redundant_type_annotation: flag when RHS is already typed #6949

Motivation

Opt-in redundant_type_annotation flags cases where the type name is restated on the RHS, e.g.:

var url: URL = URL()
let alphanumerics: CharacterSet = CharacterSet.alphanumerics

It does not flag an annotation that is redundant because the RHS is already a typed value/property of that type:

enum Metrics {
  static let avatarLabelSpacing: Double = 6
}

struct AvatarLabelStyle {
  var spacing: Double = Metrics.avatarLabelSpacing // annotation is unnecessary
}

Verified with SwiftLint 0.65.0 (only_rules: [redundant_type_annotation]): zero violations for the example above. consider_default_literal_types_redundant only adds literal cases like : Double = 6, not property references.

Feature request

Please extend redundant_type_annotation so it also treats an explicit type as redundant when the RHS expression’s type is unambiguously the same as the annotation—at least for simple cases like a reference to a static let / let / var of that type.

Example desired violation / correction:

- var spacing: Double = Metrics.avatarLabelSpacing
+ var spacing = Metrics.avatarLabelSpacing

Happy to discuss scope (e.g. identifier / member-access RHS only; skip cases that would change overload resolution). Related discussion also opened for SwiftFormat’s propertyTypes / redundantType: nicklockwood/SwiftFormat#2752