Add reflection.Type[T]() helper and use it.

fillrefs.go

@@ -17,6 +17,8 @@ package weaver
 import (
  "fmt"
  "reflect"
+
+ "github.com/ServiceWeaver/weaver/internal/reflection"
 )
 
 // fillRefs initializes Ref[T] fields in a component implement struct.
@@ -32,7 +34,7 @@ func fillRefs(impl any, get func(reflect.Type) (any, error)) error {
  if s.Kind() != reflect.Struct {
  return fmt.Errorf("not a struct pointer")
  }
- isRef := reflect.TypeOf((*interface{ isRef() })(nil)).Elem()
+ isRef := reflection.Type[interface{ isRef() }]()
  for i, n := 0, s.NumField(); i < n; i++ {
  // Handle field with type weaver.Ref[T].
  ref := s.Field(i)

godeps.txt

@@ -13,6 +13,7 @@ github.com/ServiceWeaver/weaver
  github.com/ServiceWeaver/weaver/internal/metrics
  github.com/ServiceWeaver/weaver/internal/net/call
  github.com/ServiceWeaver/weaver/internal/private
+ github.com/ServiceWeaver/weaver/internal/reflection
  github.com/ServiceWeaver/weaver/internal/register
  github.com/ServiceWeaver/weaver/internal/status
  github.com/ServiceWeaver/weaver/internal/tool/single
@@ -466,6 +467,8 @@ github.com/ServiceWeaver/weaver/internal/queue
  context
  github.com/ServiceWeaver/weaver/internal/cond
  sync
+github.com/ServiceWeaver/weaver/internal/reflection
+ reflect
 github.com/ServiceWeaver/weaver/internal/register
  fmt
  sync
@@ -901,6 +904,7 @@ github.com/ServiceWeaver/weaver/weavertest
  github.com/ServiceWeaver/weaver
  github.com/ServiceWeaver/weaver/internal/envelope/conn
  github.com/ServiceWeaver/weaver/internal/private
+ github.com/ServiceWeaver/weaver/internal/reflection
  github.com/ServiceWeaver/weaver/runtime
  github.com/ServiceWeaver/weaver/runtime/codegen
  github.com/ServiceWeaver/weaver/runtime/envelope

internal/envelope/conn/conn_test.go

@@ -25,6 +25,7 @@ import (
 
  "github.com/ServiceWeaver/weaver"
  "github.com/ServiceWeaver/weaver/internal/envelope/conn"
+ "github.com/ServiceWeaver/weaver/internal/reflection"
  "github.com/ServiceWeaver/weaver/metrics"
  "github.com/ServiceWeaver/weaver/runtime/codegen"
  "github.com/ServiceWeaver/weaver/runtime/protos"
@@ -195,7 +196,7 @@ func register[Intf, Impl any](name string) {
  var zero Impl
  codegen.Register(codegen.Registration{
  Name: name,
- Iface: reflect.TypeOf((*Intf)(nil)).Elem(),
+ Iface: reflection.Type[Intf](),
  Impl: reflect.TypeOf(zero),
  LocalStubFn: func(any, trace.Tracer) any { return nil },
  ClientStubFn: func(codegen.Stub, string) any { return nil },

internal/reflection/reflection.go

@@ -0,0 +1,26 @@
+// Copyright 2023 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http:https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// Package reflection implements helpers for reflection code.
+package reflection
+
+import "reflect"
+
+// Type returns the reflect.Type for T.
+//
+// This function is particularly useful when T is an interface
+// and it is impossible to get a value with concrete type T.
+func Type[T any]() reflect.Type {
+ return reflect.TypeOf((*T)(nil)).Elem()
+}

internal/reflection/reflection_test.go

@@ -0,0 +1,40 @@
+// Copyright 2023 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http:https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package reflection_test
+
+import (
+ "fmt"
+ "io"
+ "reflect"
+ "testing"
+
+ "github.com/ServiceWeaver/weaver/internal/reflection"
+)
+
+func TestType(t *testing.T) {
+ for _, test := range []struct {
+ want string
+ t reflect.Type
+ }{
+ {"int", reflection.Type[int]()},
+ {"io.Reader", reflection.Type[io.Reader]()},
+ } {
+ t.Run(test.want, func(t *testing.T) {
+ if got := fmt.Sprint(test.t); got != test.want {
+ t.Errorf("reflection.Type[io.Reader] = %s, expecting %s", got, test.want)
+ }
+ })
+ }
+}

runtime/codegen/registry_test.go

@@ -21,6 +21,7 @@ import (
  "testing"
 
  "github.com/ServiceWeaver/weaver"
+ "github.com/ServiceWeaver/weaver/internal/reflection"
  "github.com/ServiceWeaver/weaver/runtime/codegen"
  "go.opentelemetry.io/otel/trace"
 )
@@ -120,7 +121,7 @@ func register[Intf, Impl any](name string) {
  var zero Impl
  codegen.Register(codegen.Registration{
  Name: name,
- Iface: reflect.TypeOf((*Intf)(nil)).Elem(),
+ Iface: reflection.Type[Intf](),
  Impl: reflect.TypeOf(zero),
  LocalStubFn: func(any, trace.Tracer) any { return nil },
  ClientStubFn: func(codegen.Stub, string) any { return nil },

runtime/envelope/envelope_test.go

@@ -32,6 +32,7 @@ import (
 
  "github.com/ServiceWeaver/weaver"
  "github.com/ServiceWeaver/weaver/internal/envelope/conn"
+ "github.com/ServiceWeaver/weaver/internal/reflection"
  "github.com/ServiceWeaver/weaver/internal/traceio"
  "github.com/ServiceWeaver/weaver/runtime"
  "github.com/ServiceWeaver/weaver/runtime/codegen"
@@ -549,7 +550,7 @@ func register[Intf, Impl any](name string) {
  var zero Impl
  codegen.Register(codegen.Registration{
  Name: name,
- Iface: reflect.TypeOf((*Intf)(nil)).Elem(),
+ Iface: reflection.Type[Intf](),
  Impl: reflect.TypeOf(zero),
  LocalStubFn: func(any, trace.Tracer) any { return nil },
  ClientStubFn: func(codegen.Stub, string) any { return nil },

weavelet.go

@@ -31,6 +31,7 @@ import (
  "github.com/ServiceWeaver/weaver/internal/envelope/conn"
  "github.com/ServiceWeaver/weaver/internal/net/call"
  "github.com/ServiceWeaver/weaver/internal/private"
+ "github.com/ServiceWeaver/weaver/internal/reflection"
  "github.com/ServiceWeaver/weaver/internal/traceio"
  "github.com/ServiceWeaver/weaver/runtime"
  "github.com/ServiceWeaver/weaver/runtime/codegen"
@@ -250,7 +251,7 @@ func (w *weavelet) start() error {
 func (w *weavelet) getMainIfLocal() (*componentImpl, error) {
  // Note that a weavertest may have RunMain set to true, but no main
  // component registered.
- if m, ok := w.componentsByType[reflect.TypeOf((*Main)(nil)).Elem()]; ok && w.info.RunMain {
+ if m, ok := w.componentsByType[reflection.Type[Main]()]; ok && w.info.RunMain {
  return w.getImpl(w.ctx, m)
  }
  return nil, nil

weavertest/init.go

@@ -27,6 +27,7 @@ import (
 
  "github.com/ServiceWeaver/weaver"
  "github.com/ServiceWeaver/weaver/internal/private"
+ "github.com/ServiceWeaver/weaver/internal/reflection"
  "github.com/ServiceWeaver/weaver/runtime/logging"
 )
 
@@ -83,10 +84,11 @@ type FakeComponent struct {
 // The result is typically placed in Runner.Fakes.
 // REQUIRES: impl must implement T.
 func Fake[T any](impl any) FakeComponent {
+ t := reflection.Type[T]()
  if _, ok := impl.(T); !ok {
- panic(fmt.Sprintf("%T does not implement %v", impl, reflect.TypeOf((*T)(nil)).Elem()))
+ panic(fmt.Sprintf("%T does not implement %v", impl, t))
  }
- return FakeComponent{intf: reflect.TypeOf((*T)(nil)).Elem(), impl: impl}
+ return FakeComponent{intf: t, impl: impl}
 }
 
 // private.App object per live test or benchmark.