1 files changed, 34 insertions, 15 deletions

diff --git a/cmd/digraph/digraph.go b/cmd/digraph/digraph.go
index 88eb05bf1..0e50ad18d 100644
--- a/cmd/digraph/digraph.go
+++ b/cmd/digraph/digraph.go
@@ -34,7 +34,7 @@ The support commands are:
 	sccs
 		all strongly connected components (one per line)
 	scc <node>
-		the set of nodes nodes strongly connected to the specified one
+		the set of nodes strongly connected to the specified one
 	focus <node>
 		the subgraph containing all directed paths that pass through the specified node
 
@@ -69,11 +69,12 @@ Using digraph with existing Go tools:
 	$ go list -m all | digraph nodes # Operate on the Go package graph.
 
 Show the transitive closure of imports of the digraph tool itself:
+
 	$ go list -f '{{.ImportPath}} {{join .Imports " "}}' ... | digraph forward golang.org/x/tools/cmd/digraph
 
 Show which clothes (see above) must be donned before a jacket:
-	$ digraph reverse jacket
 
+	$ digraph reverse jacket
 */
 package main // import "golang.org/x/tools/cmd/digraph"
 
@@ -121,7 +122,8 @@ The support commands are:
 	allpaths <node> <node>
 		the set of nodes on all paths from the first node to the second
 	sccs
-		all strongly connected components (one per line)
+		all non-trivial strongly connected components, one per line
+		(single-node components are only printed for nodes with self-loops)
 	scc <node>
 		the set of nodes nodes strongly connected to the specified one
 	focus <node>
@@ -157,7 +159,7 @@ func (l nodelist) println(sep string) {
 	fmt.Fprintln(stdout)
 }
 
-type nodeset map[string]bool // TODO(deklerk): change bool to struct to reduce memory footprint
+type nodeset map[string]bool
 
 func (s nodeset) sort() nodelist {
 	nodes := make(nodelist, len(s))
@@ -265,6 +267,9 @@ func (g graph) sccs() []nodeset {
 		if !seen[top] {
 			scc = make(nodeset)
 			rvisit(top)
+			if len(scc) == 1 && !g[top][top] {
+				continue
+			}
 			sccs = append(sccs, scc)
 		}
 	}
@@ -346,25 +351,34 @@ func parse(rd io.Reader) (graph, error) {
 	g := make(graph)
 
 	var linenum int
-	in := bufio.NewScanner(rd)
-	for in.Scan() {
+	// We avoid bufio.Scanner as it imposes a (configurable) limit
+	// on line length, whereas Reader.ReadString does not.
+	in := bufio.NewReader(rd)
+	for {
 		linenum++
+		line, err := in.ReadString('\n')
+		eof := false
+		if err == io.EOF {
+			eof = true
+		} else if err != nil {
+			return nil, err
+		}
 		// Split into words, honoring double-quotes per Go spec.
-		words, err := split(in.Text())
+		words, err := split(line)
 		if err != nil {
 			return nil, fmt.Errorf("at line %d: %v", linenum, err)
 		}
 		if len(words) > 0 {
 			g.addEdges(words[0], words[1:]...)
 		}
-	}
-	if err := in.Err(); err != nil {
-		return nil, err
+		if eof {
+			break
+		}
 	}
 	return g, nil
 }
 
-// Overridable for testing purposes.
+// Overridable for redirection.
 var stdin io.Reader = os.Stdin
 var stdout io.Writer = os.Stdout
 
@@ -484,9 +498,16 @@ func digraph(cmd string, args []string) error {
 		if len(args) != 0 {
 			return fmt.Errorf("usage: digraph sccs")
 		}
+		buf := new(bytes.Buffer)
+		oldStdout := stdout
+		stdout = buf
 		for _, scc := range g.sccs() {
 			scc.sort().println(" ")
 		}
+		lines := strings.SplitAfter(buf.String(), "\n")
+		sort.Strings(lines)
+		stdout = oldStdout
+		io.WriteString(stdout, strings.Join(lines, ""))
 
 	case "scc":
 		if len(args) != 1 {
@@ -546,9 +567,8 @@ func digraph(cmd string, args []string) error {
 // spaces, but Go-style double-quoted string literals are also supported.
 // (This approximates the behaviour of the Bourne shell.)
 //
-//   `one "two three"` -> ["one" "two three"]
-//   `a"\n"b` -> ["a\nb"]
-//
+//	`one "two three"` -> ["one" "two three"]
+//	`a"\n"b` -> ["a\nb"]
 func split(line string) ([]string, error) {
 	var (
 		words   []string
@@ -605,7 +625,6 @@ func split(line string) ([]string, error) {
 // its length is returned.
 //
 // TODO(adonovan): move this into a strconv-like utility package.
-//
 func quotedLength(input string) (n int, ok bool) {
 	var offset int