AST: Take decls instead of identifiers in some conformance diagnostics.

NFC.

Author: tshortli

include/swift/AST/DiagnosticsSema.def

@@ -3126,7 +3126,7 @@ NOTE(declared_protocol_conformance_here,none,
 
 ERROR(witness_unavailable,none,
         "unavailable %kind0 was used to satisfy a requirement of protocol %1%select{|: %2}2",
-        (const ValueDecl *, Identifier, StringRef))
+        (const ValueDecl *, const ProtocolDecl *, StringRef))
 
 WARNING(witness_deprecated,none,
         "deprecated default implementation is used to satisfy %kind0 required by "
@@ -6781,7 +6781,7 @@ WARNING(availability_enum_element_no_potential_warn,
 
 ERROR(availability_protocol_requires_version,
       none, "protocol %0 requires %1 to be available in %2 %3 and newer",
-      (Identifier, DeclName, StringRef, llvm::VersionTuple))
+      (const ProtocolDecl *, const ValueDecl *, StringRef, llvm::VersionTuple))
 
 NOTE(availability_protocol_requirement_here, none,
      "protocol requirement here", ())

lib/Sema/TypeCheckProtocol.cpp

@@ -4313,8 +4313,7 @@ ConformanceChecker::resolveWitnessViaLookup(ValueDecl *requirement) {
           SourceLoc diagLoc = getLocForDiagnosingWitness(conformance, witness);
           diags.diagnose(
               diagLoc, diag::availability_protocol_requires_version,
-              conformance->getProtocol()->getName(),
-              witness->getName(),
+              conformance->getProtocol(), witness,
               prettyPlatformString(targetPlatform(ctx.LangOpts)),
               check.RequiredAvailability.getOSVersion().getLowerEndpoint());
           emitDeclaredHereIfNeeded(diags, diagLoc, witness);
@@ -4385,9 +4384,8 @@ ConformanceChecker::resolveWitnessViaLookup(ValueDecl *requirement) {
           SourceLoc diagLoc = getLocForDiagnosingWitness(conformance, witness);
           auto *attr = AvailableAttr::isUnavailable(witness);
           EncodedDiagnosticMessage EncodedMessage(attr->Message);
-          diags.diagnose(diagLoc, diag::witness_unavailable,
-                         witness, conformance->getProtocol()->getName(),
-                         EncodedMessage.Message);
+          diags.diagnose(diagLoc, diag::witness_unavailable, witness,
+                         conformance->getProtocol(), EncodedMessage.Message);
           emitDeclaredHereIfNeeded(diags, diagLoc, witness);
           diags.diagnose(requirement, diag::kind_declname_declared_here,
                          DescriptiveDeclKind::Requirement,