[SE-0497] Implement @export attribute syntax

Implement the @export(implementation) and @export(interface) attributes
to replace @_alwaysEmitIntoClient and @_neverEmitIntoClient. Provide a
warning + Fix-It to start staging out the very-new
@_neverEmitIntoClient. We'll hold off on pushing folks toward
@_alwaysEmitIntoClient for a little longer.

test/embedded/deinit-noncopyable.swift

@@ -19,7 +19,7 @@
     }
 
     @inline(__always)
-    @_alwaysEmitIntoClient
+    @export(implementation)
     deinit {
         buffer.deinitialize().deallocate()
     }

test/embedded/implementation-only-import-build.swift

@@ -25,7 +25,7 @@ private func implicitlyInlinablePrivate() {
   localInternalFunc()
 }
 
-@_neverEmitIntoClient
+@export(interface)
 public func explicitNonInliable() {
   _ = StructFromDirect()
 
@@ -33,7 +33,7 @@ public func explicitNonInliable() {
     _ = StructFromDirect()
   }
 
-  @_neverEmitIntoClient
+  @export(interface)
   func nested() {
     _ = StructFromDirect()
   }
@@ -42,7 +42,7 @@ public func explicitNonInliable() {
   localInternalFunc()
 }
 
-@_alwaysEmitIntoClient
+@export(implementation)
 public func legalAccessToIndirect() {
   _ = StructFromIndirect()
 
@@ -57,7 +57,7 @@ public func legalAccessToIndirect() {
 }
 
 extension Array {
-  @_alwaysEmitIntoClient
+  @export(implementation)
   public var myMutableSpan: Int {
     get {
       return 0

test/embedded/linkage/export_interface.swift

@@ -21,7 +21,7 @@
 //--- Library.swift
 
 // LIBRARY-IR: define {{(protected |dllexport )?}}swiftcc ptr @"$e7Library5helloSaySiGyF"()
-@_neverEmitIntoClient
+@export(interface)
 public func hello() -> [Int] {
   getArray()
 }
@@ -52,7 +52,7 @@ public func unnecessary() -> Int { 5 }
 //--- Application.swift
 import Library
 
-@_neverEmitIntoClient
+@export(interface)
 public func testMe() {
   _ = hello()
   _ = getArray()
@@ -64,8 +64,8 @@ public func testMe() {
 // APPLICATION-SIL: sil @$e7Library5helloSaySiGyF : $@convention(thin) () -> @owned Array<Int>{{$}}
 // APPLICATION-IR: declare swiftcc ptr @"$e7Library5helloSaySiGyF"()
 
-// Note: "getArray" is not @_neverEmitIntoClient, so it's definition is
-// available.
+// Note: "getArray" is not prohibited from being emitted into the client, so
+// its definition is available.
 
 // APPLICATION-SIL: sil public_external @$e7Library8getArraySaySiGyF : $@convention(thin) () -> @owned Array<Int> {
 // APPLICATION-IR: define linkonce_odr hidden swiftcc ptr @"$e7Library8getArraySaySiGyF"()

test/embedded/linkage/implementation_only_hiding.swift

@@ -28,7 +28,7 @@
 // RUN: rm -rf %t/Dependencies
 
 // Build the application against the library. This is expected to work because
-// @_neverEmitIntoClient hides the body of test().
+// @export(interface) hides the body of test().
 // RUN: %target-swift-frontend -emit-ir -parse-as-library %t/Files/Application.swift -enable-experimental-feature Embedded -I %t/Modules -o %t/Application.ir
 
 // REQUIRES: swift_in_compiler
@@ -38,7 +38,7 @@
 @_implementationOnly import CDependency // expected-warning {{using '@_implementationOnly' without enabling library evolution for 'Library' may lead to instability during execution}}
 @_implementationOnly import SwiftDependency // expected-warning {{using '@_implementationOnly' without enabling library evolution for 'Library' may lead to instability during execution}}
 
-@_neverEmitIntoClient
+@export(interface)
 public func test() {
   _ = getPoint(3.14159, 2.71828)
   A().doSomething()
@@ -46,13 +46,13 @@ public func test() {
 
 #if BAD_IOI_USAGE
 public func badCLibraryUsage() {
-  _ = getPoint(3.14159, 2.71828) // expected-error {{global function 'getPoint' cannot be used in an embedded function not marked '@_neverEmitIntoClient' because 'CDependency' was imported implementation-only}}
+  _ = getPoint(3.14159, 2.71828) // expected-error {{global function 'getPoint' cannot be used in an embedded function not marked '@export(interface)' because 'CDependency' was imported implementation-only}}
 }
 
 public func badSwiftLibraryUsage() {
-  A().doSomething() // expected-error {{struct 'A' cannot be used in an embedded function not marked '@_neverEmitIntoClient' because 'SwiftDependency' was imported implementation-only}}
-  // expected-error @-1 {{initializer 'init()' cannot be used in an embedded function not marked '@_neverEmitIntoClient' because 'SwiftDependency' was imported implementation-only}}
-  // expected-error @-2 {{instance method 'doSomething()' cannot be used in an embedded function not marked '@_neverEmitIntoClient' because 'SwiftDependency' was imported implementation-only}}
+  A().doSomething() // expected-error {{struct 'A' cannot be used in an embedded function not marked '@export(interface)' because 'SwiftDependency' was imported implementation-only}}
+  // expected-error @-1 {{initializer 'init()' cannot be used in an embedded function not marked '@export(interface)' because 'SwiftDependency' was imported implementation-only}}
+  // expected-error @-2 {{instance method 'doSomething()' cannot be used in an embedded function not marked '@export(interface)' because 'SwiftDependency' was imported implementation-only}}
 }
 #endif
 

test/embedded/linkage/leaf_application.swift

@@ -53,7 +53,7 @@ private func throughPrivate() -> [Int] {
 public func unnecessary() -> Int64 { 5 }
 
 // LIBRARY-IR: define {{.*}} @"$e7Library14unusedYetThere
-@_neverEmitIntoClient
+@export(interface)
 public func unusedYetThere() -> Int64 { 5 }
 
 open class PointClass {
@@ -81,7 +81,7 @@ extension PointClass: Reflectable {
 }
 
 // LIBRARY-IR: define {{.*}} @"$e7Library18createsExistentialAA11Reflectable_pyF"()
-@_neverEmitIntoClient
+@export(interface)
 public func createsExistential() -> any Reflectable {
   return PointClass(x: 5, y: 5)
 }