Sema: Don't expand macros when binding extensions

Fixes rdar://149798059.

Author: slavapestov

lib/AST/NameLookup.cpp

@@ -1125,6 +1125,9 @@ enum class DirectlyReferencedTypeLookupFlags {
   /// Include members that would normally be excluded because they come from
   /// modules that have not been imported directly.
   IgnoreMissingImports = 1 << 3,
+
+  /// Whenther we should exclude macro expansions.
+  ExcludeMacroExpansions = 1 << 4,
 };
 
 using DirectlyReferencedTypeLookupOptions =
@@ -3065,6 +3068,10 @@ static DirectlyReferencedTypeDecls directReferencesForUnqualifiedTypeLookup(
           DirectlyReferencedTypeLookupFlags::IgnoreMissingImports))
     options |= UnqualifiedLookupFlags::IgnoreMissingImports;
 
+  if (typeLookupOptions.contains(
+          DirectlyReferencedTypeLookupFlags::ExcludeMacroExpansions))
+    options |= UnqualifiedLookupFlags::ExcludeMacroExpansions;
+
   // Manually exclude macro expansions here since the source location
   // is overridden below.
   if (namelookup::isInMacroArgument(dc->getParentSourceFile(), loc))
@@ -3147,6 +3154,10 @@ static llvm::TinyPtrVector<TypeDecl *> directReferencesForQualifiedTypeLookup(
             DirectlyReferencedTypeLookupFlags::IgnoreMissingImports))
       options |= NL_IgnoreMissingImports;
 
+    if (typeLookupOptions.contains(
+            DirectlyReferencedTypeLookupFlags::ExcludeMacroExpansions))
+      options |= NL_ExcludeMacroExpansions;
+
     // Look through the type declarations we were given, resolving them down
     // to nominal type declarations, module declarations, and
     SmallVector<ModuleDecl *, 2> moduleDecls;
@@ -3583,9 +3594,13 @@ ExtendedNominalRequest::evaluate(Evaluator &evaluator,
 
   ASTContext &ctx = ext->getASTContext();
   auto options = defaultDirectlyReferencedTypeLookupOptions;
+
   if (ext->isInSpecializeExtensionContext()) {
     options |= DirectlyReferencedTypeLookupFlags::AllowUsableFromInline;
   }
+
+  options |= DirectlyReferencedTypeLookupFlags::ExcludeMacroExpansions;
+
   DirectlyReferencedTypeDecls referenced = directReferencesForTypeRepr(
       evaluator, ctx, typeRepr, ext->getParent(), options);
 

test/Macros/bind_extensions_request_cycle.swift

@@ -0,0 +1,29 @@
+// RUN: %target-typecheck-verify-swift %s
+
+@attached(member) @attached(peer)
+public macro Foo(_: any P) = #externalMacro(module: "FooMacros", type: "FooMacro")
+// expected-warning@-1 {{external macro implementation type 'FooMacros.FooMacro' could not be found for macro 'Foo'; plugin for module 'FooMacros' not found}}
+// expected-note@-2 2 {{'Foo' declared here}}
+
+public protocol P {}
+
+@Foo(S.s)
+struct A {
+// expected-error@-1 2 {{external macro implementation type 'FooMacros.FooMacro' could not be found for macro 'Foo'; plugin for module 'FooMacros' not found}}
+  func a() {}
+}
+
+extension A {
+  struct Nested {}
+}
+
+// Binding this extension must not trigger macro expansion, because that
+// performs a qualified lookup of S.s, which fails because the extension
+// of P declared below has not been bound yet.
+extension A.Nested {}
+
+struct S: P {}
+
+extension P where Self == S {
+  static var s: Self { Self() }
+}