status-go/vendor/go.uber.org/fx/annotated.go

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// Copyright (c) 2020-2021 Uber Technologies, Inc.
//
// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in
// all copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
// THE SOFTWARE.
package fx
import (
"context"
"errors"
"fmt"
"reflect"
"strings"
"go.uber.org/dig"
"go.uber.org/fx/internal/fxreflect"
)
// Annotated annotates a constructor provided to Fx with additional options.
//
// For example,
//
// func NewReadOnlyConnection(...) (*Connection, error)
//
// fx.Provide(fx.Annotated{
// Name: "ro",
// Target: NewReadOnlyConnection,
// })
//
// Is equivalent to,
//
// type result struct {
// fx.Out
//
// Connection *Connection `name:"ro"`
// }
//
// fx.Provide(func(...) (result, error) {
// conn, err := NewReadOnlyConnection(...)
// return result{Connection: conn}, err
// })
//
// Annotated cannot be used with constructors which produce fx.Out objects.
//
// When used with fx.Supply, the target is a value rather than a constructor function.
type Annotated struct {
// If specified, this will be used as the name for all non-error values returned
// by the constructor. For more information on named values, see the documentation
// for the fx.Out type.
//
// A name option may not be provided if a group option is provided.
Name string
// If specified, this will be used as the group name for all non-error values returned
// by the constructor. For more information on value groups, see the package documentation.
//
// A group option may not be provided if a name option is provided.
//
// Similar to group tags, the group name may be followed by a `,flatten`
// option to indicate that each element in the slice returned by the
// constructor should be injected into the value group individually.
Group string
// Target is the constructor or value being annotated with fx.Annotated.
Target interface{}
}
func (a Annotated) String() string {
var fields []string
if len(a.Name) > 0 {
fields = append(fields, fmt.Sprintf("Name: %q", a.Name))
}
if len(a.Group) > 0 {
fields = append(fields, fmt.Sprintf("Group: %q", a.Group))
}
if a.Target != nil {
fields = append(fields, fmt.Sprintf("Target: %v", fxreflect.FuncName(a.Target)))
}
return fmt.Sprintf("fx.Annotated{%v}", strings.Join(fields, ", "))
}
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var (
// field used for embedding fx.In type in generated struct.
_inAnnotationField = reflect.StructField{
Name: "In",
Type: reflect.TypeOf(In{}),
Anonymous: true,
}
// field used for embedding fx.Out type in generated struct.
_outAnnotationField = reflect.StructField{
Name: "Out",
Type: reflect.TypeOf(Out{}),
Anonymous: true,
}
)
// Annotation can be passed to Annotate(f interface{}, anns ...Annotation)
// for annotating the parameter and result types of a function.
type Annotation interface {
apply(*annotated) error
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build(*annotated) (interface{}, error)
}
var (
_typeOfError reflect.Type = reflect.TypeOf((*error)(nil)).Elem()
_nilError = reflect.Zero(_typeOfError)
)
// annotationError is a wrapper for an error that was encountered while
// applying annotation to a function. It contains the specific error
// that it encountered as well as the target interface that was attempted
// to be annotated.
type annotationError struct {
target interface{}
err error
}
func (e *annotationError) Error() string {
return e.err.Error()
}
// Unwrap the wrapped error.
func (e *annotationError) Unwrap() error {
return e.err
}
type paramTagsAnnotation struct {
tags []string
}
var _ Annotation = paramTagsAnnotation{}
var (
errTagSyntaxSpace = errors.New(`multiple tags are not separated by space`)
errTagKeySyntax = errors.New("tag key is invalid, Use group, name or optional as tag keys")
errTagValueSyntaxQuote = errors.New(`tag value should start with double quote. i.e. key:"value" `)
errTagValueSyntaxEndingQuote = errors.New(`tag value should end in double quote. i.e. key:"value" `)
)
// Collections of key value pairs within a tag should be separated by a space.
// Eg: `group:"some" optional:"true"`.
func verifyTagsSpaceSeparated(tagIdx int, tag string) error {
if tagIdx > 0 && tag != "" && tag[0] != ' ' {
return errTagSyntaxSpace
}
return nil
}
// verify tag values are delimited with double quotes.
func verifyValueQuote(value string) (string, error) {
// starting quote should be a double quote
if value[0] != '"' {
return "", errTagValueSyntaxQuote
}
// validate tag value is within quotes
i := 1
for i < len(value) && value[i] != '"' {
if value[i] == '\\' {
i++
}
i++
}
if i >= len(value) {
return "", errTagValueSyntaxEndingQuote
}
return value[i+1:], nil
}
// Check whether the tag follows valid struct.
// format and returns an error if it's invalid. (i.e. not following
// tag:"value" space-separated list )
// Currently dig accepts only 'name', 'group', 'optional' as valid tag keys.
func verifyAnnotateTag(tag string) error {
tagIdx := 0
validKeys := map[string]struct{}{"group": {}, "optional": {}, "name": {}}
for ; tag != ""; tagIdx++ {
if err := verifyTagsSpaceSeparated(tagIdx, tag); err != nil {
return err
}
i := 0
if strings.TrimSpace(tag) == "" {
return nil
}
// parsing the key i.e. till reaching colon :
for i < len(tag) && tag[i] != ':' {
i++
}
key := strings.TrimSpace(tag[:i])
if _, ok := validKeys[key]; !ok {
return errTagKeySyntax
}
value, err := verifyValueQuote(tag[i+1:])
if err != nil {
return err
}
tag = value
}
return nil
}
// Given func(T1, T2, T3, ..., TN), this generates a type roughly
// equivalent to,
//
// struct {
// fx.In
//
// Field1 T1 `$tags[0]`
// Field2 T2 `$tags[1]`
// ...
// FieldN TN `$tags[N-1]`
// }
//
// If there has already been a ParamTag that was applied, this
// will return an error.
//
// If the tag is invalid and has mismatched quotation for example,
// (`tag_name:"tag_value') , this will return an error.
func (pt paramTagsAnnotation) apply(ann *annotated) error {
if len(ann.ParamTags) > 0 {
return errors.New("cannot apply more than one line of ParamTags")
}
for _, tag := range pt.tags {
if err := verifyAnnotateTag(tag); err != nil {
return err
}
}
ann.ParamTags = pt.tags
return nil
}
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// build builds and returns a constructor after applying a ParamTags annotation
func (pt paramTagsAnnotation) build(ann *annotated) (interface{}, error) {
paramTypes, remap := pt.parameters(ann)
resultTypes, _ := ann.currentResultTypes()
origFn := reflect.ValueOf(ann.Target)
newFnType := reflect.FuncOf(paramTypes, resultTypes, false)
newFn := reflect.MakeFunc(newFnType, func(args []reflect.Value) []reflect.Value {
args = remap(args)
return origFn.Call(args)
})
return newFn.Interface(), nil
}
// parameters returns the type for the parameters of the annotated function,
// and a function that maps the arguments of the annotated function
// back to the arguments of the target function.
func (pt paramTagsAnnotation) parameters(ann *annotated) (
types []reflect.Type,
remap func([]reflect.Value) []reflect.Value,
) {
ft := reflect.TypeOf(ann.Target)
types = make([]reflect.Type, ft.NumIn())
for i := 0; i < ft.NumIn(); i++ {
types[i] = ft.In(i)
}
// No parameter annotations. Return the original types
// and an identity function.
if len(pt.tags) == 0 {
return types, func(args []reflect.Value) []reflect.Value {
return args
}
}
// Turn parameters into an fx.In struct.
inFields := []reflect.StructField{_inAnnotationField}
// there was a variadic argument, so it was pre-transformed
if len(types) > 0 && isIn(types[0]) {
paramType := types[0]
for i := 1; i < paramType.NumField(); i++ {
origField := paramType.Field(i)
field := reflect.StructField{
Name: origField.Name,
Type: origField.Type,
Tag: origField.Tag,
}
if i-1 < len(pt.tags) {
field.Tag = reflect.StructTag(pt.tags[i-1])
}
inFields = append(inFields, field)
}
types = []reflect.Type{reflect.StructOf(inFields)}
return types, func(args []reflect.Value) []reflect.Value {
param := args[0]
args[0] = reflect.New(paramType).Elem()
for i := 1; i < paramType.NumField(); i++ {
args[0].Field(i).Set(param.Field(i))
}
return args
}
}
for i, t := range types {
field := reflect.StructField{
Name: fmt.Sprintf("Field%d", i),
Type: t,
}
if i < len(pt.tags) {
field.Tag = reflect.StructTag(pt.tags[i])
}
inFields = append(inFields, field)
}
types = []reflect.Type{reflect.StructOf(inFields)}
return types, func(args []reflect.Value) []reflect.Value {
params := args[0]
args = args[:0]
for i := 0; i < ft.NumIn(); i++ {
args = append(args, params.Field(i+1))
}
return args
}
}
// ParamTags is an Annotation that annotates the parameter(s) of a function.
// When multiple tags are specified, each tag is mapped to the corresponding
// positional parameter.
//
// ParamTags cannot be used in a function that takes an fx.In struct as a
// parameter.
func ParamTags(tags ...string) Annotation {
return paramTagsAnnotation{tags}
}
type resultTagsAnnotation struct {
tags []string
}
var _ Annotation = resultTagsAnnotation{}
// Given func(T1, T2, T3, ..., TN), this generates a type roughly
// equivalent to,
//
// struct {
// fx.Out
//
// Field1 T1 `$tags[0]`
// Field2 T2 `$tags[1]`
// ...
// FieldN TN `$tags[N-1]`
// }
//
// If there has already been a ResultTag that was applied, this
// will return an error.
//
// If the tag is invalid and has mismatched quotation for example,
// (`tag_name:"tag_value') , this will return an error.
func (rt resultTagsAnnotation) apply(ann *annotated) error {
if len(ann.ResultTags) > 0 {
return errors.New("cannot apply more than one line of ResultTags")
}
for _, tag := range rt.tags {
if err := verifyAnnotateTag(tag); err != nil {
return err
}
}
ann.ResultTags = rt.tags
return nil
}
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// build builds and returns a constructor after applying a ResultTags annotation
func (rt resultTagsAnnotation) build(ann *annotated) (interface{}, error) {
paramTypes := ann.currentParamTypes()
resultTypes, remapResults := rt.results(ann)
origFn := reflect.ValueOf(ann.Target)
newFnType := reflect.FuncOf(paramTypes, resultTypes, false)
newFn := reflect.MakeFunc(newFnType, func(args []reflect.Value) []reflect.Value {
results := origFn.Call(args)
return remapResults(results)
})
return newFn.Interface(), nil
}
// results returns the types of the results of the annotated function,
// and a function that maps the results of the target function,
// into a result compatible with the annotated function.
func (rt resultTagsAnnotation) results(ann *annotated) (
types []reflect.Type,
remap func([]reflect.Value) []reflect.Value,
) {
types, hasError := ann.currentResultTypes()
if hasError {
types = types[:len(types)-1]
}
// No result annotations. Return the original types
// and an identity function.
if len(rt.tags) == 0 {
return types, func(results []reflect.Value) []reflect.Value {
return results
}
}
// if there's no Out struct among the return types, there was no As annotation applied
// just replace original result types with an Out struct and apply tags
var (
newOut outStructInfo
existingOuts []reflect.Type
)
newOut.Fields = []reflect.StructField{_outAnnotationField}
newOut.Offsets = []int{}
for i, t := range types {
if !isOut(t) {
// this must be from the original function.
// apply the tags
field := reflect.StructField{
Name: fmt.Sprintf("Field%d", i),
Type: t,
}
if i < len(rt.tags) {
field.Tag = reflect.StructTag(rt.tags[i])
}
newOut.Offsets = append(newOut.Offsets, len(newOut.Fields))
newOut.Fields = append(newOut.Fields, field)
continue
}
// this must be from an As annotation
// apply the tags to the existing type
taggedFields := make([]reflect.StructField, t.NumField())
taggedFields[0] = _outAnnotationField
for j, tag := range rt.tags {
if j+1 < t.NumField() {
field := t.Field(j + 1)
taggedFields[j+1] = reflect.StructField{
Name: field.Name,
Type: field.Type,
Tag: reflect.StructTag(tag),
}
}
}
existingOuts = append(existingOuts, reflect.StructOf(taggedFields))
}
resType := reflect.StructOf(newOut.Fields)
outTypes := []reflect.Type{resType}
// append existing outs back to outTypes
outTypes = append(outTypes, existingOuts...)
if hasError {
outTypes = append(outTypes, _typeOfError)
}
return outTypes, func(results []reflect.Value) []reflect.Value {
var (
outErr error
outResults []reflect.Value
)
outResults = append(outResults, reflect.New(resType).Elem())
tIdx := 0
for i, r := range results {
if i == len(results)-1 && hasError {
// If hasError and this is the last item,
// we are guaranteed that this is an error
// object.
if err, _ := r.Interface().(error); err != nil {
outErr = err
}
continue
}
if i < len(newOut.Offsets) {
if fieldIdx := newOut.Offsets[i]; fieldIdx > 0 {
// fieldIdx 0 is an invalid index
// because it refers to uninitialized
// outs and would point to fx.Out in the
// struct definition. We need to check this
// to prevent panic from setting fx.Out to
// a value.
outResults[0].Field(fieldIdx).Set(r)
}
continue
}
if isOut(r.Type()) {
tIdx++
if tIdx < len(outTypes) {
newResult := reflect.New(outTypes[tIdx]).Elem()
for j := 1; j < outTypes[tIdx].NumField(); j++ {
newResult.Field(j).Set(r.Field(j))
}
outResults = append(outResults, newResult)
}
}
}
if hasError {
if outErr != nil {
outResults = append(outResults, reflect.ValueOf(outErr))
} else {
outResults = append(outResults, _nilError)
}
}
return outResults
}
}
// ResultTags is an Annotation that annotates the result(s) of a function.
// When multiple tags are specified, each tag is mapped to the corresponding
// positional result.
//
// ResultTags cannot be used on a function that returns an fx.Out struct.
func ResultTags(tags ...string) Annotation {
return resultTagsAnnotation{tags}
}
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type outStructInfo struct {
Fields []reflect.StructField // fields of the struct
Offsets []int // Offsets[i] is the index of result i in Fields
}
type _lifecycleHookAnnotationType int
const (
_unknownHookType _lifecycleHookAnnotationType = iota
_onStartHookType
_onStopHookType
)
type lifecycleHookAnnotation struct {
Type _lifecycleHookAnnotationType
Target interface{}
}
var _ Annotation = (*lifecycleHookAnnotation)(nil)
func (la *lifecycleHookAnnotation) String() string {
name := "UnknownHookAnnotation"
switch la.Type {
case _onStartHookType:
name = _onStartHook
case _onStopHookType:
name = _onStopHook
}
return name
}
func (la *lifecycleHookAnnotation) apply(ann *annotated) error {
if la.Target == nil {
return fmt.Errorf(
"cannot use nil function for %q hook annotation",
la,
)
}
for _, h := range ann.Hooks {
if la.Type == h.Type {
return fmt.Errorf(
"cannot apply more than one %q hook annotation",
la,
)
}
}
ft := reflect.TypeOf(la.Target)
if ft.Kind() != reflect.Func {
return fmt.Errorf(
"must provide function for %q hook, got %v (%T)",
la,
la.Target,
la.Target,
)
}
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if n := ft.NumOut(); n > 0 {
if n > 1 || ft.Out(0) != _typeOfError {
return fmt.Errorf(
"optional hook return may only be an error, got %v (%T)",
la.Target,
la.Target,
)
}
}
if ft.IsVariadic() {
return fmt.Errorf(
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"hooks must not accept variadic parameters, got %v (%T)",
la.Target,
la.Target,
)
}
ann.Hooks = append(ann.Hooks, la)
return nil
}
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// build builds and returns a constructor after applying a lifecycle hook annotation.
func (la *lifecycleHookAnnotation) build(ann *annotated) (interface{}, error) {
resultTypes, hasError := ann.currentResultTypes()
if !hasError {
resultTypes = append(resultTypes, _typeOfError)
}
hookInstaller, paramTypes, remapParams := la.buildHookInstaller(ann)
origFn := reflect.ValueOf(ann.Target)
newFnType := reflect.FuncOf(paramTypes, resultTypes, false)
newFn := reflect.MakeFunc(newFnType, func(args []reflect.Value) []reflect.Value {
// copy the original arguments before remapping the parameters
// so that we can apply them to the hookInstaller.
origArgs := make([]reflect.Value, len(args))
copy(origArgs, args)
args = remapParams(args)
results := origFn.Call(args)
if hasError {
errVal := results[len(results)-1]
results = results[:len(results)-1]
if err, _ := errVal.Interface().(error); err != nil {
// if constructor returned error, do not call hook installer
return append(results, errVal)
}
}
hookInstallerResults := hookInstaller.Call(append(results, origArgs...))
results = append(results, hookInstallerResults[0])
return results
})
return newFn.Interface(), nil
}
var (
_typeOfLifecycle reflect.Type = reflect.TypeOf((*Lifecycle)(nil)).Elem()
_typeOfContext reflect.Type = reflect.TypeOf((*context.Context)(nil)).Elem()
)
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// buildHookInstaller returns a function that appends a hook to Lifecycle when called,
// along with the new parameter types and a function that maps arguments to the annotated constructor
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func (la *lifecycleHookAnnotation) buildHookInstaller(ann *annotated) (
hookInstaller reflect.Value,
paramTypes []reflect.Type,
remapParams func([]reflect.Value) []reflect.Value, // function to remap parameters to function being annotated
) {
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paramTypes = ann.currentParamTypes()
paramTypes, remapParams = injectLifecycle(paramTypes)
resultTypes, hasError := ann.currentResultTypes()
if hasError {
resultTypes = resultTypes[:len(resultTypes)-1]
}
// look for the context.Context type from the original hook function
// and then exclude it from the paramTypes of invokeFn because context.Context
// will be injected by the lifecycle
ctxPos := -1
ctxStructPos := -1
origHookFn := reflect.ValueOf(la.Target)
origHookFnT := reflect.TypeOf(la.Target)
invokeParamTypes := []reflect.Type{
_typeOfLifecycle,
}
for i := 0; i < origHookFnT.NumIn(); i++ {
t := origHookFnT.In(i)
if t == _typeOfContext && ctxPos < 0 {
ctxPos = i
continue
}
if !isIn(t) {
invokeParamTypes = append(invokeParamTypes, origHookFnT.In(i))
continue
}
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fields := []reflect.StructField{_inAnnotationField}
for j := 1; j < t.NumField(); j++ {
field := t.Field(j)
if field.Type == _typeOfContext && ctxPos < 0 {
ctxStructPos = i
ctxPos = j
continue
}
fields = append(fields, field)
}
invokeParamTypes = append(invokeParamTypes, reflect.StructOf(fields))
}
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invokeFnT := reflect.FuncOf(invokeParamTypes, []reflect.Type{}, false)
invokeFn := reflect.MakeFunc(invokeFnT, func(args []reflect.Value) (results []reflect.Value) {
lc := args[0].Interface().(Lifecycle)
args = args[1:]
hookArgs := make([]reflect.Value, origHookFnT.NumIn())
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hookFn := func(ctx context.Context) (err error) {
// If the hook function has multiple parameters, and the first
// parameter is a context, inject the provided context.
if ctxStructPos < 0 {
offset := 0
for i := 0; i < len(hookArgs); i++ {
if i == ctxPos {
hookArgs[i] = reflect.ValueOf(ctx)
offset = 1
continue
}
if i-offset >= 0 && i-offset < len(args) {
hookArgs[i] = args[i-offset]
}
}
} else {
for i := 0; i < origHookFnT.NumIn(); i++ {
if i != ctxStructPos {
hookArgs[i] = args[i]
continue
}
t := origHookFnT.In(i)
v := reflect.New(t).Elem()
for j := 1; j < t.NumField(); j++ {
if j < ctxPos {
v.Field(j).Set(args[i].Field(j))
} else if j == ctxPos {
v.Field(j).Set(reflect.ValueOf(ctx))
} else {
v.Field(j).Set(args[i].Field(j - 1))
}
}
hookArgs[i] = v
}
}
hookResults := origHookFn.Call(hookArgs)
if len(hookResults) > 0 && hookResults[0].Type() == _typeOfError {
err, _ = hookResults[0].Interface().(error)
}
return err
}
lc.Append(la.buildHook(hookFn))
return results
})
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installerType := reflect.FuncOf(append(resultTypes, paramTypes...), []reflect.Type{_typeOfError}, false)
hookInstaller = reflect.MakeFunc(installerType, func(args []reflect.Value) (results []reflect.Value) {
// build a private scope for hook function
var scope *dig.Scope
switch la.Type {
case _onStartHookType:
scope = ann.container.Scope("onStartHookScope")
case _onStopHookType:
scope = ann.container.Scope("onStopHookScope")
}
// provide the private scope with the current dependencies and results of the annotated function
results = []reflect.Value{_nilError}
ctor := makeHookScopeCtor(paramTypes, resultTypes, args)
if err := scope.Provide(ctor); err != nil {
results[0] = reflect.ValueOf(fmt.Errorf("error providing possible parameters for hook installer: %w", err))
return results
}
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// invoking invokeFn appends the hook function to lifecycle
if err := scope.Invoke(invokeFn.Interface()); err != nil {
results[0] = reflect.ValueOf(fmt.Errorf("error invoking hook installer: %w", err))
return results
}
return results
})
return hookInstaller, paramTypes, remapParams
}
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var (
_nameTag = "name"
_groupTag = "group"
)
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// makeHookScopeCtor makes a constructor that provides all possible parameters
// that the lifecycle hook being appended can depend on. It also deduplicates
// duplicate param and result types, which is possible when using fx.Decorate,
// and uses values from results for providing the deduplicated types.
func makeHookScopeCtor(paramTypes []reflect.Type, resultTypes []reflect.Type, args []reflect.Value) interface{} {
type key struct {
t reflect.Type
name string
group string
}
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seen := map[key]struct{}{}
outTypes := make([]reflect.Type, len(resultTypes))
for i, t := range resultTypes {
outTypes[i] = t
if isOut(t) {
for j := 1; j < t.NumField(); j++ {
field := t.Field(j)
seen[key{
t: field.Type,
name: field.Tag.Get(_nameTag),
group: field.Tag.Get(_groupTag),
}] = struct{}{}
}
continue
}
seen[key{t: t}] = struct{}{}
}
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fields := []reflect.StructField{_outAnnotationField}
skippedParams := make([][]int, len(paramTypes))
for i, t := range paramTypes {
skippedParams[i] = []int{}
if isIn(t) {
for j := 1; j < t.NumField(); j++ {
origField := t.Field(j)
k := key{
t: origField.Type,
name: origField.Tag.Get(_nameTag),
group: origField.Tag.Get(_groupTag),
}
if _, ok := seen[k]; ok {
skippedParams[i] = append(skippedParams[i], j)
continue
}
field := reflect.StructField{
Name: fmt.Sprintf("Field%d", j-1),
Type: origField.Type,
Tag: origField.Tag,
}
fields = append(fields, field)
}
continue
}
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k := key{t: t}
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if _, ok := seen[k]; ok {
skippedParams[i] = append(skippedParams[i], i)
continue
}
field := reflect.StructField{
Name: fmt.Sprintf("Field%d", i),
Type: t,
}
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fields = append(fields, field)
}
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outTypes = append(outTypes, reflect.StructOf(fields))
ctorType := reflect.FuncOf([]reflect.Type{}, outTypes, false)
ctor := reflect.MakeFunc(ctorType, func(_ []reflect.Value) []reflect.Value {
nOut := len(outTypes)
results := make([]reflect.Value, nOut)
for i := 0; i < nOut-1; i++ {
results[i] = args[i]
}
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v := reflect.New(outTypes[nOut-1]).Elem()
fieldIdx := 1
for i := nOut - 1; i < len(args); i++ {
paramIdx := i - (nOut - 1)
if isIn(paramTypes[paramIdx]) {
skippedIdx := 0
for j := 1; j < paramTypes[paramIdx].NumField(); j++ {
if len(skippedParams[paramIdx]) > 0 && skippedParams[paramIdx][skippedIdx] == j {
// skip
skippedIdx++
continue
}
v.Field(fieldIdx).Set(args[i].Field(j))
fieldIdx++
}
} else {
if len(skippedParams[paramIdx]) > 0 && skippedParams[paramIdx][0] == paramIdx {
continue
}
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v.Field(fieldIdx).Set(args[i])
fieldIdx++
}
}
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results[nOut-1] = v
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return results
})
return ctor.Interface()
}
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func injectLifecycle(paramTypes []reflect.Type) ([]reflect.Type, func([]reflect.Value) []reflect.Value) {
// since lifecycle already exists in param types, no need to inject again
if lifecycleExists(paramTypes) {
return paramTypes, func(args []reflect.Value) []reflect.Value {
return args
}
}
// If params are tagged or there's an untagged variadic argument,
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// add a Lifecycle field to the param struct
if len(paramTypes) > 0 && isIn(paramTypes[0]) {
taggedParam := paramTypes[0]
fields := []reflect.StructField{
taggedParam.Field(0),
{
Name: "Lifecycle",
Type: _typeOfLifecycle,
},
}
for i := 1; i < taggedParam.NumField(); i++ {
fields = append(fields, taggedParam.Field(i))
}
newParamType := reflect.StructOf(fields)
return []reflect.Type{newParamType}, func(args []reflect.Value) []reflect.Value {
param := args[0]
args[0] = reflect.New(taggedParam).Elem()
for i := 1; i < taggedParam.NumField(); i++ {
args[0].Field(i).Set(param.Field(i + 1))
}
return args
}
}
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return append([]reflect.Type{_typeOfLifecycle}, paramTypes...), func(args []reflect.Value) []reflect.Value {
return args[1:]
}
}
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func lifecycleExists(paramTypes []reflect.Type) bool {
for _, t := range paramTypes {
if t == _typeOfLifecycle {
return true
}
if isIn(t) {
for i := 1; i < t.NumField(); i++ {
if t.Field(i).Type == _typeOfLifecycle {
return true
}
}
}
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}
return false
}
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func (la *lifecycleHookAnnotation) buildHook(fn func(context.Context) error) (hook Hook) {
switch la.Type {
case _onStartHookType:
hook.OnStart = fn
case _onStopHookType:
hook.OnStop = fn
}
return hook
}
// OnStart is an Annotation that appends an OnStart Hook to the application
// Lifecycle when that function is called. This provides a way to create
// Lifecycle OnStart (see Lifecycle type documentation) hooks without building a
// function that takes a dependency on the Lifecycle type.
//
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// fx.Provide(
// fx.Annotate(
// NewServer,
// fx.OnStart(func(ctx context.Context, server Server) error {
// return server.Listen(ctx)
// }),
// )
// )
//
// Which is functionally the same as:
//
// fx.Provide(
// func(lifecycle fx.Lifecycle, p Params) Server {
// server := NewServer(p)
// lifecycle.Append(fx.Hook{
// OnStart: func(ctx context.Context) error {
// return server.Listen(ctx)
// },
// })
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// return server
// }
// )
//
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// It is also possible to use OnStart annotation with other parameter and result
// annotations, provided that the parameter of the function passed to OnStart
// matches annotated parameters and results.
//
// For example, the following is possible:
//
// fx.Provide(
// fx.Annotate(
// func (a A) B {...},
// fx.ParamTags(`name:"A"`),
// fx.ResultTags(`name:"B"`),
// fx.OnStart(func (p OnStartParams) {...}),
// ),
// )
//
// As long as OnStartParams looks like the following and has no other dependencies
// besides Context or Lifecycle:
//
// type OnStartParams struct {
// fx.In
// FieldA A `name:"A"`
// FieldB B `name:"B"`
// }
//
// Only one OnStart annotation may be applied to a given function at a time,
// however functions may be annotated with other types of lifecycle Hooks, such
// as OnStop. The hook function passed into OnStart cannot take any arguments
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// outside of the annotated constructor's existing dependencies or results, except
// a context.Context.
func OnStart(onStart interface{}) Annotation {
return &lifecycleHookAnnotation{
Type: _onStartHookType,
Target: onStart,
}
}
// OnStop is an Annotation that appends an OnStop Hook to the application
// Lifecycle when that function is called. This provides a way to create
// Lifecycle OnStop (see Lifecycle type documentation) hooks without building a
// function that takes a dependency on the Lifecycle type.
//
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// fx.Provide(
// fx.Annotate(
// NewServer,
// fx.OnStop(func(ctx context.Context, server Server) error {
// return server.Shutdown(ctx)
// }),
// )
// )
//
// Which is functionally the same as:
//
// fx.Provide(
// func(lifecycle fx.Lifecycle, p Params) Server {
// server := NewServer(p)
// lifecycle.Append(fx.Hook{
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// OnStop: func(ctx context.Context) error {
// return server.Shutdown(ctx)
// },
// })
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// return server
// }
// )
//
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// It is also possible to use OnStop annotation with other parameter and result
// annotations, provided that the parameter of the function passed to OnStop
// matches annotated parameters and results.
//
// For example, the following is possible:
//
// fx.Provide(
// fx.Annotate(
// func (a A) B {...},
// fx.ParamTags(`name:"A"`),
// fx.ResultTags(`name:"B"`),
// fx.OnStop(func (p OnStopParams) {...}),
// ),
// )
//
// As long as OnStopParams looks like the following and has no other dependencies
// besides Context or Lifecycle:
//
// type OnStopParams struct {
// fx.In
// FieldA A `name:"A"`
// FieldB B `name:"B"`
// }
//
// Only one OnStop annotation may be applied to a given function at a time,
// however functions may be annotated with other types of lifecycle Hooks, such
// as OnStart. The hook function passed into OnStop cannot take any arguments
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// outside of the annotated constructor's existing dependencies or results, except
// a context.Context.
func OnStop(onStop interface{}) Annotation {
return &lifecycleHookAnnotation{
Type: _onStopHookType,
Target: onStop,
}
}
type asAnnotation struct {
targets []interface{}
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types []reflect.Type
}
func isOut(t reflect.Type) bool {
return (t.Kind() == reflect.Struct &&
dig.IsOut(reflect.New(t).Elem().Interface()))
}
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func isIn(t reflect.Type) bool {
return (t.Kind() == reflect.Struct &&
dig.IsIn(reflect.New(t).Elem().Interface()))
}
var _ Annotation = (*asAnnotation)(nil)
// As is an Annotation that annotates the result of a function (i.e. a
// constructor) to be provided as another interface.
//
// For example, the following code specifies that the return type of
// bytes.NewBuffer (bytes.Buffer) should be provided as io.Writer type:
//
// fx.Provide(
// fx.Annotate(bytes.NewBuffer(...), fx.As(new(io.Writer)))
// )
//
// In other words, the code above is equivalent to:
//
// fx.Provide(func() io.Writer {
// return bytes.NewBuffer()
// // provides io.Writer instead of *bytes.Buffer
// })
//
// Note that the bytes.Buffer type is provided as an io.Writer type, so this
// constructor does NOT provide both bytes.Buffer and io.Writer type; it just
// provides io.Writer type.
//
// When multiple values are returned by the annotated function, each type
// gets mapped to corresponding positional result of the annotated function.
//
// For example,
//
// func a() (bytes.Buffer, bytes.Buffer) {
// ...
// }
// fx.Provide(
// fx.Annotate(a, fx.As(new(io.Writer), new(io.Reader)))
// )
//
// Is equivalent to,
//
// fx.Provide(func() (io.Writer, io.Reader) {
// w, r := a()
// return w, r
// }
//
// As annotation cannot be used in a function that returns an [Out] struct as a return type.
func As(interfaces ...interface{}) Annotation {
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return &asAnnotation{targets: interfaces}
}
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func (at *asAnnotation) apply(ann *annotated) error {
at.types = make([]reflect.Type, len(at.targets))
for i, typ := range at.targets {
t := reflect.TypeOf(typ)
if t.Kind() != reflect.Ptr || t.Elem().Kind() != reflect.Interface {
return fmt.Errorf("fx.As: argument must be a pointer to an interface: got %v", t)
}
t = t.Elem()
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at.types[i] = t
}
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ann.As = append(ann.As, at.types)
return nil
}
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// build implements Annotation
func (at *asAnnotation) build(ann *annotated) (interface{}, error) {
paramTypes := ann.currentParamTypes()
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resultTypes, remapResults, err := at.results(ann)
if err != nil {
return nil, err
}
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origFn := reflect.ValueOf(ann.Target)
newFnType := reflect.FuncOf(paramTypes, resultTypes, false)
newFn := reflect.MakeFunc(newFnType, func(args []reflect.Value) []reflect.Value {
results := origFn.Call(args)
return remapResults(results)
})
return newFn.Interface(), nil
}
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func (at *asAnnotation) results(ann *annotated) (
types []reflect.Type,
remap func([]reflect.Value) []reflect.Value,
err error,
) {
types, hasError := ann.currentResultTypes()
fields := []reflect.StructField{_outAnnotationField}
if hasError {
types = types[:len(types)-1]
}
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resultFields, getResult := extractResultFields(types)
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for i, f := range resultFields {
t := f.Type
field := reflect.StructField{
Name: fmt.Sprintf("Field%d", i),
Type: t,
Tag: f.Tag,
}
if i < len(at.types) {
if !t.Implements(at.types[i]) {
return nil, nil, fmt.Errorf("invalid fx.As: %v does not implement %v", t, at.types[i])
}
field.Type = at.types[i]
}
fields = append(fields, field)
}
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resType := reflect.StructOf(fields)
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var outTypes []reflect.Type
outTypes = append(types, resType)
if hasError {
outTypes = append(outTypes, _typeOfError)
}
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return outTypes, func(results []reflect.Value) []reflect.Value {
var (
outErr error
outResults []reflect.Value
)
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for i, r := range results {
if i == len(results)-1 && hasError {
// If hasError and this is the last item,
// we are guaranteed that this is an error
// object.
if err, _ := r.Interface().(error); err != nil {
outErr = err
}
continue
}
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outResults = append(outResults, r)
}
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newOutResult := reflect.New(resType).Elem()
for i := 1; i < resType.NumField(); i++ {
newOutResult.Field(i).Set(getResult(i, results))
}
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outResults = append(outResults, newOutResult)
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if hasError {
if outErr != nil {
outResults = append(outResults, reflect.ValueOf(outErr))
} else {
outResults = append(outResults, _nilError)
}
}
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return outResults
}, nil
}
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func extractResultFields(types []reflect.Type) ([]reflect.StructField, func(int, []reflect.Value) reflect.Value) {
var resultFields []reflect.StructField
if len(types) > 0 && isOut(types[0]) {
for i := 1; i < types[0].NumField(); i++ {
resultFields = append(resultFields, types[0].Field(i))
}
return resultFields, func(idx int, results []reflect.Value) reflect.Value {
return results[0].Field(idx)
}
}
for i, t := range types {
if isOut(t) {
continue
}
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field := reflect.StructField{
Name: fmt.Sprintf("Field%d", i),
Type: t,
}
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resultFields = append(resultFields, field)
}
return resultFields, func(idx int, results []reflect.Value) reflect.Value {
return results[idx-1]
}
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}
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type fromAnnotation struct {
targets []interface{}
types []reflect.Type
}
var _ Annotation = (*fromAnnotation)(nil)
// From is an [Annotation] that annotates the parameter(s) for a function (i.e. a
// constructor) to be accepted from other provided types. It is analogous to the
// [As] for parameter types to the constructor.
//
// For example,
//
// type Runner interface { Run() }
// func NewFooRunner() *FooRunner // implements Runner
// func NewRunnerWrap(r Runner) *RunnerWrap
//
// fx.Provide(
// fx.Annotate(
// NewRunnerWrap,
// fx.From(new(*FooRunner)),
// ),
// )
//
// Is equivalent to,
//
// fx.Provide(func(r *FooRunner) *RunnerWrap {
// // need *FooRunner instead of Runner
// return NewRunnerWrap(r)
// })
//
// When the annotated function takes in multiple parameters, each type gets
// mapped to corresponding positional parameter of the annotated function
//
// For example,
//
// func NewBarRunner() *BarRunner // implements Runner
// func NewRunnerWraps(r1 Runner, r2 Runner) *RunnerWraps
//
// fx.Provide(
// fx.Annotate(
// NewRunnerWraps,
// fx.From(new(*FooRunner), new(*BarRunner)),
// ),
// )
//
// Is equivalent to,
//
// fx.Provide(func(r1 *FooRunner, r2 *BarRunner) *RunnerWraps {
// return NewRunnerWraps(r1, r2)
// })
//
// From annotation cannot be used in a function that takes an [In] struct as a
// parameter.
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func From(interfaces ...interface{}) Annotation {
return &fromAnnotation{targets: interfaces}
}
func (fr *fromAnnotation) apply(ann *annotated) error {
if len(ann.From) > 0 {
return errors.New("cannot apply more than one line of From")
}
ft := reflect.TypeOf(ann.Target)
fr.types = make([]reflect.Type, len(fr.targets))
for i, typ := range fr.targets {
if ft.IsVariadic() && i == ft.NumIn()-1 {
return errors.New("fx.From: cannot annotate a variadic argument")
}
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t := reflect.TypeOf(typ)
if t == nil || t.Kind() != reflect.Ptr {
return fmt.Errorf("fx.From: argument must be a pointer to a type that implements some interface: got %v", t)
}
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fr.types[i] = t.Elem()
}
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ann.From = fr.types
return nil
}
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// build builds and returns a constructor after applying a From annotation
func (fr *fromAnnotation) build(ann *annotated) (interface{}, error) {
paramTypes, remap, err := fr.parameters(ann)
if err != nil {
return nil, err
}
resultTypes, _ := ann.currentResultTypes()
origFn := reflect.ValueOf(ann.Target)
newFnType := reflect.FuncOf(paramTypes, resultTypes, false)
newFn := reflect.MakeFunc(newFnType, func(args []reflect.Value) []reflect.Value {
args = remap(args)
return origFn.Call(args)
})
return newFn.Interface(), nil
}
// parameters returns the type for the parameters of the annotated function,
// and a function that maps the arguments of the annotated function
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// back to the arguments of the target function.
func (fr *fromAnnotation) parameters(ann *annotated) (
types []reflect.Type,
remap func([]reflect.Value) []reflect.Value,
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err error,
) {
ft := reflect.TypeOf(ann.Target)
types = make([]reflect.Type, ft.NumIn())
for i := 0; i < ft.NumIn(); i++ {
types[i] = ft.In(i)
}
// No parameter annotations. Return the original types
// and an identity function.
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if len(fr.targets) == 0 {
return types, func(args []reflect.Value) []reflect.Value {
return args
}, nil
}
// Turn parameters into an fx.In struct.
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inFields := []reflect.StructField{_inAnnotationField}
// The following situations may occur:
// 1. there was a variadic argument, so it was pre-transformed.
// 2. another parameter annotation was transformed (ex: ParamTags).
// so need to visit fields of the fx.In struct.
if len(types) > 0 && isIn(types[0]) {
paramType := types[0]
for i := 1; i < paramType.NumField(); i++ {
origField := paramType.Field(i)
field := reflect.StructField{
Name: origField.Name,
Type: origField.Type,
Tag: origField.Tag,
}
if i-1 < len(fr.types) {
t := fr.types[i-1]
if !t.Implements(field.Type) {
return nil, nil, fmt.Errorf("invalid fx.From: %v does not implement %v", t, field.Type)
}
field.Type = t
}
inFields = append(inFields, field)
}
types = []reflect.Type{reflect.StructOf(inFields)}
return types, func(args []reflect.Value) []reflect.Value {
param := args[0]
args[0] = reflect.New(paramType).Elem()
for i := 1; i < paramType.NumField(); i++ {
args[0].Field(i).Set(param.Field(i))
}
return args
}, nil
}
for i, t := range types {
field := reflect.StructField{
Name: fmt.Sprintf("Field%d", i),
Type: t,
}
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if i < len(fr.types) {
t := fr.types[i]
if !t.Implements(field.Type) {
return nil, nil, fmt.Errorf("invalid fx.From: %v does not implement %v", t, field.Type)
}
field.Type = t
}
inFields = append(inFields, field)
}
types = []reflect.Type{reflect.StructOf(inFields)}
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return types, func(args []reflect.Value) []reflect.Value {
params := args[0]
args = args[:0]
for i := 0; i < ft.NumIn(); i++ {
args = append(args, params.Field(i+1))
}
return args
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}, nil
}
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type annotated struct {
Target interface{}
Annotations []Annotation
ParamTags []string
ResultTags []string
As [][]reflect.Type
From []reflect.Type
FuncPtr uintptr
Hooks []*lifecycleHookAnnotation
// container is used to build private scopes for lifecycle hook functions
// added via fx.OnStart and fx.OnStop annotations.
container *dig.Container
}
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func (ann annotated) String() string {
var sb strings.Builder
sb.WriteString("fx.Annotate(")
sb.WriteString(fxreflect.FuncName(ann.Target))
if tags := ann.ParamTags; len(tags) > 0 {
fmt.Fprintf(&sb, ", fx.ParamTags(%q)", tags)
}
if tags := ann.ResultTags; len(tags) > 0 {
fmt.Fprintf(&sb, ", fx.ResultTags(%q)", tags)
}
if as := ann.As; len(as) > 0 {
fmt.Fprintf(&sb, ", fx.As(%v)", as)
}
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if from := ann.From; len(from) > 0 {
fmt.Fprintf(&sb, ", fx.From(%v)", from)
}
return sb.String()
}
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// Build builds and returns a constructor based on fx.In/fx.Out params and
// results wrapping the original constructor passed to fx.Annotate.
func (ann *annotated) Build() (interface{}, error) {
ann.container = dig.New()
ft := reflect.TypeOf(ann.Target)
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if ft.Kind() != reflect.Func {
return nil, fmt.Errorf("must provide constructor function, got %v (%T)", ann.Target, ann.Target)
}
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if err := ann.typeCheckOrigFn(); err != nil {
return nil, fmt.Errorf("invalid annotation function %T: %w", ann.Target, err)
}
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ann.applyOptionalTag()
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var (
err error
lcHookAnns []*lifecycleHookAnnotation
)
for _, annotation := range ann.Annotations {
if lcHookAnn, ok := annotation.(*lifecycleHookAnnotation); ok {
lcHookAnns = append(lcHookAnns, lcHookAnn)
continue
}
if ann.Target, err = annotation.build(ann); err != nil {
return nil, err
}
}
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// need to call cleanUpAsResults before applying lifecycle annotations
// to exclude the original results from the hook's scope if any
// fx.As annotations were applied
ann.cleanUpAsResults()
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for _, la := range lcHookAnns {
if ann.Target, err = la.build(ann); err != nil {
return nil, err
}
}
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return ann.Target, nil
}
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// applyOptionalTag checks if function being annotated is variadic
// and applies optional tag to the variadic argument before
// applying any other annotations
func (ann *annotated) applyOptionalTag() {
ft := reflect.TypeOf(ann.Target)
if !ft.IsVariadic() {
return
}
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resultTypes, _ := ann.currentResultTypes()
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fields := []reflect.StructField{_inAnnotationField}
for i := 0; i < ft.NumIn(); i++ {
field := reflect.StructField{
Name: fmt.Sprintf("Field%d", i),
Type: ft.In(i),
}
if i == ft.NumIn()-1 {
// Mark a variadic argument optional by default
// so that just wrapping a function in fx.Annotate does not
// suddenly introduce a required []arg dependency.
field.Tag = reflect.StructTag(`optional:"true"`)
}
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fields = append(fields, field)
}
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paramType := reflect.StructOf(fields)
origFn := reflect.ValueOf(ann.Target)
newFnType := reflect.FuncOf([]reflect.Type{paramType}, resultTypes, false)
newFn := reflect.MakeFunc(newFnType, func(args []reflect.Value) []reflect.Value {
params := args[0]
args = args[:0]
for i := 0; i < ft.NumIn(); i++ {
args = append(args, params.Field(i+1))
}
return origFn.CallSlice(args)
})
ann.Target = newFn.Interface()
}
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// cleanUpAsResults does a check to see if an As annotation was applied.
// If there was any fx.As annotation applied, cleanUpAsResults wraps the
// function one more time to remove the results from the original function.
func (ann *annotated) cleanUpAsResults() {
// clean up orig function results if there were any As annotations
if len(ann.As) < 1 {
return
}
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paramTypes := ann.currentParamTypes()
resultTypes, hasError := ann.currentResultTypes()
numRes := len(ann.As)
if hasError {
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numRes++
}
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newResultTypes := resultTypes[len(resultTypes)-numRes:]
origFn := reflect.ValueOf(ann.Target)
newFnType := reflect.FuncOf(paramTypes, newResultTypes, false)
newFn := reflect.MakeFunc(newFnType, func(args []reflect.Value) (results []reflect.Value) {
results = origFn.Call(args)
results = results[len(results)-numRes:]
return
})
ann.Target = newFn.Interface()
}
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// checks and returns a non-nil error if the target function:
// - returns an fx.Out struct as a result and has either a ResultTags or an As annotation
// - takes in an fx.In struct as a parameter and has either a ParamTags or a From annotation
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// - has an error result not as the last result.
func (ann *annotated) typeCheckOrigFn() error {
ft := reflect.TypeOf(ann.Target)
numOut := ft.NumOut()
for i := 0; i < numOut; i++ {
ot := ft.Out(i)
if ot == _typeOfError && i != numOut-1 {
return fmt.Errorf(
"only the last result can be an error: "+
"%v (%v) returns error as result %d",
fxreflect.FuncName(ann.Target), ft, i)
}
if ot.Kind() != reflect.Struct {
continue
}
if !dig.IsOut(reflect.New(ft.Out(i)).Elem().Interface()) {
continue
}
if len(ann.ResultTags) > 0 || len(ann.As) > 0 {
return errors.New("fx.Out structs cannot be annotated with fx.ResultTags or fx.As")
}
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}
for i := 0; i < ft.NumIn(); i++ {
it := ft.In(i)
if it.Kind() != reflect.Struct {
continue
}
if !dig.IsIn(reflect.New(ft.In(i)).Elem().Interface()) {
continue
}
if len(ann.ParamTags) > 0 || len(ann.From) > 0 {
return errors.New("fx.In structs cannot be annotated with fx.ParamTags or fx.From")
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}
}
return nil
}
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func (ann *annotated) currentResultTypes() (resultTypes []reflect.Type, hasError bool) {
ft := reflect.TypeOf(ann.Target)
numOut := ft.NumOut()
resultTypes = make([]reflect.Type, numOut)
for i := 0; i < numOut; i++ {
resultTypes[i] = ft.Out(i)
if resultTypes[i] == _typeOfError && i == numOut-1 {
hasError = true
}
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}
return resultTypes, hasError
}
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func (ann *annotated) currentParamTypes() []reflect.Type {
ft := reflect.TypeOf(ann.Target)
paramTypes := make([]reflect.Type, ft.NumIn())
for i := 0; i < ft.NumIn(); i++ {
paramTypes[i] = ft.In(i)
}
return paramTypes
}
// Annotate lets you annotate a function's parameters and returns
// without you having to declare separate struct definitions for them.
//
// For example,
//
// func NewGateway(ro, rw *db.Conn) *Gateway { ... }
// fx.Provide(
// fx.Annotate(
// NewGateway,
// fx.ParamTags(`name:"ro" optional:"true"`, `name:"rw"`),
// fx.ResultTags(`name:"foo"`),
// ),
// )
//
// Is equivalent to,
//
// type params struct {
// fx.In
//
// RO *db.Conn `name:"ro" optional:"true"`
// RW *db.Conn `name:"rw"`
// }
//
// type result struct {
// fx.Out
//
// GW *Gateway `name:"foo"`
// }
//
// fx.Provide(func(p params) result {
// return result{GW: NewGateway(p.RO, p.RW)}
// })
//
// Using the same annotation multiple times is invalid.
// For example, the following will fail with an error:
//
// fx.Provide(
// fx.Annotate(
// NewGateWay,
// fx.ParamTags(`name:"ro" optional:"true"`),
// fx.ParamTags(`name:"rw"), // ERROR: ParamTags was already used above
// fx.ResultTags(`name:"foo"`)
// )
// )
//
// is considered an invalid usage and will not apply any of the
// Annotations to NewGateway.
//
// If more tags are given than the number of parameters/results, only
// the ones up to the number of parameters/results will be applied.
//
// # Variadic functions
//
// If the provided function is variadic, Annotate treats its parameter as a
// slice. For example,
//
// fx.Annotate(func(w io.Writer, rs ...io.Reader) {
// // ...
// }, ...)
//
// Is equivalent to,
//
// fx.Annotate(func(w io.Writer, rs []io.Reader) {
// // ...
// }, ...)
//
// You can use variadic parameters with Fx's value groups.
// For example,
//
// fx.Annotate(func(mux *http.ServeMux, handlers ...http.Handler) {
// // ...
// }, fx.ParamTags(``, `group:"server"`))
//
// If we provide the above to the application,
// any constructor in the Fx application can inject its HTTP handlers
// by using fx.Annotate, fx.Annotated, or fx.Out.
//
// fx.Annotate(
// func(..) http.Handler { ... },
// fx.ResultTags(`group:"server"`),
// )
//
// fx.Annotated{
// Target: func(..) http.Handler { ... },
// Group: "server",
// }
func Annotate(t interface{}, anns ...Annotation) interface{} {
result := annotated{Target: t}
for _, ann := range anns {
if err := ann.apply(&result); err != nil {
return annotationError{
target: t,
err: err,
}
}
}
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result.Annotations = anns
return result
}