empty_enum_arguments false positive with static func

[keith]

New Issue Checklist

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

Describe the bug

With this code:

struct Foo: Equatable {
    static func empty() -> Foo {
        return Foo()
    }
}

func bar() {
    let foo = Foo()
    if foo == .empty() {
        print("empty")
    }
}

And this config:

whitelist_rules:
  - empty_enum_arguments

.empty() is falsely marked as something where () can be removed. But those are required to build:

foo.swift:9:16: error: member 'empty()' is a function; did you mean to call it?
    if foo == .empty {
               ^
                    ()

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

swiftlint lint --config foo.yml --path foo.swift

foo.swift:9:21: warning: Empty Enum Arguments Violation: Arguments can be omitted when matching enums with associated types if they are not used. (empty_enum_arguments)

Environment

• SwiftLint version (run swiftlint version to be sure)? 0.40.0
• Installation method used (Homebrew, CocoaPods, building from source, etc)? portable_swiftlint.zip
• Paste your configuration file: above

related to #3103 and #3122

[keith]

cc @marcelofabri @lordzsolt

[jpsim]

This is a regression from 0.39.2, which did not report any violations with the provided repro steps.

[jpsim]

Introduced in #3122

[lordzsolt]

I'll take a look.

[lordzsolt]

I tried fixing it, however I did not find any solution achievable through a simple regex change.

Attempt 1: Require to be preceded by case

Regex: case.*\.\S+\s*(\([,\s_]*\))

However, this fails when there is more than one case per line: case .bar↓(_), .bar2↓(_). This is very bad.

---

Attempt 2: Require at least 1 _ character between the parenthesis.

Regex: \.\S+\s*(\([,\s]*[,\s_]+[,\s]*\))

But this fails on an earlier example case .bar↓()

However, the only compiling code which contains case .bar↓(), that I could come up with is:

enum Foo {
	case bar(Void)
}

let foo: Foo
switch foo {
	case .bar(): break
}

Because in case of a Void type, you are allowed write either .bar() or .bar(_)

Any non-Void type will fail to compile with the error Tuple pattern cannot match values of the non-tuple type 'T'

---

Considering I don't think I've ever seen an enum-case with a Void type associated value, I would propose removing case .bar↓() and case .bar↓() where method() > 2 from the triggering examples and treat it as false-negative.

Otherwise, I am not sure how to determine that .empty() is a static function, rather than an enum-case. Does the AST contain such information?

[jpsim]

Otherwise, I am not sure how to determine that .empty() is a static function, rather than an enum-case. Does the AST contain such information?

Only the post-typechecked AST, which Analyzer Rules operate on, but not standard lint rules.

[stale]

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