SILGen: Fix key paths that reference internal private(set) decls from other files.

The setter needs to be given hidden linkage so that other files can still form key paths to it.

lib/SIL/SILDeclRef.cpp

@@ -314,8 +314,19 @@ SILLinkage SILDeclRef::getLinkage(ForDefinition_t forDefinition) const {
       neverPublic = true;
     }
   }
+  
+  auto effectiveAccess = d->getEffectiveAccess();
+  
+  // Private setter implementations for an internal storage declaration should
+  // be internal as well, so that a dynamically-writable
+  // keypath can be formed from other files.
+  if (auto accessor = dyn_cast<AccessorDecl>(d)) {
+    if (accessor->isSetter()
+       && accessor->getStorage()->getEffectiveAccess() == AccessLevel::Internal)
+      effectiveAccess = AccessLevel::Internal;
+  }
 
-  switch (d->getEffectiveAccess()) {
+  switch (effectiveAccess) {
   case AccessLevel::Private:
   case AccessLevel::FilePrivate:
     return maybeAddExternal(SILLinkage::Private);

test/SILGen/Inputs/keypaths_multi_file_b.swift

@@ -0,0 +1,11 @@
+struct A {
+  private(set) var x: Int {
+    get { return 0 }
+    set {}
+  }
+
+  private(set) subscript(x: Int) -> Int {
+    get { return x }
+    set {}
+  }
+}

test/SILGen/accessibility_warnings.swift

@@ -105,7 +105,7 @@ internal struct PrivateSettersForReadOnlyInternal : PublicReadOnlyOperations {
   // CHECK-DAG: sil hidden{{( \[.+\])*}} @$S22accessibility_warnings33PrivateSettersForReadOnlyInternalV4sizeSivg
   public private(set) var size = 0
   // CHECK-DAG: sil hidden @$S22accessibility_warnings33PrivateSettersForReadOnlyInternalVyS2icig
-  // CHECK-DAG: sil private @$S22accessibility_warnings33PrivateSettersForReadOnlyInternalVyS2icis
+  // CHECK-DAG: sil hidden @$S22accessibility_warnings33PrivateSettersForReadOnlyInternalVyS2icis
   internal private(set) subscript (_: Int) -> Int { // no-warning
     get { return 42 }
     set {}

test/SILGen/accessors.swift

@@ -213,7 +213,7 @@ struct Foo {
   private(set) subscript(withPrivateSet x: Void) -> Void {
     // CHECK-DAG: sil hidden @$S9accessors3FooV14withPrivateSetyyt_tcig : $@convention(method) (Foo) -> () {
     get {}
-    // CHECK-DAG: sil private @$S9accessors3FooV14withPrivateSetyyt_tcis : $@convention(method) (@inout Foo) -> () {
+    // CHECK-DAG: sil hidden @$S9accessors3FooV14withPrivateSetyyt_tcis : $@convention(method) (@inout Foo) -> () {
     set {}
   }
   subscript(withNestedClass x: Void) -> Void {
@@ -229,7 +229,7 @@ struct Foo {
   private(set) var variableWithPrivateSet: Void {
     // CHECK-DAG: sil hidden @$S9accessors3FooV22variableWithPrivateSetytvg : $@convention(method) (Foo) -> () {
     get {}
-    // CHECK-DAG: sil private @$S9accessors3FooV22variableWithPrivateSetytvs : $@convention(method) (@inout Foo) -> () {
+    // CHECK-DAG: sil hidden @$S9accessors3FooV22variableWithPrivateSetytvs : $@convention(method) (@inout Foo) -> () {
     set {}
   }
   var propertyWithNestedClass: Void {

test/SILGen/keypaths_multi_file.swift

@@ -0,0 +1,20 @@
+// RUN: %target-swift-emit-silgen -module-name keypaths -primary-file %s %S/Inputs/keypaths_multi_file_b.swift | %FileCheck %s
+// RUN: %target-swift-emit-silgen -module-name keypaths %s -primary-file %S/Inputs/keypaths_multi_file_b.swift | %FileCheck --check-prefix=DEFINITION %s
+
+func foo(x: Int) -> KeyPath<A, Int> {
+  switch x {
+  case 0:
+    return \A.x
+  default:
+    return \A.[0]
+  }
+  return \A.x
+}
+
+// A.x setter
+// CHECK-LABEL: sil hidden_external @$S8keypaths1AV1xSivs
+// DEFINITION-LABEL: sil hidden @$S8keypaths1AV1xSivs
+
+// A.subscript setter
+// CHECK-LABEL: sil hidden_external @$S8keypaths1AVyS2icis
+// DEFINITION-LABEL: sil hidden @$S8keypaths1AVyS2icis

test/stdlib/Inputs/KeyPathMultiFile_b.swift

@@ -0,0 +1,19 @@
+struct A {
+  private(set) var x: Int {
+    get { return 0 }
+    set {}
+  }
+
+  private(set) subscript(x: Int) -> Int {
+    get { return 0 }
+    set {}
+  }
+}
+
+func A_x_keypath() -> WritableKeyPath<A, Int> {
+  return \A.x
+}
+
+func A_subscript_0_keypath() -> WritableKeyPath<A, Int> {
+  return \A.[0]
+}

test/stdlib/KeyPath.swift

@@ -1,5 +1,5 @@
 // RUN: %empty-directory(%t)
-// RUN: %target-build-swift %s -Xfrontend -enable-sil-ownership -Xfrontend -g -o %t/a.out
+// RUN: %target-build-swift %s -o %t/a.out
 // RUN: %target-run %t/a.out
 // REQUIRES: executable_test
 

test/stdlib/KeyPathMultiFile.swift

@@ -0,0 +1,15 @@
+// RUN: %empty-directory(%t)
+// RUN: cp %s %t/main.swift
+// RUN: %target-build-swift -o %t/a.out %t/main.swift %S/Inputs/KeyPathMultiFile_b.swift
+// RUN: %target-run %t/a.out
+
+import StdlibUnittest
+
+var keyPathMultiFile = TestSuite("key paths across multiple files")
+
+keyPathMultiFile.test("identity across multiple files") {
+  expectEqual(A_x_keypath(), \A.x)
+  expectEqual(A_subscript_0_keypath(), \A.[0])
+}
+
+runAllTests()