[Macros] Eliminate ordering dependency that suppressed conformingTo protocols

lib/Sema/TypeCheckMacros.cpp

@@ -1788,8 +1788,20 @@ static TinyPtrVector<ProtocolDecl *> getIntroducedConformances(
     bool hasExistingConformance = llvm::any_of(
         existingConformances,
         [&](ProtocolConformance *conformance) {
-          return conformance->getSourceKind() !=
-              ConformanceEntryKind::PreMacroExpansion;
+          // The conformance is coming from a macro expansion, so ignore it.
+          if (conformance->getSourceKind() ==
+                ConformanceEntryKind::PreMacroExpansion)
+            return false;
+
+          // Check whether the conformance comes from an extension defined by
+          // a macro.
+          if (auto conformingExt =
+                  dyn_cast<ExtensionDecl>(conformance->getDeclContext())) {
+            if (conformingExt->isInMacroExpansionInContext())
+              return false;
+          }
+
+          return true;
         });
 
     if (!hasExistingConformance) {

test/Macros/Inputs/syntax_macro_definitions.swift

@@ -1808,6 +1808,46 @@ public struct AddAllConformancesMacro: ExtensionMacro {
   }
 }
 
+public struct ListConformancesMacro { }
+
+extension ListConformancesMacro: ExtensionMacro {
+  public static func expansion(
+    of node: AttributeSyntax,
+    attachedTo decl: some DeclGroupSyntax,
+    providingExtensionsOf type: some TypeSyntaxProtocol,
+    conformingTo protocols: [TypeSyntax],
+    in context: some MacroExpansionContext
+  ) throws -> [ExtensionDeclSyntax] {
+    protocols.map { proto in
+      let decl: DeclSyntax =
+        """
+        extension \(type): \(proto) {}
+        """
+      return decl.cast(ExtensionDeclSyntax.self)
+    }
+  }
+}
+
+extension ListConformancesMacro: MemberMacro {
+  public static func expansion(
+    of node: AttributeSyntax,
+    providingMembersOf declaration: some DeclGroupSyntax,
+    conformingTo protocols: [TypeSyntax],
+    in context: some MacroExpansionContext
+  ) throws -> [DeclSyntax] {
+    let typeName = declaration.asProtocol(NamedDeclSyntax.self)!.name.text
+
+    let protocolNames: [ExprSyntax] = protocols.map { "\(literal: $0.trimmedDescription)" }
+    let protocolsArray: ExprSyntax =
+      "[ \(raw: protocolNames.map { $0.description }.joined(separator: ", ")) ]"
+    let unknownDecl: DeclSyntax =
+    """
+    @_nonoverride static func conformances() -> [String: [String]] { [ \(literal: typeName): \(protocolsArray) ] }
+    """
+    return [unknownDecl]
+  }
+}
+
 public struct AlwaysAddCodable: ExtensionMacro {
   public static func expansion(
     of node: AttributeSyntax,

test/Macros/macro_expand_conformances_xref.swift

@@ -0,0 +1,48 @@
+// 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
+
+// Check for errors first
+// RUN: %target-swift-frontend -swift-version 5 -typecheck -load-plugin-library %t/%target-library-name(MacroDefinition) %s -I %t -disable-availability-checking
+
+// RUN: %target-swift-frontend -swift-version 5 -typecheck -load-plugin-library %t/%target-library-name(MacroDefinition) %s -I %t -disable-availability-checking -dump-macro-expansions > %t/expansions-dump.txt 2>&1
+// RUN: %FileCheck -check-prefix=CHECK-DUMP %s < %t/expansions-dump.txt
+
+
+protocol P1 {}
+protocol P2 {}
+
+@attached(extension, conformances: P1, P2)
+@attached(member, conformances: P1, P2, names: named(conformances))
+macro ListConformances() = #externalMacro(module: "MacroDefinition", type: "ListConformancesMacro")
+
+
+// CHECK-DUMP: [ "Root": [ "P1", "P2" ] ]
+// CHECK-DUMP: extension Root: P1
+// CHECK-DUMP: extension Root: P2
+@ListConformances
+class Root {
+// CHECK-DUMP: extension OtherRoot: P1
+// CHECK-DUMP: extension OtherRoot: P2
+  var other: OtherRoot?
+}
+
+// CHECK-DUMP: [ "P1Root": [ "P2" ] ]
+// CHECK-DUMP-NOT: extension P1Root: P1
+// CHECK-DUMP: extension P1Root: P2
+@ListConformances
+class P1Root: P1 { }
+
+// CHECK-DUMP: [ "OtherRoot": [ "P1", "P2" ] ]
+@ListConformances
+class OtherRoot {
+// CHECK-DUMP-NOT: extension OtherP1Root: P1
+// CHECK-DUMP: extension OtherP1Root: P2
+  var other: OtherP1Root?
+}
+
+// CHECK-DUMP: [ "OtherP1Root": [ "P2" ] ]
+@ListConformances
+class OtherP1Root: P1 { }
+