Merge pull request #66291 from apple/es-rdar56

Add a test for extension of a public type conforming to SPI protocol

Author: elsh

test/SPI/spi_extension.swift

@@ -0,0 +1,31 @@
+// RUN: %empty-directory(%t)
+// RUN: split-file %s %t
+
+// RUN: %target-swift-frontend -emit-module %t/Lib.swift \
+// RUN:   -module-name Lib -I %t \
+// RUN:   -emit-module-path %t/Lib.swiftmodule
+
+// RUN: %target-swift-frontend -typecheck -verify %t/Client.swift -I %t
+
+
+//--- Lib.swift
+@_spi(core)
+public protocol SPIProto {
+  func foo()
+}
+
+@_spi(core)
+extension SPIProto {
+  public func foo() {}
+}
+
+//--- Client.swift
+
+@_spi(core) import Lib
+
+public class Klass {}
+
+@_spi(core)
+extension Klass: SPIProto {
+  func bar() {}
+}