NFC: Increase test coverage for SPI enum elements.

These tests identified a gap in type checking the exportability of case statements. Unfortunately this gap is not simple to close, since exportability is usually checked during availability checking but availability checking isn't appropriate for case statements and there isn't existing infrastructure to check exportability independently.

Author: tshortli

test/SPI/Inputs/spi_helper.swift

@@ -89,3 +89,8 @@ public struct PublicStruct {
 @_spi(HelperSPI) public struct IntLike: ExpressibleByIntegerLiteral, Equatable {
   @_spi(HelperSPI) public init(integerLiteral: Int) {}
 }
+
+public enum PublicEnum {
+  case publicCase
+  @_spi(HelperSPI) case spiCase
+}

test/SPI/export_spi_from_spi_module.swift

@@ -11,15 +11,32 @@
   public init() {}
 }
 @_spi(S) public protocol SPIProtocol {}
+public enum PublicEnum {
+  case publicCase
+  @_spi(S) case spiCase
+}
 
 public func useOfSPITypeOk(_ p0: SPIProtocol, p1: SPIClass) -> SPIClass { fatalError() }
 
 @inlinable
-func inlinable() -> SPIClass {
+public func inlinable() -> SPIClass {
   spiFunc()
   _ = SPIClass()
 }
 
+@inlinable
+public func inlinable(_ e: PublicEnum) {
+  switch e {
+  case .publicCase: break
+  case .spiCase: break
+  @unknown default: break
+  }
+
+  if case .spiCase = e {}
+
+  _ = PublicEnum.spiCase
+}
+
 @frozen public struct FrozenStruct {
   public var spiInFrozen = SPIStruct()
   var spiTypeInFrozen = SPIStruct()

test/SPI/public_client.swift

@@ -27,6 +27,7 @@ internalFunc() // expected-error {{cannot find 'internalFunc' in scope}}
 let c = SPIClass() // expected-error {{cannot find 'SPIClass' in scope}}
 let s = SPIStruct() // expected-error {{cannot find 'SPIStruct' in scope}}
 SPIEnum().spiMethod() // expected-error {{cannot find 'SPIEnum' in scope}}
+_ = PublicEnum.spiCase // expected-error {{'spiCase' is inaccessible due to '@_spi' protection level}}
 
 var ps = PublicStruct()
 let _ = PublicStruct(alt_init: 1) // expected-error {{argument passed to call that takes no arguments}}

test/SPI/spi_client.swift

@@ -40,6 +40,7 @@ print(s.spiVar)
 
 SPIEnum().spiMethod()
 SPIEnum.A.spiMethod()
+_ = PublicEnum.spiCase
 
 var ps = PublicStruct()
 let _ = PublicStruct(alt_init: 1)

test/SPI/spi_enum_element.swift

@@ -0,0 +1,48 @@
+// RUN: %target-typecheck-verify-swift -swift-version 5
+// RUN: %target-typecheck-verify-swift -swift-version 5 -enable-library-evolution
+
+public enum PublicEnum {
+  case publicCase
+  @_spi(S) case spiCase
+}
+
+@inlinable public func publicInlinableFunc(_ e: PublicEnum) {
+  switch e {
+  case .publicCase: break
+  case .spiCase: break   // FIXME: this should be diagnosed with "cannot use enum case 'spiCase' here; it is SPI"
+  @unknown default: break
+  }
+
+  if case .spiCase = e {} // FIXME: this should be diagnosed with "cannot use enum case 'spiCase' here; it is SPI"
+
+  _ = PublicEnum.spiCase // expected-error {{enum case 'spiCase' cannot be used in an '@inlinable' function because it is SPI}}
+}
+
+@_spi(S)
+@inlinable public func spiInlinableFunc(_ e: PublicEnum) {
+  switch e {
+  case .publicCase: break
+  case .spiCase: break
+  @unknown default: break
+  }
+
+  if case .spiCase = e {}
+
+  _ = PublicEnum.spiCase
+}
+
+public struct PublicStruct {}
+@_spi(S) public struct SPIStruct {} // expected-note {{type declared here}}
+
+public enum PublicEnumWithPayloads {
+  case publicCasePublicPayload(_ s: PublicStruct)
+  case publicCaseSPIPayload(_ s: SPIStruct) // expected-error {{cannot use struct 'SPIStruct' here; it is SPI}}
+  @_spi(S) case spiCasePublicPayload(_ s: PublicStruct)
+  @_spi(S) case spiCaseSPIPayload(_ s: SPIStruct)
+}
+
+@_spi(S)
+public enum SPIEnumWithPayloads {
+  case publicPayloadCase(_ s: PublicStruct)
+  case spiPayloadCase(_ s: SPIStruct)
+}