treat normalization during ReadResource like Plan

This will allow resources to return an unexpected change to set blocks
and attributes, otherwise we could mask these changes during
normalization.

Change the "plan" argument in normalizeNullValues to "preferDst" to more
accurately describe what the option is doing, since it no longer applies
only to PlanResourceChange.

helper/plugin/grpc_provider.go

@@ -448,7 +448,7 @@ func (s *GRPCProviderServer) ReadResource(_ context.Context, req *proto.ReadReso
 		return resp, nil
 	}
 
-	newStateVal = normalizeNullValues(newStateVal, stateVal, false)
+	newStateVal = normalizeNullValues(newStateVal, stateVal, true)
 	newStateVal = copyTimeoutValues(newStateVal, stateVal)
 
 	newStateMP, err := msgpack.Marshal(newStateVal, block.ImpliedType())
@@ -1078,7 +1078,7 @@ func stripSchema(s *schema.Schema) *schema.Schema {
 // however it sees fit. This however means that a CustomizeDiffFunction may not
 // be able to change a null to an empty value or vice versa, but that should be
 // very uncommon nor was it reliable before 0.12 either.
-func normalizeNullValues(dst, src cty.Value, plan bool) cty.Value {
+func normalizeNullValues(dst, src cty.Value, preferDst bool) cty.Value {
 	ty := dst.Type()
 
 	if !src.IsNull() && !src.IsKnown() {
@@ -1121,20 +1121,20 @@ func normalizeNullValues(dst, src cty.Value, plan bool) cty.Value {
 
 			dstVal := dstMap[key]
 			if dstVal == cty.NilVal {
-				if plan && ty.IsMapType() {
+				if preferDst && ty.IsMapType() {
 					// let plan shape this map however it wants
 					continue
 				}
 				dstVal = cty.NullVal(v.Type())
 			}
-			dstMap[key] = normalizeNullValues(dstVal, v, plan)
+			dstMap[key] = normalizeNullValues(dstVal, v, preferDst)
 		}
 
 		// you can't call MapVal/ObjectVal with empty maps, but nothing was
 		// copied in anyway. If the dst is nil, and the src is known, assume the
 		// src is correct.
 		if len(dstMap) == 0 {
-			if dst.IsNull() && src.IsWhollyKnown() && !plan {
+			if dst.IsNull() && src.IsWhollyKnown() && !preferDst {
 				return src
 			}
 			return dst
@@ -1150,7 +1150,7 @@ func normalizeNullValues(dst, src cty.Value, plan bool) cty.Value {
 		// If the original was wholly known, then we expect that is what the
 		// provider applied. The apply process loses too much information to
 		// reliably re-create the set.
-		if src.IsWhollyKnown() && !plan {
+		if src.IsWhollyKnown() && !preferDst {
 			return src
 		}
 
@@ -1158,7 +1158,7 @@ func normalizeNullValues(dst, src cty.Value, plan bool) cty.Value {
 		// If the dst is nil, and the src is known, then we lost an empty value
 		// so take the original.
 		if dst.IsNull() {
-			if src.IsWhollyKnown() && src.LengthInt() == 0 && !plan {
+			if src.IsWhollyKnown() && src.LengthInt() == 0 && !preferDst {
 				return src
 			}
 			return dst
@@ -1172,7 +1172,7 @@ func normalizeNullValues(dst, src cty.Value, plan bool) cty.Value {
 			dsts := dst.AsValueSlice()
 
 			for i := 0; i < srcLen; i++ {
-				dsts[i] = normalizeNullValues(dsts[i], srcs[i], plan)
+				dsts[i] = normalizeNullValues(dsts[i], srcs[i], preferDst)
 			}
 
 			if ty.IsTupleType() {
@@ -1182,7 +1182,7 @@ func normalizeNullValues(dst, src cty.Value, plan bool) cty.Value {
 		}
 
 	case ty.IsPrimitiveType():
-		if dst.IsNull() && src.IsWhollyKnown() && !plan {
+		if dst.IsNull() && src.IsWhollyKnown() && !preferDst {
 			return src
 		}
 	}