CODEWITHSUNDEEP
goabstract-syntax-tree
Mark Nahabedian
Mark Nahabedian

Reputation: 17

Finding package references in an AST

I'm trying to use the go/ast package to perform a source to source transformation on parts of a go program. One of my goals is to automatically generate from an interface definition with stylized comments, the definition of a struct that implements that interface. I have this program (https://github.com/MarkNahabedian/defimpl) working except that my present implementation doesn't always include in the output file those packages from the input file that are required by the output file.

The current implementation is a bit kludgy in how it determines what to import. Instead I'm tryiing to use ast.Walk to look for package references. My apparently nieve assumption is that any package refe3rence would appear as the X member of an ast.BinaryExpr. From instrumenting the code that generated this (contrived test) output though

// This file was automatically generated by defimpl from c:\Users\Mark Nahabedian\go\src\defimpl\test\code.go.
package test

import "reflect"
import "defimpl/runtime"

type ThingImpl struct {
    node ast.Node
}

var _ Thing = (*ThingImpl)(nil)

func init() {
    inter := reflect.TypeOf(func(t Thing) {}).In(0)
    var impl *ThingImpl
    runtime.Register(inter, reflect.TypeOf(impl))
}

// Node is part of the Thing interface.
func (x *ThingImpl) Node() ast.Node {
    return x.node
}

I see that there are no BinaryExpr nodes in the AST. My question is: what is the AST node type of "ast.Node".

I wish that the documentation of the go/ast package provided a clear association between the interface and struct types it defines.

Upvotes: 1

Views: 1030

Answers (1)

user13631587
user13631587

Reputation:

The expression ast.Node is a selector expression. The go/ast package represents the expression with the *ast.SelectorExpr type.

To understand how a language feature is represented in go/ast, parse a small program with the feature and dump the resulting tree. The spew package is a convenient tool for dumping the tree. Run an example on the playground.

Upvotes: 1

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