Diagnose CustomAttrs as needed in @abi

CustomAttr backs four different features, each of which requires a different behavior in `@abi`:

• Global actors: Permitted (and permitted to vary) since they can affect mangling
• Result builders: Forbidden inside an `@abi` since they have no ABI impact
• Property wrappers: Forbidden both inside an `@abi` and on a decl with an `@abi` since it’s not clear how we would apply `@abi` to the auxiliary decls
• Attached macros: Forbidden inside an `@abi` since an ABI-only decl has no body, accessors, members, peers, extensions, or (currently) conformances

Implement these behaviors (outside of `ABIDeclChecker` since they can’t be described there).

Macro-related tests are not included in this commit; they require matching swift-syntax changes which are being negotiated.

Author: beccadax

include/swift/AST/DiagnosticsSema.def

@@ -7457,7 +7457,7 @@ ERROR(property_wrapper_effectful,none,
 
 ERROR(property_with_wrapper_conflict_attribute,none,
       "property %0 with a wrapper cannot also be "
-      "%select{lazy|@NSCopying|@NSManaged|weak|unowned|unmanaged}1",
+      "%select{lazy|@NSCopying|@NSManaged|@abi|weak|unowned|unmanaged}1",
       (Identifier, int))
 ERROR(property_wrapper_not_single_var, none,
       "property wrapper can only apply to a single variable", ())
@@ -8509,6 +8509,10 @@ ERROR(attr_abi_no_default_arguments,none,
       "affect the parameter's ABI",
       (Decl *))
 
+ERROR(attr_abi_no_macros,none,
+      "%kind0 cannot be expanded in '@abi' attribute",
+      (Decl *))
+
 // These macros insert 'final', 'non-final', or nothing depending on both the
 // current decl and its counterpart, such that 'non-final' is used if the
 // counterpart would be described as 'final' or 'static'. They must be kept in

lib/Sema/TypeCheckAttr.cpp

@@ -4406,6 +4406,12 @@ void AttributeChecker::visitCustomAttr(CustomAttr *attr) {
         }
       }
 
+      // Macros can't be attached to ABI-only decls. (If we diagnosed above,
+      // don't bother with this.)
+      if (attr->isValid() && !ABIRoleInfo(D).providesAPI()) {
+        diagnoseAndRemoveAttr(attr, diag::attr_abi_no_macros, macro);
+      }
+
       return;
     }
 
@@ -4487,16 +4493,25 @@ void AttributeChecker::visitCustomAttr(CustomAttr *attr) {
   // function, storage with an explicit getter, or parameter of function type.
   if (nominal->getAttrs().hasAttribute<ResultBuilderAttr>()) {
     ValueDecl *decl;
+    ValueDecl *abiRelevantDecl;
     if (auto param = dyn_cast<ParamDecl>(D)) {
       decl = param;
+      abiRelevantDecl = dyn_cast<ValueDecl>(
+                            param->getDeclContext()->getAsDecl());
     } else if (auto func = dyn_cast<FuncDecl>(D)) {
       decl = func;
+      abiRelevantDecl = func;
     } else if (auto storage = dyn_cast<AbstractStorageDecl>(D)) {
       decl = storage;
+      abiRelevantDecl = storage;
 
       // Check whether this is a storage declaration that is not permitted
       // to have a result builder attached.
       auto shouldDiagnose = [&]() -> bool {
+        // We'll diagnose use in @abi later.
+        if (!ABIRoleInfo(abiRelevantDecl).providesAPI())
+          return false;
+
         // An uninitialized stored property in a struct can have a function
         // builder attached.
         if (auto var = dyn_cast<VarDecl>(decl)) {
@@ -4540,6 +4555,14 @@ void AttributeChecker::visitCustomAttr(CustomAttr *attr) {
       return;
     }
 
+    // Result builders shouldn't be applied to an ABI-only decl because they
+    // have no ABI effect.
+    if (!ABIRoleInfo(abiRelevantDecl).providesAPI()) {
+      diagnoseAndRemoveAttr(attr, diag::attr_abi_forbidden_attr,
+                            nominal->getNameStr(), /*isModifier=*/false);
+      return;
+    }
+
     // Diagnose and ignore arguments.
     if (attr->hasArgs()) {
       diagnose(attr->getLocation(), diag::result_builder_arguments)

lib/Sema/TypeCheckMacros.cpp

@@ -1395,6 +1395,12 @@ static SourceFile *evaluateAttachedMacro(MacroDecl *macro, Decl *attachedTo,
     }
   }
 
+  // Macros are so spectacularly not valid in an `@abi` attribute that we cannot
+  // even attempt to expand them.
+  if (!ABIRoleInfo(attachedTo).providesAPI()) {
+    return nullptr;
+  }
+
   ASTContext &ctx = dc->getASTContext();
 
   auto moduleDecl = dc->getParentModule();

lib/Sema/TypeCheckPropertyWrapper.cpp

@@ -481,11 +481,15 @@ AttachedPropertyWrappersRequest::evaluate(Evaluator &evaluator,
       continue;
     }
 
+    auto abiRole = ABIRoleInfo(var);
+    bool hasOrIsABI = !abiRole.providesAPI() || !abiRole.providesABI();
+
     // Note: Getting the semantic attrs here would trigger a request cycle.
     auto attachedAttrs = var->getAttrs();
 
     // Check for conflicting attributes.
-    if (attachedAttrs.hasAttribute<LazyAttr>() ||
+    if (hasOrIsABI ||
+        attachedAttrs.hasAttribute<LazyAttr>() ||
         attachedAttrs.hasAttribute<NSCopyingAttr>() ||
         attachedAttrs.hasAttribute<NSManagedAttr>() ||
         (attachedAttrs.hasAttribute<ReferenceOwnershipAttr>() &&
@@ -498,9 +502,11 @@ AttachedPropertyWrappersRequest::evaluate(Evaluator &evaluator,
         whichKind = 1;
       else if (attachedAttrs.hasAttribute<NSManagedAttr>())
         whichKind = 2;
+      else if (hasOrIsABI)
+        whichKind = 3;
       else {
         auto attr = attachedAttrs.getAttribute<ReferenceOwnershipAttr>();
-        whichKind = 2 + static_cast<unsigned>(attr->get());
+        whichKind = 3 + static_cast<unsigned>(attr->get());
       }
       var->diagnose(diag::property_with_wrapper_conflict_attribute,
                     var->getName(), whichKind);

test/attr/attr_abi.swift

@@ -1267,6 +1267,60 @@ nonisolated func isolation17() async {}
 @abi(@concurrent func isolation19() async)
 nonisolated(nonsending) func isolation19() async {}
 
+// CustomAttr for property wrapper -- banned in and with '@abi'
+// Banned because we would need to design behavior for its auxiliary decls.
+@propertyWrapper struct PropertyWrapper {
+  var wrappedValue: Int { fatalError() }
+}
+
+struct CustomAttrPropertyWrapper {
+  @abi(@PropertyWrapper var v1: Int) // expected-error {{property 'v1' with a wrapper cannot also be @abi}}
+  @PropertyWrapper var v1: Int // expected-error {{property 'v1' with a wrapper cannot also be @abi}}
+
+  @abi(@PropertyWrapper var v2: Int) // expected-error {{property 'v2' with a wrapper cannot also be @abi}}
+  var v2: Int
+
+  @abi(var v3: Int)
+  @PropertyWrapper var v3: Int // expected-error {{property 'v3' with a wrapper cannot also be @abi}}
+}
+
+// CustomAttr for attached macro -- see Macros/macro_expand_peers.swift
+
+// CustomAttr for result builder -- banned in '@abi'
+// Has no ABI impact on either a parameter or a decl.
+@resultBuilder struct ResultBuilder {
+  static func buildBlock(_ values: Int...) -> Int { values.reduce(0, +) }
+}
+
+struct CustomAttrResultBuilder {
+  @abi(@ResultBuilder var v1: Int) // expected-error {{unused 'ResultBuilder' attribute in '@abi'}} {{8-22=}}
+  @ResultBuilder var v1: Int { 0 }
+
+  @abi(@ResultBuilder var v2: Int) // expected-error {{unused 'ResultBuilder' attribute in '@abi'}} {{8-22=}}
+  var v2: Int { 0 }
+
+  @abi(var v3: Int)
+  @ResultBuilder var v3: Int { 0 }
+
+  @abi(@ResultBuilder func fn11() -> Int) // expected-error {{unused 'ResultBuilder' attribute in '@abi'}} {{8-22=}}
+  @ResultBuilder func fn11() -> Int { 0 }
+
+  @abi(@ResultBuilder func fn21() -> Int) // expected-error {{unused 'ResultBuilder' attribute in '@abi'}} {{8-22=}}
+  func fn21() -> Int { 0 }
+
+  @abi(func fn31() -> Int)
+  @ResultBuilder func fn31() -> Int { 0 }
+
+  @abi(func fn12(@ResultBuilder _: () -> Int) -> Int) // expected-error {{unused 'ResultBuilder' attribute in '@abi'}}  {{18-32=}}
+  func fn12(@ResultBuilder _: () -> Int) -> Int { 0 }
+
+  @abi(func fn22(@ResultBuilder _: () -> Int) -> Int) // expected-error {{unused 'ResultBuilder' attribute in '@abi'}} {{18-32=}}
+  func fn22(_: () -> Int) -> Int { 0 }
+
+  @abi(func fn32(_: () -> Int) -> Int)
+  func fn32(@ResultBuilder _: () -> Int) -> Int { 0 }
+}
+
 // NSCopying - see attr/attr_abi_objc.swift
 
 // @LLDBDebuggerFunction -- banned in @abi