resolver: move dns and passthrough to internal (#3116)

Nobody should directly need to reference these packages.

This is technically a breaking change. However:

- Package dns was exporting a NewBuilder method. This should never have been necessary to use, but if so, it can be replaced by importing the "grpc" package and then using resolver.Get("dns").

- Package passthrough was not exporting any symbols and there was never a need to even blank-import it.

After as much searching as possible, it appears nobody in the open source community is referencing either of these packages.

balancer_test.go

@@ -31,11 +31,6 @@ import (
 	_ "google.golang.org/grpc/grpclog/glogger"
 	"google.golang.org/grpc/naming"
 	"google.golang.org/grpc/status"
-
-	// V1 balancer tests use passthrough resolver instead of dns.
-	// TODO(bar) remove this when removing v1 balaner entirely.
-
-	_ "google.golang.org/grpc/resolver/passthrough"
 )
 
 func pickFirstBalancerV1(r naming.Resolver) Balancer {

clientconn.go

@@ -32,7 +32,6 @@ import (
 
 	"google.golang.org/grpc/balancer"
 	"google.golang.org/grpc/balancer/base"
-	_ "google.golang.org/grpc/balancer/roundrobin" // To register roundrobin.
 	"google.golang.org/grpc/codes"
 	"google.golang.org/grpc/connectivity"
 	"google.golang.org/grpc/credentials"
@@ -43,10 +42,12 @@ import (
 	"google.golang.org/grpc/internal/transport"
 	"google.golang.org/grpc/keepalive"
 	"google.golang.org/grpc/resolver"
-	_ "google.golang.org/grpc/resolver/dns"         // To register dns resolver.
-	_ "google.golang.org/grpc/resolver/passthrough" // To register passthrough resolver.
 	"google.golang.org/grpc/serviceconfig"
 	"google.golang.org/grpc/status"
+
+	_ "google.golang.org/grpc/balancer/roundrobin"           // To register roundrobin.
+	_ "google.golang.org/grpc/internal/resolver/dns"         // To register dns resolver.
+	_ "google.golang.org/grpc/internal/resolver/passthrough" // To register passthrough resolver.
 )
 
 const (

clientconn_test.go

@@ -39,7 +39,6 @@ import (
 	"google.golang.org/grpc/naming"
 	"google.golang.org/grpc/resolver"
 	"google.golang.org/grpc/resolver/manual"
-	_ "google.golang.org/grpc/resolver/passthrough"
 	"google.golang.org/grpc/testdata"
 )
 

test/end2end_test.go

@@ -69,7 +69,6 @@ import (
 	"google.golang.org/grpc/peer"
 	"google.golang.org/grpc/resolver"
 	"google.golang.org/grpc/resolver/manual"
-	_ "google.golang.org/grpc/resolver/passthrough"
 	"google.golang.org/grpc/serviceconfig"
 	"google.golang.org/grpc/stats"
 	"google.golang.org/grpc/status"

vet.sh

@@ -128,7 +128,7 @@ google.golang.org/grpc/examples/features/debugging/client/main.go:SA1019
 google.golang.org/grpc/examples/features/load_balancing/client/main.go:SA1019
 google.golang.org/grpc/internal/transport/handler_server.go:SA1019
 google.golang.org/grpc/internal/transport/handler_server_test.go:SA1019
-google.golang.org/grpc/resolver/dns/dns_resolver.go:SA1019
+google.golang.org/grpc/internal/resolver/dns/dns_resolver.go:SA1019
 google.golang.org/grpc/stats/stats_test.go:SA1019
 google.golang.org/grpc/test/balancer_test.go:SA1019
 google.golang.org/grpc/test/channelz_test.go:SA1019