[wasm] Accept multiple @_expose on a single function decl

But multiple @_expose with the same exposure kind are still invalid.

Author: kateinoigakukun

include/swift/AST/Attr.def

@@ -398,7 +398,7 @@ SIMPLE_DECL_ATTR(_alwaysEmitConformanceMetadata, AlwaysEmitConformanceMetadata,
   OnProtocol | UserInaccessible | ABIStableToAdd | ABIStableToRemove | APIStableToAdd | APIStableToRemove,
   132)
 DECL_ATTR(_expose, Expose,
-  OnFunc | OnNominalType | OnVar | OnConstructor | LongAttribute | UserInaccessible | ABIStableToAdd | ABIStableToRemove | APIStableToAdd | APIStableToRemove,
+  OnFunc | OnNominalType | OnVar | AllowMultipleAttributes | OnConstructor | LongAttribute | UserInaccessible | ABIStableToAdd | ABIStableToRemove | APIStableToAdd | APIStableToRemove,
   133)
 SIMPLE_DECL_ATTR(_spiOnly, SPIOnly,
   OnImport | UserInaccessible | ABIStableToAdd | ABIStableToRemove | APIStableToAdd | APIStableToRemove,

lib/AST/SwiftNameTranslation.cpp

@@ -158,9 +158,9 @@ swift::cxx_translation::getNameForCxx(const ValueDecl *VD,
                                       CustomNamesOnly_t customNamesOnly) {
   ASTContext& ctx = VD->getASTContext();
 
-  if (const auto *Expose = VD->getAttrs().getAttribute<ExposeAttr>()) {
-    if (Expose->getExposureKind() == ExposureKind::Cxx && !Expose->Name.empty())
-      return Expose->Name;
+  for (auto *EA : VD->getAttrs().getAttributes<ExposeAttr>()) {
+    if (EA->getExposureKind() == ExposureKind::Cxx && !EA->Name.empty())
+      return EA->Name;
   }
 
   if (customNamesOnly)

lib/Parse/ParseDecl.cpp

@@ -3088,10 +3088,19 @@ ParserStatus Parser::parseNewDeclAttribute(DeclAttributes &Attributes,
       else if (DK == DAK_CDecl)
         Attributes.add(new (Context) CDeclAttr(AsmName.value(), AtLoc,
                                                AttrRange, /*Implicit=*/false));
-      else if (DK == DAK_Expose)
+      else if (DK == DAK_Expose) {
+        for (auto *EA : Attributes.getAttributes<ExposeAttr>()) {
+          // A single declaration cannot have two @_exported attributes with
+          // the same exposure kind.
+          if (EA->getExposureKind() == ExpKind) {
+            diagnose(Loc, diag::duplicate_attribute, false);
+            break;
+          }
+        }
         Attributes.add(new (Context) ExposeAttr(
             AsmName ? AsmName.value() : StringRef(""), AtLoc, AttrRange,
             ExpKind, /*Implicit=*/false));
+      }
       else
         llvm_unreachable("out of sync with switch");
     }

lib/PrintAsClang/DeclAndTypePrinter.cpp

@@ -2825,7 +2825,7 @@ static bool hasExposeAttr(const ValueDecl *VD, bool isExtension = false) {
   // Clang decls don't need to be explicitly exposed.
   if (VD->hasClangNode())
     return true;
-  if (auto *EA = VD->getAttrs().getAttribute<ExposeAttr>()) {
+  for (auto *EA : VD->getAttrs().getAttributes<ExposeAttr>()) {
     if (EA->getExposureKind() == ExposureKind::Cxx)
       return true;
   }

lib/SIL/IR/SILFunctionBuilder.cpp

@@ -218,7 +218,7 @@ void SILFunctionBuilder::addFunctionAttributes(
   if (Attrs.hasAttribute<SILGenNameAttr>() || Attrs.hasAttribute<CDeclAttr>())
     F->setHasCReferences(true);
 
-  if (auto *EA = Attrs.getAttribute<ExposeAttr>()) {
+  for (auto *EA : Attrs.getAttributes<ExposeAttr>()) {
     bool shouldExportDecl = true;
     if (Attrs.hasAttribute<CDeclAttr>()) {
       // If the function is marked with @cdecl, expose only C compatible

test/attr/attr_expose.swift

@@ -33,6 +33,9 @@ struct ExposedStruct {
     @_expose(Cxx, "initWith")
     init(with y: Int) {}
 }
+@_expose(Cxx)
+@_expose(Cxx) // expected-error {{duplicate attribute}}
+func exposeToCxxCxx() {}
 
 @_expose(wasm) func exposeToWasm() {}
 @_expose(wasm, "with_name") func wasmName() {}
@@ -47,3 +50,14 @@ func wasmNested() {
   func errorOnInnerExpose() {}
 }
 
+@_expose(Cxx)
+@_expose(wasm)
+func exposeToCxxWasm() {}
+
+@_expose(wasm)
+@_expose(Cxx)
+func exposeToWasmCxx() {}
+
+@_expose(wasm)
+@_expose(wasm) // expected-error {{duplicate attribute}}
+func exposeToWasmWasm() {}