Add Sema diagnostic when we cant infer lifetime dependence on a method because self is BitwiseCopyable & Escapable

Author: meg-gupta

include/swift/AST/DiagnosticsSema.def

@@ -7889,6 +7889,10 @@ ERROR(lifetime_dependence_cannot_infer_ambiguous_candidate, none,
        "invalid lifetime dependence on bitwise copyable type", ())
  ERROR(lifetime_dependence_cannot_be_applied_to_tuple_elt, none,
        "lifetime dependence specifiers cannot be applied to tuple elements", ())
+ ERROR(lifetime_dependence_method_escapable_bitwisecopyable_self, none,
+       "cannot infer lifetime dependence on a self which is BitwiseCopyable & "
+       "Escapable",
+       ())
 
  //===----------------------------------------------------------------------===//
  //                             MARK: Transferring

lib/Sema/LifetimeDependence.cpp

@@ -399,6 +399,7 @@ std::optional<LifetimeDependenceInfo>
 LifetimeDependenceInfo::infer(AbstractFunctionDecl *afd, Type resultType) {
   auto *dc = afd->getDeclContext();
   auto &ctx = dc->getASTContext();
+  auto *mod = afd->getModuleContext();
 
   if (!ctx.LangOpts.hasFeature(Feature::NonescapableTypes)) {
     return std::nullopt;
@@ -431,6 +432,19 @@ LifetimeDependenceInfo::infer(AbstractFunctionDecl *afd, Type resultType) {
 
   if (afd->getKind() != DeclKind::Constructor && afd->hasImplicitSelfDecl()) {
     Type selfTypeInContext = dc->getSelfTypeInContext();
+    if (selfTypeInContext->isEscapable()) {
+      if (ctx.LangOpts.hasFeature(Feature::BitwiseCopyable)) {
+        auto *bitwiseCopyableProtocol =
+            ctx.getProtocol(KnownProtocolKind::BitwiseCopyable);
+        if (bitwiseCopyableProtocol &&
+            mod->checkConformance(selfTypeInContext, bitwiseCopyableProtocol)) {
+          diags.diagnose(
+              returnLoc,
+              diag::lifetime_dependence_method_escapable_bitwisecopyable_self);
+          return std::nullopt;
+        }
+      }
+    }
     auto kind = getLifetimeDependenceKindFromType(selfTypeInContext);
     auto selfOwnership = afd->getImplicitSelfDecl()->getValueOwnership();
     if (!isLifetimeDependenceCompatibleWithOwnership(kind, selfOwnership,

test/Sema/explicit_lifetime_dependence_specifiers1.swift

@@ -1,4 +1,4 @@
-// RUN: %target-typecheck-verify-swift -disable-availability-checking -enable-experimental-feature NonescapableTypes -enable-experimental-feature NoncopyableGenerics
+// RUN: %target-typecheck-verify-swift -disable-availability-checking -enable-experimental-feature NonescapableTypes -enable-experimental-feature NoncopyableGenerics -enable-experimental-feature BitwiseCopyable
 // REQUIRES: asserts
 
 struct Container {
@@ -218,3 +218,17 @@ func derive(_ x: BufferView) -> dependsOn(x) BufferView { // expected-note{{'der
 func derive(_ x: BufferView) -> dependsOn(scoped x) BufferView { // expected-error{{invalid redeclaration of 'derive'}}
   return BufferView(x.ptr)
 }
+
+struct RawBufferView {
+  let ptr: UnsafeRawBufferPointer
+  @_unsafeNonescapableResult
+  init(_ ptr: UnsafeRawBufferPointer) {
+    self.ptr = ptr
+  }
+}
+
+extension RawBufferView {
+  mutating func zeroBufferView() throws -> BufferView { // expected-error{{cannot infer lifetime dependence on a self which is BitwiseCopyable & Escapable}}
+    return BufferView(ptr)
+  }
+}