stop control flow after sys.exit()

Summary: We can treat this the same as `raise` since we know what it does.

Reviewed By: grievejia

Differential Revision: D73125409

fbshipit-source-id: cb75c2264a7227420de96277775ede0a7ef3db8d

Author: yangdanny97

Diff for: pyrefly/lib/binding/expr.rs

@@ -415,6 +415,15 @@ impl<'a> BindingsBuilder<'a> {
                 self.bind_narrow_ops(&narrow_op, *range);
                 return;
             }
+            Expr::Call(ExprCall {
+                range: _,
+                func,
+                arguments: _,
+            }) if self.as_special_export(func) == Some(SpecialExport::Exit) => {
+                // Control flow doesn't proceed after sys.exit()
+                self.scopes.current_mut().flow.no_next = true;
+                false
+            }
             Expr::Name(x) => {
                 let name = Ast::expr_name_identifier(x.clone());
                 let binding = self.forward_lookup(&name);

Diff for: pyrefly/lib/export/special.rs

@@ -35,6 +35,7 @@ pub enum SpecialExport {
     Optional,
     Cast,
     Super,
+    Exit,
 }
 
 #[derive(Debug)]
@@ -70,6 +71,7 @@ impl SpecialExport {
             "Optional" => Some(Self::Optional),
             "cast" => Some(Self::Cast),
             "super" => Some(Self::Super),
+            "exit" => Some(Self::Exit),
             _ => None,
         }
     }
@@ -94,6 +96,7 @@ impl SpecialExport {
             Self::CollectionsNamedTuple => matches!(m.as_str(), "collections"),
             Self::Enum | Self::StrEnum | Self::IntEnum => matches!(m.as_str(), "enum"),
             Self::Super => matches!(m.as_str(), "builtins"),
+            Self::Exit => matches!(m.as_str(), "sys"),
         }
     }
 

Diff for: pyrefly/lib/test/narrow.rs

@@ -223,6 +223,22 @@ def f(x: str | None):
         assert_type(x, str)
     else:
         assert_type(x, None)
+    if not x:
+        assert_type(x, str | None)
+    else:
+        assert_type(x, str)
+    "#,
+);
+
+testcase!(
+    test_exit,
+    r#"
+from typing import assert_type
+import sys
+def f(x: str | None):
+    if not x:
+        sys.exit(1)
+    assert_type(x, str)
     "#,
 );