pulumi/pkg/pack/encoding/decode_statements.go
joeduffy 1948380eb2 Add custom decoders to eliminate boilerplate
This change overhauls the approach to custom decoding.  Instead of decoding
the parts of the struct that are "trivial" in one pass, and then patching up
the structure afterwards with custom decoding, the decoder itself understands
the notion of custom decoder functions.

First, the general purpose logic has moved out of pkg/pack/encoding and into
a new package, pkg/util/mapper.  Most functions are now members of a new top-
level type, Mapper, which may be initialized with custom decoders.  This
is a map from target type to a function that can decode objects into it.

Second, the AST-specific decoding logic is rewritten to use it.  All AST nodes
are now supported, including definitions, statements, and expressions.  The
overall approach here is to simply define a custom decoder for any interface
type that will occur in a node field position.  The mapper, upon encountering
such a type, will consult the custom decoder map; if a decoder is found, it
will be used, otherwise an error results.  This decoder then needs to switch
on the type discriminated kind field that is present in the metadata, creating
a concrete struct of the right type, and then converting it to the desired
interface type.  Note that, subtly, interface types used only for "marker"
purposes don't require any custom decoding, because they do not appear in
field positions and therefore won't be encountered during the decoding process.
2017-01-16 09:41:26 -08:00

163 lines
4.2 KiB
Go

// Copyright 2016 Marapongo, Inc. All rights reserved.
package encoding
import (
"reflect"
"github.com/marapongo/mu/pkg/pack/ast"
"github.com/marapongo/mu/pkg/util/contract"
"github.com/marapongo/mu/pkg/util/mapper"
)
func decodeStatement(m mapper.Mapper, tree mapper.Object) (ast.Statement, error) {
k, err := mapper.FieldString(tree, reflect.TypeOf((*ast.Statement)(nil)).Elem(), "kind", true)
if err != nil {
return nil, err
}
if k != nil {
kind := ast.NodeKind(*k)
switch kind {
// Blocks
case ast.BlockKind:
return decodeBlock(m, tree)
// Local variables
case ast.LocalVariableDeclarationKind:
return decodeLocalVariableDeclaration(m, tree)
// Try/catch/finally
case ast.TryCatchFinallyKind:
return decodeTryCatchFinally(m, tree)
// Branches
case ast.BreakStatementKind:
return decodeBreakStatement(m, tree)
case ast.ContinueStatementKind:
return decodeContinueStatement(m, tree)
case ast.IfStatementKind:
return decodeIfStatement(m, tree)
case ast.LabeledStatementKind:
return decodeLabeledStatement(m, tree)
case ast.ReturnStatementKind:
return decodeReturnStatement(m, tree)
case ast.ThrowStatementKind:
return decodeThrowStatement(m, tree)
case ast.WhileStatementKind:
return decodeWhileStatement(m, tree)
// Miscellaneous
case ast.EmptyStatementKind:
return decodeEmptyStatement(m, tree)
case ast.MultiStatementKind:
return decodeMultiStatement(m, tree)
case ast.ExpressionStatementKind:
return decodeExpressionStatement(m, tree)
default:
contract.FailMF("Unrecognized Statement kind: %v\n", kind)
}
}
return nil, nil
}
func decodeBlock(m mapper.Mapper, tree mapper.Object) (*ast.Block, error) {
var block ast.Block
if err := m.Decode(tree, &block); err != nil {
return nil, err
}
return &block, nil
}
func decodeLocalVariableDeclaration(m mapper.Mapper, tree mapper.Object) (*ast.LocalVariableDeclaration, error) {
var local ast.LocalVariableDeclaration
if err := m.Decode(tree, &local); err != nil {
return nil, err
}
return &local, nil
}
func decodeTryCatchFinally(m mapper.Mapper, tree mapper.Object) (*ast.TryCatchFinally, error) {
return nil, nil
}
func decodeBreakStatement(m mapper.Mapper, tree mapper.Object) (*ast.BreakStatement, error) {
var stmt ast.BreakStatement
if err := m.Decode(tree, &stmt); err != nil {
return nil, err
}
return &stmt, nil
}
func decodeContinueStatement(m mapper.Mapper, tree mapper.Object) (*ast.ContinueStatement, error) {
var stmt ast.ContinueStatement
if err := m.Decode(tree, &stmt); err != nil {
return nil, err
}
return &stmt, nil
}
func decodeIfStatement(m mapper.Mapper, tree mapper.Object) (*ast.IfStatement, error) {
var stmt ast.IfStatement
if err := m.Decode(tree, &stmt); err != nil {
return nil, err
}
return &stmt, nil
}
func decodeLabeledStatement(m mapper.Mapper, tree mapper.Object) (*ast.LabeledStatement, error) {
var stmt ast.LabeledStatement
if err := m.Decode(tree, &stmt); err != nil {
return nil, err
}
return &stmt, nil
}
func decodeReturnStatement(m mapper.Mapper, tree mapper.Object) (*ast.ReturnStatement, error) {
var stmt ast.ReturnStatement
if err := m.Decode(tree, &stmt); err != nil {
return nil, err
}
return &stmt, nil
}
func decodeThrowStatement(m mapper.Mapper, tree mapper.Object) (*ast.ThrowStatement, error) {
var stmt ast.ThrowStatement
if err := m.Decode(tree, &stmt); err != nil {
return nil, err
}
return &stmt, nil
}
func decodeWhileStatement(m mapper.Mapper, tree mapper.Object) (*ast.WhileStatement, error) {
var stmt ast.WhileStatement
if err := m.Decode(tree, &stmt); err != nil {
return nil, err
}
return &stmt, nil
}
func decodeEmptyStatement(m mapper.Mapper, tree mapper.Object) (*ast.EmptyStatement, error) {
var stmt ast.EmptyStatement
if err := m.Decode(tree, &stmt); err != nil {
return nil, err
}
return &stmt, nil
}
func decodeMultiStatement(m mapper.Mapper, tree mapper.Object) (*ast.MultiStatement, error) {
var stmt ast.MultiStatement
if err := m.Decode(tree, &stmt); err != nil {
return nil, err
}
return &stmt, nil
}
func decodeExpressionStatement(m mapper.Mapper, tree mapper.Object) (*ast.ExpressionStatement, error) {
var stmt ast.ExpressionStatement
if err := m.Decode(tree, &stmt); err != nil {
return nil, err
}
return &stmt, nil
}