prefer_key_path in 0.58.0 warns if {$0} instead of (\.self) for SwiftPM using Swift 5

[rgoldberg]

New Issue Checklist

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

Bug Description

prefer_key_path in 0.58.0 warns if {$0} is used instead of ()\.self for a Swift file in a SwiftPM project whose Package.swift contains // swift-tools-version:5.7.1 & swiftLanguageVersions: [.v5].

I assume that SwiftVersion.current used in SwiftVersion.current >= .six doesn't properly determine the correct version of Swift that is being used.

Mention the command or other SwiftLint integration method that caused the issue. Include stack traces or command output.

$ swiftlint --strict --quiet Sources

Environment

• SwiftLint version (run swiftlint version to be sure) 0.58.0
• Xcode version (run xcodebuild -version to be sure) 16.0 (16A242d)
• Installation method used (Homebrew, CocoaPods, building from source, etc) Homebrew
• Configuration file:

---
opt_in_rules:
  - all
disabled_rules:
  # eventually enable
  - file_header
  - one_declaration_per_file
  - trailing_comma
  # never enable
  - contrasted_opening_brace
  - explicit_acl
  - explicit_enum_raw_value
  - explicit_top_level_acl
  - explicit_type_interface
  - no_extension_access_modifier
  - no_grouping_extension
  - no_magic_numbers
  - prefixed_toplevel_constant
  - sorted_enum_cases
  - vertical_whitespace_between_cases
file_name:
  excluded: [Finder.swift, Utilities.swift]
file_types_order:
  order:
    [
      [main_type],
      [supporting_type],
      [extension],
      [preview_provider],
      [library_content_provider],
    ]
number_separator:
  minimum_length: 6
type_contents_order:
  order:
    [
      [case],
      [type_alias, associated_type],
      [subtype],
      [type_property],
      [instance_property],
      [ib_inspectable],
      [ib_outlet],
      [initializer],
      [deinitializer],
      [type_method],
      [view_life_cycle_method],
      [ib_action],
      [other_method],
      [subscript],
    ]

[SimplyDanny]

This is a valid report and something people need to be aware of.

SwiftLint doesn't care for any versions specified in the Package.swift at all - neither the tools version nor specific language versions for certain modules.

What it does is to ask SourceKit for the version which depends on the Xcode version being selected or first SourceKit binary in the PATH. If everything is configured well, this would also be what swift --version reports. So if you set a different version for some modules, this can cause problems, like in your case.

That said, you have the option to set SWIFTLINT_SWIFT_VERSION as an environment variable to overwrite whatever SourceKit reports. This is again a global version and thus applies to all modules.