optional_enum_case_matching triggers on non-enum switch

[vokal-isaac]

New Issue Checklist

• [x] Updated SwiftLint to the latest version
• [x] I searched for existing GitHub issues

Describe the bug

The optional_enum_case_matching rule is triggered when switching over an optional struct with cases that are static members of the struct. In these instances, removing the ? on the case results in code that doesn't compile (Xcode 11.1).

Complete output when running SwiftLint, including the stack trace and command used

$ swiftlint lint --use-stdin --enable-all-rules
/// Test struct
public struct Foo: Equatable {
    public static let bar: Foo = .init(foo: "bar")

    public let foo: String
}

/// Test variable
public var something: Foo?

switch something {
case .bar?:
    print("bar")

default:
    print("default")
}
<nopath>:12:10: warning: Optional Enum Case Match Violation: Matching an enum case against an optional enum without '?' is supported on Swift 5.1 and above.  (optional_enum_case_matching)
Done linting! Found 1 violation, 0 serious in 1 file.

Environment

• SwiftLint version (run swiftlint version to be sure)?
  0.38.2
• Installation method used (Homebrew, CocoaPods, building from source, etc)?
  CocoaPods
• Paste your configuration file
  n/a
• Are you using nested configurations? If so, paste their relative paths and respective contents.
  n/a
• Which Xcode version are you using (check xcodebuild -version)?
  Xcode 11.1, Build version 11A1027
• Do you have a sample that shows the issue? Run echo "[string here]" | swiftlint lint --no-cache --use-stdin --enable-all-rules to quickly test if your example is really demonstrating the issue. If your example is more complex, you can use swiftlint lint --path [file here] --no-cache --enable-all-rules.
  see above

[rogerluan]

I'm having the same issue.

Looks like this is the place to add such rule https://github.com/realm/SwiftLint/blob/master/Source/SwiftLintFramework/Rules/Style/OptionalEnumCaseMatchingRule.swift#L185 but I couldn't figure out a way to identify the type of the identifier after a quick glance.

Any help from a more avid SwiftLint contributor? :)

[rogerluan]

@marcelofabri could you shed some light here? 😊

[stale[bot]]

This issue has been automatically marked as stale because it has not had any recent activity. Please comment to prevent this issue from being closed. Thank you for your contributions!

[rogerluan]

This is still a problem! I faced this problem again last week

[jpsim]

If you'd like to try fixing this yourself, the steps in CONTRIBUTING.md should be a good start and you can ask questions here if you get stuck.

[rogerluan]

@jpsim I couldn't figure out how to determine the type of the identifier (e.g. distinguish between enum and struct, or enum and a class). Not sure if this is possible in SwiftLint either, given that we use regex for most (all?) of the parsing. Could you shed some light? 😊

[jpsim]

Look for uses of SwiftDeclarationKind.enum in the codebase, there are lots of examples. Here's one example: https://github.com/realm/SwiftLint/blob/67165f7c642179a849632f962f584ea728137dfc/Source/SwiftLintFramework/Rules/Idiomatic/ExplicitEnumRawValueRule.swift#L77

[rogerluan]

Thanks!! I'll look into this 😃

[stale[bot]]

This issue has been automatically marked as stale because it has not had any recent activity. Please comment to prevent this issue from being closed. Thank you for your contributions!

[rogerluan]

Please don't close this, bot.

[SimplyDanny]

The existing rule is unable to know the type of the identifier in the switch condition. This knowledge is only available in a type-checked AST that would be available in an Analyzer rule.

So basically a new rule would need to be introduced to handle this case properly. I'll mark this issue as a "rule request" therefore.