Add comma_inheritance_rule rule

Fixes #3950

CHANGELOG.md

@@ -31,6 +31,11 @@
   [Marcelo Fabri](https://github.com/marcelofabri)
   [#3343](https://github.com/realm/SwiftLint/issues/3343)
 
+* Add `comma_inheritance` rule to validate that inheritance clauses use commas
+  instead of `&`.    
+  [Marcelo Fabri](https://github.com/marcelofabri)
+  [#3950](https://github.com/realm/SwiftLint/issues/3950)
+
 #### Bug Fixes
 
 * Fix false positives in `unused_closure_parameter` when using parameters with

Source/SwiftLintFramework/Models/PrimaryRuleList.swift

@@ -17,6 +17,7 @@ public let primaryRuleList = RuleList(rules: [
     ClosureSpacingRule.self,
     CollectionAlignmentRule.self,
     ColonRule.self,
+    CommaInheritanceRule.self,
     CommaRule.self,
     CommentSpacingRule.self,
     CompilerProtocolInitRule.self,

Source/SwiftLintFramework/Rules/Style/CommaInheritanceRule.swift

@@ -0,0 +1,115 @@
+import Foundation
+import SourceKittenFramework
+import SwiftSyntax
+
+public struct CommaInheritanceRule: SubstitutionCorrectableRule, ConfigurationProviderRule, AutomaticTestableRule {
+    public var configuration = SeverityConfiguration(.warning)
+
+    public init() {}
+
+    public static let description = RuleDescription(
+        identifier: "comma_inheritance",
+        name: "Comma Inheritance Rule",
+        description: "Use commas to separate types in inheritance lists",
+        kind: .style,
+        nonTriggeringExamples: [
+            Example("struct A: Codable, Equatable {}"),
+            Example("enum B: Codable, Equatable {}"),
+            Example("class C: Codable, Equatable {}"),
+            Example("protocol D: Codable, Equatable {}"),
+            Example("typealias E = Equatable & Codable"),
+            Example("func foo<T: Equatable & Codable>(_ param: T) {}"),
+            Example("""
+            protocol G {
+                associatedtype Model: Codable, Equatable
+            }
+            """)
+        ],
+        triggeringExamples: [
+            Example("struct A: Codable↓ & Equatable {}"),
+            Example("struct A: Codable↓  & Equatable {}"),
+            Example("struct A: Codable↓&Equatable {}"),
+            Example("struct A: Codable↓& Equatable {}"),
+            Example("enum B: Codable↓ & Equatable {}"),
+            Example("class C: Codable↓ & Equatable {}"),
+            Example("protocol D: Codable↓ & Equatable {}"),
+            Example("""
+            protocol G {
+                associatedtype Model: Codable↓ & Equatable
+            }
+            """)
+        ],
+        corrections: [
+            Example("struct A: Codable↓ & Equatable {}"): Example("struct A: Codable, Equatable {}"),
+            Example("struct A: Codable↓  & Equatable {}"): Example("struct A: Codable, Equatable {}"),
+            Example("struct A: Codable↓&Equatable {}"): Example("struct A: Codable, Equatable {}"),
+            Example("struct A: Codable↓& Equatable {}"): Example("struct A: Codable, Equatable {}"),
+            Example("enum B: Codable↓ & Equatable {}"): Example("enum B: Codable, Equatable {}"),
+            Example("class C: Codable↓ & Equatable {}"): Example("class C: Codable, Equatable {}"),
+            Example("protocol D: Codable↓ & Equatable {}"): Example("protocol D: Codable, Equatable {}"),
+            Example("""
+            protocol G {
+                associatedtype Model: Codable↓ & Equatable
+            }
+            """): Example("""
+            protocol G {
+                associatedtype Model: Codable, Equatable
+            }
+            """)
+        ]
+    )
+
+    // MARK: - Rule
+
+    public func validate(file: SwiftLintFile) -> [StyleViolation] {
+        return violationRanges(in: file).map {
+            StyleViolation(ruleDescription: Self.description,
+                           severity: configuration.severity,
+                           location: Location(file: file, characterOffset: $0.location))
+        }
+    }
+
+    // MARK: - SubstitutionCorrectableRule
+
+    public func substitution(for violationRange: NSRange, in file: SwiftLintFile) -> (NSRange, String)? {
+        return (violationRange, ", ")
+    }
+
+    public func violationRanges(in file: SwiftLintFile) -> [NSRange] {
+        guard let tree = file.syntaxTree else {
+            return []
+        }
+
+        let visitor = CommaInheritanceRuleVisitor()
+        visitor.walk(tree)
+        return visitor.violationRanges.compactMap {
+            file.stringView.byteRangeToNSRange($0)
+        }
+    }
+}
+
+private final class CommaInheritanceRuleVisitor: SyntaxVisitor {
+    private(set) var violationRanges: [ByteRange] = []
+
+    override func visitPost(_ node: InheritedTypeSyntax) {
+        for type in node.children {
+            guard let composition = type.as(CompositionTypeSyntax.self) else {
+                continue
+            }
+
+            for ampersand in composition.elements.compactMap(\.ampersand) {
+                let position: AbsolutePosition
+                if let previousToken = ampersand.previousToken {
+                    position = previousToken.endPositionBeforeTrailingTrivia
+                } else {
+                    position = ampersand.position
+                }
+
+                violationRanges.append(ByteRange(
+                    location: ByteCount(position),
+                    length: ByteCount(ampersand.endPosition.utf8Offset - position.utf8Offset)
+                ))
+            }
+        }
+    }
+}

Tests/SwiftLintFrameworkTests/AutomaticRuleTests.generated.swift

@@ -77,6 +77,12 @@ class ClosureSpacingRuleTests: XCTestCase {
     }
 }
 
+class CommaInheritanceRuleTests: XCTestCase {
+    func testWithDefaultConfiguration() {
+        verifyRule(CommaInheritanceRule.description)
+    }
+}
+
 class CommaRuleTests: XCTestCase {
     func testWithDefaultConfiguration() {
         verifyRule(CommaRule.description)

Tests/SwiftLintFrameworkTests/CollectingRuleTests.swift

@@ -37,7 +37,7 @@ class CollectingRuleTests: XCTestCase {
     }
 
     func testCollectsAnalyzerFiles() {
-        struct Spec: MockCollectingRule & AnalyzerRule {
+        struct Spec: MockCollectingRule, AnalyzerRule {
             func collectInfo(for file: SwiftLintFile, compilerArguments: [String]) -> [String] {
                 return compilerArguments
             }
@@ -53,7 +53,7 @@ class CollectingRuleTests: XCTestCase {
     }
 
     func testCorrects() {
-        struct Spec: MockCollectingRule & CollectingCorrectableRule {
+        struct Spec: MockCollectingRule, CollectingCorrectableRule {
             func collectInfo(for file: SwiftLintFile) -> String {
                 return file.contents
             }
@@ -77,7 +77,7 @@ class CollectingRuleTests: XCTestCase {
             }
         }
 
-        struct AnalyzerSpec: MockCollectingRule & AnalyzerRule & CollectingCorrectableRule {
+        struct AnalyzerSpec: MockCollectingRule, AnalyzerRule, CollectingCorrectableRule {
             func collectInfo(for file: SwiftLintFile, compilerArguments: [String]) -> String {
                 return file.contents
             }