Add void_function_in_ternary opt-in rule (#3085)

* Add `void_function_in_ternary` opt-in rule

Fixes #2358

* Remove unused import and improve description

CHANGELOG.md

@@ -38,6 +38,11 @@
   `return <expression>` in a function that is `Void`.  
   [Marcelo Fabri](https://github.com/marcelofabri)
 
+* Add `void_function_in_ternary` opt-in rule to warn against using
+  a ternary operator to call `Void` functions.  
+  [Marcelo Fabri](https://github.com/marcelofabri)
+  [#2358](https://github.com/realm/SwiftLint/issues/2358)
+
 #### Bug Fixes
 
 * Fix `discarded_notification_center_observer` false positives when

Source/SwiftLintFramework/Models/MasterRuleList.swift

@@ -190,6 +190,7 @@ public let masterRuleList = RuleList(rules: [
     VerticalWhitespaceClosingBracesRule.self,
     VerticalWhitespaceOpeningBracesRule.self,
     VerticalWhitespaceRule.self,
+    VoidFunctionInTernaryConditionRule.self,
     VoidReturnRule.self,
     WeakDelegateRule.self,
     XCTFailMessageRule.self,

Source/SwiftLintFramework/Rules/Idiomatic/VoidFunctionInTernaryConditionRule.swift

@@ -0,0 +1,109 @@
+import SourceKittenFramework
+#if canImport(SwiftSyntax)
+import SwiftSyntax
+#endif
+
+public struct VoidFunctionInTernaryConditionRule: ConfigurationProviderRule, SyntaxRule, 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)
+            }
+            """)
+        ],
+        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)
+            }
+            """)
+        ]
+    )
+
+    public func validate(file: SwiftLintFile) -> [StyleViolation] {
+        #if canImport(SwiftSyntax)
+        return validate(file: file, visitor: TernaryVisitor())
+        #else
+        return []
+        #endif
+    }
+}
+
+#if canImport(SwiftSyntax)
+private class TernaryVisitor: SyntaxRuleVisitor {
+    private var positions = [AbsolutePosition]()
+
+    func visit(_ node: TernaryExprSyntax) -> SyntaxVisitorContinueKind {
+        if node.firstChoice is FunctionCallExprSyntax, node.secondChoice is FunctionCallExprSyntax,
+            let parent = node.parent as? ExprListSyntax, !parent.containsAssignment,
+            parent.parent is SequenceExprSyntax,
+            let blockItem = parent.parent?.parent as? CodeBlockItemSyntax, !blockItem.isClosureImplictReturn {
+            positions.append(node.questionMark.positionAfterSkippingLeadingTrivia)
+        }
+
+        return .visitChildren
+    }
+
+    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.utf8Offset)))
+        }
+    }
+}
+
+private extension ExprListSyntax {
+    var containsAssignment: Bool {
+        return children.contains(where: { $0 is AssignmentExprSyntax })
+    }
+}
+
+private extension CodeBlockItemSyntax {
+    var isClosureImplictReturn: Bool {
+        guard let parent = parent as? CodeBlockItemListSyntax else {
+            return false
+        }
+
+        return Array(parent.children).count == 1 && parent.parent is ClosureExprSyntax
+    }
+}
+#endif

SwiftLint.xcodeproj/project.pbxproj

@@ -306,6 +306,7 @@
 		D462021F1E15F52D0027AAD1 /* NumberSeparatorRuleExamples.swift in Sources */ = {isa = PBXBuildFile; fileRef = D462021E1E15F52D0027AAD1 /* NumberSeparatorRuleExamples.swift */; };
 		D46252541DF63FB200BE2CA1 /* NumberSeparatorRule.swift in Sources */ = {isa = PBXBuildFile; fileRef = D46252531DF63FB200BE2CA1 /* NumberSeparatorRule.swift */; };
 		D466B620233D229F0068190B /* FlatMapOverMapReduceRule.swift in Sources */ = {isa = PBXBuildFile; fileRef = D466B61F233D229F0068190B /* FlatMapOverMapReduceRule.swift */; };
+		D467275823DD971300DE73B6 /* VoidFunctionInTernaryConditionRule.swift in Sources */ = {isa = PBXBuildFile; fileRef = D467275723DD971300DE73B6 /* VoidFunctionInTernaryConditionRule.swift */; };
 		D46A317F1F1CEDCD00AF914A /* UnneededParenthesesInClosureArgumentRule.swift in Sources */ = {isa = PBXBuildFile; fileRef = D46A317E1F1CEDCD00AF914A /* UnneededParenthesesInClosureArgumentRule.swift */; };
 		D46C7C3E23BF2F6A007C517F /* PreferSelfTypeOverTypeOfSelfRule.swift in Sources */ = {isa = PBXBuildFile; fileRef = D46C7C3D23BF2F6A007C517F /* PreferSelfTypeOverTypeOfSelfRule.swift */; };
 		D46E041D1DE3712C00728374 /* TrailingCommaRule.swift in Sources */ = {isa = PBXBuildFile; fileRef = D46E041C1DE3712C00728374 /* TrailingCommaRule.swift */; };
@@ -836,6 +837,7 @@
 		D462021E1E15F52D0027AAD1 /* NumberSeparatorRuleExamples.swift */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.swift; path = NumberSeparatorRuleExamples.swift; sourceTree = "<group>"; };
 		D46252531DF63FB200BE2CA1 /* NumberSeparatorRule.swift */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.swift; path = NumberSeparatorRule.swift; sourceTree = "<group>"; };
 		D466B61F233D229F0068190B /* FlatMapOverMapReduceRule.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = FlatMapOverMapReduceRule.swift; sourceTree = "<group>"; };
+		D467275723DD971300DE73B6 /* VoidFunctionInTernaryConditionRule.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = VoidFunctionInTernaryConditionRule.swift; sourceTree = "<group>"; };
 		D46A317E1F1CEDCD00AF914A /* UnneededParenthesesInClosureArgumentRule.swift */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.swift; path = UnneededParenthesesInClosureArgumentRule.swift; sourceTree = "<group>"; };
 		D46C7C3D23BF2F6A007C517F /* PreferSelfTypeOverTypeOfSelfRule.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = PreferSelfTypeOverTypeOfSelfRule.swift; sourceTree = "<group>"; };
 		D46E041C1DE3712C00728374 /* TrailingCommaRule.swift */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.swift; path = TrailingCommaRule.swift; sourceTree = "<group>"; };
@@ -1381,6 +1383,7 @@
 				D4EA77C71F817FD200C315FB /* UnneededBreakInSwitchRule.swift */,
 				181D9E162038343D001F6887 /* UntypedErrorInCatchRule.swift */,
 				D43B04631E0620AB004016AF /* UnusedEnumeratedRule.swift */,
+				D467275723DD971300DE73B6 /* VoidFunctionInTernaryConditionRule.swift */,
 				41715DE023BEA08E00544BDF /* FileNameNoSpaceRule.swift */,
 				626D02961F31CBCC0054788D /* XCTFailMessageRule.swift */,
 				622AD7FF216ACE6200A002C6 /* XCTSpecificMatcherRule.swift */,
@@ -2336,6 +2339,7 @@
 				6C15818D237026AC00F582A2 /* GitHubActionsLoggingReporter.swift in Sources */,
 				62FE5D32200CABDD00F68793 /* DiscouragedOptionalCollectionExamples.swift in Sources */,
 				D41C09BD23C1B99D00F105C4 /* OrphanedDocCommentRule.swift in Sources */,
+				D467275823DD971300DE73B6 /* VoidFunctionInTernaryConditionRule.swift in Sources */,
 				D49896F12026B36C00814A83 /* RedundantSetAccessControlRule.swift in Sources */,
 				E4A6CF752363CBFB00DD5B18 /* RandomAccessCollection+Swiftlint.swift in Sources */,
 				29FFC37A1F15764D007E4825 /* FileLengthRuleConfiguration.swift in Sources */,

Tests/LinuxMain.swift

@@ -1597,6 +1597,12 @@ extension VerticalWhitespaceRuleTests {
     ]
 }
 
+extension VoidFunctionInTernaryConditionRuleTests {
+    static var allTests: [(String, (VoidFunctionInTernaryConditionRuleTests) -> () throws -> Void)] = [
+        ("testWithDefaultConfiguration", testWithDefaultConfiguration)
+    ]
+}
+
 extension VoidReturnRuleTests {
     static var allTests: [(String, (VoidReturnRuleTests) -> () throws -> Void)] = [
         ("testWithDefaultConfiguration", testWithDefaultConfiguration)
@@ -1868,6 +1874,7 @@ XCTMain([
     testCase(VerticalWhitespaceClosingBracesRuleTests.allTests),
     testCase(VerticalWhitespaceOpeningBracesRuleTests.allTests),
     testCase(VerticalWhitespaceRuleTests.allTests),
+    testCase(VoidFunctionInTernaryConditionRuleTests.allTests),
     testCase(VoidReturnRuleTests.allTests),
     testCase(WeakDelegateRuleTests.allTests),
     testCase(XCTFailMessageRuleTests.allTests),

Tests/SwiftLintFrameworkTests/AutomaticRuleTests.generated.swift

@@ -834,6 +834,12 @@ class VerticalWhitespaceOpeningBracesRuleTests: XCTestCase {
     }
 }
 
+class VoidFunctionInTernaryConditionRuleTests: XCTestCase {
+    func testWithDefaultConfiguration() {
+        verifyRule(VoidFunctionInTernaryConditionRule.description)
+    }
+}
+
 class VoidReturnRuleTests: XCTestCase {
     func testWithDefaultConfiguration() {
         verifyRule(VoidReturnRule.description)