Sema: Allow default arguments to access @usableFromInline decls.

The restriction that default arguments be disallowed from accessing
`@usableFromInline` decls is overbearing for library developers who need to
write non-trivial code to compute a default value, since it forces them to
either write a verbose closure inline in the function signature or expose a
`public` helper function which unnecessarily expands API surface. A
`@usableFromInline` function a more reasonable way to encapsulate a verbose
default value computation.

This reverses the semantic changes included in #15666.

Resolves rdar://112093794.

Author: tshortli

lib/AST/DeclContext.cpp

@@ -471,14 +471,11 @@ swift::FragileFunctionKindRequest::evaluate(Evaluator &evaluator,
       }
 
       auto effectiveAccess =
-        VD->getFormalAccessScope(/*useDC=*/nullptr,
-                                 /*treatUsableFromInlineAsPublic=*/true);
-      auto formalAccess =
-        VD->getFormalAccessScope(/*useDC=*/nullptr,
-                                 /*treatUsableFromInlineAsPublic=*/false);
+          VD->getFormalAccessScope(/*useDC=*/nullptr,
+                                   /*treatUsableFromInlineAsPublic=*/true);
       if (effectiveAccess.isPublic()) {
         return {FragileFunctionKind::DefaultArgument,
-                !formalAccess.isPublic()};
+                /*allowUsableFromInline=*/true};
       }
 
       return {FragileFunctionKind::None,

test/Constraints/type_inference_from_default_exprs.swift

@@ -208,7 +208,7 @@ protocol StorageType {
   var identifier: String { get }
 }
 
-class Storage { // expected-note {{class 'Storage' is not public}}
+class Storage { // expected-note {{class 'Storage' is not '@usableFromInline' or public}}
 }
 
 extension Storage {
@@ -256,7 +256,7 @@ struct S61061_3<T> where T:Hashable {
 
 // https://github.com/apple/swift/issues/62025
 // Syntactic checks are not run on the default argument expressions
-public struct MyStruct {} // expected-note {{initializer 'init()' is not public}}
+public struct MyStruct {} // expected-note {{initializer 'init()' is not '@usableFromInline' or public}}
 public func issue62025_with_init<T>(_: T = MyStruct()) {}
 // expected-error@-1 {{initializer 'init()' is internal and cannot be referenced from a default argument value}}
 public func issue62025_with_type<T>(_: T = Storage.self) {}

test/decl/func/default-values-swift4.swift

@@ -2,17 +2,16 @@
 // RUN: %target-typecheck-verify-swift -swift-version 4 -enable-testing
 
 private func privateFunction() {}
-// expected-note@-1 2{{global function 'privateFunction()' is not public}}
+// expected-note@-1 2{{global function 'privateFunction()' is not '@usableFromInline' or public}}
 fileprivate func fileprivateFunction() {}
-// expected-note@-1 2{{global function 'fileprivateFunction()' is not public}}
+// expected-note@-1 2{{global function 'fileprivateFunction()' is not '@usableFromInline' or public}}
 func internalFunction() {}
-// expected-note@-1 2{{global function 'internalFunction()' is not public}}
-@usableFromInline func versionedFunction() {}
-// expected-note@-1 4{{global function 'versionedFunction()' is not public}}
+// expected-note@-1 2{{global function 'internalFunction()' is not '@usableFromInline' or public}}
+@usableFromInline func usableFromInlineFunction() {}
 public func publicFunction() {}
 
 func internalIntFunction() -> Int {}
-// expected-note@-1 {{global function 'internalIntFunction()' is not public}}
+// expected-note@-1 {{global function 'internalIntFunction()' is not '@usableFromInline' or public}}
 
 private func privateFunction2() {}
 // expected-note@-1 {{global function 'privateFunction2()' is not '@usableFromInline' or public}}
@@ -31,7 +30,7 @@ func internalFunctionWithDefaultValue(
 
       publicFunction()
       // OK
-      versionedFunction()
+      usableFromInlineFunction()
       // OK
       internalFunction()
       // OK
@@ -44,16 +43,14 @@ func internalFunctionWithDefaultValue(
     }(),
     y: Int = internalIntFunction()) {}
 
-@usableFromInline func versionedFunctionWithDefaultValue(
+@usableFromInline func usableFromInlineFunctionWithDefaultValue(
     x: Int = {
       struct Nested {}
       // expected-error@-1 {{type 'Nested' cannot be nested inside a default argument value}}
 
-      // FIXME: Some errors below are diagnosed twice
-
       publicFunction()
       // OK
-      versionedFunction()
+      usableFromInlineFunction()
       // OK
       internalFunction2()
       // expected-error@-1 {{global function 'internalFunction2()' is internal and cannot be referenced from a default argument value}}
@@ -76,8 +73,7 @@ public func publicFunctionWithDefaultValue(
 
       publicFunction()
 
-      versionedFunction()
-      // expected-error@-1 {{global function 'versionedFunction()' is internal and cannot be referenced from a default argument value}}
+      usableFromInlineFunction()
 
       internalFunction()
       // expected-error@-1 {{global function 'internalFunction()' is internal and cannot be referenced from a default argument value}}
@@ -101,18 +97,16 @@ public class MyClass {
 public func evilCode(
   x: Int = {
     let _ = publicFunction()
-    let _ = versionedFunction()
-    // expected-error@-1 {{global function 'versionedFunction()' is internal and cannot be referenced from a default argument value}}
+    let _ = usableFromInlineFunction()
 
     func localFunction() {
       publicFunction()
-      versionedFunction()
-      // expected-error@-1 {{global function 'versionedFunction()' is internal and cannot be referenced from a default argument value}}
+      usableFromInlineFunction()
     }
     return 0
   }()) {}
 
-private func privateIntFunction() -> Int {} // expected-note {{global function 'privateIntFunction()' is not public}}
+private func privateIntFunction() -> Int {} // expected-note {{global function 'privateIntFunction()' is not '@usableFromInline' or public}}
 
 public struct HasSubscript {
   public subscript(x: Int = {
@@ -121,8 +115,7 @@ public struct HasSubscript {
 
     publicFunction()
 
-    versionedFunction()
-    // expected-error@-1 {{global function 'versionedFunction()' is internal and cannot be referenced from a default argument value}}
+    usableFromInlineFunction()
 
     internalFunction()
     // expected-error@-1 {{global function 'internalFunction()' is internal and cannot be referenced from a default argument value}}