command: root early handler func special case

This allows for early initialisation with access to flags on the root node. This can be useful for configuring global state used by subcommands.

Signed-off-by: Ophestra <cat@gensokyo.uk>

command/builder.go

@@ -7,8 +7,10 @@ import (
 )
 
 // New initialises a root Node.
-func New(output io.Writer, logf LogFunc, name string) Command {
+func New(output io.Writer, logf LogFunc, name string, early HandlerFunc) Command {
-	return rootNode{newNode(output, logf, name, "")}
+	c := rootNode{newNode(output, logf, name, "")}
+	c.f = early
+	return c
 }
 
 func newNode(output io.Writer, logf LogFunc, name, usage string) *node {

command/builder_test.go

@@ -7,7 +7,7 @@ import (
 )
 
 func TestBuild(t *testing.T) {
-	c := command.New(nil, nil, "test")
+	c := command.New(nil, nil, "test", nil)
 	stubHandler := func([]string) error { panic("unreachable") }
 
 	t.Run("nil direct handler", func(t *testing.T) {

command/parse.go

@@ -34,9 +34,6 @@ func (n *node) Parse(arguments []string) error {
 
 match:
 	if n.child != nil {
-		if n.f != nil {
-			panic("invalid subcommand tree state")
-		}
 		// propagate help prefix early: flag set usage dereferences help
 		n.child.prefix = append(n.prefix, n.name)
 	}
@@ -50,6 +47,17 @@ match:
 	args := n.set.Args()
 
 	if n.child != nil {
+		if n.f != nil {
+			if n.usage != "" { // root node early special case
+				panic("invalid subcommand tree state")
+			}
+
+			// special case: root node calls HandlerFunc for initialisation
+			if err := n.f(nil); err != nil {
+				return err
+			}
+		}
+
 		if len(args) == 0 {
 			return n.writeHelp()
 		}

command/parse_test.go

@@ -24,13 +24,13 @@ func TestParse(t *testing.T) {
 	}{
 		{
 			"d=0 empty sub",
-			func(wout, wlog io.Writer) command.Command { return command.New(wout, newLogFunc(wlog), "root") },
+			func(wout, wlog io.Writer) command.Command { return command.New(wout, newLogFunc(wlog), "root", nil) },
 			[]string{""},
 			"", "test: \"root\" has no subcommands\n", command.ErrEmptyTree,
 		},
 		{
 			"d=0 empty sub garbage",
-			func(wout, wlog io.Writer) command.Command { return command.New(wout, newLogFunc(wlog), "root") },
+			func(wout, wlog io.Writer) command.Command { return command.New(wout, newLogFunc(wlog), "root", nil) },
 			[]string{"a", "b", "c", "d"},
 			"", "test: \"root\" has no subcommands\n", command.ErrEmptyTree,
 		},
@@ -77,6 +77,18 @@ func TestParse(t *testing.T) {
 			"flag provided but not defined: -val\n\nUsage:\ttest flag [-h | --help] COMMAND [OPTIONS]\n\n", "",
 			errors.New("flag provided but not defined: -val"),
 		},
+		{
+			"d=0 bool flag",
+			buildTestCommand,
+			[]string{"-v", "succeed"},
+			"", "test: verbose\n", nil,
+		},
+		{
+			"d=0 bool flag early error",
+			buildTestCommand,
+			[]string{"--fail", "succeed"},
+			"", "", errSuccess,
+		},
 
 		{
 			"d=1 empty sub",
@@ -126,7 +138,7 @@ func TestParse(t *testing.T) {
 			buildTestCommand,
 			[]string{},
 			`
-Usage:	test [-h | --help] [-v] [--val <value>] COMMAND [OPTIONS]
+Usage:	test [-h | --help] [-v] [--fail] [--val <value>] COMMAND [OPTIONS]
 
 Commands:
     error      return an error
@@ -144,7 +156,7 @@ Commands:
 			buildTestCommand,
 			[]string{"-h"},
 			`
-Usage:	test [-h | --help] [-v] [--val <value>] COMMAND [OPTIONS]
+Usage:	test [-h | --help] [-v] [--fail] [--val <value>] COMMAND [OPTIONS]
 
 Commands:
     error      return an error
@@ -156,7 +168,9 @@ Commands:
     deep       top level of command tree with various levels
 
 Flags:
-  -v	verbosity
+  -fail
+    	fail early
+  -v	verbose output
   -val string
     	store val for the "flag" command (default "default")
 
@@ -239,11 +253,24 @@ var (
 )
 
 func buildTestCommand(wout, wlog io.Writer) (c command.Command) {
-	var val string
+	var (
+		flagVerbose bool
+		flagFail    bool
+		flagVal     string
+	)
 
 	logf := newLogFunc(wlog)
-	c = command.New(wout, logf, "test").
+	c = command.New(wout, logf, "test", func([]string) error {
-		Flag(new(bool), "v", command.BoolFlag(false), "verbosity").
+		if flagVerbose {
+			logf("verbose")
+		}
+		if flagFail {
+			return errSuccess
+		}
+		return nil
+	}).
+		Flag(&flagVerbose, "v", command.BoolFlag(false), "verbose output").
+		Flag(&flagFail, "fail", command.BoolFlag(false), "fail early").
 		Command("error", "return an error", func([]string) error {
 			return errSuccess
 		}).
@@ -255,9 +282,9 @@ func buildTestCommand(wout, wlog io.Writer) (c command.Command) {
 			_, err := fmt.Fprint(wout, a...)
 			return err
 		}).
-		Flag(&val, "val", command.StringFlag("default"), "store val for the \"flag\" command").
+		Flag(&flagVal, "val", command.StringFlag("default"), "store val for the \"flag\" command").
 		Command("flag", "print value passed by flag", func(args []string) error {
-			_, err := fmt.Fprint(wout, val)
+			_, err := fmt.Fprint(wout, flagVal)
 			return err
 		})
 

command/unreachable_test.go

@@ -27,7 +27,7 @@ func TestParseUnreachable(t *testing.T) {
 		n := newNode(panicWriter{}, nil, " ", " ")
 		n.adopt(newNode(panicWriter{}, nil, " ", " "))
 		n.f = func([]string) error { panic("unreachable") }
-		_ = n.Parse(nil)
+		_ = n.Parse([]string{" "})
 	})
 
 	// this would only happen if a node was matched twice