[Macros] Register the extension for a conformance macro fully.

When we form an extension for a conformance macro, make sure to
register that extension as being part of the nominal type to which the
conformance macro is attached. This ensures that the conformance is
seen everywhere. Crucially, this ensures that that protocol
conformance table handles conformances that are implied by the
conformance macro. For example, a conformance macro that introduces a
`Hashable` conformance will also imply an `Equatable` conformance;
that wasn't happening before this change.

This is needed to make the `OptionSet` macro work fully.

Author: DougGregor

lib/Sema/TypeCheckMacros.cpp

@@ -1276,34 +1276,14 @@ swift::expandConformances(CustomAttr *attr, MacroDecl *macro,
     if (!extension)
       continue;
 
-    auto &extensionCtx = extension->getASTContext();
-
     // Bind the extension to the original nominal type.
     extension->setExtendedNominal(nominal);
+    nominal->addExtension(extension);
 
-    // Resolve the protocol type.
-    assert(extension->getInherited().size() == 1);
-    auto inheritedType = evaluateOrDefault(
-        extensionCtx.evaluator,
-        InheritedTypeRequest{extension, 0, TypeResolutionStage::Interface},
-        Type());
-
-    if (!inheritedType || inheritedType->hasError())
-      continue;
-
-    auto protocolType = inheritedType->getAs<ProtocolType>();
-    if (!protocolType)
-      continue;
-
-    // Create a synthesized conformance and register it with the nominal type.
-    auto conformance = extensionCtx.getConformance(
-        nominal->getDeclaredInterfaceType(), protocolType->getDecl(),
-        nominal->getLoc(), extension, ProtocolConformanceState::Incomplete,
-        /*isUnchecked=*/false);
-    conformance->setSourceKindAndImplyingConformance(
-        ConformanceEntryKind::Synthesized, nullptr);
-
-    nominal->registerProtocolConformance(conformance, /*synthesized=*/true);
+    // Make it accessible to getTopLevelDecls()
+    if (auto file = dyn_cast<FileUnit>(
+            decl->getDeclContext()->getModuleScopeContext()))
+      file->getOrCreateSynthesizedFile().addTopLevelDecl(extension);
   }
 
   return macroSourceFile->getBufferID();

test/Macros/Inputs/syntax_macro_definitions.swift

@@ -1037,6 +1037,17 @@ public struct EquatableMacro: ConformanceMacro {
   }
 }
 
+public struct HashableMacro: ConformanceMacro {
+  public static func expansion(
+    of node: AttributeSyntax,
+    providingConformancesOf decl: some DeclGroupSyntax,
+    in context: some MacroExpansionContext
+  ) throws -> [(TypeSyntax, GenericWhereClauseSyntax?)] {
+    let protocolName: TypeSyntax = "Hashable"
+    return [(protocolName, nil)]
+  }
+}
+
 public struct DelegatedConformanceMacro: ConformanceMacro, MemberMacro {
   public static func expansion(
     of node: AttributeSyntax,

test/Macros/macro_expand_conformances.swift

@@ -13,19 +13,32 @@
 @attached(conformance)
 macro Equatable() = #externalMacro(module: "MacroDefinition", type: "EquatableMacro")
 
+@attached(conformance)
+macro Hashable() = #externalMacro(module: "MacroDefinition", type: "HashableMacro")
+
 func requireEquatable(_ value: some Equatable) {
   print(value == value)
 }
 
+func requireHashable(_ value: some Hashable) {
+  print(value.hashValue)
+}
+
 @Equatable
 struct S {}
 
+@Hashable
+struct S2 {}
+
 // CHECK-DUMP: @__swiftmacro_25macro_expand_conformances1SV9EquatablefMc_.swift
 // CHECK-DUMP: extension S : Equatable  {}
 
 // CHECK: true
 requireEquatable(S())
 
+requireEquatable(S2())
+requireHashable(S2())
+
 @attached(conformance)
 @attached(member)
 macro DelegatedConformance() = #externalMacro(module: "MacroDefinition", type: "DelegatedConformanceMacro")