Always supersede conformances implied by pre-macro-expansion conformances

Pre-macro-expansion conformances are introduced at the point where an
attached extension macro is attached to a particular nominal type, and
can imply other conformances. Once the macro is expanded, they are
expected to be replaced by the real conformance from the extension
produced by the macro. This includes any other conformances that are
implied by that conformances. Ensure that the real conformance---and
every conformances it implies---are considered "better" than the
pre-expansion conformances.

Fixes a bug where we would pick the wrong (pre-expansion)
conformances, which would then fail to get fully type-checked prior to
serialization. This could accept invalid code that then crashed the
compiler, as in rdar://112916159.

Author: DougGregor

include/swift/AST/DeclContext.h

@@ -153,15 +153,15 @@ enum class ConformanceEntryKind : unsigned {
   /// Explicitly specified.
   Explicit,
 
+  /// The conformance is generated by a macro that has not been
+  /// expanded yet.
+  PreMacroExpansion,
+
   /// Implicitly synthesized.
   Synthesized,
 
   /// Implied by an explicitly-specified conformance.
   Implied,
-
-  /// The conformance is generated by a macro that has not been
-  /// expanded yet.
-  PreMacroExpansion,
 };
 
 /// Describes the kind of conformance lookup desired.

lib/AST/ConformanceLookupTable.h

@@ -147,7 +147,7 @@ class ConformanceLookupTable : public ASTAllocated<ConformanceLookupTable> {
     ///
     /// The only difference between the ranking kind and the kind is
     /// that implied conformances originating from a synthesized
-    /// conformance are considered to be synthesized (which has a
+    /// or pre-macro-expansion conformance are considered to be synthesized (which has a
     /// lower ranking).
     ConformanceEntryKind getRankingKind() const {
       switch (auto kind = getKind()) {
@@ -157,11 +157,22 @@ class ConformanceLookupTable : public ASTAllocated<ConformanceLookupTable> {
       case ConformanceEntryKind::PreMacroExpansion:
         return kind;
 
-      case ConformanceEntryKind::Implied:
-        return (getImpliedSource()->getDeclaredConformance()->getKind()
-                  == ConformanceEntryKind::Synthesized)
-                 ? ConformanceEntryKind::Synthesized
-                 : ConformanceEntryKind::Implied;
+      case ConformanceEntryKind::Implied: {
+        auto impliedSourceKind =
+        getImpliedSource()->getDeclaredConformance()->getKind();
+        switch (impliedSourceKind) {
+          case ConformanceEntryKind::Synthesized:
+          case ConformanceEntryKind::PreMacroExpansion:
+            return impliedSourceKind;
+
+          case ConformanceEntryKind::Explicit:
+          case ConformanceEntryKind::Inherited:
+            return ConformanceEntryKind::Implied;
+
+          case ConformanceEntryKind::Implied:
+            return getImpliedSource()->getRankingKind();
+        }
+      }
       }
 
       llvm_unreachable("Unhandled ConformanceEntryKind in switch.");

test/Macros/Inputs/syntax_macro_definitions.swift

@@ -1360,6 +1360,19 @@ public struct HashableMacro: ExtensionMacro {
   }
 }
 
+public struct ImpliesHashableMacro: ExtensionMacro {
+  public static func expansion(
+    of node: AttributeSyntax,
+    attachedTo: some DeclGroupSyntax,
+    providingExtensionsOf type: some TypeSyntaxProtocol,
+    conformingTo protocols: [TypeSyntax],
+    in context: some MacroExpansionContext
+  ) throws -> [ExtensionDeclSyntax] {
+    let ext: DeclSyntax = "extension \(type.trimmed): ImpliesHashable {}"
+    return [ext.cast(ExtensionDeclSyntax.self)]
+  }
+}
+
 public struct DelegatedConformanceMacro: ExtensionMacro, MemberMacro {
   public static func expansion(
     of node: AttributeSyntax,

test/Macros/macro_expand_extensions.swift

@@ -10,6 +10,9 @@
 // RUN: not %target-swift-frontend -enable-experimental-feature ExtensionMacros -swift-version 5 -typecheck -load-plugin-library %t/%target-library-name(MacroDefinition) -module-name MacroUser -DTEST_DIAGNOSTICS -serialize-diagnostics-path %t/macro_expand.dia %s -emit-macro-expansion-files no-diagnostics
 // RUN: c-index-test -read-diagnostics %t/macro_expand.dia 2>&1 | %FileCheck -check-prefix CHECK-DIAGS %s
 
+// Ensure that we can serialize this file as a module.
+// RUN: %target-swift-frontend -swift-version 5 -load-plugin-library %t/%target-library-name(MacroDefinition) %s -I %t -disable-availability-checking -emit-module -o %t/MyModule.swiftmodule -enable-testing
+
 // RUN: %target-build-swift -enable-experimental-feature ExtensionMacros -swift-version 5 -load-plugin-library %t/%target-library-name(MacroDefinition) %s -o %t/main -module-name MacroUser -swift-version 5 -emit-tbd -emit-tbd-path %t/MacroUser.tbd -I %t
 // RUN: %target-codesign %t/main
 // RUN: %target-run %t/main | %FileCheck %s
@@ -198,3 +201,18 @@ func requiresEquatable<T: Equatable>(_: T) { }
 func testHasPropertyWrappers(hpw: HasPropertyWrappers) {
   requiresEquatable(hpw)
 }
+
+// Check that conformances implied by a macro-defined conformance are serialized
+// without issue.
+public protocol ImpliesHashable: Hashable { }
+
+@attached(extension, conformances: ImpliesHashable)
+macro ImpliesHashable() = #externalMacro(module: "MacroDefinition", type: "ImpliesHashableMacro")
+
+func requiresHashable<T: Hashable>(_: T) { }
+func testMakeMeHashable(mmh: MakeMeHashable, dict: [MakeMeHashable: Int]) {
+  requiresHashable(mmh)
+}
+
+@ImpliesHashable
+public struct MakeMeHashable { }