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registrar.go
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registrar.go
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// 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://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 sim
import (
"errors"
"fmt"
"math/rand"
"reflect"
"testing"
"github.com/ServiceWeaver/weaver/internal/reflection"
)
// registrar is the canonical Registrar implementation. A registrar is not safe
// for concurrent use by multiple goroutines. However, a registrar can be used
// across multiple executions by calling the reset method.
//
// r := newRegistrar(...)
// for {
// r.RegisterFakes(...)
// r.RegisterGenerators(...)
// r.finalize()
// r.reset()
// }
type registrar struct {
// Immutable fields.
t testing.TB // underlying test
registered map[reflect.Type]struct{} // registered component interfaces
opsByName map[string]int // index into ops, by op name
// Cached after the first execution.
typeInfo map[string][]generatorTypeInfo // generator type info
// Updated for every execution.
fakes map[reflect.Type]any // fakes, by component interface
ops []*op // operations
}
var _ Registrar = ®istrar{}
// generatorTypeInfo holds type information about a generator.
type generatorTypeInfo struct {
t reflect.Type // the type of the generator
generate reflect.Method // the Generate method
}
// newRegistrar returns a new registrar.
func newRegistrar(t testing.TB, w reflect.Type, registered map[reflect.Type]struct{}) *registrar {
// Gather the set of ops.
ops := []*op{}
opsByName := map[string]int{}
for i := 0; i < w.NumMethod(); i++ {
m := w.Method(i)
if m.Name == "Init" {
continue
}
arity := m.Type.NumIn() - 2 // ignore receiver and context arguments
ops = append(ops, &op{m, make([]generator, 0, arity)})
opsByName[m.Name] = len(ops) - 1
}
return ®istrar{
t: t,
registered: registered,
fakes: map[reflect.Type]any{},
typeInfo: map[string][]generatorTypeInfo{},
ops: ops,
opsByName: opsByName,
}
}
// reset resets a registrar.
func (r *registrar) reset() {
for k := range r.fakes {
delete(r.fakes, k)
}
for _, op := range r.ops {
op.generators = op.generators[:0]
}
}
// RegisterFake implements the Registrar interface.
func (r *registrar) RegisterFake(fake FakeComponent) {
r.t.Helper()
if err := r.registerFakes(fake); err != nil {
r.t.Fatalf("RegisterFakes: %v", err)
}
}
// RegisterGenerators implements the Registrar interface.
func (r *registrar) RegisterGenerators(method string, generators ...any) {
r.t.Helper()
if err := r.registerGenerators(method, generators...); err != nil {
r.t.Fatalf("RegisterGenerators: %v", err)
}
}
// registerFakes implements RegisterFakes.
func (r *registrar) registerFakes(fake FakeComponent) error {
if _, ok := r.fakes[fake.intf]; ok {
return fmt.Errorf("fake for %v already registered", fake.intf)
}
if _, ok := r.registered[fake.intf]; !ok {
return fmt.Errorf("component %v not found", fake.intf)
}
r.fakes[fake.intf] = fake.impl
return nil
}
// registerGenerators implements RegisterGenerators.
func (r *registrar) registerGenerators(method string, generators ...any) error {
i, ok := r.opsByName[method]
if !ok {
return fmt.Errorf("method %q not found", method)
}
op := r.ops[i]
if len(op.generators) > 0 {
return fmt.Errorf("method %q generators already registered", method)
}
arity := op.m.Type.NumIn() - 2 // ignore receiver and context arguments
if len(generators) != arity {
return fmt.Errorf("method %v: want %d generators, got %d", method, arity, len(generators))
}
if infos, ok := r.typeInfo[method]; ok {
// We have type information cached for this method.
var errs []error
for i, generator := range generators {
info := infos[i]
t := reflect.TypeOf(generator)
if t != info.t {
errs = append(errs, fmt.Errorf("method %s generator %d has type %v, but previously had type %v", method, i, t, info.t))
continue
}
generator := generator
op.generators = append(op.generators, func(r *rand.Rand) reflect.Value {
in := []reflect.Value{reflect.ValueOf(generator), reflect.ValueOf(r)}
return info.generate.Func.Call(in)[0]
})
}
return errors.Join(errs...)
}
// We don't have type information cached for this method.
var errs []error
infos := make([]generatorTypeInfo, arity)
for i, generator := range generators {
// TODO(mwhittaker): Handle the case where a generator's Generate
// method receives by pointer, but the user passed by value.
t := reflect.TypeOf(generator)
err := func() error {
return fmt.Errorf("method %s generator %d is not a generator", method, i)
}
if t == nil {
errs = append(errs, fmt.Errorf("%w: missing Generate method", err()))
continue
}
// TODO(mwhittaker): If the Generator interface looked like this:
//
// type Generator[T any] interface {
// Generate(*rand.Rand) any
// }
//
// then we could write `g, ok := generator.(Generator)`, which is much
// faster. Think about how to speed things up without making the
// interface ugly.
generate, ok := t.MethodByName("Generate")
switch {
case !ok:
errs = append(errs, fmt.Errorf("%w: missing Generate method", err()))
continue
case generate.Type.NumIn() < 2:
errs = append(errs, fmt.Errorf("%w: Generate method has no arguments", err()))
continue
case generate.Type.NumIn() > 2:
errs = append(errs, fmt.Errorf("%w: Generate method has too many arguments", err()))
continue
case generate.Type.In(1) != reflection.Type[*rand.Rand]():
errs = append(errs, fmt.Errorf("%w: Generate argument is not *rand.Rand", err()))
continue
case generate.Type.NumOut() == 0:
errs = append(errs, fmt.Errorf("%w: Generate method has no return values", err()))
continue
case generate.Type.NumOut() > 1:
errs = append(errs, fmt.Errorf("%w: Generate method has too many return values", err()))
continue
case generate.Type.Out(0) != op.m.Type.In(i+2):
errs = append(errs, fmt.Errorf("method %s invalid generator %d: got Generator[%v], want Generator[%v]", method, i, generate.Type.Out(0), op.m.Type.In(i+2)))
continue
}
generator := generator
infos[i] = generatorTypeInfo{t, generate}
op.generators = append(op.generators, func(r *rand.Rand) reflect.Value {
in := []reflect.Value{reflect.ValueOf(generator), reflect.ValueOf(r)}
return generate.Func.Call(in)[0]
})
}
err := errors.Join(errs...)
if err == nil {
r.typeInfo[method] = infos
}
return err
}
// finalize finalizes registration.
func (r *registrar) finalize() error {
var errs []error
for _, op := range r.ops {
arity := op.m.Type.NumIn() - 2 // ignore receiver and context arguments
if len(op.generators) != arity {
errs = append(errs, fmt.Errorf("no generators registered for method %s", op.m.Name))
}
}
return errors.Join(errs...)
}