Refactor and expand @objcImpl checking

Create a checker for @_objcImplementation member implementations that considers all of a class’s interface and implementation decls at once. This allows us to handle several things better:

• Unimplemented requirements are now diagnosed

• Header members that can match several implementations, or implementations that could match several header members, are now diagnosed

• Tailored diagnostic when the implementation's Swift name matches the header's selector instead of its Swift name

• Recommends inserting `@objc(<selector>)` when a Swift name matches but the implicit ObjC name doesn't

• An `@objc(<selector>)` on one implementation can eliminate its requirement from being considered for other implementations, resolving ambiguities

This does unfortunately regress the diagnostics when a requirement is implemented in the wrong extension. Some sort of whole-module checking would be needed to address this problem.

Author: beccadax

include/swift/AST/DiagnosticsSema.def

@@ -1610,6 +1610,33 @@ ERROR(objc_implementation_wrong_swift_name,none,
       "mean %2?",
       (ObjCSelector, DescriptiveDeclKind, DeclName))
 
+ERROR(objc_implementation_missing_impl,none,
+      "extension for %select{main class interface|category %0}0 should "
+      "provide implementation for %1 %2",
+      (Identifier, DescriptiveDeclKind, ValueDecl *))
+
+ERROR(objc_implementation_class_or_instance_mismatch,none,
+      "%0 %1 does not match %2 declared in header",
+      (DescriptiveDeclKind, ValueDecl *, DescriptiveDeclKind))
+
+ERROR(objc_implementation_multiple_matching_candidates,none,
+      "found multiple implementations that could match %0 %1 with selector %2",
+      (DescriptiveDeclKind, ValueDecl *, ObjCSelector))
+NOTE(objc_implementation_candidate_impl_here,none,
+     "%0 %1 is a potential match%select{|; insert '@objc(%3)' to use it}2",
+     (DescriptiveDeclKind, ValueDecl *, bool, StringRef))
+NOTE(objc_implementation_requirement_here,none,
+     "%0 %1 declared in header here",
+     (DescriptiveDeclKind, ValueDecl *))
+
+ERROR(objc_implementation_multiple_matching_requirements,none,
+      "%0 %1 could match several different members declared in the header",
+      (DescriptiveDeclKind, ValueDecl *))
+NOTE(objc_implementation_one_matched_requirement,none,
+     "%0 %1 (with selector %2) is a potential match%select{|; insert "
+     "'@objc(%4)' to use it}3",
+     (DescriptiveDeclKind, ValueDecl *, ObjCSelector, bool, StringRef))
+
 ERROR(cdecl_not_at_top_level,none,
       "@_cdecl can only be applied to global functions", ())
 ERROR(cdecl_empty_name,none,

include/swift/AST/TypeCheckRequests.h

@@ -4065,6 +4065,28 @@ class LocalDiscriminatorsRequest
   bool isCached() const { return true; }
 };
 
+/// Checks that all of a class's \c \@objcImplementation extensions provide
+/// complete and correct implementations for their corresponding interfaces.
+/// This is done on all of a class's implementations at once to improve diagnostics.
+class TypeCheckObjCImplementationRequest
+    : public SimpleRequest<TypeCheckObjCImplementationRequest,
+                           evaluator::SideEffect(ExtensionDecl *),
+                           RequestFlags::Cached> {
+public:
+  using SimpleRequest::SimpleRequest;
+
+private:
+  friend SimpleRequest;
+
+  // Evaluation.
+  evaluator::SideEffect
+  evaluate(Evaluator &evaluator, ExtensionDecl *ED) const;
+
+public:
+  // Separate caching.
+  bool isCached() const { return true; }
+};
+
 void simple_display(llvm::raw_ostream &out, ASTNode node);
 void simple_display(llvm::raw_ostream &out, Type value);
 void simple_display(llvm::raw_ostream &out, const TypeRepr *TyR);

include/swift/AST/TypeCheckerTypeIDZone.def

@@ -460,3 +460,6 @@ SWIFT_REQUEST(TypeChecker, GetRuntimeDiscoverableAttributes,
 SWIFT_REQUEST(TypeChecker, LocalDiscriminatorsRequest,
               unsigned(DeclContext *),
               Cached, NoLocationInfo)
+SWIFT_REQUEST(TypeChecker, TypeCheckObjCImplementationRequest,
+              unsigned(ExtensionDecl *),
+              Cached, NoLocationInfo)