[cxx-interop] Fix spurious lifetime dependence errors

ClangImporter will generate value and default initializers for certain
structs imported from C++. These generated initializers have no
associated lifetime dependence information so they will trigger spurious
errors for non-escapable types. This patch makes sure these are marked
as unsafe so the type checker will not generate errors for them.
Moreover, the generated default initializer would trigger a crash for
non-escapable types as the builtin to zero initialize an object does not
support non-escapable types yet.

rdar://143040862

Author: Gabor Horvath

lib/ClangImporter/ImportDecl.cpp

@@ -2041,6 +2041,18 @@ namespace {
       return semanticsKind == CxxRecordSemanticsKind::MoveOnly;
     }
 
+    void markReturnsUnsafeNonescapable(AbstractFunctionDecl *fd) {
+      if (Impl.SwiftContext.LangOpts.hasFeature(Feature::LifetimeDependence)) {
+        fd->getAttrs().add(new (Impl.SwiftContext)
+                               UnsafeNonEscapableResultAttr(/*Implicit=*/true));
+        if (Impl.SwiftContext.LangOpts.hasFeature(Feature::SafeInterop) &&
+            Impl.SwiftContext.LangOpts.hasFeature(
+                Feature::AllowUnsafeAttribute))
+          fd->getAttrs().add(new (Impl.SwiftContext)
+                                 UnsafeAttr(/*Implicit=*/true));
+      }
+    }
+
     Decl *VisitRecordDecl(const clang::RecordDecl *decl) {
       // Track whether this record contains fields we can't reference in Swift
       // as stored properties.
@@ -2236,12 +2248,14 @@ namespace {
                                    MoveOnlyAttr(/*Implicit=*/true));
       }
 
+      bool isNonEscapable = false;
       if (evaluateOrDefault(
               Impl.SwiftContext.evaluator,
               ClangTypeEscapability({decl->getTypeForDecl(), Impl}),
               CxxEscapability::Unknown) == CxxEscapability::NonEscapable) {
         result->getAttrs().add(new (Impl.SwiftContext)
                                    NonEscapableAttr(/*Implicit=*/true));
+        isNonEscapable = true;
       }
 
       // FIXME: Figure out what to do with superclasses in C++. One possible
@@ -2386,6 +2400,9 @@ namespace {
               synthesizer.createValueConstructor(result, member,
                                                  /*want param names*/ true,
                                                  /*wantBody=*/true);
+
+          if (isNonEscapable)
+            markReturnsUnsafeNonescapable(valueCtor);
           ctors.push_back(valueCtor);
         }
         // TODO: we have a problem lazily looking up members of an unnamed
@@ -2410,7 +2427,13 @@ namespace {
                                 (!cxxRecordDecl->hasDefaultConstructor() ||
                                  cxxRecordDecl->ctors().empty());
       }
-      if (hasZeroInitializableStorage && needsEmptyInitializer) {
+
+      // TODO: builtin "zeroInitializer" does not work with non-escapable
+      // types yet. Don't generate an initializer.
+      if (hasZeroInitializableStorage && needsEmptyInitializer &&
+          (!Impl.SwiftContext.LangOpts.hasFeature(
+               Feature::LifetimeDependence) ||
+           !isNonEscapable)) {
         // Add default constructor for the struct if compiling in C mode.
         // If we're compiling for C++:
         // 1. If a default constructor is declared, don't synthesize one.
@@ -2423,7 +2446,6 @@ namespace {
         //    constructor available in Swift.
         ConstructorDecl *defaultCtor =
             synthesizer.createDefaultConstructor(result);
-        ctors.push_back(defaultCtor);
         if (cxxRecordDecl) {
           auto attr = AvailableAttr::createUniversallyDeprecated(
               defaultCtor->getASTContext(),
@@ -2433,6 +2455,7 @@ namespace {
               "");
           defaultCtor->getAttrs().add(attr);
         }
+        ctors.push_back(defaultCtor);
       }
 
       bool forceMemberwiseInitializer = false;
@@ -2462,6 +2485,9 @@ namespace {
         if (!hasUnreferenceableStorage)
           valueCtor->setIsMemberwiseInitializer();
 
+        if (isNonEscapable)
+          markReturnsUnsafeNonescapable(valueCtor);
+
         ctors.push_back(valueCtor);
       }
 

test/Interop/Cxx/class/nonescapable-lifetimebound.swift

@@ -23,7 +23,6 @@ private:
 };
 
 struct SWIFT_NONESCAPABLE OtherView {
-    OtherView() : member(nullptr) {}
     OtherView(View v [[clang::lifetimebound]]) : member(v.member) {}
     OtherView(const OtherView&) = default;
 private:
@@ -105,6 +104,10 @@ CaptureView getCaptureView(const Owner& owner [[clang::lifetimebound]]) {
     return CaptureView(View{&owner.data});
 }
 
+struct SWIFT_NONESCAPABLE AggregateView {
+    const int *member;
+};
+
 // CHECK: sil [clang makeOwner] {{.*}}: $@convention(c) () -> Owner
 // CHECK: sil [clang getView] {{.*}} : $@convention(c) (@in_guaranteed Owner) -> @lifetime(borrow 0) @owned View
 // CHECK: sil [clang getViewFromFirst] {{.*}} : $@convention(c) (@in_guaranteed Owner, @in_guaranteed Owner) -> @lifetime(borrow 0) @owned View
@@ -120,18 +123,20 @@ CaptureView getCaptureView(const Owner& owner [[clang::lifetimebound]]) {
 // CHECK: sil [clang CaptureView.captureView] {{.*}} : $@convention(cxx_method) (View, @lifetime(copy 0) @inout CaptureView) -> ()
 // CHECK: sil [clang CaptureView.handOut] {{.*}} : $@convention(cxx_method) (@lifetime(copy 1) @inout View, @in_guaranteed CaptureView) -> ()
 
-// CHECK-NO-LIFETIMES: nonescapable.h:36:6: error: returning ~Escapable type requires '-enable-experimental-feature LifetimeDependence'
-// CHECK-NO-LIFETIMES: nonescapable.h:40:6: error: returning ~Escapable type requires '-enable-experimental-feature LifetimeDependence'
-// CHECK-NO-LIFETIMES: nonescapable.h:46:6: error: returning ~Escapable type requires '-enable-experimental-feature LifetimeDependence'
-// CHECK-NO-LIFETIMES: nonescapable.h:53:6: error: returning ~Escapable type requires '-enable-experimental-feature LifetimeDependence'
-// CHECK-NO-LIFETIMES: nonescapable.h:23:10: error: returning ~Escapable type requires '-enable-experimental-feature LifetimeDependence'
-// CHECK-NO-LIFETIMES: nonescapable.h:27:10: error: returning ~Escapable type requires '-enable-experimental-feature LifetimeDependence'
+// CHECK-NO-LIFETIMES: nonescapable.h:35:6: error: returning ~Escapable type requires '-enable-experimental-feature LifetimeDependence'
+// CHECK-NO-LIFETIMES: nonescapable.h:39:6: error: returning ~Escapable type requires '-enable-experimental-feature LifetimeDependence'
+// CHECK-NO-LIFETIMES: nonescapable.h:45:6: error: returning ~Escapable type requires '-enable-experimental-feature LifetimeDependence'
+// CHECK-NO-LIFETIMES: nonescapable.h:52:6: error: returning ~Escapable type requires '-enable-experimental-feature LifetimeDependence'
+// CHECK-NO-LIFETIMES: nonescapable.h:22:10: error: returning ~Escapable type requires '-enable-experimental-feature LifetimeDependence'
+// CHECK-NO-LIFETIMES: nonescapable.h:26:10: error: returning ~Escapable type requires '-enable-experimental-feature LifetimeDependence'
 // CHECK-NO-LIFETIMES: nonescapable.h:4:5: error: returning ~Escapable type requires '-enable-experimental-feature LifetimeDependence'
 // CHECK-NO-LIFETIMES: nonescapable.h:5:5: error: returning ~Escapable type requires '-enable-experimental-feature LifetimeDependence'
 // CHECK-NO-LIFETIMES: nonescapable.h:13:5: error: returning ~Escapable type requires '-enable-experimental-feature LifetimeDependence'
-// CHECK-NO-LIFETIMES: nonescapable.h:14:5: error: returning ~Escapable type requires '-enable-experimental-feature LifetimeDependence'
-// CHECK-NO-LIFETIMES: nonescapable.h:68:6: error: returning ~Escapable type requires '-enable-experimental-feature LifetimeDependence'
-// CHECK-NO-LIFETIMES: nonescapable.h:91:13: error: returning ~Escapable type requires '-enable-experimental-feature LifetimeDependence'
+// CHECK-NO-LIFETIMES: nonescapable.h:12:27: error: returning ~Escapable type requires '-enable-experimental-feature LifetimeDependence'
+// CHECK-NO-LIFETIMES: nonescapable.h:67:6: error: returning ~Escapable type requires '-enable-experimental-feature LifetimeDependence'
+// CHECK-NO-LIFETIMES: nonescapable.h:90:13: error: returning ~Escapable type requires '-enable-experimental-feature LifetimeDependence'
+// CHECK-NO-LIFETIMES: nonescapable.h:94:27: error: returning ~Escapable type requires '-enable-experimental-feature LifetimeDependence'
+// CHECK-NO-LIFETIMES: nonescapable.h:94:27: error: returning ~Escapable type requires '-enable-experimental-feature LifetimeDependence'
 // CHECK-NO-LIFETIMES-NOT: error
 
 //--- test.swift
@@ -155,3 +160,7 @@ public func test() {
     cv.captureView(v1)
     cv.handOut(&v1)
 }
+
+public func test2(_ x: AggregateView) {
+    let _ = AggregateView(member: x.member)
+}