[Macros] Separate each protocol name with commas when forming the conformance

list buffer for extension macro expansion.

(cherry picked from commit 0be80c8)

Author: hborla

lib/Sema/TypeCheckMacros.cpp

@@ -1238,9 +1238,13 @@ static SourceFile *evaluateAttachedMacro(MacroDecl *macro, Decl *attachedTo,
   {
     llvm::raw_string_ostream OS(conformanceList);
     if (role == MacroRole::Extension) {
-      for (auto *protocol : conformances) {
-        protocol->getDeclaredType()->print(OS);
-      }
+      llvm::interleave(
+          conformances,
+          [&](const ProtocolDecl *protocol) {
+            protocol->getDeclaredType()->print(OS);
+          },
+          [&] { OS << ", "; }
+      );
     } else {
       OS << "";
     }

test/Macros/Inputs/syntax_macro_definitions.swift

@@ -1481,6 +1481,24 @@ public struct ConditionallyAvailableConformance: ExtensionMacro {
   }
 }
 
+public struct AddAllConformancesMacro: 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)
+    }
+  }
+}
+
 public struct AlwaysAddCodable: ExtensionMacro {
   public static func expansion(
     of node: AttributeSyntax,

test/Macros/macro_expand_extensions.swift

@@ -165,3 +165,17 @@ macro AvailableEquatable() = #externalMacro(module: "MacroDefinition", type: "Co
 struct TestAvailability {
   static let x : any Equatable.Type = TestAvailability.self
 }
+
+protocol P1 {}
+protocol P2 {}
+
+@attached(extension, conformances: P1, P2)
+macro AddAllConformances() = #externalMacro(module: "MacroDefinition", type: "AddAllConformancesMacro")
+
+@AddAllConformances
+struct MultipleConformances {}
+
+// CHECK-DUMP: extension MultipleConformances: P1 {
+// CHECK-DUMP: }
+// CHECK-DUMP: extension MultipleConformances: P2 {
+// CHECK-DUMP: }