Add include_bare_init option to explicit_init rule (#5203)

CHANGELOG.md

@@ -39,7 +39,7 @@
   Bash, Zsh and fish.  
   [SimplyDanny](https://github.com/SimplyDanny)
 
-* Add new `private_swiftui_state_property` opt-in rule to encourage setting 
+* Add new `private_swiftui_state_property` opt-in rule to encourage setting
   SwiftUI `@State` and `@StateObject` properties to private.  
   [mt00chikin](https://github.com/mt00chikin)
   [#3173](https://github.com/realm/SwiftLint/issues/3173)
@@ -53,10 +53,10 @@
   [keith](https://github.com/keith)
   [5139](https://github.com/realm/SwiftLint/pull/5139)
 
-* Show a rule's active YAML configuration in output of 
+* Show a rule's active YAML configuration in output of
   `swiftlint rules <rule>`.  
   [SimplyDanny](https://github.com/SimplyDanny)
-  
+
 * Add `invokeTest()` to `overridden_super_call` defaults.  
   [DylanBettermannDD](https://github.com/DylanBettermannDD)
 
@@ -68,6 +68,11 @@
   values for configurations being printed for a single rule or all rules.  
   [SimplyDanny](https://github.com/SimplyDanny)
 
+* Add `include_bare_init` option to the `explicit_init` rule. `include_bare_init`
+  encourages using named constructors over `.init()` and type inference.  
+  [Martin Redington](https://github.com/mildm8nnered)
+  [#5203](https://github.com/realm/SwiftLint/issues/5203)
+
 #### Bug Fixes
 
 * Fix false positive in `control_statement` rule that triggered on conditions

Source/SwiftLintBuiltInRules/Rules/Idiomatic/ExplicitInitRule.swift

@@ -2,7 +2,7 @@ import SwiftSyntax
 import SwiftSyntaxBuilder
 
 struct ExplicitInitRule: SwiftSyntaxCorrectableRule, ConfigurationProviderRule, OptInRule {
-    var configuration = SeverityConfiguration<Self>(.warning)
+    var configuration = ExplicitInitConfiguration()
 
     static let description = RuleDescription(
         identifier: "explicit_init",
@@ -170,28 +170,36 @@ struct ExplicitInitRule: SwiftSyntaxCorrectableRule, ConfigurationProviderRule,
     )
 
     func makeVisitor(file: SwiftLintFile) -> ViolationsSyntaxVisitor {
-        Visitor(viewMode: .sourceAccurate)
+        Visitor(viewMode: .sourceAccurate, includeBareInit: configuration.includeBareInit)
     }
 
     func makeRewriter(file: SwiftLintFile) -> ViolationsSyntaxRewriter? {
-        Rewriter(
-            locationConverter: file.locationConverter,
-            disabledRegions: disabledRegions(file: file)
-        )
+        Rewriter(locationConverter: file.locationConverter, disabledRegions: disabledRegions(file: file))
     }
 }
 
 private extension ExplicitInitRule {
     final class Visitor: ViolationsSyntaxVisitor {
+        private let includeBareInit: Bool
+
+        init(viewMode: SyntaxTreeViewMode, includeBareInit: Bool) {
+            self.includeBareInit = includeBareInit
+            super.init(viewMode: .sourceAccurate)
+        }
+
         override func visitPost(_ node: FunctionCallExprSyntax) {
-            guard
-                let calledExpression = node.calledExpression.as(MemberAccessExprSyntax.self),
-                let violationPosition = calledExpression.explicitInitPosition
-            else {
+            guard let calledExpression = node.calledExpression.as(MemberAccessExprSyntax.self) else {
                 return
             }
 
-            violations.append(violationPosition)
+            if let violationPosition = calledExpression.explicitInitPosition {
+                violations.append(violationPosition)
+            }
+
+            if includeBareInit, let violationPosition = calledExpression.bareInitPosition {
+                let reason = "Prefer named constructors over .init and type inference"
+                violations.append(ReasonedRuleViolation(position: violationPosition, reason: reason))
+            }
         }
     }
 
@@ -230,6 +238,14 @@ private extension MemberAccessExprSyntax {
             return nil
         }
     }
+
+    var bareInitPosition: AbsolutePosition? {
+        if base == nil, declName.baseName.text == "init" {
+            return period.positionAfterSkippingLeadingTrivia
+        } else {
+            return nil
+        }
+    }
 }
 
 private extension ExprSyntax {

Source/SwiftLintBuiltInRules/Rules/RuleConfigurations/ExplicitInitConfiguration.swift

@@ -0,0 +1,22 @@
+struct ExplicitInitConfiguration: SeverityBasedRuleConfiguration, Equatable {
+    typealias Parent = ExplicitInitRule
+
+    @ConfigurationElement(key: "severity")
+    private(set) var severityConfiguration = SeverityConfiguration<Parent>(.warning)
+    @ConfigurationElement(key: "include_bare_init")
+    private(set) var includeBareInit = false
+
+    mutating func apply(configuration: Any) throws {
+        guard let configuration = configuration as? [String: Any] else {
+            throw Issue.unknownConfiguration(ruleID: Parent.identifier)
+        }
+
+        if let severityString = configuration[$severityConfiguration] as? String {
+            try severityConfiguration.apply(configuration: severityString)
+        }
+
+        if let includeBareInit = configuration[$includeBareInit] as? Bool {
+            self.includeBareInit = includeBareInit
+        }
+    }
+}

Source/SwiftLintCore/Models/RuleConfigurationDescription.swift

@@ -501,7 +501,7 @@ public extension SeverityConfiguration {
         guard let option = description.options.onlyElement?.value, case .symbol = option else {
             queuedFatalError(
                 """
-                Severity configurations must have exaclty one option that is a violation severity.
+                Severity configurations must have exactly one option that is a violation severity.
                 """
             )
         }

Tests/SwiftLintFrameworkTests/ExplicitInitRuleTests.swift

@@ -0,0 +1,23 @@
+@testable import SwiftLintBuiltInRules
+
+class ExplicitInitRuleTests: SwiftLintTestCase {
+    func testIncludeBareInit() {
+        let nonTriggeringExamples = [
+            Example("let foo = Foo()"),
+            Example("let foo = init()")
+        ] + ExplicitInitRule.description.nonTriggeringExamples
+
+        let triggeringExamples = [
+            Example("let foo: Foo = ↓.init()"),
+            Example("let foo: [Foo] = [↓.init(), ↓.init()]"),
+            Example("foo(↓.init())")
+        ]
+
+        let description = ExplicitInitRule.description
+            .with(nonTriggeringExamples: nonTriggeringExamples)
+            .with(triggeringExamples: triggeringExamples)
+            .with(corrections: [:])
+
+        verifyRule(description, ruleConfiguration: ["include_bare_init": true])
+    }
+}