[Archetype builder] Make compareDependentTypes() a more sane total ordering.

Author: DougGregor

lib/AST/ArchetypeBuilder.cpp

@@ -402,35 +402,46 @@ static int compareDependentTypes(
       if (int compareProtocols
             = ProtocolType::compareProtocols(&protoa, &protob))
         return compareProtocols;
+
+      // Error case: if we have two associated types with the same name in the
+      // same protocol, just tie-break based on address.
+      if (aa != ab)
+        return aa < ab ? -1 : +1;
     } else {
       // A resolved archetype is always ordered before an unresolved one.
       return -1;
     }
+  } else {
+    // A resolved archetype is always ordered before an unresolved one.
+    if (b->getResolvedAssociatedType())
+      return +1;
   }
 
-  // A resolved archetype is always ordered before an unresolved one.
-  if (b->getResolvedAssociatedType())
-    return +1;
-
   // Make sure typealiases are properly ordered, to avoid crashers.
   // FIXME: Ideally we would eliminate typealiases earlier.
   if (auto *aa = a->getTypeAliasDecl()) {
     if (auto *ab = b->getTypeAliasDecl()) {
       // - by protocol, so t_n_m.`P.T` < t_n_m.`Q.T` (given P < Q)
-      auto protoa = aa->getDeclContext()->getAsProtocolOrProtocolExtensionContext();
-      auto protob = ab->getDeclContext()->getAsProtocolOrProtocolExtensionContext();
+      auto protoa =
+        aa->getDeclContext()->getAsProtocolOrProtocolExtensionContext();
+      auto protob =
+        ab->getDeclContext()->getAsProtocolOrProtocolExtensionContext();
+
       if (int compareProtocols
             = ProtocolType::compareProtocols(&protoa, &protob))
         return compareProtocols;
-    }
 
+      // FIXME: Arbitrarily break the result here.
+      if (aa != ab)
+        return aa < ab ? -1 : +1;
+    } else {
+      // A resolved archetype is always ordered before an unresolved one.
+      return -1;
+    }
+  } else if (b->getTypeAliasDecl()) {
     // A resolved archetype is always ordered before an unresolved one.
-    return -1;
-  }
-
-  // A resolved archetype is always ordered before an unresolved one.
-  if (b->getTypeAliasDecl())
     return +1;
+  }
 
   // Along the error path where one or both of the potential archetypes was
   // renamed due to typo correction,

test/Generics/associated_type_typo.swift

@@ -39,11 +39,10 @@ func typoAssoc4<T : P2>(_: T) where T.Assocp2.assoc : P3 {}
 // CHECK-GENERIC-LABEL: .typoAssoc4@
 // CHECK-GENERIC-NEXT: Requirements:
 // CHECK-GENERIC-NEXT:   T : P2 [explicit
-// CHECK-GENERIC-NEXT:   T[.P2].AssocP2 == T[.P2].AssocP2 [redundant]
 // CHECK-GENERIC-NEXT:   T[.P2].AssocP2 : P1 [protocol
-// CHECK-GENERIC-NEXT:   T[.P2].AssocP2[.P1].Assoc == T[.P2].AssocP2[.P1].Assoc [redundant
+// CHECK-GENERIC-NEXT:   T[.P2].AssocP2 == T[.P2].AssocP2 [redundant]
 // CHECK-GENERIC-NEXT:   T[.P2].AssocP2[.P1].Assoc : P3 [explicit
-// CHECK-GENERIC-NEXT:   T[.P2].AssocP2[.P1].Assoc == T[.P2].AssocP2[.P1].Assoc [redundant]
+// CHECK-GENERIC-NEXT:   T[.P2].AssocP2[.P1].Assoc == T[.P2].AssocP2[.P1].Assoc [redundant
 // CHECK-GENERIC-NEXT: Generic signature
 
 // <rdar://problem/19620340>
@@ -73,7 +72,6 @@ protocol Pattern {
   associatedtype Element : Equatable
 
   // FIXME: Diagnostics here are very poor
-  // expected-error@+4{{'C.Slice' does not have a member type named 'Iterator'; did you mean 'Slice'?}}
   // expected-error@+3{{'C' does not have a member type named 'Iterator'; did you mean 'Slice'?}}
   // expected-error@+2{{'C.Slice' does not have a member type named 'Element'; did you mean 'Slice'?}}
   // expected-error@+1{{'C.Slice' does not have a member type named 'Iterator'; did you mean 'Slice'?}}