cmd/digraph: use graphfmt.Dot

Change-Id: Icddd469995974dbf9681b126330db284a95adc4f
Reviewed-on: https://go-review.googlesource.com/c/tools/+/747369
Reviewed-by: Alan Donovan <adonovan@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>

cmd/digraph/digraph.go

diff --git a/cmd/digraph/digraph.go b/cmd/digraph/digraph.go
index a31e13e..9e527c6 100644
--- a/cmd/digraph/digraph.go
+++ b/cmd/digraph/digraph.go
@@ -29,6 +29,7 @@
 	"unicode/utf8"
 
 	"golang.org/x/tools/internal/graph"
+	"golang.org/x/tools/internal/graph/graphfmt"
 )
 
 func usage() {
@@ -171,20 +172,6 @@
 	return nil
 }
 
-func (g digraph) toDot(w *bytes.Buffer) {
-	fmt.Fprintln(w, "digraph {")
-	for _, src := range g.nodelist() {
-		for _, dst := range g[src].sort() {
-			// Dot's quoting rules appear to align with Go's for escString,
-			// which is the syntax of node IDs. Labels require significantly
-			// more quoting, but that appears not to be necessary if the node ID
-			// is implicitly used as the label.
-			fmt.Fprintf(w, "\t%q -> %q;\n", src, dst)
-		}
-	}
-	fmt.Fprintln(w, "}")
-}
-
 func parse(rd io.Reader) (digraph, error) {
 	g := make(digraph)
 
@@ -398,9 +385,7 @@
 		if len(args) != 1 || args[0] != "dot" {
 			return fmt.Errorf("usage: digraph to dot")
 		}
-		var b bytes.Buffer
-		g.toDot(&b)
-		stdout.Write(b.Bytes())
+		stdout.Write([]byte(graphfmt.Dot[string]{}.Sprint(g)))
 
 	default:
 		return fmt.Errorf("no such command %q", cmd)

cmd/digraph/digraph_test.go

diff --git a/cmd/digraph/digraph_test.go b/cmd/digraph/digraph_test.go
index 74e61ee..dcef4c9 100644
--- a/cmd/digraph/digraph_test.go
+++ b/cmd/digraph/digraph_test.go
@@ -387,11 +387,15 @@
 	in := `a b c
 b "d\"\\d"
 c "d\"\\d"`
-	want := `digraph {
-	"a" -> "b";
-	"a" -> "c";
-	"b" -> "d\"\\d";
-	"c" -> "d\"\\d";
+	want := `digraph "" {
+n0 [label="a"];
+n1 [label="b"];
+n2 [label="c"];
+n3 [label="d\"\\d"];
+n0 -> n1;
+n0 -> n2;
+n1 -> n3;
+n2 -> n3;
 }
 `
 	defer func(in io.Reader, out io.Writer) { stdin, stdout = in, out }(stdin, stdout)
@@ -402,7 +406,6 @@
 	}
 	got := stdout.(fmt.Stringer).String()
 	if got != want {
-		t.Errorf("digraph(to, dot) = got %q, want %q", got, want)
+		t.Errorf("digraph(to, dot) = got\n  %q\nwant\n  %q", got, want)
 	}
-
 }