[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.

Resolves SR-8008

Author: hamishknight

include/swift/AST/DiagnosticsSema.def

@@ -1834,6 +1834,11 @@ 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

@@ -285,14 +285,17 @@ void TypeChecker::checkInheritanceClause(Decl *decl,
     resolver = &defaultResolver;
 
   MutableArrayRef<TypeLoc> inheritedClause;
+  Type declInterfaceTy;
 
   if (auto type = dyn_cast<TypeDecl>(decl)) {
+    declInterfaceTy = type->getDeclaredInterfaceType();
     inheritedClause = type->getInherited();
   } else {
     auto ext = cast<ExtensionDecl>(decl);
     if (!ext->getExtendedType())
       return;
 
+    declInterfaceTy = ext->getExtendedType();
     inheritedClause = ext->getInherited();
 
     // Protocol extensions cannot have inheritance clauses.
@@ -379,16 +382,37 @@ void TypeChecker::checkInheritanceClause(Decl *decl,
     if (inheritedTy->hasError())
       continue;
 
-    // Check whether we inherited from the same type twice.
     CanType inheritedCanTy = inheritedTy->getCanonicalType();
+    auto isConstraint =
+        isa<AbstractTypeParamDecl>(decl) || isa<ProtocolDecl>(decl);
+
+    // 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 are handled by the generic signature builder along with redundant
+    // constraints that appear in 'where' clauses.
+    if (inheritedCanTy == Context.TheAnyType) {
+      if (!isConstraint) {
+        auto diagLoc = inherited.getSourceRange().Start;
+        auto removalRange = getRemovalRange(i);
+
+        diagnose(diagLoc, diag::redundant_conformance_warning, declInterfaceTy,
+                 inheritedTy)
+            .highlight(inherited.getSourceRange())
+            .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
       // written as 'class'. Downgrade the error to a warning in such cases
       // for backward compatibility with Swift <= 4.
       if (!Context.LangOpts.isSwiftVersionAtLeast(5) &&
-          inheritedTy->isAnyObject() &&
-          (isa<ProtocolDecl>(decl) || isa<AbstractTypeParamDecl>(decl)) &&
+          inheritedTy->isAnyObject() && isConstraint &&
           Lexer::getTokenAtLocation(Context.SourceMgr,
                                     knownType->second.second.Start)
             .is(tok::kw_class)) {
@@ -432,8 +456,7 @@ void TypeChecker::checkInheritanceClause(Decl *decl,
       //
       // Extensions, structs and enums can only inherit from protocol
       // compositions that do not contain AnyObject or class members.
-      if (isa<ProtocolDecl>(decl) ||
-          isa<AbstractTypeParamDecl>(decl) ||
+      if (isConstraint ||
           (!layout.hasExplicitAnyObject &&
            !layout.explicitSuperclass)) {
         continue;

test/decl/inherit/inherit.swift

@@ -21,11 +21,15 @@ class D : P, A { } // expected-error{{superclass 'A' must appear first in the in
 
 // SR-8160
 class D1 : Any, A { } // expected-error{{superclass 'A' must appear first in the inheritance clause}}{{15-18=}}{{12-12=A, }}
+// expected-warning@-1 {{redundant conformance of 'D1' to 'Any'}}
+// expected-note@-2 {{all types implicitly conform to 'Any'}}
 
 class D2 : P & P1, A { } // expected-error{{superclass 'A' must appear first in the inheritance clause}}{{18-21=}}{{12-12=A, }}
 
 @usableFromInline
 class D3 : Any, A { } // expected-error{{superclass 'A' must appear first in the inheritance clause}}{{15-18=}}{{12-12=A, }}
+// expected-warning@-1 {{redundant conformance of 'D3' to 'Any'}}
+// expected-note@-2 {{all types implicitly conform to 'Any'}}
 
 @usableFromInline
 class D4 : P & P1, A { } // expected-error{{superclass 'A' must appear first in the inheritance clause}}{{18-21=}}{{12-12=A, }}

test/decl/protocol/protocols.swift

@@ -51,26 +51,80 @@ 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'}}
+
+typealias AnyAnyAlias = Any & Any
+
+class X11 : AnyAnyAlias {} // expected-warning {{redundant conformance of 'X11' to 'AnyAnyAlias' (aka 'Any')}} {{10-24=}}
+// expected-note@-1 {{all types implicitly conform to 'AnyAnyAlias' (aka 'Any')}}
+
+struct X12 : Any, Any {}
+// expected-warning@-1 {{redundant conformance of 'X12' to 'Any'}} {{14-19=}}
+// expected-note@-2 {{all types implicitly conform to 'Any'}}
+// expected-warning@-3 {{redundant conformance of 'X12' to 'Any'}} {{17-22=}}
+// expected-note@-4 {{all types implicitly conform to 'Any'}}
+
 // 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'}}