Ban explicit lifetime dependence on bitwise copyable type

Author: meg-gupta

include/swift/AST/DiagnosticsSema.def

@@ -7835,6 +7835,8 @@ ERROR(lifetime_dependence_ctor_non_self_or_nil_return, none,
 ERROR(lifetime_dependence_cannot_use_infer, none,
        "invalid use of %0 lifetime dependence on Escapable type",
        (StringRef))
+ERROR(lifetime_dependence_on_bitwise_copyable, none,
+      "invalid lifetime dependence on bitwise copyable type", ())
 
 //===----------------------------------------------------------------------===//
 //                             MARK: Transferring

lib/Sema/LifetimeDependence.cpp

@@ -107,6 +107,7 @@ LifetimeDependenceInfo::fromTypeRepr(AbstractFunctionDecl *afd, Type resultType,
                                      bool allowIndex) {
   auto *dc = afd->getDeclContext();
   auto &ctx = dc->getASTContext();
+  auto *mod = afd->getModuleContext();
   auto &diags = ctx.Diags;
   auto capacity = afd->getParameters()->size() + 1;
   auto lifetimeDependentRepr =
@@ -156,6 +157,16 @@ LifetimeDependenceInfo::fromTypeRepr(AbstractFunctionDecl *afd, Type resultType,
         return true;
       }
     }
+
+    if (ctx.LangOpts.hasFeature(Feature::BitwiseCopyable)) {
+      auto *bitwiseCopyableProtocol =
+          ctx.getProtocol(KnownProtocolKind::BitwiseCopyable);
+      if (bitwiseCopyableProtocol && mod->checkConformance(type, bitwiseCopyableProtocol)) {
+        diags.diagnose(loc, diag::lifetime_dependence_on_bitwise_copyable);
+        return true;
+      }
+    }
+
     if (inheritLifetimeParamIndices.test(paramIndexToSet) ||
         scopeLifetimeParamIndices.test(paramIndexToSet)) {
       diags.diagnose(loc, diag::lifetime_dependence_duplicate_param_id);

test/Sema/explicit_lifetime_dependence_specifiers.swift

@@ -1,12 +1,20 @@
-// RUN: %target-typecheck-verify-swift -disable-availability-checking -enable-experimental-feature NonescapableTypes -disable-experimental-parser-round-trip   -enable-experimental-feature NoncopyableGenerics -enable-builtin-module
+// RUN: %target-typecheck-verify-swift -disable-availability-checking -enable-experimental-feature NonescapableTypes -disable-experimental-parser-round-trip   -enable-experimental-feature NoncopyableGenerics -enable-builtin-module -enable-experimental-feature BitwiseCopyable
 // REQUIRES: noncopyable_generics
 import Builtin
 
+struct Container {
+  let ptr: UnsafeRawBufferPointer
+}
+
 struct BufferView : ~Escapable {
   let ptr: UnsafeRawBufferPointer
   init(_ ptr: UnsafeRawBufferPointer) {
     self.ptr = ptr
   }
+  init(_ c: borrowing Container) -> _borrow(c) Self { // expected-error{{invalid lifetime dependence on bitwise copyable type}}
+    self.ptr = c.ptr
+    return self
+  }
 }
 
 struct MutableBufferView : ~Escapable, ~Copyable {