Merge pull request #59919 from etcwilde/ewilde/improve-main-error

Adding actionable note to @main error

Author: etcwilde

include/swift/AST/DiagnosticsSema.def

@@ -3255,6 +3255,10 @@ ERROR(attr_ApplicationMain_with_script,none,
       "%" SELECT_APPLICATION_MAIN "0 attribute cannot be used in a module that contains "
       "top-level code",
       (unsigned))
+
+NOTE(attr_ApplicationMain_parse_as_library,none,
+     "pass '-parse-as-library' to compiler invocation if this is intentional",
+     ())
 NOTE(attr_ApplicationMain_script_here,none,
      "top-level code defined in this source file",
      ())

lib/AST/Module.cpp

@@ -1841,6 +1841,8 @@ bool ModuleDecl::registerEntryPointFile(FileUnit *file, SourceLoc diagLoc,
       if (existingDiagLoc.isValid()) {
         getASTContext().Diags.diagnose(existingDiagLoc,
                            diag::attr_ApplicationMain_script_here);
+        getASTContext().Diags.diagnose(existingDiagLoc,
+                           diag::attr_ApplicationMain_parse_as_library);
       }
     }
   }

test/attr/ApplicationMain/attr_NSApplicationMain_with_main/main.swift

@@ -1,4 +1,5 @@
 // expected-note{{top-level code defined in this source file}}
+// expected-note@-1{{pass '-parse-as-library' to compiler invocation if this is intentional}}
 // RUN: %target-swift-frontend(mock-sdk: %clang-importer-sdk) -typecheck -verify %s %S/delegate.swift
 
 // Serialized partial AST support:

test/attr/ApplicationMain/attr_UIApplicationMain_with_main/main.swift

@@ -1,4 +1,5 @@
 // expected-note{{top-level code defined in this source file}}
+// expected-note@-1{{pass '-parse-as-library' to compiler invocation if this is intentional}}
 // RUN: %target-swift-frontend(mock-sdk: %clang-importer-sdk) -typecheck -verify %s %S/delegate.swift
 
 // REQUIRES: objc_interop

test/attr/ApplicationMain/attr_main_with_maindotswift/main.swift

@@ -1,4 +1,5 @@
 // expected-note{{top-level code defined in this source file}}
+// expected-note@-1{{pass '-parse-as-library' to compiler invocation if this is intentional}}
 // RUN: %target-swift-frontend(mock-sdk: %clang-importer-sdk) -typecheck -verify %s %S/file.swift
 
 hi()