Add `CalledAs` method to cobra.Command (w/ tests) (#567)

* Add `CalledAs` method to Command (w/ tests)

The `CalledAs` method returns the name of the command or alias that
invoked the command -- as long as the command was actually invoked.
Otherwise, it returns the empty string.

The opens up possibilies for commands to behave differently based on
which alias invoked the command (in the same vein as Linux programs
which adjust their behavior based on the value of argv[0]).

* Fixed formatting

command.go

@@ -147,6 +147,11 @@ type Command struct {
 	commandsMaxNameLen        int
 	// commandsAreSorted defines, if command slice are sorted or not.
 	commandsAreSorted bool
+	// commandCalledAs is the name or alias value used to call this command.
+	commandCalledAs struct {
+		name   string
+		called bool
+	}
 
 	// args is actual args parsed from flags.
 	args []string
@@ -557,6 +562,7 @@ func (c *Command) findNext(next string) *Command {
 	matches := make([]*Command, 0)
 	for _, cmd := range c.commands {
 		if cmd.Name() == next || cmd.HasAlias(next) {
+			cmd.commandCalledAs.name = next
 			return cmd
 		}
 		if EnablePrefixMatching && cmd.hasNameOrAliasPrefix(next) {
@@ -567,6 +573,7 @@ func (c *Command) findNext(next string) *Command {
 	if len(matches) == 1 {
 		return matches[0]
 	}
+
 	return nil
 }
 
@@ -828,6 +835,11 @@ func (c *Command) ExecuteC() (cmd *Command, err error) {
 		return c, err
 	}
 
+	cmd.commandCalledAs.called = true
+	if cmd.commandCalledAs.name == "" {
+		cmd.commandCalledAs.name = cmd.Name()
+	}
+
 	err = cmd.execute(flags)
 	if err != nil {
 		// Always show help if requested, even if SilenceErrors is in
@@ -1135,14 +1147,25 @@ func (c *Command) HasAlias(s string) bool {
 	return false
 }
 
+// CalledAs returns the command name or alias that was used to invoke
+// this command or an empty string if the command has not been called.
+func (c *Command) CalledAs() string {
+	if c.commandCalledAs.called {
+		return c.commandCalledAs.name
+	}
+	return ""
+}
+
 // hasNameOrAliasPrefix returns true if the Name or any of aliases start
 // with prefix
 func (c *Command) hasNameOrAliasPrefix(prefix string) bool {
 	if strings.HasPrefix(c.Name(), prefix) {
+		c.commandCalledAs.name = c.Name()
 		return true
 	}
 	for _, alias := range c.Aliases {
 		if strings.HasPrefix(alias, prefix) {
+			c.commandCalledAs.name = alias
 			return true
 		}
 	}

command_test.go

@@ -1563,3 +1563,66 @@ func TestUpdateName(t *testing.T) {
 		t.Error("c.Name() should be updated on changed c.Use")
 	}
 }
+
+type calledAsTestcase struct {
+	args []string
+	call string
+	want string
+	epm  bool
+	tc   bool
+}
+
+func (tc *calledAsTestcase) test(t *testing.T) {
+	defer func(ov bool) { EnablePrefixMatching = ov }(EnablePrefixMatching)
+	EnablePrefixMatching = tc.epm
+
+	var called *Command
+	run := func(c *Command, _ []string) { t.Logf("called: %q", c.Name()); called = c }
+
+	parent := &Command{Use: "parent", Run: run}
+	child1 := &Command{Use: "child1", Run: run, Aliases: []string{"this"}}
+	child2 := &Command{Use: "child2", Run: run, Aliases: []string{"that"}}
+
+	parent.AddCommand(child1)
+	parent.AddCommand(child2)
+	parent.SetArgs(tc.args)
+
+	output := new(bytes.Buffer)
+	parent.SetOutput(output)
+
+	parent.Execute()
+
+	if called == nil {
+		if tc.call != "" {
+			t.Errorf("missing expected call to command: %s", tc.call)
+		}
+		return
+	}
+
+	if called.Name() != tc.call {
+		t.Errorf("called command == %q; Wanted %q", called.Name(), tc.call)
+	} else if got := called.CalledAs(); got != tc.want {
+		t.Errorf("%s.CalledAs() == %q; Wanted: %q", tc.call, got, tc.want)
+	}
+}
+
+func TestCalledAs(t *testing.T) {
+	tests := map[string]calledAsTestcase{
+		"find/no-args":            {nil, "parent", "parent", false, false},
+		"find/real-name":          {[]string{"child1"}, "child1", "child1", false, false},
+		"find/full-alias":         {[]string{"that"}, "child2", "that", false, false},
+		"find/part-no-prefix":     {[]string{"thi"}, "", "", false, false},
+		"find/part-alias":         {[]string{"thi"}, "child1", "this", true, false},
+		"find/conflict":           {[]string{"th"}, "", "", true, false},
+		"traverse/no-args":        {nil, "parent", "parent", false, true},
+		"traverse/real-name":      {[]string{"child1"}, "child1", "child1", false, true},
+		"traverse/full-alias":     {[]string{"that"}, "child2", "that", false, true},
+		"traverse/part-no-prefix": {[]string{"thi"}, "", "", false, true},
+		"traverse/part-alias":     {[]string{"thi"}, "child1", "this", true, true},
+		"traverse/conflict":       {[]string{"th"}, "", "", true, true},
+	}
+
+	for name, tc := range tests {
+		t.Run(name, tc.test)
+	}
+}