Fix module docstring global name resolution (#9095)

* Fix module docstring global name resolution

Assisted-by: Claude Code:claude-opus-5-5

* Move module docstring test into syntax_doc.py

Assisted-by: Claude Code:claude-opus-5-5

crates/codegen/src/compile.rs

@@ -2996,8 +2996,7 @@ impl<'warnings> Compiler<'warnings> {
             self.emit_load_const(ConstantData::Str {
                 value: value.into(),
             });
-            let doc = self.name("__doc__");
-            emit!(self, Instruction::StoreName { namei: doc });
+            self.store_name(&"__doc__".into())?;
             self.set_no_location();
             self.set_source_range(saved_range);
         }
@@ -20054,6 +20053,54 @@ class C:
         }));
     }
 
+    fn find_module_doc_store(code: &CodeObject) -> Option<&Instruction> {
+        code.instructions.iter().find_map(|unit| match unit.op {
+            Instruction::StoreName { namei } | Instruction::StoreGlobal { namei } => {
+                let idx = namei.get(OpArg::new(u32::from(u8::from(unit.arg))));
+                (code.names[usize::try_from(idx).unwrap()].as_str() == "__doc__")
+                    .then_some(&unit.op)
+            }
+            _ => None,
+        })
+    }
+
+    #[test]
+    fn module_docstring_store_uses_global_when_nested_scope_declares_global() {
+        let code = compile_exec(
+            "\
+\"module doc\"
+def f():
+    global __doc__
+",
+        );
+
+        let op = find_module_doc_store(&code).expect("missing module docstring store");
+        assert!(
+            matches!(op, Instruction::StoreGlobal { .. }),
+            "module docstring store should resolve through name resolution to StoreGlobal \
+             when a nested scope declares `global __doc__`, got instructions={:?}",
+            code.instructions
+        );
+    }
+
+    #[test]
+    fn module_docstring_store_stays_name_without_nested_global() {
+        let code = compile_exec(
+            "\
+\"module doc\"
+x = 1
+",
+        );
+
+        let op = find_module_doc_store(&code).expect("missing module docstring store");
+        assert!(
+            matches!(op, Instruction::StoreName { .. }),
+            "module docstring store should remain StoreName without a nested \
+             `global __doc__` declaration, got instructions={:?}",
+            code.instructions
+        );
+    }
+
     #[test]
     fn conditional_return_epilogue_is_duplicated() {
         let code = compile_exec(

extra_tests/snippets/syntax_doc.py

@@ -13,3 +13,77 @@ def f2():
     """
 
 assert f2.__doc__ == '\nx\n    y\n'
+
+
+# Regression test: a module docstring must be stored through module name
+# resolution, so a nested `global __doc__` declaration makes the module body
+# emit STORE_GLOBAL (writing module globals) instead of STORE_NAME (writing
+# the provided locals mapping). Mirrors CPython codegen_nameop behavior.
+
+import dis
+
+
+def opnames(code):
+    return [instr.opname for instr in dis.get_instructions(code)]
+
+
+def run_split(src, optimize=0):
+    code = compile(src, "<test>", "exec", optimize=optimize)
+    g, loc = {}, {}
+    exec(code, g, loc)
+    return code, g, loc
+
+
+# A nested function declaring `global __doc__` makes the module docstring
+# store target module globals.
+src_global = '"module doc"\ndef f():\n    global __doc__\n'
+code, g, loc = run_split(src_global)
+ops = opnames(code)
+assert "STORE_GLOBAL" in ops, ops
+assert "STORE_NAME" not in ops or "__doc__" not in [
+    instr.argval for instr in dis.get_instructions(code) if instr.opname == "STORE_NAME"
+], ops
+assert g.get("__doc__") == "module doc", g
+assert "__doc__" not in loc, loc
+
+# The declaration may be nested more than one scope deep.
+src_deep = '"module doc"\ndef f():\n    def g():\n        global __doc__\n'
+code, g, loc = run_split(src_deep)
+assert "STORE_GLOBAL" in opnames(code), opnames(code)
+assert g.get("__doc__") == "module doc", g
+assert "__doc__" not in loc, loc
+
+# Control: without a nested global declaration the docstring stays a
+# STORE_NAME and lands in the provided locals mapping.
+src_plain = '"module doc"\nx = 1\n'
+code, g, loc = run_split(src_plain)
+doc_stores = [
+    instr.opname
+    for instr in dis.get_instructions(code)
+    if instr.argval == "__doc__" and instr.opname.startswith("STORE_")
+]
+assert doc_stores == ["STORE_NAME"], doc_stores
+assert loc.get("__doc__") == "module doc", loc
+assert "__doc__" not in g, g
+
+# optimize=1 keeps the docstring and the same global resolution.
+code, g, loc = run_split(src_global, optimize=1)
+assert "STORE_GLOBAL" in opnames(code), opnames(code)
+assert g.get("__doc__") == "module doc", g
+
+# optimize=2 strips the docstring entirely: no __doc__ store in either dict.
+code, g, loc = run_split(src_global, optimize=2)
+assert not any(
+    instr.argval == "__doc__" and instr.opname.startswith("STORE_")
+    for instr in dis.get_instructions(code)
+), opnames(code)
+assert "__doc__" not in g and "__doc__" not in loc, (g, loc)
+
+# A class docstring still belongs to the class namespace even when a nested
+# scope declares `global __doc__`.
+src_class = '"module doc"\ndef f():\n    global __doc__\nclass C:\n    "class doc"\n'
+g, loc = {}, {}
+exec(compile(src_class, "<test>", "exec"), g, loc)
+assert g.get("__doc__") == "module doc", g
+assert loc["C"].__doc__ == "class doc", loc["C"].__doc__
+assert "__doc__" not in loc, loc