[Sema] Warn about stated conformances to 'Any'

Such a stated conformance is always redundant. This patch purposefully ignores conformance constraints that are parsed as inheritance clauses, such as with protocols and generic placeholders (e.g '<T : Any>'). These are best diagnosed in the generic signature builder.

Author: hamishknight

include/swift/AST/DiagnosticsSema.def

@@ -1724,6 +1724,11 @@ WARNING(redundant_conformance_adhoc_conditional,none,
 NOTE(redundant_conformance_witness_ignored,none,
      "%0 %1 will not be used to satisfy the conformance to %2",
      (DescriptiveDeclKind, DeclName, DeclName))
+WARNING(redundant_conformance_warning,none,
+        "redundant conformance of %0 to %1", (Type, Type))
+NOTE(all_types_implicitly_conform_to,none,
+     "all types implicitly conform to %0", (Type))
+
 
 // "Near matches"
 WARNING(req_near_match,none,

lib/Sema/TypeCheckDecl.cpp

@@ -325,12 +325,15 @@ void TypeChecker::checkInheritanceClause(Decl *decl,
     resolver = &defaultResolver;
 
   MutableArrayRef<TypeLoc> inheritedClause;
+  Type declInterfaceTy;
 
   // If we already checked the inheritance clause, don't do so again.
   if (auto type = dyn_cast<TypeDecl>(decl)) {
     if (type->checkedInheritanceClause())
       return;
 
+    declInterfaceTy = type->getDeclaredInterfaceType();
+
     // This breaks infinite recursion, which will be diagnosed separately.
     type->setCheckedInheritanceClause();
     inheritedClause = type->getInherited();
@@ -343,6 +346,8 @@ void TypeChecker::checkInheritanceClause(Decl *decl,
         ext->checkedInheritanceClause())
       return;
 
+    declInterfaceTy = ext->getExtendedType();
+
     // This breaks infinite recursion, which will be diagnosed separately.
     ext->setCheckedInheritanceClause();
     inheritedClause = ext->getInherited();
@@ -447,8 +452,26 @@ void TypeChecker::checkInheritanceClause(Decl *decl,
     if (inheritedTy->hasArchetype() && !isa<GenericTypeParamDecl>(decl))
       inheritedTy = inheritedTy->mapTypeOutOfContext();
 
-    // Check whether we inherited from the same type twice.
     CanType inheritedCanTy = inheritedTy->getCanonicalType();
+
+    // Check for a stated conformance to Any, which is redundant.
+    // Ignore cases of ': Any' *constraints* that are parsed as inheritance
+    // clauses, such as with protocol and placeholder decls e.g <T : Any>, as
+    // these should be handled by the generic signature builder along with
+    // redundant constraints that appear as a part of a 'where' clause.
+    if (inheritedCanTy == Context.TheAnyType &&
+        !isa<AbstractTypeParamDecl>(decl) && !isa<ProtocolDecl>(decl)) {
+      auto diagLoc = inherited.getSourceRange().Start;
+      auto removalRange = getRemovalRange(i);
+
+      diagnose(diagLoc, diag::redundant_conformance_warning, declInterfaceTy,
+               inheritedTy)
+          .fixItRemoveChars(removalRange.Start, removalRange.End);
+      diagnose(diagLoc, diag::all_types_implicitly_conform_to, inheritedTy);
+      continue;
+    }
+
+    // Check whether we inherited from the same type twice.
     auto knownType = inheritedTypes.find(inheritedCanTy);
     if (knownType != inheritedTypes.end()) {
       // If the duplicated type is 'AnyObject', check whether the first was

test/decl/protocol/protocols.swift

@@ -51,26 +51,73 @@ protocol FormattedPrintable : CustomStringConvertible {
   func print(format: TestFormat)
 }
 
+// expected-warning@+2 {{redundant conformance of 'X0' to 'Any'}} {{13-18=}}
+// expected-note@+1 {{all types implicitly conform to 'Any'}}
 struct X0 : Any, CustomStringConvertible {
   func print() {}
 }
 
+// expected-warning@+2 {{redundant conformance of 'X1' to 'Any'}} {{12-17=}}
+// expected-note@+1 {{all types implicitly conform to 'Any'}}
 class X1 : Any, CustomStringConvertible {
   func print() {}
 }
 
+// expected-warning@+2 {{redundant conformance of 'X2' to 'Any'}} {{8-14=}}
+// expected-note@+1 {{all types implicitly conform to 'Any'}}
 enum X2 : Any { }
 
 extension X2 : CustomStringConvertible {
   func print() {}
 }
 
+struct X5 {
+  func print() {}
+}
+extension X5 : Any {} // expected-warning {{redundant conformance of 'X5' to 'Any'}} {{13-19=}}
+// expected-note@-1 {{all types implicitly conform to 'Any'}}
+
+extension X5 : Any, CustomStringConvertible {} // expected-warning {{redundant conformance of 'X5' to 'Any'}} {{16-21=}}
+// expected-note@-1 {{all types implicitly conform to 'Any'}}
+
+struct X6 {
+  func print() {}
+}
+extension X6 : CustomStringConvertible, Any {} // expected-warning {{redundant conformance of 'X6' to 'Any'}} {{39-44=}}
+// expected-note@-1 {{all types implicitly conform to 'Any'}}
+
+struct X7<T> : Any {} // expected-warning {{redundant conformance of 'X7<T>' to 'Any'}} {{13-19=}}
+// expected-note@-1 {{all types implicitly conform to 'Any'}}
+
+struct X8<T> {
+  func print() {}
+}
+extension X8 : Any where T : CustomStringConvertible {} // expected-warning {{redundant conformance of 'X8<T>' to 'Any'}} {{13-19=}}
+// expected-note@-1 {{all types implicitly conform to 'Any'}}
+
+typealias AnyAlias = Any
+class X9 : AnyAlias {} // expected-warning {{redundant conformance of 'X9' to 'AnyAlias' (aka 'Any')}} {{9-20=}}
+// expected-note@-1 {{all types implicitly conform to 'AnyAlias' (aka 'Any')}}
+
+struct X10 : Any & Any {} // expected-warning {{redundant conformance of 'X10' to 'Any'}} {{11-23=}}
+// expected-note@-1 {{all types implicitly conform to 'Any'}}
+
+// FIX-ME(SR-8009): Handle these cases.
+protocol P5 : Any {}
+func foo<T : Any>(_ x: T) {}
+
 // Explicit conformance checks (unsuccessful)
 
+// expected-warning@+2 {{redundant conformance of 'NotPrintableS' to 'Any'}} {{24-29=}}
+// expected-note@+1 {{all types implicitly conform to 'Any'}}
 struct NotPrintableS : Any, CustomStringConvertible {} // expected-error{{type 'NotPrintableS' does not conform to protocol 'CustomStringConvertible'}}
 
+// expected-warning@+2 {{redundant conformance of 'NotPrintableC' to 'Any'}} {{46-51=}}
+// expected-note@+1 {{all types implicitly conform to 'Any'}}
 class NotPrintableC : CustomStringConvertible, Any {} // expected-error{{type 'NotPrintableC' does not conform to protocol 'CustomStringConvertible'}}
 
+// expected-warning@+2 {{redundant conformance of 'NotPrintableO' to 'Any'}} {{22-27=}}
+// expected-note@+1 {{all types implicitly conform to 'Any'}}
 enum NotPrintableO : Any, CustomStringConvertible {} // expected-error{{type 'NotPrintableO' does not conform to protocol 'CustomStringConvertible'}}
 
 struct NotFormattedPrintable : FormattedPrintable { // expected-error{{type 'NotFormattedPrintable' does not conform to protocol 'CustomStringConvertible'}}