Merge pull request #30693 from nate-chandler/main-attribute

@main: Attribute to add an entry point to a type.

include/swift/AST/Decl.h

@@ -272,6 +272,13 @@ bool conflicting(ASTContext &ctx,
                  bool *wouldConflictInSwift5 = nullptr,
                  bool skipProtocolExtensionCheck = false);
 
+/// The kind of artificial main to generate.
+enum class ArtificialMainKind : uint8_t {
+  NSApplicationMain,
+  UIApplicationMain,
+  TypeMain,
+};
+
 /// Decl - Base class for all declarations in Swift.
 class alignas(1 << DeclAlignInBits) Decl {
 protected:
@@ -779,6 +786,13 @@ public:
 
   SourceLoc TrailingSemiLoc;
 
+  /// Returns the appropriate kind of entry point to generate for this class,
+  /// based on its attributes.
+  ///
+  /// It is an error to call this on a type that does not have either an
+  /// *ApplicationMain or an main attribute.
+  ArtificialMainKind getArtificialMainKind() const;
+
   SWIFT_DEBUG_DUMP;
   SWIFT_DEBUG_DUMPER(dump(const char *filename));
   void dump(raw_ostream &OS, unsigned Indent = 0) const;
@@ -3814,12 +3828,6 @@ public:
   }
 };
 
-/// The kind of artificial main to generate for a class.
-enum class ArtificialMainKind : uint8_t {
-  NSApplicationMain,
-  UIApplicationMain,
-};
-
 /// This is the base type for AncestryOptions. Each flag describes possible
 /// interesting kinds of superclasses that a class may have.
 enum class AncestryFlags : uint8_t {
@@ -4087,13 +4095,6 @@ public:
   /// the Objective-C runtime.
   StringRef getObjCRuntimeName(llvm::SmallVectorImpl<char> &buffer) const;
 
-  /// Returns the appropriate kind of entry point to generate for this class,
-  /// based on its attributes.
-  ///
-  /// It is an error to call this on a class that does not have a
-  /// *ApplicationMain attribute.
-  ArtificialMainKind getArtificialMainKind() const;
-
   using NominalTypeDecl::lookupDirect;
 
   /// Look in this class and its extensions (but not any of its protocols or
@@ -6297,6 +6298,8 @@ public:
   }
   bool isCallAsFunctionMethod() const;
 
+  bool isMainTypeMainMethod() const;
+
   SelfAccessKind getSelfAccessKind() const;
 
   void setSelfAccessKind(SelfAccessKind mod) {