optional_enum_case_matching false positive

[allen-zeng]

New Issue Checklist

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

Describe the bug

The rule picks up the pattern _?. This is incorrect, especially when the pattern _? is used to distinguish between nil and non-nil.

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

$ echo "import Foundation enum Test {     case a, b, c } let x: Test? = .c let y: Test? = nil switch (x, y) { case (.c, _?):     print(\"this shouldn't print\") case (.c, nil):     print(\"this is the correct print\") case (_, _):     print(\"this is to make the compiler happy\") }" | swiftlint lint --no-cache --use-stdin --enable-all-rules
Loading configuration from '.swiftlint.yml'
<nopath>:1:29: warning: Closure Spacing Violation: Closure expressions should have a single space inside each brace. (closure_spacing)
<nopath>:1:19: warning: Explicit ACL Violation: All declarations should specify Access Control Level keywords explicitly. (explicit_acl)
<nopath>:1:50: warning: Explicit ACL Violation: All declarations should specify Access Control Level keywords explicitly. (explicit_acl)
<nopath>:1:68: warning: Explicit ACL Violation: All declarations should specify Access Control Level keywords explicitly. (explicit_acl)
<nopath>:1:19: warning: Explicit Top Level ACL Violation: Top-level declarations should specify Access Control Level keywords explicitly. (explicit_top_level_acl)
<nopath>:1:50: warning: Explicit Top Level ACL Violation: Top-level declarations should specify Access Control Level keywords explicitly. (explicit_top_level_acl)
<nopath>:1:68: warning: Explicit Top Level ACL Violation: Top-level declarations should specify Access Control Level keywords explicitly. (explicit_top_level_acl)
<nopath>:1:40: error: Identifier Name Violation: Enum element name should be between 3 and 40 characters long: 'a' (identifier_name)
<nopath>:1:43: error: Identifier Name Violation: Enum element name should be between 3 and 40 characters long: 'b' (identifier_name)
<nopath>:1:46: error: Identifier Name Violation: Enum element name should be between 3 and 40 characters long: 'c' (identifier_name)
<nopath>:1:50: error: Identifier Name Violation: Variable name should be between 3 and 40 characters long: 'x' (identifier_name)
<nopath>:1:68: error: Identifier Name Violation: Variable name should be between 3 and 40 characters long: 'y' (identifier_name)
<nopath>:1:1: error: Line Length Violation: Line should be 120 characters or less: currently 268 characters (line_length)
<nopath>:1:114: 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)
<nopath>:1:54: warning: Prefixed Top-Level Constant Violation: Top-level constants should be prefixed by `k`. (prefixed_toplevel_constant)
<nopath>:1:72: warning: Prefixed Top-Level Constant Violation: Top-level constants should be prefixed by `k`. (prefixed_toplevel_constant)
<nopath>:1:103: warning: Switch and Case Statement Alignment Violation: Case statements should vertically align with their enclosing switch statement. (switch_case_alignment)
<nopath>:1:152: warning: Switch and Case Statement Alignment Violation: Case statements should vertically align with their enclosing switch statement. (switch_case_alignment)
<nopath>:1:207: warning: Switch and Case Statement Alignment Violation: Case statements should vertically align with their enclosing switch statement. (switch_case_alignment)
<nopath>:1:103: warning: Switch Case on Newline Violation: Cases inside a switch should always be on a newline (switch_case_on_newline)
<nopath>:1:152: warning: Switch Case on Newline Violation: Cases inside a switch should always be on a newline (switch_case_on_newline)
<nopath>:1:207: warning: Switch Case on Newline Violation: Cases inside a switch should always be on a newline (switch_case_on_newline)
Done linting! Found 22 violations, 6 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)?
  Homebrew and CocoaPods, ran both
• Paste your configuration file:

opt_in_rules:
- optional_enum_case_matching

• Are you using nested configurations?
  No
• Which Xcode version are you using (check xcodebuild -version)?
  Xcode 11.3.1
  Build version 11C504
• Do you have a sample that shows the issue?

import Foundation

enum Test {
    case a, b, c
}

let x: Test? = .c
let y: Test? = nil

switch (x, y) {
// If we remove the `?`, the compiler will warn that the second `case` is already covered by this, and the output will be `this shouldn't print`.
case (.c, _?): 
    print("this shouldn't print")
case (.c, nil):
    print("this is the correct print")
case (_, _):
    print("this is to make the compiler happy")
}

[marcelofabri]

@allen-zeng do you want to give this a shot? shouldn't be too hard to fix

[allen-zeng]

I sure can but I won't be able to immediately. If anyone else gets a chance definitely jump in!