MM-12359 Add 'command show' CLI command (#10073)

* MM-12359 Add 'command show' CLI command

This new CLI command prints out the detailed information of a given
slash command.

* Fix typo in error returned when moving slash commands

* Move prettyPrint CLI functions to util

* Move prettyPrint CLI tests to util

cmd/mattermost/commands/utils.go

@@ -0,0 +1,89 @@
+// Copyright (c) 2019-present Mattermost, Inc. All Rights Reserved.
+// See License.txt for license information.
+
+package commands
+
+import (
+	"bytes"
+	"fmt"
+	"reflect"
+	"strings"
+
+	"github.com/mattermost/mattermost-server/mlog"
+)
+
+// prettyPrintStruct will return a prettyPrint version of a given struct
+func prettyPrintStruct(t interface{}) string {
+	return prettyPrintMap(structToMap(t))
+}
+
+// structToMap converts a struct into a map
+func structToMap(t interface{}) map[string]interface{} {
+	defer func() {
+		if r := recover(); r != nil {
+			mlog.Error(fmt.Sprintf("Panicked in structToMap. This should never happen. %v", r))
+		}
+	}()
+
+	val := reflect.ValueOf(t)
+
+	if val.Kind() != reflect.Struct {
+		return nil
+	}
+
+	out := map[string]interface{}{}
+
+	for i := 0; i < val.NumField(); i++ {
+		field := val.Field(i)
+
+		var value interface{}
+
+		switch field.Kind() {
+		case reflect.Struct:
+			value = structToMap(field.Interface())
+		case reflect.Ptr:
+			indirectType := field.Elem()
+
+			if indirectType.Kind() == reflect.Struct {
+				value = structToMap(indirectType.Interface())
+			} else {
+				value = indirectType.Interface()
+			}
+		default:
+			value = field.Interface()
+		}
+
+		out[val.Type().Field(i).Name] = value
+	}
+
+	return out
+}
+
+// prettyPrintMap will return a prettyPrint version of a given map
+func prettyPrintMap(configMap map[string]interface{}) string {
+	value := reflect.ValueOf(configMap)
+	return printMap(value, 0)
+}
+
+// printMap takes a reflect.Value and prints it out, recursively if it's a map with the given tab settings
+func printMap(value reflect.Value, tabVal int) string {
+	out := &bytes.Buffer{}
+
+	for _, key := range value.MapKeys() {
+		val := value.MapIndex(key)
+		if newVal, ok := val.Interface().(map[string]interface{}); !ok {
+			fmt.Fprintf(out, "%s", strings.Repeat("\t", tabVal))
+			fmt.Fprintf(out, "%v: \"%v\"\n", key.Interface(), val.Interface())
+		} else {
+			fmt.Fprintf(out, "%s", strings.Repeat("\t", tabVal))
+			fmt.Fprintf(out, "%v:\n", key.Interface())
+			// going one level in, increase the tab
+			tabVal++
+			fmt.Fprintf(out, "%s", printMap(reflect.ValueOf(newVal), tabVal))
+			// coming back one level, decrease the tab
+			tabVal--
+		}
+	}
+
+	return out.String()
+}