github.com/tilt-dev/tilt@v0.33.15-0.20240515162809-0a22ed45d8a0/internal/tiltfile/starkit/set_state.go (about)

     1  package starkit
     2  
     3  import (
     4  	"fmt"
     5  	"reflect"
     6  
     7  	"go.starlark.net/starlark"
     8  )
     9  
    10  // SetState works like SetState in React. It can take a value or a function.
    11  //
    12  // That function should transform old state into new state. It can have the signature `func(T) T` or `func(T) (T, error)`.
    13  //
    14  // For example, an plugin that accumulated strings might use
    15  // SetState() like this:
    16  //
    17  //	err := starkit.SetState(t, func(strings []string) {
    18  //	  return append([]string{newString}, strings...)
    19  //	})
    20  //
    21  // This would be so much easier with generics :grimace:
    22  //
    23  // SetState will return an error if it can't match the type
    24  // of anything in the state store.
    25  func SetState(t *starlark.Thread, valOrFn interface{}) error {
    26  	typ := reflect.TypeOf(valOrFn)
    27  	model, ok := t.Local(modelKey).(Model)
    28  	if !ok {
    29  		return fmt.Errorf("Internal error: Starlark not initialized correctly: starkit.Model not found")
    30  	}
    31  
    32  	if typ.Kind() != reflect.Func {
    33  		return setStateVal(model, typ, valOrFn)
    34  	} else {
    35  		return setStateFn(model, typ, valOrFn)
    36  	}
    37  }
    38  
    39  func setStateVal(model Model, typ reflect.Type, val interface{}) error {
    40  	// If there's already a value with this type in the state store, overwrite it.
    41  	_, ok := model.state[typ]
    42  	if !ok {
    43  		return fmt.Errorf("Internal error: Type not found in state store: %T", val)
    44  	}
    45  	model.state[typ] = val
    46  	return nil
    47  }
    48  
    49  func setStateFn(model Model, typ reflect.Type, fn interface{}) error {
    50  	// Validate the function signature.
    51  	if typ.NumIn() != 1 ||
    52  		typ.NumOut() < 1 || typ.NumOut() > 2 ||
    53  		typ.In(0) != typ.Out(0) ||
    54  		(typ.NumOut() == 2 && typ.Out(1) != reflect.TypeOf((*error)(nil)).Elem()) {
    55  		return fmt.Errorf("Internal error: invalid SetState call: signature must be `func(T) T` or `func(t) (T, error)`")
    56  	}
    57  
    58  	inTyp := typ.In(0)
    59  	// Overwrite the value in the state store.
    60  	existing, ok := model.state[inTyp]
    61  	if !ok {
    62  		return fmt.Errorf("Internal error: Type not found in state store: %s", inTyp)
    63  	}
    64  
    65  	outs := reflect.ValueOf(fn).Call([]reflect.Value{reflect.ValueOf(existing)})
    66  
    67  	if typ.NumOut() == 2 && !outs[1].IsNil() {
    68  		return outs[1].Interface().(error)
    69  	}
    70  
    71  	// We know this is valid because of the type validation check above.
    72  	model.state[inTyp] = outs[0].Interface()
    73  
    74  	return nil
    75  }