add subcommand aliases

parse.go

@@ -62,6 +62,7 @@ type spec struct {
 // command represents a named subcommand, or the top-level command
 type command struct {
 	name        string
+	aliases     []string
 	help        string
 	dest        path
 	specs       []*spec
@@ -153,7 +154,7 @@ type Parser struct {
 	epilogue    string
 
 	// the following field changes during processing of command line arguments
-	lastCmd *command
+	subcommand []string
 }
 
 // Versioned is the interface that the destination struct should implement to
@@ -384,18 +385,24 @@ func cmdFromStruct(name string, dest path, t reflect.Type) (*command, error) {
 				}
 			case key == "subcommand":
 				// decide on a name for the subcommand
-				cmdname := value
-				if cmdname == "" {
-					cmdname = strings.ToLower(field.Name)
+				var cmdnames []string
+				if value == "" {
+					cmdnames = []string{strings.ToLower(field.Name)}
+				} else {
+					cmdnames = strings.Split(value, "|")
+				}
+				for i := range cmdnames {
+					cmdnames[i] = strings.TrimSpace(cmdnames[i])
 				}
 
 				// parse the subcommand recursively
-				subcmd, err := cmdFromStruct(cmdname, subdest, field.Type)
+				subcmd, err := cmdFromStruct(cmdnames[0], subdest, field.Type)
 				if err != nil {
 					errs = append(errs, err.Error())
 					return false
 				}
 
+				subcmd.aliases = cmdnames[1:]
 				subcmd.parent = &cmd
 				subcmd.help = field.Tag.Get("help")
 
@@ -514,13 +521,13 @@ func (p *Parser) MustParse(args []string) {
 	err := p.Parse(args)
 	switch {
 	case err == ErrHelp:
-		p.writeHelpForSubcommand(p.config.Out, p.lastCmd)
+		p.WriteHelpForSubcommand(p.config.Out, p.subcommand...)
 		p.config.Exit(0)
 	case err == ErrVersion:
 		fmt.Fprintln(p.config.Out, p.version)
 		p.config.Exit(0)
 	case err != nil:
-		p.failWithSubcommand(err.Error(), p.lastCmd)
+		p.FailSubcommand(err.Error(), p.subcommand...)
 	}
 }
 
@@ -577,7 +584,7 @@ func (p *Parser) process(args []string) error {
 
 	// union of specs for the chain of subcommands encountered so far
 	curCmd := p.cmd
-	p.lastCmd = curCmd
+	p.subcommand = nil
 
 	// make a copy of the specs because we will add to this list each time we expand a subcommand
 	specs := make([]*spec, len(curCmd.specs))
@@ -648,7 +655,7 @@ func (p *Parser) process(args []string) error {
 			}
 
 			curCmd = subcmd
-			p.lastCmd = curCmd
+			p.subcommand = append(p.subcommand, arg)
 			continue
 		}
 
@@ -842,6 +849,11 @@ func findSubcommand(cmds []*command, name string) *command {
 		if cmd.name == name {
 			return cmd
 		}
+		for _, alias := range cmd.aliases {
+			if alias == name {
+				return cmd
+			}
+		}
 	}
 	return nil
 }

parse_test.go

@@ -883,7 +883,8 @@ func TestEnvironmentVariableInSubcommandIgnored(t *testing.T) {
 	require.NoError(t, err)
 
 	err = p.Parse([]string{"sub"})
-	assert.NoError(t, err)
+	require.NoError(t, err)
+	require.NotNil(t, args.Sub)
 	assert.Equal(t, "", args.Sub.Foo)
 }
 
@@ -1731,7 +1732,8 @@ func TestSubcommandGlobalFlag_InCommand_Strict_Inner(t *testing.T) {
 	require.NoError(t, err)
 
 	err = p.Parse([]string{"sub", "-g"})
-	assert.NoError(t, err)
+	require.NoError(t, err)
 	assert.False(t, args.Global)
+	require.NotNil(t, args.Sub)
 	assert.True(t, args.Sub.Guard)
 }

subcommand.go

@@ -1,37 +1,43 @@
 package arg
 
+import "fmt"
+
 // Subcommand returns the user struct for the subcommand selected by
 // the command line arguments most recently processed by the parser.
 // The return value is always a pointer to a struct. If no subcommand
 // was specified then it returns the top-level arguments struct. If
 // no command line arguments have been processed by this parser then it
 // returns nil.
 func (p *Parser) Subcommand() interface{} {
-	if p.lastCmd == nil || p.lastCmd.parent == nil {
+	if len(p.subcommand) == 0 {
+		return nil
+	}
+	cmd, err := p.lookupCommand(p.subcommand...)
+	if err != nil {
 		return nil
 	}
-	return p.val(p.lastCmd.dest).Interface()
+	return p.val(cmd.dest).Interface()
 }
 
 // SubcommandNames returns the sequence of subcommands specified by the
 // user. If no subcommands were given then it returns an empty slice.
 func (p *Parser) SubcommandNames() []string {
-	if p.lastCmd == nil {
-		return nil
-	}
-
-	// make a list of ancestor commands
-	var ancestors []string
-	cur := p.lastCmd
-	for cur.parent != nil { // we want to exclude the root
-		ancestors = append(ancestors, cur.name)
-		cur = cur.parent
-	}
+	return p.subcommand
+}
 
-	// reverse the list
-	out := make([]string, len(ancestors))
-	for i := 0; i < len(ancestors); i++ {
-		out[i] = ancestors[len(ancestors)-i-1]
+// lookupCommand finds a subcommand based on a sequence of subcommand names. The
+// first string should be a top-level subcommand, the next should be a child
+// subcommand of that subcommand, and so on. If no strings are given then the
+// root command is returned. If no such subcommand exists then an error is
+// returned.
+func (p *Parser) lookupCommand(path ...string) (*command, error) {
+	cmd := p.cmd
+	for _, name := range path {
+		found := findSubcommand(cmd.subcommands, name)
+		if found == nil {
+			return nil, fmt.Errorf("%q is not a subcommand of %s", name, cmd.name)
+		}
+		cmd = found
 	}
-	return out
+	return cmd, nil
 }

subcommand_test.go

@@ -83,6 +83,19 @@ func TestNamedSubcommand(t *testing.T) {
 	assert.Equal(t, []string{"ls"}, p.SubcommandNames())
 }
 
+func TestSubcommandAliases(t *testing.T) {
+	type listCmd struct {
+	}
+	var args struct {
+		List *listCmd `arg:"subcommand:list|ls"`
+	}
+	p, err := pparse("ls", &args)
+	require.NoError(t, err)
+	assert.NotNil(t, args.List)
+	assert.Equal(t, args.List, p.Subcommand())
+	assert.Equal(t, []string{"ls"}, p.SubcommandNames())
+}
+
 func TestEmptySubcommand(t *testing.T) {
 	type listCmd struct {
 	}
@@ -113,6 +126,23 @@ func TestTwoSubcommands(t *testing.T) {
 	assert.Equal(t, []string{"list"}, p.SubcommandNames())
 }
 
+func TestTwoSubcommandsWithAliases(t *testing.T) {
+	type getCmd struct {
+	}
+	type listCmd struct {
+	}
+	var args struct {
+		Get  *getCmd  `arg:"subcommand:get|g"`
+		List *listCmd `arg:"subcommand:list|ls"`
+	}
+	p, err := pparse("ls", &args)
+	require.NoError(t, err)
+	assert.Nil(t, args.Get)
+	assert.NotNil(t, args.List)
+	assert.Equal(t, args.List, p.Subcommand())
+	assert.Equal(t, []string{"ls"}, p.SubcommandNames())
+}
+
 func TestSubcommandsWithOptions(t *testing.T) {
 	type getCmd struct {
 		Name string
@@ -275,6 +305,60 @@ func TestNestedSubcommands(t *testing.T) {
 	}
 }
 
+func TestNestedSubcommandsWithAliases(t *testing.T) {
+	type child struct{}
+	type parent struct {
+		Child *child `arg:"subcommand:child|ch"`
+	}
+	type grandparent struct {
+		Parent *parent `arg:"subcommand:parent|pa"`
+	}
+	type root struct {
+		Grandparent *grandparent `arg:"subcommand:grandparent|gp"`
+	}
+
+	{
+		var args root
+		p, err := pparse("gp parent child", &args)
+		require.NoError(t, err)
+		require.NotNil(t, args.Grandparent)
+		require.NotNil(t, args.Grandparent.Parent)
+		require.NotNil(t, args.Grandparent.Parent.Child)
+		assert.Equal(t, args.Grandparent.Parent.Child, p.Subcommand())
+		assert.Equal(t, []string{"gp", "parent", "child"}, p.SubcommandNames())
+	}
+
+	{
+		var args root
+		p, err := pparse("grandparent pa", &args)
+		require.NoError(t, err)
+		require.NotNil(t, args.Grandparent)
+		require.NotNil(t, args.Grandparent.Parent)
+		require.Nil(t, args.Grandparent.Parent.Child)
+		assert.Equal(t, args.Grandparent.Parent, p.Subcommand())
+		assert.Equal(t, []string{"grandparent", "pa"}, p.SubcommandNames())
+	}
+
+	{
+		var args root
+		p, err := pparse("grandparent", &args)
+		require.NoError(t, err)
+		require.NotNil(t, args.Grandparent)
+		require.Nil(t, args.Grandparent.Parent)
+		assert.Equal(t, args.Grandparent, p.Subcommand())
+		assert.Equal(t, []string{"grandparent"}, p.SubcommandNames())
+	}
+
+	{
+		var args root
+		p, err := pparse("", &args)
+		require.NoError(t, err)
+		require.Nil(t, args.Grandparent)
+		assert.Nil(t, p.Subcommand())
+		assert.Empty(t, p.SubcommandNames())
+	}
+}
+
 func TestSubcommandsWithPositionals(t *testing.T) {
 	type listCmd struct {
 		Pattern string `arg:"positional"`
@@ -411,3 +495,14 @@ func TestValForNilStruct(t *testing.T) {
 	v := p.val(path{fields: []reflect.StructField{subField, subField}})
 	assert.False(t, v.IsValid())
 }
+
+func TestSubcommandInvalidInternal(t *testing.T) {
+	// this situation should never arise in practice but still good to test for it
+	var cmd struct{}
+	p, err := NewParser(Config{}, &cmd)
+	require.NoError(t, err)
+
+	p.subcommand = []string{"should", "never", "happen"}
+	sub := p.Subcommand()
+	assert.Nil(t, sub)
+}