[snapshot] Improve SnapshotHelper.swift handling if file doesn't exist

[janpio]

Feature Request

Motivation Behind Feature

Running fastlane snapshot handles outdated SnapshotHelper.swift (either too old version or empty file), but not a completely missing file:

Old SnapshotHelper.swift:

MacBook-Pro:FastlaneDemoIonic sujan$ fastlane snapshot
[✔] 🚀 
[13:27:13]: Successfully loaded '/Users/sujan/fastlane-demo/ionic/FastlaneDemoIonic/fastlane/Snapfile' 📄

+---------+-----------------------------------------+
|    Detected Values from './fastlane/Snapfile'     |
+---------+-----------------------------------------+
| project | platforms/ios/FastlaneDemoIonic.xcodep  |
|         | roj                                     |
+---------+-----------------------------------------+

[13:27:13]: $ xcodebuild -showBuildSettings -scheme FastlaneDemoIonic -project platforms/ios/FastlaneDemoIonic.xcodeproj
[13:27:20]: Your './fastlane/SnapshotHelper.swift' is outdated, please run `fastlane snapshot update`
[13:27:20]: to update your Helper file

[!] Please update your Snapshot Helper file using `fastlane snapshot update`

Empty SnapshotHelper.swift:

MacBook-Pro:FastlaneDemoIonic sujan$ fastlane snapshot
[✔] 🚀 
[13:27:13]: Successfully loaded '/Users/sujan/fastlane-demo/ionic/FastlaneDemoIonic/fastlane/Snapfile' 📄

+---------+-----------------------------------------+
|    Detected Values from './fastlane/Snapfile'     |
+---------+-----------------------------------------+
| project | platforms/ios/FastlaneDemoIonic.xcodep  |
|         | roj                                     |
+---------+-----------------------------------------+

[13:27:13]: $ xcodebuild -showBuildSettings -scheme FastlaneDemoIonic -project platforms/ios/FastlaneDemoIonic.xcodeproj
[13:27:20]: Your './fastlane/SnapshotHelper.swift' is outdated, please run `fastlane snapshot update`
[13:27:20]: to update your Helper file

[!] Please update your Snapshot Helper file using `fastlane snapshot update`

Missing SnapshotHelper.swift:

MacBook-Pro:FastlaneDemoIonic sujan$ fastlane snapshot
[✔] 🚀 
[13:40:03]: Successfully loaded '/Users/sujan/fastlane-demo/ionic/FastlaneDemoIonic/fastlane/Snapfile' 📄

+---------+-----------------------------------------+
|    Detected Values from './fastlane/Snapfile'     |
+---------+-----------------------------------------+
| project | platforms/ios/FastlaneDemoIonic.xcodep  |
|         | roj                                     |
+---------+-----------------------------------------+

[13:40:03]: $ xcodebuild -showBuildSettings -scheme FastlaneDemoIonic -project platforms/ios/FastlaneDemoIonic.xcodeproj

+----------------------------+-----------------------------------------+
|                     Summary for snapshot 2.101.1                     |
+----------------------------+-----------------------------------------+
| scheme                     | FastlaneDemoIonic                       |
| devices                    | ["iPhone 7", "iPhone 7 Plus", "iPhone   |
|                            | 8", "iPhone 8 Plus", "iPhone X", "iPad  |
|                            | (5th generation)", "iPad Pro            |
|                            | (9.7-inch)", "iPad Pro (12.9-inch)",    |
|                            | "iPad Pro (10.5-inch)"]                 |
| output_directory           | /Users/sujan/fastlane-demo/ionic/Fastl  |
|                            | aneDemoIonic/fastlane/screenshots       |
| project                    | platforms/ios/FastlaneDemoIonic.xcodep  |
|                            | roj                                     |
| languages                  | ["en-US"]                               |
| launch_arguments           | [""]                                    |
| output_simulator_logs      | false                                   |
| skip_open_summary          | false                                   |
| skip_helper_version_check  | false                                   |
| clear_previous_screenshots | false                                   |
| reinstall_app              | false                                   |
| erase_simulator            | false                                   |
| localize_simulator         | false                                   |
| buildlog_path              | ~/Library/Logs/snapshot                 |
| clean                      | false                                   |
| number_of_retries          | 1                                       |
| stop_after_first_error     | false                                   |
| result_bundle              | false                                   |
| concurrent_simulators      | true                                    |
...

Feature Description

Improve or rework the verify_helper_is_current method to also check if the file exists at all and output an appropriate error message if it does not.

fastlane/snapshot/lib/snapshot/runner.rb

Lines 119 to 134 in e8abaad

	def verify_helper_is_current
	return if Snapshot.config[:skip_helper_version_check]
	current_version = version_of_bundled_helper
	UI.verbose("Checking that helper files contain #{current_version}")
	helper_files = Update.find_helper
	helper_files.each do |path|
	content = File.read(path)
	unless content.include?(current_version)
	UI.error("Your '#{path}' is outdated, please run `fastlane snapshot update`")
	UI.error("to update your Helper file")
	UI.user_error!("Please update your Snapshot Helper file using `fastlane snapshot update`")
	end
	end
	end

Alternatives or Workarounds