Merge pull request #62309 from tshortli/allow-inlinable-backdeployed-functions

Sema: Allow `@inlinable` on back deployed functions

Author: tshortli

lib/Sema/TypeCheckAttr.cpp

@@ -4391,21 +4391,16 @@ void AttributeChecker::checkBackDeployAttrs(ArrayRef<BackDeployAttr *> Attrs) {
   if (Attrs.empty())
     return;
 
-  // Diagnose conflicting attributes. @_alwaysEmitIntoClient, @inlinable, and
-  // @_transparent all conflict with back deployment because they each cause the
-  // body of a function to be copied into the client under certain conditions
-  // and would defeat the goal of back deployment, which is to always use the
-  // ABI version of the declaration when it is available.
+  // Diagnose conflicting attributes. @_alwaysEmitIntoClient and @_transparent
+  // conflict with back deployment because they each cause the body of a
+  // function to always be copied into the client and would defeat the goal of
+  // back deployment, which is to use the ABI version of the declaration when it
+  // is available.
   if (auto *AEICA = D->getAttrs().getAttribute<AlwaysEmitIntoClientAttr>()) {
     diagnoseAndRemoveAttr(AEICA, diag::attr_incompatible_with_back_deploy,
                           AEICA, D->getDescriptiveKind());
   }
 
-  if (auto *IA = D->getAttrs().getAttribute<InlinableAttr>()) {
-    diagnoseAndRemoveAttr(IA, diag::attr_incompatible_with_back_deploy, IA,
-                          D->getDescriptiveKind());
-  }
-
   if (auto *TA = D->getAttrs().getAttribute<TransparentAttr>()) {
     diagnoseAndRemoveAttr(TA, diag::attr_incompatible_with_back_deploy, TA,
                           D->getDescriptiveKind());

test/attr/Inputs/BackDeployHelper.swift

@@ -140,6 +140,7 @@ extension IntArray {
 
   @available(BackDeploy 1.0, *)
   @_backDeploy(before: BackDeploy 2.0)
+  @inlinable
   public subscript(_ i: Int) -> Int {
     get { _values[i] }
     _modify { yield &_values[i] }
@@ -180,6 +181,7 @@ extension ReferenceIntArray {
 
   @available(BackDeploy 1.0, *)
   @_backDeploy(before: BackDeploy 2.0)
+  @inlinable
   public final subscript(_ i: Int) -> Int {
     get { _values[i] }
     _modify { yield &_values[i] }

test/attr/attr_backDeploy.swift

@@ -243,7 +243,7 @@ public func alwaysEmitIntoClientFunc() {}
 
 @available(macOS 11.0, *)
 @_backDeploy(before: macOS 12.0)
-@inlinable // expected-error {{'@inlinable' cannot be applied to a back deployed global function}}
+@inlinable // OK
 public func inlinableFunc() {}
 
 @available(macOS 11.0, *)