Merge pull request #82922 from xedin/nonexhaustive-enums-6.2

[6.2][AST/Sema] SE-0487: Implement `@nonexhaustive` attribute and new enum exhaustivity checking rule

Author: xedin

include/swift/AST/Attr.h

@@ -244,6 +244,10 @@ class DeclAttribute : public AttributeBase {
     SWIFT_INLINE_BITFIELD(LifetimeAttr, DeclAttribute, 1,
       isUnderscored : 1
     );
+
+    SWIFT_INLINE_BITFIELD(NonexhaustiveAttr, DeclAttribute, NumNonexhaustiveModeBits,
+      mode : NumNonexhaustiveModeBits
+    );
   } Bits;
   // clang-format on
 
@@ -3334,6 +3338,35 @@ class ABIAttr : public DeclAttribute {
   }
 };
 
+/// Defines a @nonexhaustive attribute.
+class NonexhaustiveAttr : public DeclAttribute {
+public:
+  NonexhaustiveAttr(SourceLoc atLoc, SourceRange range, NonexhaustiveMode mode,
+                    bool implicit = false)
+      : DeclAttribute(DeclAttrKind::Nonexhaustive, atLoc, range, implicit) {
+    Bits.NonexhaustiveAttr.mode = unsigned(mode);
+  }
+
+  NonexhaustiveAttr(NonexhaustiveMode mode)
+    : NonexhaustiveAttr(SourceLoc(), SourceRange(), mode) {}
+
+  NonexhaustiveMode getMode() const {
+    return NonexhaustiveMode(Bits.NonexhaustiveAttr.mode);
+  }
+
+  static bool classof(const DeclAttribute *DA) {
+    return DA->getKind() == DeclAttrKind::Nonexhaustive;
+  }
+
+  NonexhaustiveAttr *clone(ASTContext &ctx) const {
+    return new (ctx) NonexhaustiveAttr(AtLoc, Range, getMode(), isImplicit());
+  }
+
+  bool isEquivalent(const NonexhaustiveAttr *other, Decl *attachedTo) const {
+    return getMode() == other->getMode();
+  }
+};
+
 /// Attributes that may be applied to declarations.
 class DeclAttributes {
   /// Linked list of declaration attributes.

include/swift/AST/AttrKind.h

@@ -158,6 +158,17 @@ enum : unsigned {
       InheritActorContextModifier::Last_InheritActorContextKind))
 };
 
+enum class NonexhaustiveMode : uint8_t {
+  Error = 0,
+  Warning,
+  Last_NonexhaustiveMode = Warning
+};
+
+enum : unsigned {
+  NumNonexhaustiveModeBits = countBitsUsed(static_cast<unsigned>(
+      NonexhaustiveMode::Last_NonexhaustiveMode))
+};
+
 enum class DeclAttrKind : unsigned {
 #define DECL_ATTR(_, CLASS, ...) CLASS,
 #define LAST_DECL_ATTR(CLASS) Last_DeclAttr = CLASS,

include/swift/AST/Decl.h

@@ -751,7 +751,7 @@ class alignas(1 << DeclAlignInBits) Decl : public ASTAllocated<Decl>, public Swi
     HasAnyUnavailableDuringLoweringValues : 1
   );
 
-  SWIFT_INLINE_BITFIELD(ModuleDecl, TypeDecl, 1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+8,
+  SWIFT_INLINE_BITFIELD(ModuleDecl, TypeDecl, 1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+8,
     /// If the module is compiled as static library.
     StaticLibrary : 1,
 
@@ -820,10 +820,7 @@ class alignas(1 << DeclAlignInBits) Decl : public ASTAllocated<Decl>, public Swi
     SerializePackageEnabled : 1,
 
     /// Whether this module has enabled strict memory safety checking.
-    StrictMemorySafety : 1,
-
-    /// Whether this module has enabled `ExtensibleEnums` feature.
-    ExtensibleEnums : 1
+    StrictMemorySafety : 1
   );
 
   SWIFT_INLINE_BITFIELD(PrecedenceGroupDecl, Decl, 1+2,

include/swift/AST/DeclAttr.def

@@ -876,11 +876,19 @@ SIMPLE_DECL_ATTR(constInitialized, ConstInitialized,
   168)
 DECL_ATTR_FEATURE_REQUIREMENT(ConstInitialized, CompileTimeValues)
 
+DECL_ATTR(nonexhaustive, Nonexhaustive,
+  OnEnum,
+  ABIStableToAdd | ABIStableToRemove | APIBreakingToAdd | APIStableToRemove | ForbiddenInABIAttr,
+  169)
+DECL_ATTR_FEATURE_REQUIREMENT(Nonexhaustive, NonexhaustiveAttribute)
+
 SIMPLE_DECL_ATTR(concurrent, Concurrent,
   OnFunc | OnConstructor | OnSubscript | OnVar,
   ABIBreakingToAdd | ABIBreakingToRemove | APIBreakingToAdd | APIBreakingToRemove | UnconstrainedInABIAttr,
   170)
 
+// Unused '171': Used to be `@preEnumExtensibility`
+
 LAST_DECL_ATTR(Concurrent)
 
 #undef DECL_ATTR_ALIAS

include/swift/AST/DiagnosticsSema.def

@@ -8714,6 +8714,19 @@ GROUPED_WARNING(
     "behavior",
     (StringRef))
 
+//===----------------------------------------------------------------------===//
+// MARK: @nonexhaustive and @preEnumExtensibility Attributes
+//===----------------------------------------------------------------------===//
+
+ERROR(nonexhaustive_attr_on_frozen_type,none,
+      "cannot use '@nonexhaustive' together with '@frozen'", ())
+
+ERROR(nonexhaustive_attr_on_internal_type,none,
+      "'@nonexhaustive' attribute can only be applied to public or package "
+      "declarations, but %0 is "
+      "%select{private|fileprivate|internal|%error|%error|%error}1",
+      (DeclName, AccessLevel))
+
 //===----------------------------------------------------------------------===//
 // MARK: `using` declaration
 //===----------------------------------------------------------------------===//

include/swift/AST/KnownIdentifiers.def

@@ -169,6 +169,7 @@ IDENTIFIER(value)
 IDENTIFIER_WITH_NAME(value_, "_value")
 IDENTIFIER(Void)
 IDENTIFIER(WinSDK)
+IDENTIFIER(warn)
 IDENTIFIER(with)
 IDENTIFIER(withArguments)
 IDENTIFIER(withKeywordArguments)

include/swift/AST/Module.h

@@ -835,14 +835,6 @@ class ModuleDecl
     Bits.ModuleDecl.ObjCNameLookupCachePopulated = value;
   }
 
-  bool supportsExtensibleEnums() const {
-    return Bits.ModuleDecl.ExtensibleEnums;
-  }
-
-  void setSupportsExtensibleEnums(bool value = true) {
-    Bits.ModuleDecl.ExtensibleEnums = value;
-  }
-
   /// For the main module, retrieves the list of primary source files being
   /// compiled, that is, the files we're generating code for.
   ArrayRef<SourceFile *> getPrimarySourceFiles() const;

include/swift/Basic/Features.def

@@ -268,6 +268,7 @@ LANGUAGE_FEATURE(BuiltinSelect, 0, "Builtin.select")
 LANGUAGE_FEATURE(AlwaysInheritActorContext, 472, "@_inheritActorContext(always)")
 LANGUAGE_FEATURE(NonescapableAccessorOnTrivial, 0, "Support UnsafeMutablePointer.mutableSpan")
 LANGUAGE_FEATURE(InlineArrayTypeSugar, 483, "Type sugar for InlineArray")
+SUPPRESSIBLE_LANGUAGE_FEATURE(NonexhaustiveAttribute, 487, "Nonexhaustive Enums")
 
 // Swift 6
 UPCOMING_FEATURE(ConciseMagicFile, 274, 6)
@@ -505,11 +506,6 @@ SUPPRESSIBLE_EXPERIMENTAL_FEATURE(AddressableTypes, true)
 /// Allow custom availability domains to be defined and referenced.
 EXPERIMENTAL_FEATURE(CustomAvailability, true)
 
-/// Allow public enumerations to be extensible by default
-/// regardless of whether the module they are declared in
-/// is resilient or not.
-EXPERIMENTAL_FEATURE(ExtensibleEnums, true)
-
 /// Syntax sugar features for concurrency.
 EXPERIMENTAL_FEATURE(ConcurrencySyntaxSugar, true)
 

include/swift/Parse/IDEInspectionCallbacks.h

@@ -40,7 +40,8 @@ enum class ParameterizedDeclAttributeKind {
   FreestandingMacro,
   AttachedMacro,
   StorageRestrictions,
-  InheritActorContext
+  InheritActorContext,
+  Nonexhaustive,
 };
 
 /// A bit of a hack. When completing inside the '@storageRestrictions'

include/swift/Serialization/Validation.h

@@ -150,7 +150,6 @@ class ExtendedValidationInfo {
     unsigned AllowNonResilientAccess: 1;
     unsigned SerializePackageEnabled: 1;
     unsigned StrictMemorySafety: 1;
-    unsigned SupportsExtensibleEnums : 1;
   } Bits;
 
 public:
@@ -272,11 +271,6 @@ class ExtendedValidationInfo {
             version, SourceLoc(), /*Diags=*/nullptr))
       SwiftInterfaceCompilerVersion = genericVersion.value();
   }
-
-  bool supportsExtensibleEnums() const { return Bits.SupportsExtensibleEnums; }
-  void setSupportsExtensibleEnums(bool val) {
-    Bits.SupportsExtensibleEnums = val;
-  }
 };
 
 struct SearchPath {