[Macros] Eliminate ordering dependency that suppressed conformingTo protocols

When a macro that has both 'member' and 'extension' roles is on a type,
and both list conforming protocols, the order in which those roles were
evaluated in the compiler could change the set of protocols passed to
the macro expansion function (via `conformingTo:`). Specifically, if
the extension macro was expanded first, the member macro would see the
extension providing the conformance to one of its protocols, and not
pass down that protocol to the member macro's `conformingTo:`.

Ensure that we account for already-expanded extension macros that
define conformances.

Fixes rdar://137080876.

Author: DougGregor

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 { }
+