RequirementMachine: Rule::isProtocolRefinementRule() allows transitive refinement

Without this, we only considered a protocol refinement rule redundant if
it was derived by directly-stated protocol refinements. But this broke
when completion introduced a 'transitive' refinement [P].[R] => [P]
from two directly-stated refinements [P].[Q] => [P] and [Q].[R] => [Q].

Fixes rdar://problem/90402503.

Author: slavapestov

lib/AST/RequirementMachine/MinimalConformances.cpp

@@ -396,7 +396,7 @@ void MinimalConformances::collectConformanceRules() {
       continue;
 
     // Save protocol refinement relations in a side table.
-    if (rule.isProtocolRefinementRule())
+    if (rule.isProtocolRefinementRule(Context))
       ProtocolRefinements.insert(ruleID);
 
     if (!System.isInMinimizationDomain(rule.getLHS().getRootProtocol()))

lib/AST/RequirementMachine/Rule.cpp

@@ -93,7 +93,7 @@ bool Rule::isIdentityConformanceRule() const {
 
 /// If this is a rule of the form [P].[Q] => [P] where [P] and [Q] are
 /// protocol symbols, return true, otherwise return false.
-bool Rule::isProtocolRefinementRule() const {
+bool Rule::isProtocolRefinementRule(RewriteContext &ctx) const {
   if (LHS.size() == 2 &&
       RHS.size() == 1 &&
       LHS[0] == RHS[0] &&
@@ -111,7 +111,7 @@ bool Rule::isProtocolRefinementRule() const {
     auto *proto = LHS[0].getProtocol();
     auto *otherProto = LHS[1].getProtocol();
 
-    auto inherited = proto->getInheritedProtocols();
+    auto inherited = ctx.getInheritedProtocols(proto);
     return (std::find(inherited.begin(), inherited.end(), otherProto)
             != inherited.end());
   }

lib/AST/RequirementMachine/Rule.h

@@ -108,7 +108,7 @@ class Rule final {
 
   bool isIdentityConformanceRule() const;
 
-  bool isProtocolRefinementRule() const;
+  bool isProtocolRefinementRule(RewriteContext &ctx) const;
 
   bool isCircularConformanceRule() const;
 

test/Generics/redundant_protocol_refinement.swift

@@ -1,22 +1,29 @@
 // RUN: %target-typecheck-verify-swift
 // RUN: %target-swift-frontend -typecheck -debug-generic-signatures -requirement-machine-protocol-signatures=verify %s 2>&1 | %FileCheck %s
 
-protocol Base {}
-
 // CHECK-LABEL: redundant_protocol_refinement.(file).Base@
 // CHECK-LABEL: Requirement signature: <Self>
-
-protocol Middle : Base {}
+protocol Base {}
 
 // CHECK-LABEL: redundant_protocol_refinement.(file).Middle@
 // CHECK-LABEL: Requirement signature: <Self where Self : Base>
+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'}}
 
-// CHECK-LABEL: redundant_protocol_refinement.(file).Derived@
+// CHECK-LABEL: redundant_protocol_refinement.(file).Derived2@
 // CHECK-LABEL: Requirement signature: <Self where Self : Middle>
+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'}}
 
 protocol P1 {}