Sema: Diagnose missing entries in protocol inheritance clause when requirement machine is enabled

This diagnostic used to be emitted by the GenericSignatureBuilder when
building a requirement signature, but we can just do the check in
Sema using generic signature queries instead.

Fixes rdar://problem/90192939.

Author: slavapestov

lib/Sema/TypeCheckDeclPrimary.cpp

@@ -1695,6 +1695,39 @@ static void diagnoseWrittenPlaceholderTypes(ASTContext &Ctx,
   }
 }
 
+/// Make sure that every protocol conformance requirement on 'Self' is
+/// directly stated in the protocol's inheritance clause.
+///
+/// This disallows protocol declarations where a conformance requirement on
+/// 'Self' is implied by some other requirement, such as this:
+///
+///    protocol Other { ... }
+///    protocol Foo { associatedtype A : Other }
+///    protocol Bar {
+///      associatedtype A : Foo where Self == A.A
+///    }
+///
+/// Since name lookup is upstream of generic signature computation, we
+/// want 'Other' to appear in the inheritance clause of 'Bar', so that
+/// name lookup on Bar can find members of Other.
+static void checkProtocolRefinementRequirements(ProtocolDecl *proto) {
+  auto requiredProtos = proto->getGenericSignature()->getRequiredProtocols(
+      proto->getSelfInterfaceType());
+
+  for (auto *otherProto : requiredProtos) {
+    // Every protocol 'P' has an implied requirement 'Self : P'; skip it.
+    if (otherProto == proto)
+      continue;
+
+    // GenericSignature::getRequiredProtocols() canonicalizes the protocol
+    // list by dropping protocols that are inherited by other protocols in
+    // the list. Any protocols that remain in the list other than 'proto'
+    // itself are implied by a conformance requirement on 'Self', but are
+    // not (transitively) inherited by 'proto'.
+    proto->diagnose(diag::missing_protocol_refinement, proto, otherProto);
+  }
+}
+
 namespace {
 class DeclChecker : public DeclVisitor<DeclChecker> {
 public:
@@ -2670,6 +2703,11 @@ class DeclChecker : public DeclVisitor<DeclChecker> {
 
     checkInheritanceClause(PD);
 
+    if (PD->getASTContext().LangOpts.RequirementMachineProtocolSignatures
+        == RequirementMachineMode::Enabled) {
+      checkProtocolRefinementRequirements(PD);
+    }
+
     TypeChecker::checkDeclCircularity(PD);
     if (PD->isResilient())
       if (!SF || SF->Kind != SourceFileKind::Interface)

test/Generics/rdar51908331.swift

@@ -32,6 +32,10 @@ protocol PH {
 }
 
 protocol PI {
+// expected-warning@-1 {{protocol 'PI' should be declared to refine 'Decodable' due to a same-type constraint on 'Self'}}
+// expected-warning@-2 {{protocol 'PI' should be declared to refine 'Encodable' due to a same-type constraint on 'Self'}}
+// expected-warning@-3 {{protocol 'PI' should be declared to refine 'Hashable' due to a same-type constraint on 'Self'}}
+// expected-warning@-4 {{protocol 'PI' should be declared to refine 'SIMDScalar' due to a same-type constraint on 'Self'}}
   associatedtype A8 where A8.A7 == Self // expected-warning {{redundant same-type constraint 'Self.A8.A7' == 'Self'}}
   associatedtype A9 where A9.A7 == Self, A9.A8 == A8
   associatedtype A10 where A10.A7 == Self, A10.A8 == A8, A10.A9 == A9 // expected-warning {{redundant same-type constraint 'Self.A10.A7' == 'Self'}}

test/Generics/redundant_protocol_refinement.swift

@@ -1,5 +1,5 @@
-// RUN: %target-typecheck-verify-swift -requirement-machine-protocol-signatures=verify -requirement-machine-inferred-signatures=verify
-// RUN: %target-swift-frontend -typecheck -debug-generic-signatures -requirement-machine-protocol-signatures=verify %s 2>&1 | %FileCheck %s
+// RUN: %target-typecheck-verify-swift -requirement-machine-protocol-signatures=on
+// RUN: %target-swift-frontend -typecheck -debug-generic-signatures -requirement-machine-protocol-signatures=on %s 2>&1 | %FileCheck %s
 
 // CHECK-LABEL: redundant_protocol_refinement.(file).Base@
 // CHECK-LABEL: Requirement signature: <Self>
@@ -12,8 +12,7 @@ protocol Middle : Base {}
 // CHECK-LABEL: redundant_protocol_refinement.(file).Derived@
 // CHECK-LABEL: Requirement signature: <Self where Self : Middle>
 protocol Derived : Middle, Base {}
-// expected-note@-1 {{conformance constraint 'Self' : 'Base' implied here}}
-// expected-warning@-2 {{redundant conformance constraint 'Self' : 'Base'}}
+// expected-warning@-1 {{redundant conformance constraint 'Self' : 'Base'}}
 
 // CHECK-LABEL: redundant_protocol_refinement.(file).Derived2@
 // CHECK-LABEL: Requirement signature: <Self where Self : Middle>
@@ -22,8 +21,7 @@ protocol Derived2 : Middle {}
 // CHECK-LABEL: redundant_protocol_refinement.(file).MoreDerived@
 // CHECK-LABEL: Requirement signature: <Self where Self : Derived2>
 protocol MoreDerived : Derived2, Base {}
-// expected-note@-1 {{conformance constraint 'Self' : 'Base' implied here}}
-// expected-warning@-2 {{redundant conformance constraint 'Self' : 'Base'}}
+// expected-warning@-1 {{redundant conformance constraint 'Self' : 'Base'}}
 
 protocol P1 {}
 
@@ -40,7 +38,6 @@ protocol Good: P2, P1 where Assoc == Self {}
 // missing refinement of 'P1'
 protocol Bad: P2 where Assoc == Self {}
 // expected-warning@-1 {{protocol 'Bad' should be declared to refine 'P1' due to a same-type constraint on 'Self'}}
-// expected-note@-2 {{conformance constraint 'Self' : 'P1' implied here}}
 
 // CHECK-LABEL: redundant_protocol_refinement.(file).Bad@
 // CHECK-LABEL: Requirement signature: <Self where Self : P2, Self == Self.[P2]Assoc>