Type check @abi for compatibility

This commit compares the decl inside the `@abi` attribute to the decl it’s attached to, diagnosing ABI-incompatible differences or attributes that don’t need to be specified.

It includes logic which ensures that some of the fundamental properties of a declaration, such as its availability, access control, and @objc-ness, are shared between an ABI-only declaration and its counterpart. (Specifically, the ABI-only declaration delegates the computation to its counterpart.) This allows these attributes to be omitted from the `@abi` attribute instead of forcing developers to repeat themselves.

Author: beccadax

include/swift/AST/Attr.h

@@ -1050,6 +1050,10 @@ class alignas(1 << DeclAlignInBits) Decl : public ASTAllocated<Decl>, public Swi
   /// from source code.
   void attachParsedAttrs(DeclAttributes attrs);
 
+  /// Retrieve the custom name in the \c @objc attribute, if present.
+  std::optional<ObjCSelector>
+  getExplicitObjCName(bool allowInvalid = false) const;
+
   /// True if this declaration provides an implementation for an imported
   /// Objective-C declaration. This implies various restrictions and special
   /// behaviors for it and, if it's an extension, its members.

include/swift/AST/Decl.h

@@ -8276,16 +8276,16 @@ ERROR(attr_abi_mismatched_kind,none,
 
 ERROR(attr_abi_mismatched_arity,none,
       "cannot give %kind0 the ABI of a %kindonly0 with a different number of "
-      "low-level parameters",
-      (ValueDecl *))
+      "%select{|generic }1parameters",
+      (Decl *, /*genericParams=*/bool))
 
 ERROR(attr_abi_mismatched_throws,none,
       "cannot give %0 the ABI of a %kindonly0 which %select{cannot|can}1 throw",
-      (ValueDecl *, /*abiCanThrow=*/bool))
+      (Decl *, /*abiCanThrow=*/bool))
 
 ERROR(attr_abi_mismatched_async,none,
       "cannot give %0 the ABI of %select{a non-async|an async}1 %kindonly0",
-      (ValueDecl *, /*abiIsAsync=*/bool))
+      (Decl *, /*abiIsAsync=*/bool))
 
 ERROR(attr_abi_mismatched_pbd_size,none,
       "cannot give pattern binding the ABI of a binding with "
@@ -8294,13 +8294,86 @@ ERROR(attr_abi_mismatched_pbd_size,none,
 
 ERROR(attr_abi_mismatched_var,none,
       "no match for %select{%kind0 in the ABI|ABI %kind0}1",
-      (ValueDecl *, /*isABI=*/bool))
+      (Decl *, /*isABI=*/bool))
 
 ERROR(attr_abi_incompatible_with_silgen_name,none,
       "cannot use '@_silgen_name' and '@abi' on the same %0 because they serve "
       "the same purpose",
       (DescriptiveDeclKind))
 
+ERROR(attr_abi_missing_attr,none,
+      "missing '%0' %select{attribute|modifier}1 in '@abi'",
+      (StringRef, bool))
+ERROR(attr_abi_extra_attr,none,
+      "extra %select{|implicit }2'%0' %select{attribute|modifier}1 in '@abi'",
+      (StringRef, bool, /*isImplicit=*/bool))
+ERROR(attr_abi_forbidden_attr,none,
+      "unused '%0' %select{attribute|modifier}1 in '@abi'",
+      (StringRef, bool))
+REMARK(abi_attr_inferred_attribute,none,
+       "inferred '%0' in '@abi' to match %select{attribute|modifier}1 on API",
+       (StringRef, bool))
+
+ERROR(attr_abi_mismatched_attr,none,
+      "'%0' %select{attribute|modifier}1 in '@abi' should match '%2'",
+      (StringRef, bool, StringRef))
+NOTE(attr_abi_matching_attr_here,none,
+     "%select{should match|matches}0 %select{attribute|modifier}1 "
+     "%select{|implicitly added }2here",
+     (/*matches=*/bool, /*isModifier=*/bool, /*isImplicit=*/bool))
+
+ERROR(attr_abi_mismatched_type,none,
+      "type %0 in '@abi' should match %1",
+      (Type, Type))
+NOTE(attr_abi_should_match_type_here,none,
+     "should match type here", ())
+
+ERROR(attr_abi_mismatched_generic_signature,none,
+      "generic signature '%0' in '@abi' is not compatible with '%1'",
+      (StringRef, StringRef))
+ERROR(attr_abi_missing_generic_signature,none,
+      "declaration in '@abi' should have generic signature compatible with "
+      "'%0'",
+      (StringRef))
+ERROR(attr_abi_extra_generic_signature,none,
+      "declaration in '@abi' should not have generic signature because %0 "
+      "is not generic",
+      (Decl *))
+
+ERROR(attr_abi_mismatched_param_modifier,none,
+      "%select{default |}0%3 %select{attribute|modifier}2 "
+      "%select{|'%0' }0in '@abi' is not compatible with %select{default|'%1'}1",
+      (StringRef, StringRef, /*isModifier=*/bool, DescriptiveDeclKind))
+ERROR(attr_abi_no_default_arguments,none,
+      "%kind0 in '@abi' should not have a default argument; it does not "
+      "affect the parameter's ABI",
+      (Decl *))
+
+// These macros insert 'final', 'non-final', or nothing depending on both the
+// current decl and its counterpart, such that 'non-final' is used if the
+// counterpart would be described as 'final' or 'static'. They must be kept in
+// sync with `StaticnessAndFinality`.
+#define NONFINAL_OR_NOTHING(COUNTERPART) \
+      "%select{||non-final |non-final |non-final |%error}" #COUNTERPART
+#define FINAL_OR_NONFINAL_OR_NOTHING(CURRENT, COUNTERPART, FINAL_OK) \
+      "%select{|%select{" NONFINAL_OR_NOTHING(COUNTERPART) \
+                      "|" NONFINAL_OR_NOTHING(COUNTERPART) \
+                      "|final |final ||%error}" #CURRENT "}" #FINAL_OK
+
+ERROR(attr_abi_static_final_mismatch,none,
+      FINAL_OR_NONFINAL_OR_NOTHING(0, 2, 4) "%kind1 in '@abi' should be "
+      FINAL_OR_NONFINAL_OR_NOTHING(2, 0, 4) "%kindonly3 to ensure ABI "
+      "compatibility",
+      (uint8_t, Decl *, uint8_t, Decl *, /*isClass=*/bool))
+
+#undef NONFINAL_OR_NOTHING
+#undef FINAL_OR_NONFINAL_OR_NOTHING
+
+ERROR(attr_abi_failable_mismatch,none,
+      "cannot give %select{non-failable|failable}1 %kind0 the ABI of a "
+      "%select{non-failable|failable}2 %kindonly0",
+      (Decl *, bool, bool))
+
 //===----------------------------------------------------------------------===//
 // MARK: Isolated conformances
 //===----------------------------------------------------------------------===//

include/swift/AST/DeclAttr.def

@@ -263,6 +263,9 @@ namespace swift {
     /// Emit a remark on early exit in explicit interface build
     bool EnableSkipExplicitInterfaceModuleBuildRemarks = false;
 
+    /// Emit a remark when \c \@abi infers an attribute or modifier.
+    bool EnableABIInferenceRemarks = false;
+
     ///
     /// Support for alternate usage modes
     ///

include/swift/AST/DiagnosticsSema.def

@@ -468,6 +468,10 @@ def remark_module_serialization : Flag<["-"], "Rmodule-serialization">,
   Flags<[FrontendOption, DoesNotAffectIncrementalBuild]>,
   HelpText<"Emit remarks about module serialization">;
 
+def remark_abi_inference : Flag<["-"], "Rabi-inference">,
+  Flags<[FrontendOption, DoesNotAffectIncrementalBuild]>,
+  HelpText<"Emit a remark when an '@abi' attribute adds an attribute or modifier to the ABI declaration based on its presence in the API">;
+
 def emit_tbd : Flag<["-"], "emit-tbd">,
   HelpText<"Emit a TBD file">,
   Flags<[FrontendOption, NoInteractiveOption, SupplementaryOutput]>;

include/swift/Basic/LangOptions.h

@@ -1128,11 +1128,9 @@ getOverriddenSwiftProtocolObjCName(const ValueDecl *decl,
     return std::nullopt;
 
   // If there is an 'objc' attribute with a name, use that name.
-  if (auto objc = proto->getAttrs().getAttribute<ObjCAttr>()) {
-    if (auto name = objc->getName()) {
-      llvm::SmallString<4> buffer;
-      return std::string(name->getString(buffer));
-    }
+  if (auto objcName = proto->getExplicitObjCName()) {
+    llvm::SmallString<4> buffer;
+    return std::string(objcName->getString(buffer));
   }
 
   return std::nullopt;

include/swift/Option/Options.td

@@ -43,6 +43,11 @@ AccessLevel
 AccessLevelRequest::evaluate(Evaluator &evaluator, ValueDecl *D) const {
   assert(!D->hasAccess());
 
+  // ABI decls share the access level of their API decl.
+  auto abiRole = ABIRoleInfo(D);
+  if (!abiRole.providesAPI() && abiRole.getCounterpart())
+    return abiRole.getCounterpart()->getFormalAccess();
+
   // Check if the decl has an explicit access control attribute.
   if (auto *AA = D->getAttrs().getAttribute<AccessControlAttr>())
     return AA->getAccess();
@@ -201,6 +206,12 @@ AccessLevel
 SetterAccessLevelRequest::evaluate(Evaluator &evaluator,
                                    AbstractStorageDecl *ASD) const {
   assert(!ASD->Accessors.getInt().hasValue());
+
+  // ABI decls share the access level of their API decl.
+  auto abiRole = ABIRoleInfo(ASD);
+  if (!abiRole.providesAPI() && abiRole.getCounterpart())
+    return abiRole.getCounterpart()->getSetterFormalAccess();
+
   if (auto *SAA = ASD->getAttrs().getAttribute<SetterAccessAttr>())
     return SAA->getAccess();