[Macros] Fix a few issues with invalid macro expansion diagnostics, and add tests.

Author: hborla

include/swift/AST/DiagnosticsSema.def

@@ -6910,7 +6910,7 @@ ERROR(external_macro_arg_not_type_name,none,
 ERROR(attached_declaration_macro_not_supported,none,
       "attached declaration macros are not yet supported", ())
 ERROR(invalid_decl_in_macro_expansion,none,
-      "macro expansion cannot introduce %1",
+      "macro expansion cannot introduce %0",
       (DescriptiveDeclKind))
 ERROR(invalid_main_type_in_macro_expansion,none,
       "macro expansion cannot introduce '@main' type'",

lib/Sema/TypeCheckMacros.cpp

@@ -512,13 +512,20 @@ static void validateMacroExpansion(SourceFile *expansionBuffer,
         isa<ExtensionDecl>(decl)) {
       decl->diagnose(diag::invalid_decl_in_macro_expansion,
                      decl->getDescriptiveKind());
+      decl->setInvalid();
+
+      if (auto *extension = dyn_cast<ExtensionDecl>(decl)) {
+        extension->setExtendedNominal(nullptr);
+      }
+
+      continue;
     }
 
     // Diagnose `@main` types.
-    if (auto *typeDecl = dyn_cast<TypeDecl>(decl)) {
-      if (typeDecl->getAttrs().hasAttribute<MainTypeAttr>()) {
-        typeDecl->diagnose(diag::invalid_main_type_in_macro_expansion);
-      }
+    if (auto *mainAttr = decl->getAttrs().getAttribute<MainTypeAttr>()) {
+      ctx.Diags.diagnose(mainAttr->getLocation(),
+                         diag::invalid_main_type_in_macro_expansion);
+      mainAttr->setInvalid();
     }
 
     // Diagnose default literal type overrides.

test/Macros/Inputs/syntax_macro_definitions.swift

@@ -764,6 +764,27 @@ public struct AddCompletionHandler: PeerMacro {
   }
 }
 
+public struct InvalidMacro: PeerMacro {
+  public static func expansion(
+    of node: AttributeSyntax,
+    providingPeersOf declaration: some DeclSyntaxProtocol,
+    in context: some MacroExpansionContext
+  ) throws -> [DeclSyntax] {
+    return [
+      "import Swift",
+      "precedencegroup MyPrecedence {}",
+      "@attached(member) macro myMacro()",
+      "extension Int {}",
+      """
+      @main
+      struct MyMain {
+        static func main() {}
+      }
+      """,
+    ]
+  }
+}
+
 public struct WrapInType: PeerMacro {
   public static func expansion(
     of node: AttributeSyntax,

test/Macros/macro_expand.swift

@@ -26,6 +26,39 @@
 // FIXME: Swift parser is not enabled on Linux CI yet.
 // REQUIRES: OS=macosx
 
+#if TEST_DIAGNOSTICS
+@attached(peer)
+macro Invalid() = #externalMacro(module: "MacroDefinition", type: "InvalidMacro")
+
+@Invalid
+struct Bad {}
+// expected-note@-1 7 {{in expansion of macro 'Invalid' here}}
+
+// CHECK-DIAGS: error: macro expansion cannot introduce import
+// CHECK-DIAGS: CONTENTS OF FILE @__swiftmacro_9MacroUser3BadV7InvalidfMp_.swift
+// CHECK-DIAGS: import Swift
+
+// CHECK-DIAGS: error: macro expansion cannot introduce precedence group
+// CHECK-DIAGS: CONTENTS OF FILE @__swiftmacro_9MacroUser3BadV7InvalidfMp_.swift
+// CHECK-DIAGS: precedencegroup MyPrecedence {}
+
+// CHECK-DIAGS: error: macro expansion cannot introduce macro
+// CHECK-DIAGS: CONTENTS OF FILE @__swiftmacro_9MacroUser3BadV7InvalidfMp_.swift
+// CHECK-DIAGS: @attached(member) macro myMacro()
+
+// CHECK-DIAGS: error: macro expansion cannot introduce extension
+// CHECK-DIAGS: CONTENTS OF FILE @__swiftmacro_9MacroUser3BadV7InvalidfMp_.swift
+// CHECK-DIAGS: extension Int {}
+
+// CHECK-DIAGS: error: macro expansion cannot introduce '@main' type'
+// CHECK-DIAGS: CONTENTS OF FILE @__swiftmacro_9MacroUser3BadV7InvalidfMp_.swift
+// CHECK-DIAGS: @main
+
+// CHECK-DIAGS: error: declaration name 'MyMain' is not covered by macro 'Invalid'
+// CHECK-DIAGS: CONTENTS OF FILE @__swiftmacro_9MacroUser3BadV7InvalidfMp_.swift
+// CHECK-DIAGS: struct MyMain {
+#endif
+
 @freestanding(expression) macro customFileID() -> String = #externalMacro(module: "MacroDefinition", type: "FileIDMacro")
 @freestanding(expression) macro stringify<T>(_ value: T) -> (T, String) = #externalMacro(module: "MacroDefinition", type: "StringifyMacro")
 @freestanding(expression) macro fileID<T: ExpressibleByStringLiteral>() -> T = #externalMacro(module: "MacroDefinition", type: "FileIDMacro")