[Macros] Don't allow types to shadow freestanding macros.

When performing name lookup for freestanding macros (e.g., after the
`#`), don't allow types to shadow macros from imported libraries.

Fixes rdar://110429368.

Author: DougGregor

include/swift/AST/LookupKinds.h

@@ -56,6 +56,9 @@ enum NLOptions : unsigned {
   /// Exclude names introduced by macro expansions in the top-level module.
   NL_ExcludeMacroExpansions = 1 << 7,
 
+  /// This lookup should only return macro declarations.
+  NL_OnlyMacros = 1 << 8,
+
   /// The default set of options used for qualified name lookup.
   ///
   /// FIXME: Eventually, add NL_ProtocolMembers to this, once all of the

include/swift/AST/ModuleNameLookup.h

@@ -36,7 +36,10 @@ enum class ResolutionKind {
   Overloadable,
 
   /// Lookup should match a single decl that declares a type.
-  TypesOnly
+  TypesOnly,
+
+  /// Lookup should only match macros.
+  MacrosOnly,
 };
 
 void simple_display(llvm::raw_ostream &out, ResolutionKind kind);

include/swift/AST/NameLookup.h

@@ -242,6 +242,8 @@ enum class UnqualifiedLookupFlags {
   IncludeUsableFromInline = 1 << 5,
   /// This lookup should exclude any names introduced by macro expansions.
   ExcludeMacroExpansions = 1 << 6,
+  /// This lookup should only return macros.
+  MacroLookup            = 1 << 7,
 };
 
 using UnqualifiedLookupOptions = OptionSet<UnqualifiedLookupFlags>;

lib/AST/ModuleNameLookup.cpp

@@ -162,6 +162,8 @@ void ModuleNameLookup<LookupStrategy>::lookupInModule(
       [&](ValueDecl *VD) {
         if (resolutionKind == ResolutionKind::TypesOnly && !isa<TypeDecl>(VD))
           return true;
+        if (resolutionKind == ResolutionKind::MacrosOnly && !isa<MacroDecl>(VD))
+          return true;
         if (respectAccessControl &&
             !VD->isAccessibleFrom(moduleScopeContext, false,
                                   includeUsableFromInline))
@@ -311,6 +313,9 @@ void namelookup::simple_display(llvm::raw_ostream &out, ResolutionKind kind) {
   case ResolutionKind::TypesOnly:
     out << "TypesOnly";
     return;
+  case ResolutionKind::MacrosOnly:
+    out << "MacrosOnly";
+    return;
   }
   llvm_unreachable("Unhandled case in switch");
 }

lib/AST/NameLookup.cpp

@@ -112,6 +112,7 @@ void swift::simple_display(llvm::raw_ostream &out,
       {UnqualifiedLookupFlags::IgnoreAccessControl, "IgnoreAccessControl"},
       {UnqualifiedLookupFlags::IncludeOuterResults, "IncludeOuterResults"},
       {UnqualifiedLookupFlags::TypeLookup, "TypeLookup"},
+      {UnqualifiedLookupFlags::MacroLookup, "MacroLookup"},
   };
 
   auto flagsToPrint = llvm::make_filter_range(
@@ -1618,6 +1619,11 @@ namelookup::lookupMacros(DeclContext *dc, DeclNameRef macroName,
   auto moduleScopeDC = dc->getModuleScopeContext();
   ASTContext &ctx = moduleScopeDC->getASTContext();
 
+  // When performing lookup for freestanding macro roles, only consider
+  // macro names, ignoring types.
+  bool onlyMacros = static_cast<bool>(roles & getFreestandingMacroRoles()) &&
+      !(roles - getFreestandingMacroRoles());
+
   // Macro lookup should always exclude macro expansions; macro
   // expansions cannot introduce new macro declarations. Note that
   // the source location here doesn't matter.
@@ -1626,8 +1632,12 @@ namelookup::lookupMacros(DeclContext *dc, DeclNameRef macroName,
     UnqualifiedLookupFlags::ExcludeMacroExpansions
   };
 
+  if (onlyMacros)
+    descriptor.Options |= UnqualifiedLookupFlags::MacroLookup;
+
   auto lookup = evaluateOrDefault(
       ctx.evaluator, UnqualifiedLookupRequest{descriptor}, {});
+
   for (const auto &found : lookup.allResults()) {
     if (auto macro = dyn_cast<MacroDecl>(found.getValueDecl())) {
       auto candidateRoles = macro->getMacroRoles();
@@ -1638,6 +1648,7 @@ namelookup::lookupMacros(DeclContext *dc, DeclNameRef macroName,
       }
     }
   }
+
   return choices;
 }
 
@@ -2408,6 +2419,11 @@ QualifiedLookupRequest::evaluate(Evaluator &eval, const DeclContext *DC,
       if ((options & NL_OnlyTypes) && !isa<TypeDecl>(decl))
         continue;
 
+      // If we're performing a macro lookup, don't even attempt to validate
+      // the decl if its not a macro.
+      if ((options & NL_OnlyMacros) && !isa<MacroDecl>(decl))
+        continue;
+
       if (isAcceptableLookupResult(DC, options, decl, onlyCompleteObjectInits))
         decls.push_back(decl);
     }
@@ -2491,8 +2507,8 @@ ModuleQualifiedLookupRequest::evaluate(Evaluator &eval, const DeclContext *DC,
   using namespace namelookup;
   QualifiedLookupResult decls;
 
-  auto kind = (options & NL_OnlyTypes
-               ? ResolutionKind::TypesOnly
+  auto kind = (options & NL_OnlyTypes ? ResolutionKind::TypesOnly
+               : options & NL_OnlyMacros ? ResolutionKind::MacrosOnly
                : ResolutionKind::Overloadable);
   auto topLevelScope = DC->getModuleScopeContext();
   if (module == topLevelScope->getParentModule()) {
@@ -2534,8 +2550,8 @@ AnyObjectLookupRequest::evaluate(Evaluator &evaluator, const DeclContext *dc,
   using namespace namelookup;
   QualifiedLookupResult decls;
 
-  // Type-only lookup won't find anything on AnyObject.
-  if (options & NL_OnlyTypes)
+  // Type-only and macro lookup won't find anything on AnyObject.
+  if (options & (NL_OnlyTypes | NL_OnlyMacros))
     return decls;
 
   // Collect all of the visible declarations.
@@ -4027,6 +4043,7 @@ void swift::simple_display(llvm::raw_ostream &out, NLOptions options) {
     FLAG(NL_RemoveOverridden)
     FLAG(NL_IgnoreAccessControl)
     FLAG(NL_OnlyTypes)
+    FLAG(NL_OnlyMacros)
     FLAG(NL_IncludeAttributeImplements)
 #undef FLAG
   };

lib/AST/UnqualifiedLookup.cpp

@@ -106,6 +106,7 @@ namespace {
 
     const Options options;
     const bool isOriginallyTypeLookup;
+    const bool isOriginallyMacroLookup;
     const NLOptions baseNLOptions;
 
     // Outputs
@@ -167,7 +168,8 @@ namespace {
 #pragma mark common helper declarations
     static NLOptions
     computeBaseNLOptions(const UnqualifiedLookupOptions options,
-                         const bool isOriginallyTypeLookup);
+                         const bool isOriginallyTypeLookup,
+                         const bool isOriginallyMacroLookup);
 
     void findResultsAndSaveUnavailables(
         const DeclContext *lookupContextForThisContext,
@@ -260,7 +262,10 @@ UnqualifiedLookupFactory::UnqualifiedLookupFactory(
   DebugClient(M.getDebugClient()),
   options(options),
   isOriginallyTypeLookup(options.contains(Flags::TypeLookup)),
-  baseNLOptions(computeBaseNLOptions(options, isOriginallyTypeLookup)),
+  isOriginallyMacroLookup(options.contains(Flags::MacroLookup)),
+  baseNLOptions(
+      computeBaseNLOptions(
+        options, isOriginallyTypeLookup, isOriginallyMacroLookup)),
   Results(Results),
   IndexOfFirstOuterResult(IndexOfFirstOuterResult)
 {}
@@ -525,7 +530,8 @@ void UnqualifiedLookupFactory::addImportedResults(const DeclContext *const dc) {
   using namespace namelookup;
   SmallVector<ValueDecl *, 8> CurModuleResults;
   auto resolutionKind = isOriginallyTypeLookup ? ResolutionKind::TypesOnly
-                                               : ResolutionKind::Overloadable;
+                      : isOriginallyMacroLookup ? ResolutionKind::MacrosOnly
+                      : ResolutionKind::Overloadable;
   auto nlOptions = NL_UnqualifiedDefault;
   if (options.contains(Flags::IncludeUsableFromInline))
     nlOptions |= NL_IncludeUsableFromInline;
@@ -619,12 +625,15 @@ void UnqualifiedLookupFactory::findResultsAndSaveUnavailables(
 
 NLOptions UnqualifiedLookupFactory::computeBaseNLOptions(
     const UnqualifiedLookupOptions options,
-    const bool isOriginallyTypeLookup) {
+    const bool isOriginallyTypeLookup,
+    const bool isOriginallyMacroLookup) {
   NLOptions baseNLOptions = NL_UnqualifiedDefault;
   if (options.contains(Flags::AllowProtocolMembers))
     baseNLOptions |= NL_ProtocolMembers;
   if (isOriginallyTypeLookup)
     baseNLOptions |= NL_OnlyTypes;
+  if (isOriginallyMacroLookup)
+    baseNLOptions |= NL_OnlyMacros;
   if (options.contains(Flags::IgnoreAccessControl))
     baseNLOptions |= NL_IgnoreAccessControl;
   return baseNLOptions;

test/Macros/macro_shadowing.swift

@@ -0,0 +1,20 @@
+// REQUIRES: swift_swift_parser, executable_test
+
+// RUN: %empty-directory(%t)
+
+// Build macro implementations
+// 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 -swift-version 5
+
+// Build library that declares macros
+// RUN: %target-swift-frontend -swift-version 5 -emit-module -o %t/freestanding_macro_library.swiftmodule %S/Inputs/freestanding_macro_library.swift -module-name freestanding_macro_library -load-plugin-library %t/%target-library-name(MacroDefinition)
+
+// 
+// RUN: %target-typecheck-verify-swift -swift-version 5 -load-plugin-library %t/%target-library-name(MacroDefinition) -module-name MacroUser -I %t
+
+import freestanding_macro_library
+
+struct stringify<T> { }
+
+func testStringify(a: Int, b: Int) {
+  _ = #stringify(a + b)
+}