RequirementMachine: Relax assertions in verifyRewriteSystem()

We don't care as much about rules with weird shapes as long
as they're LHS- or RHS-simplified, since the new minimal conformances
algorithm no longer relies on certain invariants.

Fixes rdar://problem/94746399.

Author: slavapestov

lib/AST/RequirementMachine/RewriteSystem.cpp

@@ -549,14 +549,21 @@ void RewriteSystem::verifyRewriteRules(ValidityPolicy policy) const {
 
       if (index != lhs.size() - 1) {
         ASSERT_RULE(symbol.getKind() != Symbol::Kind::Layout);
-        ASSERT_RULE(!symbol.hasSubstitutions());
+        ASSERT_RULE(symbol.getKind() != Symbol::Kind::Superclass);
+        ASSERT_RULE(symbol.getKind() != Symbol::Kind::ConcreteType);
+      }
+
+      if (!rule.isLHSSimplified() &&
+          index != lhs.size() - 1) {
+        ASSERT_RULE(symbol.getKind() != Symbol::Kind::ConcreteConformance);
       }
 
       if (index != 0) {
         ASSERT_RULE(symbol.getKind() != Symbol::Kind::GenericParam);
       }
 
-      if (index != 0 && index != lhs.size() - 1) {
+      if (!rule.isLHSSimplified() &&
+          index != 0 && index != lhs.size() - 1) {
         ASSERT_RULE(symbol.getKind() != Symbol::Kind::Protocol);
       }
     }
@@ -585,13 +592,29 @@ void RewriteSystem::verifyRewriteRules(ValidityPolicy policy) const {
       }
 
       ASSERT_RULE(symbol.getKind() != Symbol::Kind::Layout);
-      ASSERT_RULE(!symbol.hasSubstitutions());
+      ASSERT_RULE(symbol.getKind() != Symbol::Kind::Superclass);
+      ASSERT_RULE(symbol.getKind() != Symbol::Kind::ConcreteType);
+
+      // Completion can introduce a rule of the form
+      //
+      // (T.[P] => T.[concrete: C : P])
+      //
+      // Such rules are immediately simplified away. Otherwise, we should
+      // never see a symbol with substitutions (concrete type, superclass,
+      // concrete conformance) on the right hand side of a rule.
+      if (!(rule.isRHSSimplified() &&
+            index == rhs.size() - 1)) {
+        ASSERT_RULE(symbol.getKind() != Symbol::Kind::Superclass);
+        ASSERT_RULE(symbol.getKind() != Symbol::Kind::ConcreteType);
+        ASSERT_RULE(symbol.getKind() != Symbol::Kind::ConcreteConformance);
+      }
 
       if (index != 0) {
         ASSERT_RULE(symbol.getKind() != Symbol::Kind::GenericParam);
       }
 
-      if (index != 0 && !rule.isRHSSimplified()) {
+      if (!rule.isRHSSimplified() &&
+          index != 0) {
         ASSERT_RULE(symbol.getKind() != Symbol::Kind::Protocol);
       }
     }

test/Generics/rdar9474639.swift

@@ -0,0 +1,27 @@
+// RUN: %target-swift-frontend -typecheck %s -debug-generic-signatures 2>&1 | %FileCheck %s
+
+// CHECK-LABEL: .P1@
+// CHECK-NEXT: Requirement signature: <Self where Self == Self.[P1]T.[P2]T, Self.[P1]T : P2>
+protocol P1 {
+  associatedtype T: P2 where T.T == Self
+}
+
+// CHECK-LABEL: .P2@
+// CHECK-NEXT: Requirement signature: <Self where Self == Self.[P2]T.[P1]T, Self.[P2]T : P1>
+protocol P2 {
+  associatedtype T: P1 where T.T == Self
+}
+
+class SomeClass {}
+
+// CHECK-LABEL: .P3@
+// CHECK-NEXT: Requirement signature: <Self where Self : P2, Self.[P2]T : SomeClass>
+protocol P3: P2 where T: SomeClass {}
+
+protocol P4 {
+  associatedtype T
+}
+
+// CHECK-LABEL: .foo@
+// CHECK-NEXT: Generic signature: <T where T : P4, T.[P4]T : P1, T.[P4]T.[P1]T : P3>
+func foo<T: P4>(_: T) where T.T: P1, T.T.T: P3 {}