Add back void_function_in_ternary rule

CHANGELOG.md

@@ -25,6 +25,10 @@
   a custom rule.  
   [Marcelo Fabri](https://github.com/marcelofabri)
 
+* Add back `void_function_in_ternary` opt-in rule to warn against using
+  a ternary operator to call `Void` functions.  
+  [Marcelo Fabri](https://github.com/marcelofabri)
+
 #### Bug Fixes
 
 * Ignore array types in `syntactic_sugar` rule if their associated `Index` is

Source/SwiftLintFramework/Models/PrimaryRuleList.swift

@@ -210,6 +210,7 @@ public let primaryRuleList = RuleList(rules: [
     VerticalWhitespaceClosingBracesRule.self,
     VerticalWhitespaceOpeningBracesRule.self,
     VerticalWhitespaceRule.self,
+    VoidFunctionInTernaryConditionRule.self,
     VoidReturnRule.self,
     WeakDelegateRule.self,
     XCTFailMessageRule.self,

Source/SwiftLintFramework/Rules/Idiomatic/VoidFunctionInTernaryConditionRule.swift

@@ -0,0 +1,228 @@
+import SourceKittenFramework
+import SwiftSyntax
+
+public struct VoidFunctionInTernaryConditionRule: ConfigurationProviderRule, AutomaticTestableRule {
+    public var configuration = SeverityConfiguration(.warning)
+
+    public init() {}
+
+    public static let description = RuleDescription(
+        identifier: "void_function_in_ternary",
+        name: "Void Function in Ternary",
+        description: "Using ternary to call Void functions should be avoided.",
+        kind: .idiomatic,
+        minSwiftVersion: .fiveDotOne,
+        nonTriggeringExamples: [
+            Example("let result = success ? foo() : bar()"),
+            Example("""
+            if success {
+                askQuestion()
+            } else {
+                exit()
+            }
+            """),
+            Example("""
+            var price: Double {
+                return hasDiscount ? calculatePriceWithDiscount() : calculateRegularPrice()
+            }
+            """),
+            Example("foo(x == 2 ? a() : b())"),
+            Example("""
+            chevronView.image = collapsed ? .icon(.mediumChevronDown) : .icon(.mediumChevronUp)
+            """),
+            Example("""
+            array.map { elem in
+                elem.isEmpty() ? .emptyValue() : .number(elem)
+            }
+            """),
+            Example("""
+            func compute(data: [Int]) -> Int {
+                data.isEmpty ? 0 : expensiveComputation(data)
+            }
+            """),
+            Example("""
+            var value: Int {
+                mode == .fast ? fastComputation() : expensiveComputation()
+            }
+            """),
+            Example("""
+            var value: Int {
+                get {
+                    mode == .fast ? fastComputation() : expensiveComputation()
+                }
+            }
+            """),
+            Example("""
+            subscript(index: Int) -> Int {
+                get {
+                    index == 0 ? defaultValue() : compute(index)
+                }
+            """),
+            Example("""
+            subscript(index: Int) -> Int {
+                index == 0 ? defaultValue() : compute(index)
+            """)
+        ],
+        triggeringExamples: [
+            Example("success ↓? askQuestion() : exit()"),
+            Example("""
+            perform { elem in
+                elem.isEmpty() ↓? .emptyValue() : .number(elem)
+                return 1
+            }
+            """),
+            Example("""
+            DispatchQueue.main.async {
+                self.sectionViewModels[section].collapsed.toggle()
+                self.sectionViewModels[section].collapsed
+                    ↓? self.tableView.deleteRows(at: [IndexPath(row: 0, section: section)], with: .automatic)
+                    : self.tableView.insertRows(at: [IndexPath(row: 0, section: section)], with: .automatic)
+                self.tableView.scrollToRow(at: IndexPath(row: NSNotFound, section: section), at: .top, animated: true)
+            }
+            """),
+            Example("""
+            subscript(index: Int) -> Int {
+                index == 0 ↓? something() : somethingElse(index)
+                return index
+            """),
+            Example("""
+            var value: Int {
+                mode == .fast ↓? something() : somethingElse()
+                return 0
+            }
+            """),
+            Example("""
+            var value: Int {
+                get {
+                    mode == .fast ↓? something() : somethingElse()
+                    return 0
+                }
+            }
+            """),
+            Example("""
+            subscript(index: Int) -> Int {
+                get {
+                    index == 0 ↓? something() : somethingElse(index)
+                    return index
+                }
+            """)
+        ]
+    )
+
+    public func validate(file: SwiftLintFile) -> [StyleViolation] {
+        let visitor = VoidFunctionInTernaryConditionVisitor()
+        return visitor.walk(file: file) { visitor in
+            visitor.violations(for: self, in: file)
+        }
+    }
+}
+
+private class VoidFunctionInTernaryConditionVisitor: SyntaxVisitor {
+    private var positions = [AbsolutePosition]()
+
+    override func visitPost(_ node: TernaryExprSyntax) {
+        guard node.firstChoice.is(FunctionCallExprSyntax.self),
+              node.secondChoice.is(FunctionCallExprSyntax.self),
+              let parent = node.parent?.as(ExprListSyntax.self),
+              !parent.containsAssignment,
+              let grandparent = parent.parent,
+              grandparent.is(SequenceExprSyntax.self),
+              let blockItem = grandparent.parent?.as(CodeBlockItemSyntax.self),
+              !blockItem.isImplicitReturn else {
+            return
+        }
+
+        positions.append(node.questionMark.positionAfterSkippingLeadingTrivia)
+    }
+
+    func violations(for rule: VoidFunctionInTernaryConditionRule, in file: SwiftLintFile) -> [StyleViolation] {
+        return positions.map { position in
+            StyleViolation(ruleDescription: type(of: rule).description,
+                           severity: rule.configuration.severity,
+                           location: Location(file: file, byteOffset: ByteCount(position)))
+        }
+    }
+}
+
+private extension ExprListSyntax {
+    var containsAssignment: Bool {
+        return children.contains(where: { $0.is(AssignmentExprSyntax.self) })
+    }
+}
+
+private extension CodeBlockItemSyntax {
+    var isImplicitReturn: Bool {
+        isClosureImplictReturn || isFunctionImplicitReturn ||
+        isVariableImplicitReturn || isSubscriptImplicitReturn ||
+        isAcessorImplicitReturn
+    }
+
+    var isClosureImplictReturn: Bool {
+        guard let parent = parent?.as(CodeBlockItemListSyntax.self),
+              let grandparent = parent.parent else {
+            return false
+        }
+
+        return parent.children.count == 1 && grandparent.is(ClosureExprSyntax.self)
+    }
+
+    var isFunctionImplicitReturn: Bool {
+        guard let parent = parent?.as(CodeBlockItemListSyntax.self),
+              let functionDecl = parent.parent?.parent?.as(FunctionDeclSyntax.self) else {
+            return false
+        }
+
+        return parent.children.count == 1 && functionDecl.signature.allowsImplicitReturns
+    }
+
+    var isVariableImplicitReturn: Bool {
+        guard let parent = parent?.as(CodeBlockItemListSyntax.self) else {
+            return false
+        }
+
+        let isVariableDecl = parent.parent?.parent?.as(PatternBindingSyntax.self) != nil
+        return parent.children.count == 1 && isVariableDecl
+    }
+
+    var isSubscriptImplicitReturn: Bool {
+        guard let parent = parent?.as(CodeBlockItemListSyntax.self),
+              let subscriptDecl = parent.parent?.parent?.as(SubscriptDeclSyntax.self) else {
+            return false
+        }
+
+        return parent.children.count == 1 && subscriptDecl.allowsImplicitReturns
+    }
+
+    var isAcessorImplicitReturn: Bool {
+        guard let parent = parent?.as(CodeBlockItemListSyntax.self),
+              parent.parent?.parent?.as(AccessorDeclSyntax.self) != nil else {
+            return false
+        }
+
+        return parent.children.count == 1
+    }
+}
+
+private extension FunctionSignatureSyntax {
+     var allowsImplicitReturns: Bool {
+         output?.allowsImplicitReturns ?? false
+     }
+}
+
+private extension SubscriptDeclSyntax {
+    var allowsImplicitReturns: Bool {
+        result.allowsImplicitReturns
+    }
+}
+
+private extension ReturnClauseSyntax {
+    var allowsImplicitReturns: Bool {
+        if let simpleType = returnType.as(SimpleTypeIdentifierSyntax.self) {
+            return simpleType.name.text != "Void" && simpleType.name.text != "Never"
+        } else if let tupleType = returnType.as(TupleTypeSyntax.self) {
+            return !tupleType.elements.isEmpty
+        } else {
+            return true
+        }
+    }
+}

Tests/SwiftLintFrameworkTests/AutomaticRuleTests.generated.swift

@@ -923,6 +923,12 @@ class VerticalWhitespaceOpeningBracesRuleTests: XCTestCase {
     }
 }
 
+class VoidFunctionInTernaryConditionRuleTests: XCTestCase {
+    func testWithDefaultConfiguration() {
+        verifyRule(VoidFunctionInTernaryConditionRule.description)
+    }
+}
+
 class VoidReturnRuleTests: XCTestCase {
     func testWithDefaultConfiguration() {
         verifyRule(VoidReturnRule.description)