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54 lines
1.9 KiB
Go
54 lines
1.9 KiB
Go
/*
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Copyright 2020 The Compose Specification Authors.
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Licensed under the Apache License, Version 2.0 (the "License");
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you may not use this file except in compliance with the License.
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You may obtain a copy of the License at
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http://www.apache.org/licenses/LICENSE-2.0
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Unless required by applicable law or agreed to in writing, software
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distributed under the License is distributed on an "AS IS" BASIS,
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WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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See the License for the specific language governing permissions and
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limitations under the License.
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*/
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package loader
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import "reflect"
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// comparable to yaml.Unmarshaler, decoder allow a type to define it's own custom logic to convert value
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// see https://github.com/mitchellh/mapstructure/pull/294
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type decoder interface {
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DecodeMapstructure(interface{}) error
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}
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// see https://github.com/mitchellh/mapstructure/issues/115#issuecomment-735287466
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// adapted to support types derived from built-in types, as DecodeMapstructure would not be able to mutate internal
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// value, so need to invoke DecodeMapstructure defined by pointer to type
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func decoderHook(from reflect.Value, to reflect.Value) (interface{}, error) {
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// If the destination implements the decoder interface
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u, ok := to.Interface().(decoder)
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if !ok {
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// for non-struct types we need to invoke func (*type) DecodeMapstructure()
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if to.CanAddr() {
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pto := to.Addr()
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u, ok = pto.Interface().(decoder)
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}
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if !ok {
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return from.Interface(), nil
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}
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}
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// If it is nil and a pointer, create and assign the target value first
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if to.Type().Kind() == reflect.Ptr && to.IsNil() {
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to.Set(reflect.New(to.Type().Elem()))
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u = to.Interface().(decoder)
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}
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// Call the custom DecodeMapstructure method
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if err := u.DecodeMapstructure(from.Interface()); err != nil {
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return to.Interface(), err
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}
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return to.Interface(), nil
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}
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