How to Write Custom AST-Based Code Generators in Go

Core
2026-04-17T12:05:42+00:00
Write custom AST-based code generators in Go by parsing source files with go/parser, inspecting the AST with ast.Inspect, and printing generated code.

You write custom AST-based code generators in Go by parsing source code into an AST, traversing it to find specific nodes, and emitting new code based on those nodes.

package main

import (
	"fmt"
	"go/ast"
	"go/parser"
	"go/token"
	"go/types"
	"os"
)

func main() {
	fset := token.NewFileSet()
	node, err := parser.ParseFile(fset, "main.go", nil, parser.ParseComments)
	if err != nil {
		fmt.Fprintln(os.Stderr, err)
		os.Exit(1)
	}

	// Configure type checker
	conf := types.Config{Importer: nil}
	_, err = conf.Check("main", fset, []*ast.File{node}, nil)
	if err != nil {
		fmt.Fprintln(os.Stderr, err)
		os.Exit(1)
	}

	// Traverse AST and generate code
	ast.Inspect(node, func(n ast.Node) bool {
		if fn, ok := n.(*ast.FuncDecl); ok {
			fmt.Printf("// Generated wrapper for %s\n", fn.Name.Name)
			fmt.Printf("func wrap%s() { %s() }\n", fn.Name.Name, fn.Name.Name)
		}
		return true
	})
}