[Macros] Suppress the conformance macro diagnostic in swiftinterfaces.

Author: hborla

lib/Sema/TypeCheckAttr.cpp

@@ -7131,11 +7131,17 @@ void AttributeChecker::visitMacroRoleAttr(MacroRoleAttr *attr) {
       break;
     case MacroRole::Peer:
       break;
-    case MacroRole::Conformance:
+    case MacroRole::Conformance: {
+      // Suppress the conformance macro error in swiftinterfaces.
+      SourceFile *file = D->getDeclContext()->getParentSourceFile();
+      if (file && file->Kind == SourceFileKind::Interface)
+        break;
+
       diagnoseAndRemoveAttr(attr, diag::conformance_macro)
           .fixItReplace(attr->getRange(),
                         "@attached(extension, conformances: <#Protocol#>)");
       break;
+    }
     case MacroRole::Extension:
       break;
     default:

test/Macros/Inputs/ConformanceMacroLib.swiftinterface

@@ -0,0 +1,5 @@
+// swift-interface-format-version: 1.0
+// swift-module-flags: -module-name ConformanceMacroLib
+
+@attached(conformance)
+public macro Equatable() = #externalMacro(module: "MacroDefinition", type: "EquatableMacro")

test/Macros/imported_conformance_macro.swift

@@ -0,0 +1,18 @@
+// REQUIRES: swift_swift_parser, executable_test
+
+// RUN: %empty-directory(%t)
+// RUN: %host-build-swift -swift-version 5 -emit-library -o %t/%target-library-name(MacroDefinition) -module-name=MacroDefinition %S/Inputs/syntax_macro_definitions.swift -g -no-toolchain-stdlib-rpath
+
+
+// RUN: %target-swift-frontend -compile-module-from-interface -module-name ConformanceMacroLib %S/Inputs/ConformanceMacroLib.swiftinterface -o %t/ConformanceMacroLib.swiftmodule
+
+// RUN: %target-swift-frontend -swift-version 5 -typecheck -I%t -verify %s -verify-ignore-unknown  -load-plugin-library %t/%target-library-name(MacroDefinition) -dump-macro-expansions > %t/expansions-dump.txt 2>&1
+// RUN: %FileCheck -check-prefix=CHECK-DUMP %s < %t/expansions-dump.txt
+
+import ConformanceMacroLib
+
+@Equatable
+struct S {}
+
+// CHECK-DUMP: extension S: Equatable  {
+// CHECK-DUMP: }