Sema: Diagnose references to soft-deprecated declarations.

When `-warn-soft-deprecated` is specified, diagnose references to declarations
that are deprecated in future OS versions.

Resolves rdar://130424183.

Author: tshortli

lib/Sema/TypeCheckAvailability.cpp

@@ -2214,9 +2214,17 @@ void TypeChecker::diagnosePotentialUnavailability(
 }
 
 const AvailableAttr *TypeChecker::getDeprecated(const Decl *D) {
-  if (auto *Attr = D->getAttrs().getDeprecated(D->getASTContext()))
+  auto &Ctx = D->getASTContext();
+  if (auto *Attr = D->getAttrs().getDeprecated(Ctx))
     return Attr;
 
+  if (Ctx.LangOpts.WarnSoftDeprecated) {
+    // When -warn-soft-deprecated is specified, treat any declaration that is
+    // deprecated in the future as deprecated.
+    if (auto *Attr = D->getAttrs().getSoftDeprecated(Ctx))
+      return Attr;
+  }
+
   // Treat extensions methods as deprecated if their extension
   // is deprecated.
   DeclContext *DC = D->getDeclContext();

test/Sema/availability_soft_deprecated.swift

@@ -0,0 +1,46 @@
+// RUN: %target-typecheck-verify-swift
+// RUN: %target-typecheck-verify-swift -warn-soft-deprecated -verify-additional-prefix soft-deprecated-
+
+// REQUIRES: OS=macosx || OS=ios || OS=tvos || OS=watchos || OS=xros
+
+@available(*, deprecated)
+func alwaysDeprecated() {}
+
+@available(macOS, deprecated: 1.0)
+@available(iOS, deprecated: 1.0)
+@available(tvOS, deprecated: 1.0)
+@available(watchOS, deprecated: 1.0)
+@available(visionOS, deprecated: 1.0)
+func deprecatedEarly() {}
+
+@available(macOS, deprecated: 10000)
+@available(iOS, deprecated: 10000)
+@available(tvOS, deprecated: 10000)
+@available(watchOS, deprecated: 10000)
+@available(visionOS, deprecated: 10000)
+func deprecatedFarFuture() {}
+
+protocol Proto {}
+struct HasSoftDeprecatedConformanceToProto {}
+
+@available(macOS, deprecated: 10000)
+@available(iOS, deprecated: 10000)
+@available(tvOS, deprecated: 10000)
+@available(watchOS, deprecated: 10000)
+@available(visionOS, deprecated: 10000)
+extension HasSoftDeprecatedConformanceToProto: Proto {}
+
+func test() {
+  alwaysDeprecated() // expected-warning {{'alwaysDeprecated()' is deprecated}}
+  deprecatedEarly() // expected-warning {{'deprecatedEarly()' was deprecated in}}
+  deprecatedFarFuture() // expected-soft-deprecated-warning {{'deprecatedFarFuture()' was deprecated in}}
+  let _: any Proto = HasSoftDeprecatedConformanceToProto() // expected-soft-deprecated-warning {{conformance of 'HasSoftDeprecatedConformanceToProto' to 'Proto' was deprecated in}}
+}
+
+@available(*, deprecated)
+func testDeprecated() {
+  alwaysDeprecated()
+  deprecatedEarly()
+  deprecatedFarFuture()
+  let _: any Proto = HasSoftDeprecatedConformanceToProto()
+}