AST: Inherit access level of opaque type decls from naming decl.

When an `OpaqueTypeDecl` is constructed, the access level attributes of the
decl that names the opaque type are copied on to it. However, the
`@usableFromInline` attribute is not permitted on every decl, so it does not get
copied. This in turn causes effective access level computations for opaque
types to fail to take `@usableFromInline` into account and that results in the
emitted symbol getting the wrong linkage during IRGen. The fix is to make the
effective access computation take this quirk of opaque types into account
directly, instead of relying on copying of attributes.

Resolves rdar://110544170

Author: tshortli

lib/AST/Decl.cpp

@@ -3868,6 +3868,12 @@ getAdjustedFormalAccess(const ValueDecl *VD, const DeclContext *useDC,
 }
 
 AccessLevel ValueDecl::getEffectiveAccess() const {
+  // Opaque type decls inherit accessibility from their naming decl.
+  if (auto *opaqueType = dyn_cast<OpaqueTypeDecl>(this)) {
+    if (auto *namingDecl = opaqueType->getNamingDecl())
+      return namingDecl->getEffectiveAccess();
+  }
+
   auto effectiveAccess =
     getAdjustedFormalAccess(this, /*useDC=*/nullptr,
                             /*treatUsableFromInlineAsPublic=*/true);

test/IRGen/Inputs/AlwaysInlineIntoWithOpaque.swift

@@ -14,3 +14,16 @@ public func testInlineWithOpaque() -> some P {
   }
   return 2.0
 }
+
+@_alwaysEmitIntoClient
+public func testInlineWithOpaqueUsableFromInline() -> some P {
+  if #available(macOS 9.0, *) {
+    return usableFromInline()
+  }
+  return 4.0
+}
+
+@usableFromInline
+func usableFromInline() -> some P {
+  return 3
+}

test/IRGen/Inputs/AlwaysInlineIntoWithOpaqueReplacement.swift

@@ -6,3 +6,8 @@ extension Int : P {
 
 extension Double : P {
 }
+
+@usableFromInline
+func usableFromInline() -> some P {
+  return 3
+}

test/IRGen/opaque_result_alwaysInlineIntoClient.swift

@@ -1,11 +1,11 @@
 // RUN: %empty-directory(%t)
-// RUN: %target-build-swift -target %target-cpu-apple-macosx10.15 -parse-as-library -emit-library -emit-module-path %t/AlwaysInlineIntoWithOpaque.swiftmodule -module-name AlwaysInlineIntoWithOpaque %S/Inputs/AlwaysInlineIntoWithOpaque.swift -o %t/%target-library-name(AlwaysInlineIntoWithOpaque)
+// RUN: %target-build-swift -target %target-cpu-apple-macosx10.15 -parse-as-library -emit-library -emit-module-path %t/AlwaysInlineIntoWithOpaque.swiftmodule -module-name AlwaysInlineIntoWithOpaque -enable-library-evolution %S/Inputs/AlwaysInlineIntoWithOpaque.swift -o %t/%target-library-name(AlwaysInlineIntoWithOpaque)
 // RUN: %target-codesign %t/%target-library-name(AlwaysInlineIntoWithOpaque)
 // RUN: %target-build-swift -target %target-cpu-apple-macosx10.15 -lAlwaysInlineIntoWithOpaque -module-name main -I %t -L %t %s -o %t/a.out
 // RUN: %target-codesign %t/a.out
 // RUN: %target-run %t/a.out | %FileCheck %s
 
-// RUN: %target-build-swift -target %target-cpu-apple-macosx10.15 -parse-as-library -emit-library -emit-module-path %t/AlwaysInlineIntoWithOpaque.swiftmodule -module-name AlwaysInlineIntoWithOpaque %S/Inputs/AlwaysInlineIntoWithOpaqueReplacement.swift -o %t/%target-library-name(AlwaysInlineIntoWithOpaque)
+// RUN: %target-build-swift -target %target-cpu-apple-macosx10.15 -parse-as-library -emit-library -emit-module-path %t/AlwaysInlineIntoWithOpaque.swiftmodule -module-name AlwaysInlineIntoWithOpaque  -enable-library-evolution %S/Inputs/AlwaysInlineIntoWithOpaqueReplacement.swift -o %t/%target-library-name(AlwaysInlineIntoWithOpaque)
 // RUN: %target-codesign %t/a.out
 // RUN: %target-run %t/a.out | %FileCheck %s
 
@@ -27,3 +27,11 @@ public func test() {
 
 test()
 // CHECK: 1
+
+public func testUsableFromInline() {
+  let p = testInlineWithOpaqueUsableFromInline()
+  print(p)
+}
+
+testUsableFromInline()
+// CHECK: 3

test/TBD/opaque_result_type.swift

@@ -77,6 +77,11 @@ public func dynReplacement(x: String) -> some P {
   return "replaced"
 }
 
+@usableFromInline
+func ufi() -> some O {
+  return 1
+}
+
 extension String: P {
   public func poo() -> some O {
     return 0