Add return annotation to __annotations__ last (#6071)

jackoconnordev · web-flow · commit 33ea50c2e910 · 2025-08-08T23:31:12.000+09:00
Functions like `functools.singledispatch` are sensitive to the order of
items in the `__annotations__` map.

CPython puts returns last.
diff --git a/compiler/codegen/src/compile.rs b/compiler/codegen/src/compile.rs
@@ -2254,15 +2254,6 @@ impl Compiler {
     ) -> CompileResult<u32> {
         let mut num_annotations = 0;
 
-        // Handle return annotation first
-        if let Some(annotation) = returns {
-            self.emit_load_const(ConstantData::Str {
-                value: "return".into(),
-            });
-            self.compile_annotation(annotation)?;
-            num_annotations += 1;
-        }
-
         // Handle parameter annotations
         let parameters_iter = std::iter::empty()
             .chain(&parameters.posonlyargs)
@@ -2282,6 +2273,15 @@ impl Compiler {
             }
         }
 
+        // Handle return annotation last
+        if let Some(annotation) = returns {
+            self.emit_load_const(ConstantData::Str {
+                value: "return".into(),
+            });
+            self.compile_annotation(annotation)?;
+            num_annotations += 1;
+        }
+
         Ok(num_annotations)
     }
 
diff --git a/extra_tests/snippets/syntax_annotations.py b/extra_tests/snippets/syntax_annotations.py
@@ -0,0 +1,10 @@
+from typing import get_type_hints
+
+def func(s: str) -> int:
+    return int(s)
+
+hints = get_type_hints(func)
+
+# The order of type hints matters for certain functions
+# e.g. functools.singledispatch
+assert list(hints.items()) == [('s', str), ('return', int)]
