ClangImporter: fix C++ memberwise inits to use @Lifetime(immortal)

_unsafeNonEscapableResult no longer dsiables diagnostics at the call site. We
need to use a proper lifetime annotation for that.

Author: atrick

lib/ClangImporter/ImportDecl.cpp

@@ -2036,9 +2036,20 @@ namespace {
     }
 
     void markReturnsUnsafeNonescapable(AbstractFunctionDecl *fd) {
-      fd->getAttrs().add(new (Impl.SwiftContext)
-                             UnsafeNonEscapableResultAttr(/*Implicit=*/true));
       fd->getAttrs().add(new (Impl.SwiftContext) UnsafeAttr(/*Implicit=*/true));
+
+      unsigned resultIndex = fd->getParameters()->size();
+      if (fd->hasImplicitSelfDecl()) {
+        ++resultIndex;
+      }
+      SmallVector<LifetimeDependenceInfo, 1> lifetimeDependencies;
+      LifetimeDependenceInfo immortalLifetime(nullptr, nullptr, resultIndex,
+                                              /*isImmortal*/ true);
+      lifetimeDependencies.push_back(immortalLifetime);
+      Impl.SwiftContext.evaluator.cacheOutput(
+        LifetimeDependenceInfoRequest{fd},
+        Impl.SwiftContext.AllocateCopy(lifetimeDependencies));
+      return;
     }
 
     Decl *VisitRecordDecl(const clang::RecordDecl *decl) {
@@ -4060,6 +4071,9 @@ namespace {
                    CxxEscapability::Unknown) != CxxEscapability::NonEscapable;
       };
 
+      // FIXME: this uses '0' as the result index. That only works for
+      // standalone functions with no parameters.
+      // See markReturnsUnsafeNonescapable() for a general approach.
       auto &ASTContext = result->getASTContext();
       SmallVector<LifetimeDependenceInfo, 1> lifetimeDependencies;
       LifetimeDependenceInfo immortalLifetime(nullptr, nullptr, 0,