow,
+            MergeStyle::BoolOp => false,
+            _ => is_name_exists_in_all_branch_flow,
         };
         match value_idxs.len() {
             // If there are no values, then this name isn't assigned at all

pyrefly/lib/test/callable.rs

@@ -1145,6 +1145,82 @@ def f():
     "#,
 );
 
+fn env_singleton_attribute_assignment() -> TestEnv {
+    TestEnv::one(
+        "singleton",
+        r#"
+class GlobalInventory:
+    _instance: GlobalInventory | None = None
+    _initialized: bool = False
+
+    initialization_status: bool
+    config_file_inventory: dict[str, int]
+
+    def __new__(cls) -> GlobalInventory:
+        if cls._instance is None:
+            cls._instance = super().__new__(cls)
+        assert cls._instance is not None, "GlobalInventory instance creation failed"
+        return cls._instance
+
+    def __init__(self) -> None:
+        if not self._initialized:
+            self.initialization_status = False
+            self.config_file_inventory = {}
+            GlobalInventory._initialized = True
+
+globals_inv: GlobalInventory = GlobalInventory()
+        "#,
+    )
+}
+
+testcase!(
+    test_attribute_assignment_to_imported_singleton_in_method,
+    env_singleton_attribute_assignment(),
+    r#"
+from singleton import globals_inv
+
+class Foo:
+    def __init__(self) -> None:
+        globals_inv.config_file_inventory = {"foo": 1}
+        for _ in globals_inv.config_file_inventory.values():
+            if globals_inv.initialization_status:
+                break
+        globals_inv.initialization_status = True
+    "#,
+);
+
+testcase!(
+    test_walrus_reuse_name_in_if_condition,
+    r#"
+from re import compile
+
+interface_re = compile(r"^foo")
+ipv4_re = compile(r"bar$")
+line = str()
+
+if match := interface_re.match(line):
+    pass
+
+if line and (match := ipv4_re.search(line)):
+    print(match)
+    "#,
+);
+
+testcase!(
+    test_walrus_getattr_items_then_iterate,
+    r#"
+from typing import Any
+
+def test(thing: Any) -> None:
+    if not (items := getattr(thing, "items")):
+        return
+    if not isinstance(items, tuple | list):
+        items = (items,)
+    for item in items:
+        print(item)
+    "#,
+);
+
 testcase!(
     test_unbound_local_name_error_in_def,
     r#"