[AST] Choose an implied conformance source next to the type, if possible.

If a conformance to a protocol is implied by several other
conformances (i.e. protocol P: Equatable {} and protocol Q: Equatable {} and a
type declares conformance to both P and Q), we should choose a source that's in
the same file as the type, if we can, because automatic synthesis of
conformances (for Equatable, Hashable, etc.) only works in that case.

Fixes rdar://problem/41852654.

lib/AST/ConformanceLookupTable.cpp

@@ -661,6 +661,19 @@ ConformanceLookupTable::Ordering ConformanceLookupTable::compareConformances(
              : Ordering::After;
   }
 
+  // If one of the conformances comes from the same file as the type
+  // declaration, pick that one; this is so that conformance synthesis works if
+  // there's any implied conformance in the same file as the type.
+  auto NTD =
+      lhs->getDeclContext()->getAsNominalTypeOrNominalTypeExtensionContext();
+  auto typeSF = NTD->getParentSourceFile();
+  if (typeSF) {
+    if (typeSF == lhsSF)
+      return Ordering::Before;
+    if (typeSF == rhsSF)
+      return Ordering::After;
+  }
+
   // Otherwise, pick the earlier file unit.
   auto lhsFileUnit
     = dyn_cast<FileUnit>(lhs->getDeclContext()->getModuleScopeContext());

test/Sema/Inputs/enum_conformance_synthesis_other.swift

@@ -23,3 +23,9 @@ enum GenericOtherFileNonconforming<T> {
 // expected-note@-1 {{type declared here}}
     case A(T)
 }
+
+protocol ImplierOther: Equatable {}
+extension ImpliedMain: ImplierMain {}
+enum ImpliedOther: ImplierOther {
+    case a(Int)
+}

test/Sema/Inputs/struct_equatable_hashable_other.swift

@@ -22,3 +22,7 @@ struct GenericOtherFileNonconforming<T> {
 // expected-note@-1{{type declared here}}
     let v: T
 }
+
+protocol ImplierOther: Equatable {}
+extension ImpliedMain: ImplierOther {}
+struct ImpliedOther: ImplierOther {}

test/Sema/enum_conformance_synthesis.swift

@@ -314,6 +314,18 @@ extension UnusedGenericDeriveExtension: Hashable {}
 extension GenericOtherFileNonconforming: Equatable where T: Equatable {}
 // expected-error@-1{{implementation of 'Equatable' cannot be automatically synthesized in an extension in a different file to the type}}
 
+// rdar://problem/41852654
+
+// There is a conformance to Equatable (or at least, one that implies Equatable)
+// in the same file as the type, so the synthesis is okay. Both orderings are
+// tested, to catch choosing extensions based on the order of the files, etc.
+protocol ImplierMain: Equatable {}
+enum ImpliedMain: ImplierMain {
+  case a(Int)
+}
+extension ImpliedOther: ImplierMain {}
+
+
 // FIXME: Remove -verify-ignore-unknown.
 // <unknown>:0: error: unexpected error produced: invalid redeclaration of 'hashValue'
 // <unknown>:0: error: unexpected note produced: candidate has non-matching type '(Foo, Foo) -> Bool'

test/Sema/struct_equatable_hashable.swift

@@ -253,6 +253,15 @@ extension UnusedGenericDeriveExtension: Hashable {}
 extension GenericOtherFileNonconforming: Equatable where T: Equatable {}
 // expected-error@-1{{implementation of 'Equatable' cannot be automatically synthesized in an extension in a different file to the type}}
 
+// rdar://problem/41852654
+
+// There is a conformance to Equatable (or at least, one that implies Equatable)
+// in the same file as the type, so the synthesis is okay. Both orderings are
+// tested, to catch choosing extensions based on the order of the files, etc.
+protocol ImplierMain: Equatable {}
+struct ImpliedMain: ImplierMain {}
+extension ImpliedOther: ImplierMain {}
+
 // FIXME: Remove -verify-ignore-unknown.
 // <unknown>:0: error: unexpected error produced: invalid redeclaration of 'hashValue'
 // <unknown>:0: error: unexpected note produced: candidate has non-matching type '(Foo, Foo) -> Bool'