Find all functions and methods in a Go source file

main.go

package main

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

func main() {
	args := os.Args[1:]

	file, err := parser.ParseFile(&token.FileSet{}, args[0], nil, parser.AllErrors)
	if err != nil {
		log.Fatal(fmt.Errorf("couldn't parse source file at %s: %s", args[0], err))
	}

	for _, decl := range file.Decls {
		switch fn := decl.(type) {
		case *ast.FuncDecl:
			fmt.Println(fmt.Sprintf("func %s receiver for %s", fn.Name, "nil"))
		default:
			break
		}
	}
}