Sema: Diagnose invalid back deployed declarations. Back deployed declarations must:

- have public visibility
- have at most one back deployment version per-platform
- specify an introduced version for each platform with a back deployment version using @available
- have a back deployment version that is greater than the introduced version
- not have conflicting attributes like @_alwaysEmitIntoClient

Refactor to share code with type checking for @_originallyDefinedIn which has overlapping diagnostics.

Author: tshortli

include/swift/AST/DiagnosticsSema.def

@@ -1599,26 +1599,12 @@ WARNING(option_set_zero_constant,none,
 NOTE(option_set_empty_set_init,none,
      "use [] to silence this warning", ())
 
-// FIXME(backDeploy): Refactor to share with back deployment attr
-ERROR(originally_defined_in_dupe_platform,none,
-      "duplicate version number for platform %0", (StringRef))
-
 ERROR(originally_definedin_topleve_decl,none,
       "@%0 is only applicable to top-level decl", (StringRef))
 
-// FIXME(backDeploy): Refactor to share with back deployment attr
-ERROR(originally_definedin_need_available,none,
-      "need @available attribute for @%0", (StringRef))
-
 ERROR(originally_definedin_must_not_before_available_version,none,
       "symbols are moved to the current module before they were available in the OSs", (StringRef))
 
-// FIXME(backDeploy): Refactor to share with back deployment attr
-WARNING(originally_defined_in_on_non_public,
-       none, "@%0 does not have any effect on "
-       "%select{private|fileprivate|internal|%error|%error}1 declarations",
-       (StringRef, AccessLevel))
-
 // Alignment attribute
 ERROR(alignment_not_power_of_two,none,
       "alignment value must be a power of two", ())
@@ -3140,9 +3126,25 @@ ERROR(attr_not_on_variadic_parameters,none,
 ERROR(attr_not_on_subscript_parameters,none,
       "'%0' must not be used on subscript parameters", (StringRef))
 
+WARNING(attr_has_no_effect_on_decl_with_access_level,none,
+       "'%0' does not have any effect on "
+       "%select{private|fileprivate|internal|%error|%error}1 declarations",
+       (DeclAttribute, AccessLevel))
+ERROR(attr_not_on_decl_with_invalid_access_level,none,
+      "'%0' may not be used on "
+      "%select{private|fileprivate|internal|%error|%error}1 declarations",
+      (DeclAttribute, AccessLevel))
+
+ERROR(attr_has_no_effect_decl_not_available_before,none,
+      "'%0' has no effect because %1 is not available before %2 %3",
+      (DeclAttribute, DeclName, StringRef, llvm::VersionTuple))
+
 ERROR(attr_ambiguous_reference_to_decl,none,
       "ambiguous reference to %0 in '@%1' attribute", (DeclNameRef, StringRef))
 
+ERROR(attr_contains_multiple_versions_for_platform,none,
+      "'%0' contains multiple versions for %1", (DeclAttribute, StringRef))
+
 ERROR(override_final,none,
       "%0 overrides a 'final' %1", (DescriptiveDeclKind, DescriptiveDeclKind))
 
@@ -5614,6 +5616,14 @@ ERROR(availability_macro_in_inlinable, none,
       "availability macro cannot be used in inlinable %0",
       (DescriptiveDeclKind))
 
+ERROR(attr_requires_decl_availability_for_platform,none,
+      "'%0' requires that %1 have explicit availability for %2",
+      (DeclAttribute, DeclName, StringRef))
+
+ERROR(attr_requires_availability_for_platform,none,
+      "'%0' requires explicit availability for %1",
+      (DeclAttribute, StringRef))
+
 // This doesn't display as an availability diagnostic, but it's
 // implemented there and fires when these subscripts are marked
 // unavailable, so it seems appropriate to put it here.
@@ -6163,6 +6173,10 @@ ERROR(differentiable_programming_attr_used_without_required_module, none,
       "'@%0' attribute used without importing module %1",
       (StringRef, Identifier))
 
+//------------------------------------------------------------------------------
+// MARK: OSLog
+//------------------------------------------------------------------------------
+
 ERROR(oslog_arg_must_be_bool_literal, none,
       "argument must be a bool literal", ())
 ERROR(oslog_arg_must_be_integer_literal, none,
@@ -6270,5 +6284,12 @@ ERROR(cannot_convert_default_value_type_to_argument_type, none,
       "cannot convert default value of type %0 to expected argument type %1 for parameter #%2",
       (Type, Type, unsigned))
 
+//------------------------------------------------------------------------------
+// MARK: Back deployment
+//------------------------------------------------------------------------------
+
+ERROR(attr_incompatible_with_back_deploy,none,
+      "'%0' cannot be applied to back deployed declarations", (DeclAttribute))
+
 #define UNDEFINE_DIAGNOSTIC_MACROS
 #include "DefineDiagnosticMacros.h"

lib/Sema/TypeCheckAttr.cpp

@@ -66,6 +66,45 @@ class AttributeChecker : public AttributeVisitor<AttributeChecker> {
                                         std::forward<ArgTypes>(Args)...);
   }
 
+  /// Emits a diagnostic with a fixit to remove the attribute if the attribute
+  /// is applied to a non-public declaration. Returns true if a diagnostic was
+  /// emitted.
+  bool diagnoseAndRemoveAttrIfDeclIsNonPublic(DeclAttribute *attr,
+                                              bool isError) {
+    if (auto *VD = dyn_cast<ValueDecl>(D)) {
+      auto access =
+          VD->getFormalAccessScope(/*useDC=*/nullptr,
+                                   /*treatUsableFromInlineAsPublic=*/true);
+      if (!access.isPublic()) {
+        diagnoseAndRemoveAttr(
+            attr,
+            isError ? diag::attr_not_on_decl_with_invalid_access_level
+                    : diag::attr_has_no_effect_on_decl_with_access_level,
+            attr, VD->getFormalAccess());
+        return true;
+      }
+    }
+    return false;
+  }
+
+  /// Emits a diagnostic if there is no availability specified for the given
+  /// platform, as required by the given attribute. Returns true if a diagnostic
+  /// was emitted.
+  bool diagnoseMissingAvailability(DeclAttribute *attr, PlatformKind platform) {
+    auto IntroVer = D->getIntroducedOSVersion(platform);
+    if (IntroVer.hasValue())
+      return false;
+
+    if (auto *VD = dyn_cast<ValueDecl>(D)) {
+      diagnose(attr->AtLoc, diag::attr_requires_decl_availability_for_platform,
+               attr, VD->getName(), prettyPlatformString(platform));
+    } else {
+      diagnose(attr->AtLoc, diag::attr_requires_availability_for_platform, attr,
+               prettyPlatformString(platform));
+    }
+    return true;
+  }
+
   template <typename... ArgTypes>
   InFlightDiagnostic diagnose(ArgTypes &&... Args) const {
     return Ctx.Diags.diagnose(std::forward<ArgTypes>(Args)...);
@@ -256,7 +295,7 @@ class AttributeChecker : public AttributeVisitor<AttributeChecker> {
 
   void visitImplementationOnlyAttr(ImplementationOnlyAttr *attr);
   void visitNonEphemeralAttr(NonEphemeralAttr *attr);
-  void checkOriginalDefinedInAttrs(Decl *D, ArrayRef<OriginallyDefinedInAttr*> Attrs);
+  void checkOriginalDefinedInAttrs(ArrayRef<OriginallyDefinedInAttr *> Attrs);
 
   void visitDifferentiableAttr(DifferentiableAttr *attr);
   void visitDerivativeAttr(DerivativeAttr *attr);
@@ -279,7 +318,7 @@ class AttributeChecker : public AttributeVisitor<AttributeChecker> {
 
   void visitPrimaryAssociatedTypeAttr(PrimaryAssociatedTypeAttr *attr);
 
-  void checkBackDeployAttrs(Decl *D, ArrayRef<BackDeployAttr *> Attrs);
+  void checkBackDeployAttrs(ArrayRef<BackDeployAttr *> Attrs);
 };
 
 } // end anonymous namespace
@@ -1268,8 +1307,9 @@ void TypeChecker::checkDeclAttributes(Decl *D) {
     TypeChecker::applyAccessNote(VD);
 
   AttributeChecker Checker(D);
-  // We need to check all OriginallyDefinedInAttr relative to each other, so
-  // collect them and check in batch later.
+  // We need to check all OriginallyDefinedInAttr and BackDeployAttr relative
+  // to each other, so collect them and check in batch later.
+  llvm::SmallVector<BackDeployAttr *, 4> backDeployAttrs;
   llvm::SmallVector<OriginallyDefinedInAttr*, 4> ODIAttrs;
   for (auto attr : D->getAttrs()) {
     if (!attr->isValid()) continue;
@@ -1279,6 +1319,8 @@ void TypeChecker::checkDeclAttributes(Decl *D) {
     if (attr->canAppearOnDecl(D)) {
       if (auto *ODI = dyn_cast<OriginallyDefinedInAttr>(attr)) {
         ODIAttrs.push_back(ODI);
+      } else if (auto *BD = dyn_cast<BackDeployAttr>(attr)) {
+        backDeployAttrs.push_back(BD);
       } else {
         // Otherwise, check it.
         Checker.visit(attr);
@@ -1319,7 +1361,8 @@ void TypeChecker::checkDeclAttributes(Decl *D) {
     else
       Checker.diagnoseAndRemoveAttr(attr, diag::invalid_decl_attribute, attr);
   }
-  Checker.checkOriginalDefinedInAttrs(D, ODIAttrs);
+  Checker.checkBackDeployAttrs(backDeployAttrs);
+  Checker.checkOriginalDefinedInAttrs(ODIAttrs);
 }
 
 /// Returns true if the given method is an valid implementation of a
@@ -3409,8 +3452,8 @@ void AttributeChecker::visitNonEphemeralAttr(NonEphemeralAttr *attr) {
   attr->setInvalid();
 }
 
-void AttributeChecker::checkOriginalDefinedInAttrs(Decl *D,
-    ArrayRef<OriginallyDefinedInAttr*> Attrs) {
+void AttributeChecker::checkOriginalDefinedInAttrs(
+    ArrayRef<OriginallyDefinedInAttr *> Attrs) {
   if (Attrs.empty())
     return;
   auto &Ctx = D->getASTContext();
@@ -3421,20 +3464,9 @@ void AttributeChecker::checkOriginalDefinedInAttrs(Decl *D,
   for (auto *Attr: Attrs) {
     static StringRef AttrName = "_originallyDefinedIn";
 
-    if (auto *VD = dyn_cast<ValueDecl>(D)) {
-      // This attribute does not make sense on private declarations since
-      // clients can't use them.
-      auto access =
-        VD->getFormalAccessScope(/*useDC=*/nullptr,
-                                 /*treatUsableFromInlineAsPublic=*/true);
-      if (!access.isPublic()) {
-        diagnoseAndRemoveAttr(Attr,
-                              diag::originally_defined_in_on_non_public,
-                              AttrName, VD->getFormalAccess());
-        continue;
-      }
-    }
-    
+    if (diagnoseAndRemoveAttrIfDeclIsNonPublic(Attr, /*isError=*/false))
+      continue;
+
     if (!Attr->isActivePlatform(Ctx))
       continue;
     auto AtLoc = Attr->AtLoc;
@@ -3443,20 +3475,19 @@ void AttributeChecker::checkOriginalDefinedInAttrs(Decl *D,
       // We've seen the platform before, emit error to the previous one which
       // comes later in the source order.
       diagnose(seenPlatforms[Platform],
-               diag::originally_defined_in_dupe_platform,
+               diag::attr_contains_multiple_versions_for_platform, Attr,
                platformString(Platform));
       return;
     }
     if (!D->getDeclContext()->isModuleScopeContext()) {
       diagnose(AtLoc, diag::originally_definedin_topleve_decl, AttrName);
       return;
     }
-    auto IntroVer = D->getIntroducedOSVersion(Platform);
-    if (!IntroVer.hasValue()) {
-      diagnose(AtLoc, diag::originally_definedin_need_available,
-               AttrName);
+
+    if (diagnoseMissingAvailability(Attr, Platform))
       return;
-    }
+
+    auto IntroVer = D->getIntroducedOSVersion(Platform);
     if (IntroVer.getValue() > Attr->MovedVersion) {
       diagnose(AtLoc,
                diag::originally_definedin_must_not_before_available_version,
@@ -3466,9 +3497,64 @@ void AttributeChecker::checkOriginalDefinedInAttrs(Decl *D,
   }
 }
 
-void AttributeChecker::checkBackDeployAttrs(Decl *D,
-    ArrayRef<BackDeployAttr *> Attrs) {
-  // FIXME(backDeploy): Diagnose incompatible uses of `@_backDeploy
+void AttributeChecker::checkBackDeployAttrs(ArrayRef<BackDeployAttr *> Attrs) {
+  if (Attrs.empty())
+    return;
+
+  // Diagnose conflicting attributes. @_alwaysEmitIntoClient, @inlinable, and
+  // @_transparent all conflict with back deployment because they each cause the
+  // body of a function to be copied into the client under certain conditions
+  // and would defeat the goal of back deployment, which is to always use the
+  // ABI version of the declaration when it is available.
+  if (auto *AEICA = D->getAttrs().getAttribute<AlwaysEmitIntoClientAttr>()) {
+    diagnoseAndRemoveAttr(AEICA, diag::attr_incompatible_with_back_deploy,
+                          AEICA);
+  }
+
+  if (auto *IA = D->getAttrs().getAttribute<InlinableAttr>()) {
+    diagnoseAndRemoveAttr(IA, diag::attr_incompatible_with_back_deploy, IA);
+  }
+
+  if (auto *TA = D->getAttrs().getAttribute<TransparentAttr>()) {
+    diagnoseAndRemoveAttr(TA, diag::attr_incompatible_with_back_deploy, TA);
+  }
+
+  std::map<PlatformKind, SourceLoc> seenPlatforms;
+
+  for (auto *Attr : Attrs) {
+    // Back deployment only makes sense for public declarations.
+    if (diagnoseAndRemoveAttrIfDeclIsNonPublic(Attr, /*isError=*/true))
+      continue;
+
+    auto AtLoc = Attr->AtLoc;
+    auto Platform = Attr->Platform;
+
+    if (!seenPlatforms.insert({Platform, AtLoc}).second) {
+      // We've seen the platform before, emit error to the previous one which
+      // comes later in the source order.
+      diagnose(seenPlatforms[Platform],
+               diag::attr_contains_multiple_versions_for_platform, Attr,
+               platformString(Platform));
+      continue;
+    }
+
+    // Require explicit availability for back deployed decls.
+    if (diagnoseMissingAvailability(Attr, Platform))
+      continue;
+
+    // Verify that the decl is available before the back deployment boundary.
+    // If it's not, the attribute doesn't make sense since the back deployment
+    // fallback could never be executed at runtime.
+    auto IntroVer = D->getIntroducedOSVersion(Platform);
+    if (Attr->Version <= IntroVer.getValue()) {
+      // Only functions, methods, computed properties, and subscripts are
+      // back-deployable.
+      auto *VD = cast<ValueDecl>(D);
+      diagnose(AtLoc, diag::attr_has_no_effect_decl_not_available_before, Attr,
+               VD->getName(), prettyPlatformString(Platform), Attr->Version);
+      continue;
+    }
+  }
 }
 
 Type TypeChecker::checkReferenceOwnershipAttr(VarDecl *var, Type type,

test/ModuleInterface/back-deploy-attr.swift

@@ -25,7 +25,7 @@ public struct TopLevelStruct {
   // CHECK: @_backDeploy(iOS 15.0)
   // FROMSOURCE: public func backDeployedFunc2_MultiPlatform() -> Swift.Int { return 43 }
   // FROMMODULE: public func backDeployedFunc2_MultiPlatform() -> Swift.Int
-  @available(macOS 11.0, *)
+  @available(macOS 11.0, iOS 14.0, *)
   @_backDeploy(macOS 12.0, iOS 15.0)
   public func backDeployedFunc2_MultiPlatform() -> Int { return 43 }
 }

test/Parse/original_defined_in_attr.swift

@@ -1,13 +1,13 @@
 // RUN: %target-typecheck-verify-swift
 // REQUIRES: OS=macosx
 
-@_originallyDefinedIn(module: "foo", OSX 13.13) // expected-error {{need @available attribute for @_originallyDefinedIn}}
+@_originallyDefinedIn(module: "foo", OSX 13.13) // expected-error {{'@_originallyDefinedIn' requires that 'foo()' have explicit availability for macOS}}
 public func foo() {}
 
 @_originallyDefinedIn(modulename: "foo", OSX 13.13) // expected-error {{expected 'module: "original"' in the first argument to @_originallyDefinedIn}}
 public func foo1() {}
 
-@_originallyDefinedIn(module: "foo", OSX 13.13.3) // expected-warning {{@_originallyDefinedIn only uses major and minor version number}} expected-error {{need @available attribute for @_originallyDefinedIn}}
+@_originallyDefinedIn(module: "foo", OSX 13.13.3) // expected-warning {{@_originallyDefinedIn only uses major and minor version number}} expected-error {{'@_originallyDefinedIn' requires that 'ToplevelClass' have explicit availability for macOS}}
 public class ToplevelClass {}
 
 @_originallyDefinedIn(module: "foo") // expected-error {{expected at least one platform version in @_originallyDefinedIn}}
@@ -22,7 +22,7 @@ public class ToplevelClass3 {}
 @available(OSX 13.10, *)
 @_originallyDefinedIn(module: "foo", * 13.13) // expected-warning {{* as platform name has no effect}} expected-error {{expected at least one platform version in @_originallyDefinedIn}}
 @_originallyDefinedIn(module: "foo", OSX 13.13, iOS 7.0)
-@_originallyDefinedIn(module: "foo", OSX 13.14, * 7.0) // expected-warning {{* as platform name has no effect}} expected-error {{duplicate version number for platform macOS}}
+@_originallyDefinedIn(module: "foo", OSX 13.14, * 7.0) // expected-warning {{* as platform name has no effect}} expected-error {{'@_originallyDefinedIn' contains multiple versions for macOS}}
 public class ToplevelClass4 {
 	@_originallyDefinedIn(module: "foo", OSX 13.13) // expected-error {{'@_originallyDefinedIn' attribute cannot be applied to this declaration}}
 	subscript(index: Int) -> Int {
@@ -32,16 +32,16 @@ public class ToplevelClass4 {
 }
 
 @available(OSX 13.10, *)
-@_originallyDefinedIn(module: "foo", OSX 13.13) // expected-warning {{@_originallyDefinedIn does not have any effect on internal declarations}}
-@_originallyDefinedIn(module: "foo", iOS 7.0) // expected-warning {{@_originallyDefinedIn does not have any effect on internal declarations}}
+@_originallyDefinedIn(module: "foo", OSX 13.13) // expected-warning {{'@_originallyDefinedIn' does not have any effect on internal declarations}}
+@_originallyDefinedIn(module: "foo", iOS 7.0) // expected-warning {{'@_originallyDefinedIn' does not have any effect on internal declarations}}
 internal class ToplevelClass5 {}
 
 @available(OSX 13.10, *)
-@_originallyDefinedIn(module: "foo", OSX 13.13) // expected-warning {{@_originallyDefinedIn does not have any effect on private declarations}}
-@_originallyDefinedIn(module: "foo", iOS 7.0) // expected-warning {{@_originallyDefinedIn does not have any effect on private declarations}}
+@_originallyDefinedIn(module: "foo", OSX 13.13) // expected-warning {{'@_originallyDefinedIn' does not have any effect on private declarations}}
+@_originallyDefinedIn(module: "foo", iOS 7.0) // expected-warning {{'@_originallyDefinedIn' does not have any effect on private declarations}}
 private class ToplevelClass6 {}
 
 @available(OSX 13.10, *)
-@_originallyDefinedIn(module: "foo", OSX 13.13) // expected-warning {{@_originallyDefinedIn does not have any effect on fileprivate declarations}}
-@_originallyDefinedIn(module: "foo", iOS 7.0) // expected-warning {{@_originallyDefinedIn does not have any effect on fileprivate declarations}}
+@_originallyDefinedIn(module: "foo", OSX 13.13) // expected-warning {{'@_originallyDefinedIn' does not have any effect on fileprivate declarations}}
+@_originallyDefinedIn(module: "foo", iOS 7.0) // expected-warning {{'@_originallyDefinedIn' does not have any effect on fileprivate declarations}}
 fileprivate class ToplevelClass7 {}

test/Sema/diag_originally_definedin.swift

@@ -2,7 +2,7 @@
 // RUN:   -define-availability "_myProject 1.0:macOS 10.10"
 // REQUIRES: OS=macosx
 
-@_originallyDefinedIn(module: "original", OSX 10.13) // expected-error {{need @available attribute for @_originallyDefinedIn}}
+@_originallyDefinedIn(module: "original", OSX 10.13) // expected-error {{'@_originallyDefinedIn' requires that 'foo()' have explicit availability for macOS}}
 public func foo() {}
 
 @available(macOS 10.13, *)