You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: main.go
    path of file: ./repos/cockroach/pkg/sql/colexec/execgen/cmd/execgen
    
    the code of the file until where you have to start completion: // Copyright 2018 The Cockroach Authors.
//
// Use of this software is governed by the Business Source License
// included in the file licenses/BSL.txt.
//
// As of the Change Date specified in that file, in accordance with
// the Business Source License, use of this software will be governed
// by the Apache License, Version 2.0, included in the file
// licenses/APL.txt.

package main

import (
	"bytes"
	"flag"
	"fmt"
	"io"
	"os"
	"path/filepath"
	"regexp"

	"github.com/cockroachdb/cockroach/pkg/sql/colexec/execgen"
	"github.com/cockroachdb/cockroach/pkg/sql/colexecerror"
	"github.com/cockroachdb/errors"
	"github.com/cockroachdb/gostdlib/x/tools/imports"
)

func main() {
	gen := execgenTool{stdErr: os.Stderr}
	if !gen.run(os.Args[1:]...) {
		os.Exit(2)
	}
}

type execgenTool struct {
	// fmtSources runs the go fmt tool on code generated by execgenTool, if this
	// setting is true.
	fmtSources bool

	// stdErr is the writer to which all standard error output will be redirected.
	stdErr io.Writer

	// cmdLine stores the set of flags used to invoke the Execgen tool.
	cmdLine *flag.FlagSet
	verbose bool
}

// generator is a func that, given an input file's contents as a string,
// outputs the result of execgen to the outputFile.
type generator func(inputFileContents string, outputFile io.Writer) error

var generators = make(map[string]entry)

type entry struct {
	fn        generator
	inputFile string
}

func registerGenerator(g generator, outputFile, inputFile string) {
	if _, ok := generators[outputFile]; ok {
		colexecerror.InternalError(errors.AssertionFailedf("%s generator already registered", outputFile))
	}
	generators[outputFile] = entry{fn: g, inputFile: inputFile}
}

func (g *execgenTool) run(args ...string) bool {
	// Parse command line.
	var printDeps bool
	var template string
	g.cmdLine = flag.NewFlagSet("execgen", flag.ContinueOnError)
	g.cmdLine.SetOutput(g.stdErr)
	g.cmdLine.Usage = g.usage
	g.cmdLine.BoolVar(&g.fmtSources, "fmt", true, "format and imports-p
    
func (g *execgenTool) generate(path string, entry entry) error {
	var buf bytes.Buffer
	buf.WriteString("// Code generated by execgen; DO NOT EDIT.\n")

	var inputFileContents string
	var err error
	if entry.inputFile != "" {
		inputFileBytes, err := os.ReadFile(entry.inputFile)
		if err != nil {
			return err
		}
		// Delete execgen_template build tag.
		inputFileBytes = bytes.ReplaceAll(inputFileBytes, []byte("// +build execgen_template"), []byte{})
		inputFileContents, err = execgen.Generate(string(inputFileBytes))
		if err != nil {
			return err
		}
		if g.verbose {
			fmt.Fprintln(os.Stderr, "generated code before text/template runs")
			fmt.Fprintln(os.Stderr, "-----------------------------------")
			fmt.Fprintln(os.Stderr, inputFileContents)
			fmt.Fprintln(os.Stderr, "-----------------------------------")
		}
	}

	err = entry.fn(inputFileContents, &buf)
	if err != nil {
		return err
	}

	b := buf.Bytes()
	// Delete execgen_template build tag.
	b = bytes.ReplaceAll(b, []byte("//go:build execgen_template"), []byte{})
	b = bytes.ReplaceAll(b, []byte("// +build execgen_template"), []byte{})

	// Delete empty comments (/* */) that tend to get generated by templating.
	// As well as empty line comments that are _not_ at the beginning of a line.
	// As well as run-ins of multiple empty line comments at the beginning of a line
	// (when there is more than one).
	// As well as solitary empty line comments.
	//
	// Note: we do not remove single empty single-line comments (//)
	// that appear in the middle of a larger documentation
	// comment, because removing them can break the formatting inside the
	// comment and make gofmt unhappy.
	b = emptyBlockCommentRegex.ReplaceAllLiteral(b, []byte{})
	b = emptyInlineCommentRegex.ReplaceAllLiteral(b, []byte{})
	b = multiEmptyCommentRegex.ReplaceAllLiteral(b, []byte("//\n"))
	b = solitaryEmptyCommentRegex.ReplaceAllLiteral(b, []byte("\n"))
	b = emptyFuncTypeCommentRegex.ReplaceAll(b, []byte("$1"))

	if g.fmtSources {
		oldB := b
		b, err = imports.Process(path, b,
			&imports.Options{Comments: true, TabIndent: true, TabWidth: 2})
		if err != nil {
			// Write out incorrect source for easier debugging.
			b = oldB
			err = errors.Wrap(err, "Code formatting failed with Go parse error")
		}
	}

	// Ignore any write error if another error already occurred.
	_, writeErr := os.Stdout.Write(b)
	if err != nil {
		return err
	}
	return writeErr
}