Forbid lazy with @abi

It’s not clear how `@abi` would apply to the auxiliary decl used for `lazy`.

Author: beccadax

include/swift/AST/DeclAttr.def

@@ -143,7 +143,7 @@ SIMPLE_DECL_ATTR(NSManaged, NSManaged,
 
 CONTEXTUAL_SIMPLE_DECL_ATTR(lazy, Lazy,
   OnVar,
-  DeclModifier | ABIStableToAdd | ABIStableToRemove | APIStableToAdd | APIStableToRemove | InferredInABIAttr,
+  DeclModifier | ABIStableToAdd | ABIStableToRemove | APIStableToAdd | APIStableToRemove | UnconstrainedInABIAttr,
   16)
 
 SIMPLE_DECL_ATTR(LLDBDebuggerFunction, LLDBDebuggerFunction,

include/swift/AST/DiagnosticsSema.def

@@ -8501,6 +8501,9 @@ ERROR(attr_abi_no_default_arguments,none,
 ERROR(attr_abi_no_macros,none,
       "%kind0 cannot be expanded in '@abi' attribute",
       (Decl *))
+ERROR(attr_abi_no_lazy,none,
+      "'lazy' is not compatible with '@abi' attribute",
+      ())
 
 // 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

lib/Sema/TypeCheckAttr.cpp

@@ -1110,6 +1110,11 @@ void AttributeChecker::visitLazyAttr(LazyAttr *attr) {
   // are already lazily initialized).
   if (VD->isStatic() || varDC->isModuleScopeContext())
     diagnoseAndRemoveAttr(attr, diag::lazy_on_already_lazy_global);
+
+  // 'lazy' can't be used in or with `@abi` because it has auxiliary decls.
+  auto abiRole = ABIRoleInfo(D);
+  if (!abiRole.providesABI() || !abiRole.providesAPI())
+    diagnoseAndRemoveAttr(attr, diag::attr_abi_no_lazy);
 }
 
 bool AttributeChecker::visitAbstractAccessControlAttr(

test/attr/attr_abi.swift

@@ -1946,16 +1946,17 @@ class Required {
   required init(i3: Void) { fatalError() } // expected-note {{should match modifier here}}
 }
 
-// lazy -- automatically cloned into @abi
+// lazy -- banned both in and with @abi
+// This introduces auxiliary decls whose ABI could not be controlled.
 class Lazy {
-  @abi(lazy var v1: Int)
-  lazy var v1: Int = 0
+  @abi(lazy var v1: Int) // expected-error {{'lazy' is not compatible with '@abi' attribute}} {{8-12=}}
+  lazy var v1: Int = 0 // expected-error {{'lazy' is not compatible with '@abi' attribute}} {{3-8=}}
 
-  @abi(lazy var v2: Int) // expected-error {{extra 'lazy' modifier in '@abi'}} {{8-12=}}
+  @abi(lazy var v2: Int) // expected-error {{'lazy' is not compatible with '@abi' attribute}} {{8-12=}}
   var v2: Int = 0
 
-  @abi(var v3: Int) // expected-remark {{inferred 'lazy' in '@abi' to match modifier on API}}
-  lazy var v3: Int = 0 // expected-note {{matches modifier here}}
+  @abi(var v3: Int)
+  lazy var v3: Int = 0 // expected-error {{'lazy' is not compatible with '@abi' attribute}} {{3-8=}}
 }
 
 // @_fixed_layout -- banned in @abi