Add new opaque_over_existential rule

CHANGELOG.md

@@ -36,6 +36,10 @@
 * Support replacing identity expressions with `\.self` in `prefer_key_path` rule from Swift 6 on.  
   [SimplyDanny](https://github.com/SimplyDanny)
 
+* Add new `opaque_over_existential` opt-in rule that triggers when the existential `any` type of a
+  function parameter can be replaced with an opaque `some` type.  
+  [SimplyDanny](https://github.com/SimplyDanny)
+
 * Support linting only provided file paths with command plugins.  
   [DanSkeel](https://github.com/DanSkeel)
 

Source/SwiftLintBuiltInRules/Models/BuiltInRules.swift

@@ -139,6 +139,7 @@ public let builtInRules: [any Rule.Type] = [
     NumberSeparatorRule.self,
     ObjectLiteralRule.self,
     OneDeclarationPerFileRule.self,
+    OpaqueOverExistentialParameterRule.self,
     OpeningBraceRule.self,
     OperatorFunctionWhitespaceRule.self,
     OperatorUsageWhitespaceRule.self,

Source/SwiftLintBuiltInRules/Rules/Lint/OpaqueOverExistentialParameterRule.swift

@@ -0,0 +1,51 @@
+import SwiftSyntax
+
+@SwiftSyntaxRule(correctable: true, optIn: true)
+struct OpaqueOverExistentialParameterRule: Rule {
+    var configuration = SeverityConfiguration<Self>(.warning)
+
+    static let description = RuleDescription(
+        identifier: "opaque_over_existential",
+        name: "Opaque Over Existential Parameter",
+        description: "Prefer opaque type over existential type in function parameter",
+        kind: .lint,
+        nonTriggeringExamples: [
+            Example("func f(_: some P) {}"),
+            Example("func f(_: some P & Q) {}"),
+            Example("func f(_: any P.Type) {}"),
+        ],
+        triggeringExamples: [
+            Example("func f(_: ↓any P) {}"),
+            Example("func f(_: ↓any P & Q) {}"),
+        ],
+        corrections: [
+            Example("func f(_: any P) {}"):
+                Example("func f(_: some P) {}"),
+            Example("func f(_: any P & Q) {}"):
+                Example("func f(_: some P & Q) {}"),
+            Example("func f(_: /* comment */ any P/* comment*/) {}"):
+                Example("func f(_: /* comment */ some P/* comment*/) {}"),
+        ]
+    )
+}
+
+private extension OpaqueOverExistentialParameterRule {
+    final class Visitor: ViolationsSyntaxVisitor<ConfigurationType> {
+        override func visitPost(_ node: FunctionParameterSyntax) {
+            guard let type = node.type.as(SomeOrAnyTypeSyntax.self) else {
+                return
+            }
+            let specifier = type.someOrAnySpecifier
+            if specifier.tokenKind == .keyword(.any), !type.constraint.is(MetatypeTypeSyntax.self) {
+                violations.append(.init(
+                    position: specifier.positionAfterSkippingLeadingTrivia,
+                    correction: .init(
+                        start: specifier.positionAfterSkippingLeadingTrivia,
+                        end: specifier.endPositionBeforeTrailingTrivia,
+                        replacement: "some"
+                    )
+                ))
+            }
+        }
+    }
+}

Source/SwiftLintCore/Protocols/CollectingRule.swift

@@ -157,7 +157,12 @@ package extension CollectingCorrectableRule where Self: AnalyzerRule {
 /// :nodoc:
 public extension Array where Element == any Rule {
     static func == (lhs: Array, rhs: Array) -> Bool {
-        if lhs.count != rhs.count { return false }
-        return !zip(lhs, rhs).contains { !$0.0.isEqualTo($0.1) }
+        guard lhs.count == rhs.count else {
+            return false
+        }
+        return !zip(lhs, rhs).contains { pair in
+            let first = pair.0, second = pair.1
+            return !first.isEqualTo(second)
+        }
     }
 }

Source/SwiftLintCore/Protocols/Rule.swift

@@ -48,7 +48,7 @@ public protocol Rule {
     /// - parameter rule: The `rule` value to compare against.
     ///
     /// - returns: Whether or not the specified rule is equivalent to the current rule.
-    func isEqualTo(_ rule: any Rule) -> Bool
+    func isEqualTo(_ rule: some Rule) -> Bool
 
     /// Collects information for the specified file in a storage object, to be analyzed by a `CollectedLinter`.
     ///
@@ -110,7 +110,7 @@ public extension Rule {
         validate(file: file)
     }
 
-    func isEqualTo(_ rule: any Rule) -> Bool {
+    func isEqualTo(_ rule: some Rule) -> Bool {
         if let rule = rule as? Self {
             return configuration == rule.configuration
         }

Source/swiftlint/Commands/Rules.swift

@@ -36,10 +36,7 @@ extension SwiftLint {
                 .list
                 .sorted { $0.0 < $1.0 }
             if configOnly {
-                rules
-                    .map(\.value)
-                    .map { createInstance(of: $0, using: configuration, configure: !defaultConfig) }
-                    .forEach { printConfig(for: $0) }
+                rules.forEach { printConfig(for: createInstance(of: $0.value, using: configuration)) }
             } else {
                 let table = TextTable(
                     ruleList: rules,
@@ -54,7 +51,7 @@ extension SwiftLint {
         private func printDescription(for ruleType: any Rule.Type, with configuration: Configuration) {
             let description = ruleType.description
 
-            let rule = createInstance(of: ruleType, using: configuration, configure: !defaultConfig)
+            let rule = createInstance(of: ruleType, using: configuration)
             if configOnly {
                 printConfig(for: rule)
                 return
@@ -76,20 +73,18 @@ extension SwiftLint {
             }
         }
 
-        private func printConfig(for rule: any Rule) {
+        private func printConfig(for rule: some Rule) {
             let configDescription = rule.createConfigurationDescription()
             if configDescription.hasContent {
                 print("\(type(of: rule).identifier):")
                 print(configDescription.yaml().indent(by: 2))
             }
         }
 
-        private func createInstance(of ruleType: any Rule.Type,
-                                    using config: Configuration,
-                                    configure: Bool) -> any Rule {
-            configure
-                ? config.configuredRule(forID: ruleType.identifier) ?? ruleType.init()
-                : ruleType.init()
+        private func createInstance(of ruleType: any Rule.Type, using config: Configuration) -> any Rule {
+            defaultConfig
+                ? ruleType.init()
+                : config.configuredRule(forID: ruleType.identifier) ?? ruleType.init()
         }
     }
 }

Tests/GeneratedTests/GeneratedTests.swift

@@ -823,6 +823,12 @@ final class OneDeclarationPerFileRuleGeneratedTests: SwiftLintTestCase {
     }
 }
 
+final class OpaqueOverExistentialParameterRuleGeneratedTests: SwiftLintTestCase {
+    func testWithDefaultConfiguration() {
+        verifyRule(OpaqueOverExistentialParameterRule.description)
+    }
+}
+
 final class OpeningBraceRuleGeneratedTests: SwiftLintTestCase {
     func testWithDefaultConfiguration() {
         verifyRule(OpeningBraceRule.description)

Tests/IntegrationTests/default_rule_configurations.yml

@@ -649,6 +649,10 @@ one_declaration_per_file:
   severity: warning
   meta:
     opt-in: true
+opaque_over_existential:
+  severity: warning
+  meta:
+    opt-in: true
 opening_brace:
   severity: warning
   ignore_multiline_type_headers: false