cmd/modgraphviz/main.go

// Copyright 2019 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

// Modgraphviz converts “go mod graph” output into Graphviz's DOT language,
// for use with Graphviz visualization and analysis tools like dot, dotty, and sccmap.
//
// Usage:
//
//	go mod graph | modgraphviz > graph.dot
//	go mod graph | modgraphviz | dot -Tpng -o graph.png
//
// Modgraphviz takes no options or arguments; it reads a graph in the format
// generated by “go mod graph” on standard input and writes DOT language
// on standard output.
//
// See http://www.graphviz.org/doc/info/lang.html for details of the DOT language
// and http://www.graphviz.org/about/ for Graphviz itself.
//
// See also golang.org/x/tools/cmd/digraph for general queries and analysis
// of “go mod graph” output.
package main

import (
	"bufio"
	"bytes"
	"flag"
	"fmt"
	"io"
	"log"
	"os"
	"strings"
)

func usage() {
	fmt.Fprintf(os.Stderr, "Usage: go mod graph | modgraphviz | dot -Tpng -o graph.png\n")
	os.Exit(2)
}

func main() {
	log.SetFlags(0)
	log.SetPrefix("modgraphviz: ")

	flag.Usage = usage
	flag.Parse()
	if flag.NArg() != 0 {
		usage()
	}

	graph, err := convert(os.Stdin)
	if err != nil {
		log.Fatal(err)
	}
	if _, err := os.Stdout.Write(graph); err != nil {
		log.Fatal(err)
	}
}

// convert reads “go mod graph” output from r
// and returns the equivalent DOT digraph.
func convert(r io.Reader) ([]byte, error) {
	var buf bytes.Buffer
	fmt.Fprintf(&buf, "digraph gomodgraph {\n")

	scanner := bufio.NewScanner(r)
	for scanner.Scan() {
		parts := strings.Fields(scanner.Text())
		if len(parts) != 2 {
			continue
		}
		fmt.Fprintf(&buf, "\t%q -> %q\n", parts[0], parts[1])
	}
	if err := scanner.Err(); err != nil {
		return nil, err
	}

	fmt.Fprintf(&buf, "}\n")
	return buf.Bytes(), nil
}