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Add support for func-types to fx.As() #1249

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Add support for func-types to fx.As() #1249

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31 changes: 26 additions & 5 deletions annotated.go
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Original file line number Diff line number Diff line change
Expand Up @@ -28,6 +28,7 @@ import (
"strings"

"go.uber.org/dig"

"go.uber.org/fx/internal/fxreflect"
)

Expand Down Expand Up @@ -1145,6 +1146,19 @@ var _ Annotation = (*asAnnotation)(nil)
// constructor does NOT provide both bytes.Buffer and io.Writer type; it just
// provides io.Writer type.
//
// Example for function-types:
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Let's update line 1129 as well:

- // constructor) to be provided as another interface.
+ // constructor) to be provided as another type.

//
// type domainHandler func(ctx context.Context) error
//
// func anyHandlerProvider() func(ctx context.Context) error {
// ...
// }
//
// fx.Provider(
// anyHandlerProvider(),
// fx.As(new(domainHandler)),
// )
//
// When multiple values are returned by the annotated function, each type
// gets mapped to corresponding positional result of the annotated function.
//
Expand Down Expand Up @@ -1211,8 +1225,8 @@ func (at *asAnnotation) apply(ann *annotated) error {
continue
}
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)
if t.Kind() != reflect.Ptr || !(t.Elem().Kind() == reflect.Interface || t.Elem().Kind() == reflect.Func) {
return fmt.Errorf("fx.As: argument must be a pointer to an interface or function: got %v", t)
}
t = t.Elem()
at.types[i] = asType{typ: t}
Expand Down Expand Up @@ -1265,8 +1279,11 @@ func (at *asAnnotation) results(ann *annotated) (
continue
}

if !t.Implements(at.types[i].typ) {
return nil, nil, fmt.Errorf("invalid fx.As: %v does not implement %v", t, at.types[i])
if !((at.types[i].typ.Kind() == reflect.Interface && t.Implements(at.types[i].typ)) ||
t.ConvertibleTo(at.types[i].typ)) {
return nil,
nil,
fmt.Errorf("invalid fx.As: %v does not implement or is not convertible to %v", t, at.types[i])
Comment on lines +1282 to +1286
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@JacobOaks JacobOaks Dec 4, 2024 •
edited
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Should we make these two separate checks? This will keep the code cleaner and give better error messages.

if at.types[i].typ.Kind() == reflect.Interface {
    if !t.Implements(at.types[i].typ) {
        return nil, nil, fmt.Errorf("invalid fx.As: %v does not implement %v", t, at.types[i])
    }
} else if !t.ConvertibleTo(at.types[i].typ) {
        return nil, nil, fmt.Errorf("invalid fx.As: %v cannot be converted to %v", t, at.types[i])
}

}
field.Type = at.types[i].typ
fields = append(fields, field)
Expand Down Expand Up @@ -1300,7 +1317,11 @@ func (at *asAnnotation) results(ann *annotated) (

newOutResult := reflect.New(resType).Elem()
for i := 1; i < resType.NumField(); i++ {
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Is there any reason we would need to check Value.CanConvert first since technically Value.Convert can panic even if Type.ConvertibleTo returns true? I can't think of any reason why a func value wouldn't be convertible if its type is though.

newOutResult.Field(i).Set(getResult(i, results))
if newOutResult.Field(i).Kind() == reflect.Func {
newOutResult.Field(i).Set(getResult(i, results).Convert(newOutResult.Field(i).Type()))
} else {
newOutResult.Field(i).Set(getResult(i, results))
}
Comment on lines +1320 to +1324
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@JacobOaks JacobOaks Dec 4, 2024 •
edited
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nit: should we flip these conditions to make the control flow more/appear consistent with the check above?

if newOutResult.Field(i).Kind() == reflect.Interface {
    newOutResult.Field(i).Set(getResult(i, results))
} else {
    newOutResult.Field(i).Set(getResult(i, results).Convert(newOutResult.Field(i).Type()))
}

}
outResults = append(outResults, newOutResult)

Expand Down
35 changes: 32 additions & 3 deletions annotated_test.go
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Original file line number Diff line number Diff line change
Expand Up @@ -33,6 +33,7 @@ import (

"github.com/stretchr/testify/assert"
"github.com/stretchr/testify/require"

"go.uber.org/fx"
"go.uber.org/fx/fxevent"
"go.uber.org/fx/fxtest"
Expand Down Expand Up @@ -442,6 +443,8 @@ func TestAnnotatedAs(t *testing.T) {
type myStringer interface {
String() string
}
type myProvideFunc func() string
type myInvokeFunc func() string

newAsStringer := func() *asStringer {
return &asStringer{
Expand Down Expand Up @@ -477,6 +480,32 @@ func TestAnnotatedAs(t *testing.T) {
assert.Equal(t, s.String(), "another stringer")
},
},
{
desc: "value type convertible to target type",
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nit: consider downscoping the names of these cases since convertible types are locked down to just functions right now

Suggested change
desc: "value type convertible to target type",
desc: "function value convertible to target type",

provide: fx.Provide(
fx.Annotate(func() myProvideFunc {
return func() string {
return "provide func example"
}
}, fx.As(new(myInvokeFunc))),
),
invoke: func(h myInvokeFunc) {
assert.Equal(t, "provide func example", h())
},
},
{
desc: "anonymous value type convertible to target type",
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should we add a test case for a function vaoue that is not convertible to the target type?

provide: fx.Provide(
fx.Annotate(func() func() string {
return func() string {
return "anonymous func example"
}
}, fx.As(new(myInvokeFunc))),
),
invoke: func(h myInvokeFunc) {
assert.Equal(t, "anonymous func example", h())
},
},
{
desc: "provide with multiple types As",
provide: fx.Provide(fx.Annotate(func() (*asStringer, *bytes.Buffer) {
Expand Down Expand Up @@ -1806,9 +1835,9 @@ func TestAnnotateApplySuccess(t *testing.T) {
func assertApp(
t *testing.T,
app interface {
Start(context.Context) error
Stop(context.Context) error
},
Start(context.Context) error
Stop(context.Context) error
},
started *bool,
stopped *bool,
invoked *bool,
Expand Down