go/cmd/guru/main.go

// Copyright 2013 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.

// guru: a tool for answering questions about Go source code.
//
//    http://golang.org/s/oracle-design
//    http://golang.org/s/oracle-user-manual
//
// Run with -help flag or help subcommand for usage information.
//
package main // import "golang.org/x/tools/cmd/guru"

import (
	"bufio"
	"encoding/json"
	"encoding/xml"
	"flag"
	"fmt"
	"go/build"
	"io"
	"log"
	"os"
	"runtime/pprof"
	"strings"

	"golang.org/x/tools/go/buildutil"
)

// flags
var (
	scopeFlag      = flag.String("scope", "", "comma-separated list of `packages` to which the analysis should be limited (default=all)")
	ptalogFlag     = flag.String("ptalog", "", "write points-to analysis log to `file`")
	formatFlag     = flag.String("format", "plain", "output `format`; one of {plain,json,xml}")
	reflectFlag    = flag.Bool("reflect", false, "analyze reflection soundly (slow)")
	cpuprofileFlag = flag.String("cpuprofile", "", "write CPU profile to `file`")
)

func init() {
	flag.Var((*buildutil.TagsFlag)(&build.Default.BuildTags), "tags", buildutil.TagsFlagDoc)
}

const useHelp = "Run 'guru -help' for more information.\n"

const helpMessage = `Go source code guru.
Usage: guru [flags] <mode> <position>

The mode argument determines the query to perform:

	callees	  	show possible targets of selected function call
	callers	  	show possible callers of selected function
	callstack 	show path from callgraph root to selected function
	definition	show declaration of selected identifier
	describe  	describe selected syntax: definition, methods, etc
	freevars  	show free variables of selection
	implements	show 'implements' relation for selected type or method
	peers     	show send/receive corresponding to selected channel op
	pointsto	show variables to which the selected pointer may point
	referrers 	show all refs to entity denoted by selected identifier
	what		show basic information about the selected syntax node
	whicherrs	show possible values of the selected error variable

The position argument specifies the filename and byte offset (or range)
of the syntax element to query.  For example:

	foo.go:#123,#128
	bar.go:#123

The -format flag controls the output format:
	plain	an editor-friendly format in which every line of output
		is of the form "pos: text", where pos is "-" if unknown.
	json	structured data in JSON syntax.
	xml	structured data in XML syntax.

User manual: http://golang.org/s/oracle-user-manual

Example: describe syntax at offset 530 in this file (an import spec):

  $ guru describe src/golang.org/x/tools/cmd/guru/main.go:#530 
`

func printHelp() {
	fmt.Fprintln(os.Stderr, helpMessage)
	fmt.Fprintln(os.Stderr, "Flags:")
	flag.PrintDefaults()
}

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

	// Don't print full help unless -help was requested.
	// Just gently remind users that it's there.
	flag.Usage = func() { fmt.Fprint(os.Stderr, useHelp) }
	flag.CommandLine.Init(os.Args[0], flag.ContinueOnError) // hack
	if err := flag.CommandLine.Parse(os.Args[1:]); err != nil {
		// (err has already been printed)
		if err == flag.ErrHelp {
			printHelp()
		}
		os.Exit(2)
	}

	args := flag.Args()
	if len(args) != 2 {
		flag.Usage()
		os.Exit(2)
	}
	mode, posn := args[0], args[1]

	if mode == "help" {
		printHelp()
		os.Exit(2)
	}

	// Set up points-to analysis log file.
	var ptalog io.Writer
	if *ptalogFlag != "" {
		if f, err := os.Create(*ptalogFlag); err != nil {
			log.Fatalf("Failed to create PTA log file: %s", err)
		} else {
			buf := bufio.NewWriter(f)
			ptalog = buf
			defer func() {
				if err := buf.Flush(); err != nil {
					log.Printf("flush: %s", err)
				}
				if err := f.Close(); err != nil {
					log.Printf("close: %s", err)
				}
			}()
		}
	}

	// Profiling support.
	if *cpuprofileFlag != "" {
		f, err := os.Create(*cpuprofileFlag)
		if err != nil {
			log.Fatal(err)
		}
		pprof.StartCPUProfile(f)
		defer pprof.StopCPUProfile()
	}

	// -format flag
	switch *formatFlag {
	case "json", "plain", "xml":
		// ok
	default:
		log.Fatalf("illegal -format value: %q.\n"+useHelp, *formatFlag)
	}

	// Ask the guru.
	query := Query{
		Mode:       mode,
		Pos:        posn,
		Build:      &build.Default,
		Scope:      strings.Split(*scopeFlag, ","),
		PTALog:     ptalog,
		Reflection: *reflectFlag,
	}

	if err := Run(&query); err != nil {
		log.Fatal(err)
	}

	// Print the result.
	switch *formatFlag {
	case "json":
		b, err := json.MarshalIndent(query.Serial(), "", "\t")
		if err != nil {
			log.Fatalf("JSON error: %s", err)
		}
		os.Stdout.Write(b)

	case "xml":
		b, err := xml.MarshalIndent(query.Serial(), "", "\t")
		if err != nil {
			log.Fatalf("XML error: %s", err)
		}
		os.Stdout.Write(b)

	case "plain":
		query.WriteTo(os.Stdout)
	}
}