[NFC] Extract Decl::getExplicitObjCName()

Create a helper method which looks for an `@objc` attribute with an explicit name and returns it, and adopt it in various existing places.

Author: beccadax

include/swift/AST/Decl.h

@@ -1041,6 +1041,10 @@ class alignas(1 << DeclAlignInBits) Decl : public ASTAllocated<Decl>, public Swi
   /// from source code.
   void attachParsedAttrs(DeclAttributes attrs);
 
+  /// Retrieve the custom name in the \c @objc attribute, if present.
+  std::optional<ObjCSelector>
+  getExplicitObjCName(bool allowInvalid = false) const;
+
   /// True if this declaration provides an implementation for an imported
   /// Objective-C declaration. This implies various restrictions and special
   /// behaviors for it and, if it's an extension, its members.

lib/AST/ASTMangler.cpp

@@ -1193,11 +1193,9 @@ getOverriddenSwiftProtocolObjCName(const ValueDecl *decl,
     return std::nullopt;
 
   // If there is an 'objc' attribute with a name, use that name.
-  if (auto objc = proto->getAttrs().getAttribute<ObjCAttr>()) {
-    if (auto name = objc->getName()) {
-      llvm::SmallString<4> buffer;
-      return std::string(name->getString(buffer));
-    }
+  if (auto objcName = proto->getExplicitObjCName()) {
+    llvm::SmallString<4> buffer;
+    return std::string(objcName->getString(buffer));
   }
 
   return std::nullopt;

lib/AST/Decl.cpp

@@ -4408,6 +4408,14 @@ ValueDecl::getObjCRuntimeName(bool skipIsObjCResolution) const {
   return std::nullopt;
 }
 
+std::optional<ObjCSelector>
+Decl::getExplicitObjCName(bool allowInvalid) const {
+  auto objcAttr = getAttrs().getAttribute<ObjCAttr>(allowInvalid);
+  if (objcAttr && !objcAttr->isNameImplicit())
+    return objcAttr->getName();
+  return std::nullopt;
+}
+
 bool ValueDecl::canInferObjCFromRequirement(ValueDecl *requirement) {
   // Only makes sense for a requirement of an @objc protocol.
   auto proto = cast<ProtocolDecl>(requirement->getDeclContext());
@@ -4420,9 +4428,8 @@ bool ValueDecl::canInferObjCFromRequirement(ValueDecl *requirement) {
 
   // If there is already an @objc attribute with an explicit name, we
   // can't infer a name (it's already there).
-  if (auto objcAttr = getAttrs().getAttribute<ObjCAttr>()) {
-    if (objcAttr->hasName() && !objcAttr->isNameImplicit())
-      return false;
+  if (getExplicitObjCName().has_value()) {
+    return false;
   }
 
   // If the nominal type doesn't conform to the protocol at all, we

lib/Sema/TypeCheckProtocol.cpp

@@ -6285,11 +6285,7 @@ static bool hasExplicitObjCName(ClassDecl *classDecl) {
   if (classDecl->getAttrs().hasAttribute<ObjCRuntimeNameAttr>())
     return true;
 
-  auto objcAttr = classDecl->getAttrs().getAttribute<ObjCAttr>();
-  if (!objcAttr)
-    return false;
-
-  return objcAttr->hasName() && !objcAttr->isNameImplicit();
+  return classDecl->getExplicitObjCName().has_value();
 }
 
 /// Check if the name of a class might be unstable, and if so, emit a

tools/SourceKit/lib/SwiftLang/SwiftEditor.cpp

@@ -1454,9 +1454,8 @@ class SwiftDocumentStructureWalker: public ide::SyntaxModelWalker {
     // We only report runtime name for classes and protocols with an explicitly
     // defined ObjC name, i.e. those that have @objc("SomeName")
     if (D && (isa<ClassDecl>(D) || isa<ProtocolDecl>(D))) {
-      auto *ObjCNameAttr = D->getAttrs().getAttribute<ObjCAttr>();
-      if (ObjCNameAttr && ObjCNameAttr->hasName())
-        return ObjCNameAttr->getName()->getString(Buf);
+      if (auto objcName = D->getExplicitObjCName())
+        return objcName->getString(Buf);
     }
     return StringRef();
   }