enh: suppress false-positive unknown-name errors after short-circuit boolean ops

pyrefly/lib/binding/expr.rs

@@ -399,6 +399,9 @@ impl<'a> BindingsBuilder<'a> {
                 self.defer_bound_name(key, lookup_result_idx, usage, promote)
             }
             NameLookupResult::NotFound => {
+                if self.scopes.is_definitely_unreachable() {
+                    return self.insert_binding(key, Binding::Any(AnyStyle::Implicit));
+                }
                 let suggestion = self
                     .scopes
                     .suggest_similar_name(&name.id, name.range.start());
@@ -764,6 +767,14 @@ impl<'a> BindingsBuilder<'a> {
                     self.ensure_expr(value, &mut Usage::narrowing_from(usage));
                     self.start_fork_and_branch(*range);
                     let mut narrow_ops = get_narrow_ops(self, value, *op);
+
+                    let short_circuit_trigger: Option<bool> = match op {
+                        BoolOp::And => Some(false),
+                        BoolOp::Or => Some(true),
+                    };
+                    if self.sys_info.evaluate_bool(value) == short_circuit_trigger {
+                        self.scopes.set_definitely_unreachable(true);
+                    }
                     for value in values {
                         self.bind_narrow_ops(
                             &narrow_ops,
@@ -773,6 +784,9 @@ impl<'a> BindingsBuilder<'a> {
                         self.ensure_expr(value, &mut Usage::narrowing_from(usage));
                         let new_narrow_ops = get_narrow_ops(self, value, *op);
                         narrow_ops.and_all(new_narrow_ops);
+                        if self.sys_info.evaluate_bool(value) == short_circuit_trigger {
+                            self.scopes.set_definitely_unreachable(true);
+                        }
                     }
                     // Negate the narrow ops in the base flow and merge.
                     // TODO(stroxler): We eventually want to drop all narrows but merge values.

pyrefly/lib/test/sys_info.rs

@@ -323,6 +323,64 @@ def f(**kwargs: Unpack[Kwargs]) -> None:
 "#,
 );
 
+testcase!(
+    test_version_guard_and_short_circuit,
+    r#"
+if False:
+    A = 3
+
+if False:
+    B = 3
+
+if False:
+    C = 3
+
+
+def test_and_basic() -> None:
+    # `and` short-circuits on False: A in the condition and body are unreachable.
+    if False and A:
+        _ = A
+
+def test_and_longer_chain() -> None:
+    # Both B and C are gated: the guard short-circuits before reaching them.
+    if False and B and C:
+        _ = B
+        _ = C
+
+def test_and_three_guards() -> None:
+    # Three consecutive False guards in a single and-chain.
+    if False and A and B and C:
+        _ = A
+        _ = B
+        _ = C
+
+def test_or_basic() -> None:
+    # `or` short-circuits when the left side is *true*. False on the left
+    # means the right side IS evaluated — the name is unknown.
+    if False or A:  # E: Could not find name `A`
+        pass
+
+def test_or_always_true_guard() -> None:
+    # True → right side is unreachable.
+    if True or A:
+        pass
+
+def test_or_longer_chain() -> None:
+    # Chain: first element is always-true, so B and C are never evaluated.
+    if True or B or C:
+        pass
+
+def test_and_body_unreachable() -> None:
+    # An `if False` body is also unreachable; accessing A inside it is fine.
+    if False:
+        _ = A
+
+def test_no_guard_produces_error() -> None:
+    # Baseline: without any guard, accessing A must produce an error.
+    A  # E: Could not find name `A`
+"#,
+);
+
 testcase!(
     test_typechecking_unpack_alias,
     r#"