From 2718122853081fe45512edcc774ddcb936092cbb Mon Sep 17 00:00:00 2001
From: Yuta Saito <kateinoigakukun@gmail.com>
Date: Thu, 11 Sep 2025 07:22:22 +0000
Subject: [PATCH] [wasm] Fix `@_expose(wasm)` serialization crash

https://github.com/swiftlang/swift/pull/82616 added a new exposure kind
for the `@_expose` attribute, but did not update the serialization
format to account for the new kind. This caused a crash when
serializing a module that used `@_expose(wasm)`.
---
 lib/Serialization/ModuleFormat.h     |  2 +-
 test/Serialization/attr-expose.swift | 31 ++++++++++++++++++++++++++++
 2 files changed, 32 insertions(+), 1 deletion(-)
 create mode 100644 test/Serialization/attr-expose.swift

diff --git a/lib/Serialization/ModuleFormat.h b/lib/Serialization/ModuleFormat.h
index 004131ee7bdb7..0d5294cf0aade 100644
--- a/lib/Serialization/ModuleFormat.h
+++ b/lib/Serialization/ModuleFormat.h
@@ -2531,7 +2531,7 @@ namespace decls_block {
   >;
 
   using ExposeDeclAttrLayout = BCRecordLayout<Expose_DECL_ATTR,
-                                              BCFixed<1>, // exposure kind
+                                              BCFixed<2>, // exposure kind
                                               BCFixed<1>, // implicit flag
                                               BCBlob      // declaration name
                                               >;
diff --git a/test/Serialization/attr-expose.swift b/test/Serialization/attr-expose.swift
new file mode 100644
index 0000000000000..b57b6f5f87cb8
--- /dev/null
+++ b/test/Serialization/attr-expose.swift
@@ -0,0 +1,31 @@
+// RUN: %empty-directory(%t)
+// RUN: %target-swift-frontend  -module-name attr_expose -emit-module -parse-as-library -o %t %s
+// RUN: %target-sil-opt -enable-sil-verify-all %t/attr_expose.swiftmodule | %FileCheck %s
+
+// @_expose
+// -----------------------------------------------------------------------------
+
+// CHECK:      @_expose(Cxx)
+// CHECK-NEXT: func exposeToCxx()
+@_expose(Cxx)
+func exposeToCxx() -> Int { return 42 }
+
+// CHECK:      @_expose(Cxx, "custom_name")
+// CHECK-NEXT: func exposeToCxxWithName()
+@_expose(Cxx, "custom_name")
+func exposeToCxxWithName() -> Int { return 24 }
+
+// CHECK:      @_expose(!Cxx)
+// CHECK-NEXT: func dontExposeToCxx()
+@_expose(!Cxx)
+func dontExposeToCxx() -> Int { return 13 }
+
+// CHECK:      @_expose(wasm)
+// CHECK-NEXT: func exposeToWasm()
+@_expose(wasm)
+func exposeToWasm() -> Int { return 99 }
+
+// CHECK:     @_expose(wasm, "wasm_custom")
+// CHECK-NEXT func exposeToWasmWithName()
+@_expose(wasm, "wasm_custom")
+func exposeToWasmWithName() -> Int { return 88 }