go/cmd/digraph/digraph.go

// The digraph command performs queries over unlabelled directed graphs
// represented in text form.  It is intended to integrate nicely with
// typical UNIX command pipelines.
//
// Since directed graphs (import graphs, reference graphs, call graphs,
// etc) often arise during software tool development and debugging, this
// command is included in the go.tools repository.
//
// TODO(adonovan):
// - support input files other than stdin
// - suport alternative formats (AT&T GraphViz, CSV, etc),
//   a comment syntax, etc.
// - allow queries to nest, like Blaze query language.
//
package main

import (
	"bufio"
	"flag"
	"fmt"
	"io"
	"os"
	"sort"
	"strings"
)

const Usage = `digraph: queries over directed graphs in text form.

Graph format:

  Each line contains zero or more whitespace-separated fields.
  Each field declares a node, and if there are more than one,
  an edge from the first to each subsequent one.
  The graph is provided on the standard input.

  For instance, the following (acyclic) graph specifies a partial order
  among the subtasks of getting dressed:

	% cat clothes.txt
	socks shoes
	shorts pants
	pants belt shoes
	shirt tie sweater
	sweater jacket
	hat

  The line "shirt tie sweater" indicates the two edges shirt -> tie and
  shirt -> sweater, not shirt -> tie -> sweater.

Supported queries:

  nodes
	the set of all nodes
  degree
	the in-degree and out-degree of each node.
  preds <label> ...
	the set of immediate predecessors of the specified nodes
  succs <label> ...
	the set of immediate successors of the specified nodes
  forward <label> ...
	the set of nodes transitively reachable from the specified nodes
  reverse <label> ...
	the set of nodes that transitively reach the specified nodes
  somepath <label> <label>
	the list of nodes on some arbitrary path from the first node to the second
  allpaths <label> <label>
	the set of nodes on all paths from the first node to the second
  sccs
	all strongly connected components (one per line)
  scc <label>
	the set of nodes nodes strongly connected to the specified one

Example usage:

   Show the transitive closure of imports of the digraph tool itself:
   % go list -f '{{.ImportPath}}{{.Imports}}' ... | tr '[]' '  ' |
         digraph forward golang.org/x/tools/cmd/digraph

   Show which clothes (see above) must be donned before a jacket:
   %  digraph reverse jacket <clothes.txt

`

func main() {
	flag.Parse()

	args := flag.Args()
	if len(args) == 0 {
		fmt.Println(Usage)
		return
	}

	if err := digraph(args[0], args[1:]); err != nil {
		fmt.Fprintf(os.Stderr, "Error: %s\n", err)
		os.Exit(1)
	}
}

type nodelist []string

func (l nodelist) println(sep string) {
	for i, label := range l {
		if i > 0 {
			fmt.Fprint(stdout, sep)
		}
		fmt.Fprint(stdout, label)
	}
	fmt.Fprintln(stdout)
}

type nodeset map[string]bool

func (s nodeset) sort() nodelist {
	labels := make(nodelist, len(s))
	var i int
	for label := range s {
		labels[i] = label
		i++
	}
	sort.Strings(labels)
	return labels
}

func (s nodeset) addAll(x nodeset) {
	for label := range x {
		s[label] = true
	}
}

// A graph maps nodes to the non-nil set of their immediate successors.
type graph map[string]nodeset

func (g graph) addNode(label string) nodeset {
	edges := g[label]
	if edges == nil {
		edges = make(nodeset)
		g[label] = edges
	}
	return edges
}

func (g graph) addEdges(from string, to ...string) {
	edges := g.addNode(from)
	for _, to := range to {
		g.addNode(to)
		edges[to] = true
	}
}

func (g graph) reachableFrom(roots nodeset) nodeset {
	seen := make(nodeset)
	var visit func(label string)
	visit = func(label string) {
		if !seen[label] {
			seen[label] = true
			for e := range g[label] {
				visit(e)
			}
		}
	}
	for root := range roots {
		visit(root)
	}
	return seen
}

func (g graph) transpose() graph {
	rev := make(graph)
	for label, edges := range g {
		rev.addNode(label)
		for succ := range edges {
			rev.addEdges(succ, label)
		}
	}
	return rev
}

func (g graph) sccs() []nodeset {
	// Kosaraju's algorithm---Tarjan is overkill here.

	// Forward pass.
	S := make(nodelist, 0, len(g)) // postorder stack
	seen := make(nodeset)
	var visit func(label string)
	visit = func(label string) {
		if !seen[label] {
			seen[label] = true
			for e := range g[label] {
				visit(e)
			}
			S = append(S, label)
		}
	}
	for label := range g {
		visit(label)
	}

	// Reverse pass.
	rev := g.transpose()
	var scc nodeset
	seen = make(nodeset)
	var rvisit func(label string)
	rvisit = func(label string) {
		if !seen[label] {
			seen[label] = true
			scc[label] = true
			for e := range rev[label] {
				rvisit(e)
			}
		}
	}
	var sccs []nodeset
	for len(S) > 0 {
		top := S[len(S)-1]
		S = S[:len(S)-1] // pop
		if !seen[top] {
			scc = make(nodeset)
			rvisit(top)
			sccs = append(sccs, scc)
		}
	}
	return sccs
}

func parse(rd io.Reader) (graph, error) {
	g := make(graph)

	in := bufio.NewScanner(rd)
	for in.Scan() {
		words := strings.Fields(in.Text())
		if len(words) > 0 {
			g.addEdges(words[0], words[1:]...)
		}
	}
	if err := in.Err(); err != nil {
		return nil, err
	}
	return g, nil
}

var stdin io.Reader = os.Stdin
var stdout io.Writer = os.Stdout

func digraph(cmd string, args []string) error {
	// Parse the input graph.
	g, err := parse(stdin)
	if err != nil {
		return err
	}

	// Parse the command line.
	switch cmd {
	case "nodes":
		if len(args) != 0 {
			return fmt.Errorf("usage: nodes")
		}
		nodes := make(nodeset)
		for label := range g {
			nodes[label] = true
		}
		nodes.sort().println("\n")

	case "degree":
		if len(args) != 0 {
			return fmt.Errorf("usage: degree")
		}
		nodes := make(nodeset)
		for label := range g {
			nodes[label] = true
		}
		rev := g.transpose()
		for _, label := range nodes.sort() {
			fmt.Fprintf(stdout, "%d\t%d\t%s\n", len(rev[label]), len(g[label]), label)
		}

	case "succs", "preds":
		if len(args) == 0 {
			return fmt.Errorf("usage: %s <label> ...", cmd)
		}
		g := g
		if cmd == "preds" {
			g = g.transpose()
		}
		result := make(nodeset)
		for _, root := range args {
			edges := g[root]
			if edges == nil {
				return fmt.Errorf("no such node %q", root)
			}
			result.addAll(edges)
		}
		result.sort().println("\n")

	case "forward", "reverse":
		if len(args) == 0 {
			return fmt.Errorf("usage: %s <label> ...", cmd)
		}
		roots := make(nodeset)
		for _, root := range args {
			if g[root] == nil {
				return fmt.Errorf("no such node %q", root)
			}
			roots[root] = true
		}
		g := g
		if cmd == "reverse" {
			g = g.transpose()
		}
		g.reachableFrom(roots).sort().println("\n")

	case "somepath":
		if len(args) != 2 {
			return fmt.Errorf("usage: somepath <from> <to>")
		}
		from, to := args[0], args[1]
		if g[from] == nil {
			return fmt.Errorf("no such 'from' node %q", from)
		}
		if g[to] == nil {
			return fmt.Errorf("no such 'to' node %q", to)
		}

		seen := make(nodeset)
		var visit func(path nodelist, label string) bool
		visit = func(path nodelist, label string) bool {
			if !seen[label] {
				seen[label] = true
				if label == to {
					append(path, label).println("\n")
					return true // unwind
				}
				for e := range g[label] {
					if visit(append(path, label), e) {
						return true
					}
				}
			}
			return false
		}
		if !visit(make(nodelist, 0, 100), from) {
			return fmt.Errorf("no path from %q to %q", args[0], args[1])
		}

	case "allpaths":
		if len(args) != 2 {
			return fmt.Errorf("usage: allpaths <from> <to>")
		}
		from, to := args[0], args[1]
		if g[from] == nil {
			return fmt.Errorf("no such 'from' node %q", from)
		}
		if g[to] == nil {
			return fmt.Errorf("no such 'to' node %q", to)
		}

		seen := make(nodeset) // value of seen[x] indicates whether x is on some path to 'to'
		var visit func(label string) bool
		visit = func(label string) bool {
			reachesTo, ok := seen[label]
			if !ok {
				reachesTo = label == to

				seen[label] = reachesTo
				for e := range g[label] {
					if visit(e) {
						reachesTo = true
					}
				}
				seen[label] = reachesTo
			}
			return reachesTo
		}
		if !visit(from) {
			return fmt.Errorf("no path from %q to %q", from, to)
		}
		for label, reachesTo := range seen {
			if !reachesTo {
				delete(seen, label)
			}
		}
		seen.sort().println("\n")

	case "sccs":
		if len(args) != 0 {
			return fmt.Errorf("usage: sccs")
		}
		for _, scc := range g.sccs() {
			scc.sort().println(" ")
		}

	case "scc":
		if len(args) != 1 {
			return fmt.Errorf("usage: scc <label>")
		}
		label := args[0]
		if g[label] == nil {
			return fmt.Errorf("no such node %q", label)
		}
		for _, scc := range g.sccs() {
			if scc[label] {
				scc.sort().println("\n")
				break
			}
		}

	default:
		return fmt.Errorf("no such command %q", cmd)
	}

	return nil
}