coder · fuskovic · Jul 22, 2020 · Jul 20, 2020
diff --git a/README.md b/README.md
@@ -95,6 +95,7 @@ func (c *subcmd) Spec() cli.CommandSpec {
     return cli.CommandSpec{
         Name:  "sub",
         Usage: "",
+        Aliases: []string{"s"},
         Desc:  `This is a simple subcommand.`,
     }
 }
@@ -134,5 +135,5 @@ Usage: subcommand [flags]
 This is a simple example of subcommands.
 
 Commands:
-	sub	This is a simple subcommand.
+	s,sub -	This is a simple subcommand.
 ```
diff --git a/command.go b/command.go
@@ -23,17 +23,23 @@ type CommandSpec struct {
 	// RawArgs indicates that flags should not be parsed, and they should be deferred
 	// to the command.
 	RawArgs bool
-
 	// Hidden indicates that this command should not show up in it's parent's
 	// subcommand help.
 	Hidden bool
+	// Aliases contains a list of alternative names that can be used for a particular command.
+	Aliases []string
 }
 
 // ShortDesc returns the first line of Desc.
 func (c CommandSpec) ShortDesc() string {
 	return strings.Split(c.Desc, "\n")[0]
 }
 
+// HasAliases evaluates whether particular command has any alternative names.
+func (c CommandSpec) HasAliases() bool {
+	return len(c.Aliases) > 0
+}
+
 // Command describes a command or subcommand.
 type Command interface {
 	// Spec returns metadata about the command.

diff --git a/command_test.go b/command_test.go
@@ -0,0 +1,105 @@
+package cli
+
+import (
+	"bytes"
+	"os"
+	"testing"
+
+	"cdr.dev/slog/sloggers/slogtest/assert"
+	"github.com/spf13/pflag"
+)
+
+const (
+	success = "test successful"
+
+	expectedParentCmdHelpOutput = `Usage: mockParentCmd Mock parent command usage.
+
+Mock parent command description.
+
+Commands:
+	s,sc,sub,mockSubCmd  - A simple mock subcommand with aliases.
+`
+)
+
+var subCmd = &mockSubCmd{buf: new(bytes.Buffer)}
+
+type (
+	mockParentCmd struct{}
+	mockSubCmd    struct{ buf *bytes.Buffer }
+)
+
+func (c *mockParentCmd) Run(fl *pflag.FlagSet) {}
+
+func (c *mockParentCmd) Subcommands() []Command { return []Command{subCmd} }
+
+func (c *mockParentCmd) Spec() CommandSpec {
+	return CommandSpec{
+		Name:  "mockParentCmd",
+		Usage: "Mock parent command usage.",
+		Desc:  "Mock parent command description.",
+	}
+}
+
+func (c *mockSubCmd) Run(fl *pflag.FlagSet) {
+	c.buf = new(bytes.Buffer)
+	if _, err := c.Write([]byte(success)); err != nil {
+		fl.Usage()
+	}
+}
+
+func (c *mockSubCmd) Write(b []byte) (int, error) { return c.buf.Write(b) }
+
+func (c *mockSubCmd) Spec() CommandSpec {
+	return CommandSpec{
+		Name:    "mockSubCmd",
+		Usage:   "Test a subcommand.",
+		Aliases: []string{"s", "sc", "sub"},
+		Desc:    "A simple mock subcommand with aliases.",
+	}
+}
+
+func TestSubCmdAliases(t *testing.T) {
+	for _, test := range []struct {
+		name, expected string
+	}{
+		{
+			name:     "s",
+			expected: success,
+		},
+		{
+			name:     "sc",
+			expected: success,
+		},
+		{
+			name:     "sub",
+			expected: success,
+		},
+	} {
+		t.Run(test.name, func(t *testing.T) {
+			// Since the alias is the name of the test
+			// we can just pass it as the alias arg.
+			os.Args = []string{"mockParentCmd", test.name}
+			// Based on os.Args, when splitArgs is invoked,
+			// it should be able to deduce the subcommand we want
+			// based on the new alias map it's being passed.
+			RunRoot(&mockParentCmd{})
+			// The success const is never written into the buffer
+			// if the subcommand fails to be invoked by alias.
+			got := string(subCmd.buf.Bytes())
+			assert.Equal(t, test.name, test.expected, got)
+		})
+	}
+}
+
+func TestSubcmdAliasesInParentCmdHelpOutput(t *testing.T) {
+	buf := new(bytes.Buffer)
+	cmd := &mockParentCmd{}
+	name := cmd.Spec().Name
+	fl := pflag.NewFlagSet(name, pflag.ExitOnError)
+	// If the help output is not written to the buffer
+	// in the format we expect then the test will fail.
+	renderHelp(name, cmd, fl, buf)
+	got := string(buf.Bytes())
+	expected := expectedParentCmdHelpOutput
+	assert.Equal(t, "display_subcmd_aliases_in_parentcmd_help_output", expected, got)
+}
diff --git a/go.mod b/go.mod
@@ -2,4 +2,8 @@ module go.coder.com/cli
 
 go 1.12
 
-require github.com/spf13/pflag v1.0.3
+require (
+	cdr.dev/slog v1.3.0
+	github.com/spf13/pflag v1.0.3
+	github.com/stretchr/testify v1.6.1 // indirect
+)