Restrict cross-module struct initializers to be delegating

Slava already had most of this in place as a prototype for the
restrictions on what's currently spelled '@_fixed_layout'. Tidy it up
and make it apply all the time across module boundaries.

rdar://problem/34777878

Author: jrose-apple

include/swift/AST/DiagnosticsSema.def

@@ -3674,19 +3674,16 @@ NOTE(resilience_decl_declared_here,
 NOTE(resilience_decl_declared_here_versioned,
      none, "%0 %1 is not '@_versioned' or public", (DescriptiveDeclKind, DeclName))
 
-ERROR(designated_init_in_extension_resilient,none,
-      "initializer declared in an extension of "
-      "non-'@_fixed_layout' type %0 must delegate to another initializer", (Type))
+ERROR(designated_init_in_cross_module_extension,none,
+      "initializer for %0 %1 must use \"self.init(...)\" or \"self = ...\" "
+      "because it is not in module %2",
+      (DescriptiveDeclKind, Type, Identifier))
 
 ERROR(designated_init_inlineable_resilient,none,
-      "initializer for non-'@_fixed_layout' type %0 is "
-      "'%select{@_transparent|@inline(__always)|@_inlineable|%error}1' and must "
-      "delegate to another initializer", (Type, unsigned))
-
-ERROR(class_designated_init_inlineable_resilient,none,
-      "initializer for class %0 is "
-      "'%select{@_transparent|@inline(__always)|@_inlineable|%error}1' and must "
-      "delegate to another initializer", (Type, unsigned))
+      "initializer for %select{non-'@_fixed_layout' struct|class}0 %1 is "
+      "'%select{@_transparent|@inline(__always)|@_inlineable|%error}2' and must "
+      "delegate to another initializer",
+      (bool, Type, /*FragileFunctionKind*/unsigned))
 
 ERROR(inlineable_stored_property,
       none, "'@_inlineable' attribute cannot be applied to stored properties", ())

lib/Sema/ResilienceDiagnostics.cpp

@@ -136,38 +136,47 @@ bool TypeChecker::diagnoseInlineableDeclRef(SourceLoc loc,
 }
 
 void TypeChecker::diagnoseResilientConstructor(ConstructorDecl *ctor) {
-  auto nominalDecl = ctor->getDeclContext()
-    ->getAsNominalTypeOrNominalTypeExtensionContext();
+  const DeclContext *containingContext = ctor->getDeclContext();
+  const NominalTypeDecl *nominalDecl =
+      containingContext->getAsNominalTypeOrNominalTypeExtensionContext();
 
-  // These restrictions only apply to concrete types, and not protocol
-  // extensions.
-  if (isa<ProtocolDecl>(nominalDecl))
+  // These restrictions only apply to structs and classes.
+  if (isa<ProtocolDecl>(nominalDecl) || isa<EnumDecl>(nominalDecl))
     return;
 
-  bool isDelegating =
-      (ctor->getDelegatingOrChainedInitKind(&Diags) ==
-       ConstructorDecl::BodyInitKind::Delegating);
-
-  if (!isDelegating &&
-      !nominalDecl->hasFixedLayout(ctor->getParentModule(),
-                                   ctor->getResilienceExpansion())) {
-    if (ctor->getResilienceExpansion() == ResilienceExpansion::Minimal) {
-      // An @_inlineable designated initializer defined in a resilient type
-      // cannot initialize stored properties directly, and must chain to
-      // another initializer.
-      diagnose(ctor->getLoc(),
-               isa<ClassDecl>(nominalDecl)
-                 ? diag::class_designated_init_inlineable_resilient
-                 : diag::designated_init_inlineable_resilient,
-               nominalDecl->getDeclaredInterfaceType(),
-               getFragileFunctionKind(ctor));
-    } else {
-      // A designated initializer defined on an extension of a resilient
-      // type from a different resilience domain cannot initialize stored
-      // properties directly, and must chain to another initializer.
-      diagnose(ctor->getLoc(),
-               diag::designated_init_in_extension_resilient,
-               nominalDecl->getDeclaredInterfaceType());
-    }
+  if (ctor->getDelegatingOrChainedInitKind(&Diags) ==
+        ConstructorDecl::BodyInitKind::Delegating) {
+    return;
+  }
+
+  // An initializer defined on an extension of a struct from another module
+  // cannot initialize stored properties directly, and must chain to another
+  // initializer.
+  if (isa<ExtensionDecl>(containingContext) &&
+      nominalDecl->getParentModule() != containingContext->getParentModule()) {
+    // Classes already can't have designated initializers in extensions, and
+    // we diagnose this elsewhere.
+    if (isa<ClassDecl>(nominalDecl))
+      return;
+
+    diagnose(ctor->getLoc(),
+             diag::designated_init_in_cross_module_extension,
+             nominalDecl->getDescriptiveKind(),
+             nominalDecl->getDeclaredInterfaceType(),
+             nominalDecl->getParentModule()->getName());
+    return;
+  }
+
+  // Within the module, we're only concerned about inlinable initializers on
+  // non-fixed-layout types.
+  if (ctor->getResilienceExpansion() == ResilienceExpansion::Minimal &&
+      !nominalDecl->hasFixedLayout()) {
+    // An @_inlineable designated initializer defined in a resilient type
+    // cannot initialize stored properties directly, and must chain to
+    // another initializer.
+    diagnose(ctor->getLoc(), diag::designated_init_inlineable_resilient,
+             isa<ClassDecl>(nominalDecl),
+             nominalDecl->getDeclaredInterfaceType(),
+             getFragileFunctionKind(ctor));
   }
 }

test/decl/init/resilience.swift

@@ -6,9 +6,10 @@
 import resilient_struct
 import resilient_protocol
 
-// Point is @_fixed_layout -- this is OK
+// Even though Point is @_fixed_layout this is not allowed.
 extension Point {
   init(xx: Int, yy: Int) {
+  // expected-error@-1 {{initializer for struct 'Point' must use "self.init(...)" or "self = ..." because it is not in module 'resilient_struct'}}
     self.x = xx
     self.y = yy
   }
@@ -17,7 +18,7 @@ extension Point {
 // Size is not @_fixed_layout, so we cannot define a new designated initializer
 extension Size {
   init(ww: Int, hh: Int) {
-  // expected-error@-1 {{initializer declared in an extension of non-'@_fixed_layout' type 'Size' must delegate to another initializer}}
+  // expected-error@-1 {{initializer for struct 'Size' must use "self.init(...)" or "self = ..." because it is not in module 'resilient_struct'}}
     self.w = ww
     self.h = hh
   }
@@ -30,7 +31,7 @@ extension Size {
   // FIXME: This should be allowed, but Sema doesn't distinguish this
   // case from memberwise initialization, and DI explodes the value type
   init(other: Size) {
-  // expected-error@-1 {{initializer declared in an extension of non-'@_fixed_layout' type 'Size' must delegate to another initializer}}
+  // expected-error@-1 {{initializer for struct 'Size' must use "self.init(...)" or "self = ..." because it is not in module 'resilient_struct'}}
     self = other
   }
 }
@@ -41,17 +42,17 @@ public struct Animal {
   public let name: String
 
   @_inlineable public init(name: String) {
-  // expected-error@-1 {{initializer for non-'@_fixed_layout' type 'Animal' is '@_inlineable' and must delegate to another initializer}}
+  // expected-error@-1 {{initializer for non-'@_fixed_layout' struct 'Animal' is '@_inlineable' and must delegate to another initializer}}
     self.name = name
   }
 
   @inline(__always) public init(dog: String) {
-  // expected-error@-1 {{initializer for non-'@_fixed_layout' type 'Animal' is '@inline(__always)' and must delegate to another initializer}}
+  // expected-error@-1 {{initializer for non-'@_fixed_layout' struct 'Animal' is '@inline(__always)' and must delegate to another initializer}}
     self.name = dog
   }
 
   @_transparent public init(cat: String) {
-  // expected-error@-1 {{initializer for non-'@_fixed_layout' type 'Animal' is '@_transparent' and must delegate to another initializer}}
+  // expected-error@-1 {{initializer for non-'@_fixed_layout' struct 'Animal' is '@_transparent' and must delegate to another initializer}}
     self.name = cat
   }
 
@@ -63,7 +64,7 @@ public struct Animal {
   // FIXME: This should be allowed, but Sema doesn't distinguish this
   // case from memberwise initialization, and DI explodes the value type
   @_inlineable public init(other: Animal) {
-  // expected-error@-1 {{initializer for non-'@_fixed_layout' type 'Animal' is '@_inlineable' and must delegate to another initializer}}
+  // expected-error@-1 {{initializer for non-'@_fixed_layout' struct 'Animal' is '@_inlineable' and must delegate to another initializer}}
     self = other
   }
 }