Add loading for alternative help plugin

src/command.ts

@@ -2,11 +2,11 @@ const pjson = require('../package.json')
 import * as Config from '@oclif/config'
 import * as Errors from '@oclif/errors'
 import * as Parser from '@oclif/parser'
-import Help from '@oclif/plugin-help'
+import {HelpBase} from '@oclif/plugin-help'
 import {format, inspect} from 'util'
 
 import * as flags from './flags'
-import {sortBy, uniqBy} from './util'
+import {sortBy, uniqBy, getHelpPluginPackage} from './util'
 
 /**
  * swallows stdout epipe errors
@@ -186,8 +186,9 @@ export default abstract class Command {
   }
 
   protected _help() {
-    const HHelp: typeof Help = require('@oclif/plugin-help').default
-    const help = new HHelp(this.config)
+    const pluginPackage = getHelpPluginPackage(pjson)
+    const HHelp = require(pluginPackage).default
+    const help: HelpBase = new HHelp(this.config)
     const cmd = Config.Command.toCached(this.ctor as any as Config.Command.Class)
     if (!cmd.id) cmd.id = ''
     let topics = this.config.topics

src/main.ts

@@ -1,7 +1,8 @@
 import * as Config from '@oclif/config'
-import Help from '@oclif/plugin-help'
+import {HelpBase} from '@oclif/plugin-help'
 
 import {Command} from '.'
+import {getHelpPluginPackage} from './util'
 
 export class Main extends Command {
   static run(argv = process.argv.slice(2), options?: Config.LoadOptions) {
@@ -36,8 +37,9 @@ export class Main extends Command {
   }
 
   protected _help() {
-    const HHelp: typeof Help = require('@oclif/plugin-help').default
-    const help = new HHelp(this.config)
+    const pluginPackage = getHelpPluginPackage(this.config.pjson)
+    const HHelp = require(pluginPackage).default
+    const help: HelpBase = new HHelp(this.config)
     help.showHelp(this.argv)
     return this.exit(0)
   }

src/util.ts

@@ -1,3 +1,5 @@
+import {Config} from '@oclif/config'
+
 export function compact<T>(a: (T | undefined)[]): T[] {
   return a.filter((a): a is T => Boolean(a))
 }
@@ -31,3 +33,17 @@ export function sortBy<T>(arr: T[], fn: (i: T) => sort.Types | sort.Types[]): T[
 
   return arr.sort((a, b) => compare(fn(a), fn(b)))
 }
+
+export function getHelpPluginPackage(pjson: Config['pjson']): string {
+  const configuredHelpPlugin = pjson && pjson.oclif && pjson.oclif.helpPlugin
+  const defaultHelpPlugin = '@oclif/plugin-help'
+
+  if (configuredHelpPlugin) {
+    try {
+      require(configuredHelpPlugin)
+      return configuredHelpPlugin
+    } catch {}
+  }
+
+  return defaultHelpPlugin
+}