Revert "conformance location" back to what it was

We moved some diagnostics around, which ended up breaking some downstream
tests that we don't want to break. Restore the location.

Author: DougGregor

include/swift/AST/ProtocolConformance.h

@@ -530,6 +530,9 @@ class NormalProtocolConformance : public RootProtocolConformance,
   /// The location of this protocol conformance in the source.
   SourceLoc Loc;
 
+  /// The location of the protocol name within the conformance.
+  SourceLoc ProtocolNameLoc;
+
   /// The location of the `@preconcurrency` attribute, if any.
   SourceLoc PreconcurrencyLoc;
 
@@ -569,7 +572,8 @@ class NormalProtocolConformance : public RootProtocolConformance,
                             SourceLoc preconcurrencyLoc)
       : RootProtocolConformance(ProtocolConformanceKind::Normal,
                                 conformingType),
-        Protocol(protocol), Loc(loc), PreconcurrencyLoc(preconcurrencyLoc),
+        Protocol(protocol), Loc(extractNearestSourceLoc(dc)),
+        ProtocolNameLoc(loc), PreconcurrencyLoc(preconcurrencyLoc),
         Context(dc) {
     assert(!conformingType->hasArchetype() &&
            "ProtocolConformances should store interface types");
@@ -590,6 +594,9 @@ class NormalProtocolConformance : public RootProtocolConformance,
   /// Retrieve the location of this conformance.
   SourceLoc getLoc() const { return Loc; }
 
+  /// Retrieve the name of the protocol location.
+  SourceLoc getProtocolNameLoc() const { return ProtocolNameLoc; }
+
   /// Get the declaration context that contains the conforming extension or
   /// nominal type declaration.
   DeclContext *getDeclContext() const { return Context; }

lib/Sema/TypeCheckProtocol.cpp

@@ -3313,10 +3313,10 @@ ConformanceChecker::checkActorIsolation(ValueDecl *requirement,
         !Conformance->isPreconcurrency() &&
         !suggestedPreconcurrency &&
         !requirementIsolation.isActorIsolated()) {
-      Context.Diags.diagnose(Conformance->getLoc(),
+      Context.Diags.diagnose(Conformance->getProtocolNameLoc(),
                              diag::add_preconcurrency_to_conformance,
                              Proto->getName())
-          .fixItInsert(Conformance->getLoc(), "@preconcurrency ");
+          .fixItInsert(Conformance->getProtocolNameLoc(), "@preconcurrency ");
       suggestedPreconcurrency = true;
     }
   }

test/APINotes/versioned-objc.swift

@@ -9,7 +9,7 @@ import APINotesFrameworkTest
 
 // CHECK-DIAGS-5-NOT: versioned-objc.swift:[[@LINE-1]]:
 class ProtoWithVersionedUnavailableMemberImpl: ProtoWithVersionedUnavailableMember {
-  // CHECK-DIAGS-4: versioned-objc.swift:[[@LINE-1]]:48: error: type 'ProtoWithVersionedUnavailableMemberImpl' cannot conform to protocol 'ProtoWithVersionedUnavailableMember' because it has requirements that cannot be satisfied
+  // CHECK-DIAGS-4: versioned-objc.swift:[[@LINE-1]]:7: error: type 'ProtoWithVersionedUnavailableMemberImpl' cannot conform to protocol 'ProtoWithVersionedUnavailableMember' because it has requirements that cannot be satisfied
   func requirement() -> Any? { return nil }
 }
 

test/decl/protocol/req/missing_conformance.swift

@@ -144,10 +144,10 @@ struct CountSteps1<T> : Collection {
   subscript(i: Int) -> Int { return i }
 }
 
-extension CountSteps1 // expected-error {{type 'CountSteps1<T>' does not conform to protocol 'BidirectionalCollection'}}
+extension CountSteps1 // expected-error {{type 'CountSteps1<T>' does not conform to protocol 'RandomAccessCollection'}}
   // expected-error@-1 {{conditional conformance of type 'CountSteps1<T>' to protocol 'RandomAccessCollection' does not imply conformance to inherited protocol 'BidirectionalCollection'}}
   // expected-note@-2 {{did you mean to explicitly state the conformance like 'extension CountSteps1: BidirectionalCollection where ...'?}}
-  // expected-error@+1 {{type 'CountSteps1<T>' does not conform to protocol 'RandomAccessCollection'}}
+  // expected-error@-3 {{type 'CountSteps1<T>' does not conform to protocol 'BidirectionalCollection'}}
   : RandomAccessCollection
      where T : Equatable
 {