61 lines
2.7 KiB
Go
61 lines
2.7 KiB
Go
// Copyright 2016 Marapongo, Inc. All rights reserved.
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// Package encoding can unmarshal MuPack and MuIL metadata formats. Because of their complex structure, we cannot rely
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// on the standard JSON marshaling and unmarshaling routines. Instead, we will need to do it mostly "by hand".
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package encoding
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import (
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"reflect"
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"github.com/marapongo/mu/pkg/compiler/ast"
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"github.com/marapongo/mu/pkg/pack"
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"github.com/marapongo/mu/pkg/util/mapper"
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)
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// Decode unmarshals the entire contents of the given byte array into a Package object.
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func Decode(m Marshaler, b []byte) (*pack.Package, error) {
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// First convert the whole contents of the metadata into a map. Although it would be more efficient to walk the
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// token stream, token by token, this allows us to reuse existing YAML packages in addition to JSON ones.
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var tree mapper.Object
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if err := m.Unmarshal(b, &tree); err != nil {
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return nil, err
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}
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// Now decode the top-level Package metadata; this will automatically recurse throughout the whole structure.
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md := mapper.New(customDecoders())
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var pack pack.Package
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if err := md.Decode(tree, &pack); err != nil {
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return nil, err
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}
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return &pack, nil
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}
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// customDecoders makes a complete map of all known custom AST decoders. In general, any polymorphic node kind that
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// appears as a field in another concrete marshalable structure must have an associated custom decoder. If not, the
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// Mapper will error out. This is typically an interface type and that method typically switches on the kind property.
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// Note that interfaces that are used as "markers" and don't show up in fields are okay and don't require a decoder.
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func customDecoders() mapper.Decoders {
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return mapper.Decoders{
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reflect.TypeOf((*ast.ModuleMember)(nil)).Elem(): moduleMemberDecoder,
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reflect.TypeOf((*ast.ClassMember)(nil)).Elem(): classMemberDecoder,
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reflect.TypeOf((*ast.Statement)(nil)).Elem(): statementDecoder,
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reflect.TypeOf((*ast.Expression)(nil)).Elem(): expressionDecoder,
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}
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}
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// Each of the custom decoders is a varaible that points to a decoder function; this is done so that the decode*
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// functions can remain strongly typed, as the mapper's decoder signature requires a weakly-typed interface{} return.
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var moduleMemberDecoder = func(m mapper.Mapper, tree mapper.Object) (interface{}, error) {
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return decodeModuleMember(m, tree)
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}
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var classMemberDecoder = func(m mapper.Mapper, tree mapper.Object) (interface{}, error) {
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return decodeClassMember(m, tree)
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}
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var statementDecoder = func(m mapper.Mapper, tree mapper.Object) (interface{}, error) {
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return decodeStatement(m, tree)
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}
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var expressionDecoder = func(m mapper.Mapper, tree mapper.Object) (interface{}, error) {
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return decodeExpression(m, tree)
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}
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