initial cognito

actual

vendor/github.com/lestrrat-go/blackmagic/blackmagic.go

@@ -0,0 +1,90 @@
+package blackmagic
+
+import (
+	"fmt"
+	"reflect"
+)
+
+// AssignField is a convenience function to assign a value to
+// an optional struct field. In Go, an optional struct field is
+// usually denoted by a pointer to T instead of T:
+//
+//	type Object struct {
+//	  Optional *T
+//	}
+//
+// This gets a bit cumbersome when you want to assign literals
+// or you do not want to worry about taking the address of a
+// variable.
+//
+//	Object.Optional = &"foo" // doesn't compile!
+//
+// Instead you can use this function to do it in one line:
+//
+//	blackmagic.AssignOptionalField(&Object.Optionl, "foo")
+func AssignOptionalField(dst, src interface{}) error {
+	dstRV := reflect.ValueOf(dst)
+	srcRV := reflect.ValueOf(src)
+	if dstRV.Kind() != reflect.Pointer || dstRV.Elem().Kind() != reflect.Pointer {
+		return fmt.Errorf(`dst must be a pointer to a field that is turn a pointer of src (%T)`, src)
+	}
+
+	if !dstRV.Elem().CanSet() {
+		return fmt.Errorf(`dst (%T) is not assignable`, dstRV.Elem().Interface())
+	}
+	if !reflect.PtrTo(srcRV.Type()).AssignableTo(dstRV.Elem().Type()) {
+		return fmt.Errorf(`cannot assign src (%T) to dst (%T)`, src, dst)
+	}
+
+	ptr := reflect.New(srcRV.Type())
+	ptr.Elem().Set(srcRV)
+	dstRV.Elem().Set(ptr)
+	return nil
+}
+
+// AssignIfCompatible is a convenience function to safely
+// assign arbitrary values. dst must be a pointer to an
+// empty interface, or it must be a pointer to a compatible
+// variable type that can hold src.
+func AssignIfCompatible(dst, src interface{}) error {
+	orv := reflect.ValueOf(src) // save this value for error reporting
+	result := orv
+
+	// t can be a pointer or a slice, and the code will slightly change
+	// depending on this
+	var isPtr bool
+	var isSlice bool
+	switch result.Kind() {
+	case reflect.Ptr:
+		isPtr = true
+	case reflect.Slice:
+		isSlice = true
+	}
+
+	rv := reflect.ValueOf(dst)
+	if rv.Kind() != reflect.Ptr {
+		return fmt.Errorf(`destination argument to AssignIfCompatible() must be a pointer: %T`, dst)
+	}
+
+	actualDst := rv.Elem()
+	switch actualDst.Kind() {
+	case reflect.Interface:
+		// If it's an interface, we can just assign the pointer to the interface{}
+	default:
+		// If it's a pointer to the struct we're looking for, we need to set
+		// the de-referenced struct
+		if !isSlice && isPtr {
+			result = result.Elem()
+		}
+	}
+	if !result.Type().AssignableTo(actualDst.Type()) {
+		return fmt.Errorf(`argument to AssignIfCompatible() must be compatible with %T (was %T)`, orv.Interface(), dst)
+	}
+
+	if !actualDst.CanSet() {
+		return fmt.Errorf(`argument to AssignIfCompatible() must be settable`)
+	}
+	actualDst.Set(result)
+
+	return nil
+}