Merge pull request #62747 from DougGregor/expression-macro-attr

[Macro] Add the expression attribute for macro declarations

Author: DougGregor

include/swift/AST/Decl.h

@@ -8297,6 +8297,17 @@ class MissingMemberDecl : public Decl {
   }
 };
 
+/// The context in which a macro can be used, which determines the syntax it
+/// uses.
+enum class MacroContext: uint8_t {
+  /// An expression macro, referenced explicitly via "#stringify" or similar
+  /// in the source code.
+  Expression = 0x01,
+};
+
+/// The contexts in which a particular macro declaration can be used.
+using MacroContexts = OptionSet<MacroContext>;
+
 /// Provides a declaration of a macro.
 ///
 /// Macros are declared within the source code with the `macro` introducer.
@@ -8348,6 +8359,9 @@ class MacroDecl : public GenericContext, public ValueDecl {
   /// Retrieve the interface type produced when expanding this macro.
   Type getResultInterfaceType() const;
 
+  /// Determine the contexts in which this macro can be applied.
+  MacroContexts getMacroContexts() const;
+
   static bool classof(const DeclContext *C) {
     if (auto D = C->getAsDecl())
       return classof(D);

include/swift/AST/DiagnosticsSema.def

@@ -6781,6 +6781,9 @@ WARNING(macro_type_access_warn,none,
         (bool, AccessLevel, AccessLevel, bool))
 ERROR(macro_in_nested,none,
       "macro %0 can only be declared at file scope", (DeclName))
+ERROR(macro_without_context,none,
+      "macro %0 must declare its applicable contexts (e.g., '@expression')",
+       (DeclName))
 
 //------------------------------------------------------------------------------
 // MARK: Move Only Errors

include/swift/AST/MacroDefinition.h

@@ -25,12 +25,6 @@ namespace swift {
 /// Provides the definition of a macro.
 class MacroDefinition {
 public:
-  /// The kind of macro, which determines how it can be used in source code.
-  enum Kind: uint8_t {
-    /// An expression macro.
-    Expression,
-  };
-
   /// Describes a missing macro definition.
   struct MissingDefinition {
     Identifier externalModuleName;
@@ -50,19 +44,18 @@ class MacroDefinition {
     InProcess,
   };
 
-  Kind kind;
   ImplementationKind implKind;
 
 private:
   void *opaqueHandle;
 
-  MacroDefinition(Kind kind, ImplementationKind implKind, void *opaqueHandle)
-    : kind(kind), implKind(implKind), opaqueHandle(opaqueHandle) { }
+  MacroDefinition(ImplementationKind implKind, void *opaqueHandle)
+    : implKind(implKind), opaqueHandle(opaqueHandle) { }
 
 public:
   static MacroDefinition forUndefined() {
     return MacroDefinition{
-      Kind::Expression, ImplementationKind::Undefined, nullptr
+      ImplementationKind::Undefined, nullptr
     };
   }
 
@@ -72,8 +65,8 @@ class MacroDefinition {
       Identifier externalMacroTypeName
   );
 
-  static MacroDefinition forInProcess(Kind kind, void *opaqueHandle) {
-    return MacroDefinition{kind, ImplementationKind::InProcess, opaqueHandle};
+  static MacroDefinition forInProcess(void *opaqueHandle) {
+    return MacroDefinition{ImplementationKind::InProcess, opaqueHandle};
   }
 
   /// Return the opaque handle for an in-process macro definition.

lib/AST/Decl.cpp

@@ -9670,6 +9670,13 @@ SourceRange MacroDecl::getSourceRange() const {
   return SourceRange(macroLoc, endLoc);
 }
 
+MacroContexts MacroDecl::getMacroContexts() const {
+  MacroContexts contexts = None;
+  if (getAttrs().hasAttribute<ExpressionAttr>())
+    contexts |= MacroContext::Expression;
+  return contexts;
+}
+
 SourceRange MacroExpansionDecl::getSourceRange() const {
   SourceLoc endLoc;
   if (ArgList)
@@ -9689,9 +9696,7 @@ MacroDefinition MacroDefinition::forMissing(
   auto def = ctx.AllocateObjectCopy(
     MissingDefinition{externalModuleName, externalMacroTypeName}
   );
-  return MacroDefinition{
-    Kind::Expression, ImplementationKind::Missing, def
-  };
+  return MacroDefinition{ImplementationKind::Missing, def};
 }
 
 NominalTypeDecl *

lib/Sema/TypeCheckAttr.cpp

@@ -159,6 +159,7 @@ class AttributeChecker : public AttributeVisitor<AttributeChecker> {
   IGNORED_ATTR(Preconcurrency)
   IGNORED_ATTR(BackDeploy)
   IGNORED_ATTR(Documentation)
+  IGNORED_ATTR(Expression)
 #undef IGNORED_ATTR
 
   void visitAlignmentAttr(AlignmentAttr *attr) {

lib/Sema/TypeCheckDeclOverride.cpp

@@ -1625,6 +1625,8 @@ namespace  {
     UNINTERESTING_ATTR(NoEagerMove)
 
     UNINTERESTING_ATTR(RuntimeMetadata)
+
+    UNINTERESTING_ATTR(Expression)
 #undef UNINTERESTING_ATTR
 
     void visitAvailableAttr(AvailableAttr *attr) {

lib/Sema/TypeCheckDeclPrimary.cpp

@@ -2000,6 +2000,8 @@ class DeclChecker : public DeclVisitor<DeclChecker> {
 
     if (!MD->getDeclContext()->isModuleScopeContext())
       MD->diagnose(diag::macro_in_nested, MD->getName());
+    if (!MD->getMacroContexts())
+      MD->diagnose(diag::macro_without_context, MD->getName());
   }
 
   void visitMacroExpansionDecl(MacroExpansionDecl *MED) {

lib/Sema/TypeCheckMacros.cpp

@@ -113,8 +113,7 @@ MacroDefinition MacroDefinitionRequest::evaluate(
         swift_ASTGen_destroyMacro(inProcess);
       });
 
-      return MacroDefinition::forInProcess(
-          MacroDefinition::Expression, inProcess);
+      return MacroDefinition::forInProcess(inProcess);
     }
   }
 #endif

test/IDE/complete_decl_attribute.swift

@@ -315,6 +315,7 @@ struct _S {
 // ON_MEMBER_LAST-DAG: Keyword/None:                       typeWrapper[#Declaration Attribute#]; name=typeWrapper
 // ON_MEMBER_LAST-DAG: Keyword/None:                       typeWrapperIgnored[#Declaration Attribute#]; name=typeWrapperIgnored
 // ON_MEMBER_LAST-DAG: Keyword/None:                       runtimeMetadata[#Declaration Attribute#]; name=runtimeMetadata
+// ON_MEMBER_LAST-DAG: Keyword/None:                       expression[#Declaration Attribute#]; name=expression
 // ON_MEMBER_LAST-NOT: Keyword
 // ON_MEMBER_LAST-DAG: Decl[Struct]/CurrModule:            MyStruct[#MyStruct#]; name=MyStruct
 // ON_MEMBER_LAST-DAG: Decl[Struct]/CurrModule/TypeRelation[Convertible]: MyPropertyWrapper[#MyPropertyWrapper#]; name=MyPropertyWrapper
@@ -387,6 +388,7 @@ func dummy2() {}
 // KEYWORD_LAST-DAG: Keyword/None:                       typeWrapper[#Declaration Attribute#]; name=typeWrapper
 // KEYWORD_LAST-DAG: Keyword/None:                       typeWrapperIgnored[#Declaration Attribute#]; name=typeWrapperIgnored
 // KEYWORD_LAST-DAG: Keyword/None:                       runtimeMetadata[#Declaration Attribute#]; name=runtimeMetadata
+// KEYWORD_LAST-DAG: Keyword/None:                       expression[#Declaration Attribute#]; name=expression
 // KEYWORD_LAST-NOT: Keyword
 // KEYWORD_LAST-DAG: Decl[Struct]/CurrModule:            MyStruct[#MyStruct#]; name=MyStruct
 // KEYWORD_LAST-DAG: Decl[Struct]/CurrModule/TypeRelation[Convertible]: MyPropertyWrapper[#MyPropertyWrapper#]; name=MyPropertyWrapper

test/Macros/macro_availability_macosx.swift

@@ -4,7 +4,7 @@
 @available(macOS 12.0, *)
 struct X { }
 
-macro m1: X = A.B // expected-error{{'X' is only available in macOS 12.0 or newer}}
+@expression macro m1: X = A.B // expected-error{{'X' is only available in macOS 12.0 or newer}}
 
 @available(macOS 12.0, *)
-macro m2: X = A.B
+@expression macro m2: X = A.B