From 2020e54057f2afb674126cc6a837f6002db8c5e1 Mon Sep 17 00:00:00 2001
From: Martin Redington <mildm8nnered@gmail.com>
Date: Sat, 21 Sep 2024 12:17:57 +0100
Subject: [PATCH] Dont trigger for non-optional type casting, or for optional
 types

---
 CHANGELOG.md                                  |  5 +++++
 .../Idiomatic/PreferTypeCheckingRule.swift    | 21 ++++++++++++-------
 2 files changed, 19 insertions(+), 7 deletions(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 7257d37b63..3596e31d18 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -28,6 +28,11 @@
   [chipp](https://github.com/chipp)
   [#5791](https://github.com/realm/SwiftLint/issues/5791)
 
+* The `prefer_type_checking` rule will no longer trigger for non-optional
+  type casting (`as`), or for comparisons to optional types.  
+  [Martin Redington](https://github.com/mildm8nnered)
+  [#5802](https://github.com/realm/SwiftLint/issues/5802)
+
 ## 0.57.0: Squeaky Clean Cycle
 
 #### Breaking
diff --git a/Source/SwiftLintBuiltInRules/Rules/Idiomatic/PreferTypeCheckingRule.swift b/Source/SwiftLintBuiltInRules/Rules/Idiomatic/PreferTypeCheckingRule.swift
index c0ae6731d7..49bd78af04 100644
--- a/Source/SwiftLintBuiltInRules/Rules/Idiomatic/PreferTypeCheckingRule.swift
+++ b/Source/SwiftLintBuiltInRules/Rules/Idiomatic/PreferTypeCheckingRule.swift
@@ -24,6 +24,8 @@ struct PreferTypeCheckingRule: Rule {
                 foo.run()
             }
             """),
+            Example("bar as Foo? != nil"),
+            Example("bar as? Foo? != nil"),
         ],
         triggeringExamples: [
             Example("bar ↓as? Foo != nil"),
@@ -53,7 +55,7 @@ struct PreferTypeCheckingRule: Rule {
 private extension PreferTypeCheckingRule {
     final class Visitor: ViolationsSyntaxVisitor<ConfigurationType> {
         override func visitPost(_ node: InfixOperatorExprSyntax) {
-            if node.typeChecksWithAsCasting, let asExpr = node.leftOperand.as(AsExprSyntax.self) {
+            if let asExpr = node.asExprWithOptionalTypeChecking {
                 violations.append(asExpr.asKeyword.positionAfterSkippingLeadingTrivia)
             }
         }
@@ -61,8 +63,7 @@ private extension PreferTypeCheckingRule {
 
     final class Rewriter: ViolationsSyntaxRewriter<ConfigurationType> {
         override func visit(_ node: InfixOperatorExprSyntax) -> ExprSyntax {
-            guard node.typeChecksWithAsCasting,
-                  let asExpr = node.leftOperand.as(AsExprSyntax.self) else {
+            guard let asExpr = node.asExprWithOptionalTypeChecking else {
                 return super.visit(node)
             }
 
@@ -79,9 +80,15 @@ private extension PreferTypeCheckingRule {
 }
 
 private extension InfixOperatorExprSyntax {
-    var typeChecksWithAsCasting: Bool {
-        self.leftOperand.is(AsExprSyntax.self)
-        && self.operator.as(BinaryOperatorExprSyntax.self)?.operator.tokenKind == .binaryOperator("!=")
-        && self.rightOperand.is(NilLiteralExprSyntax.self)
+    var asExprWithOptionalTypeChecking: AsExprSyntax? {
+        if let asExpr = leftOperand.as(AsExprSyntax.self),
+           asExpr.questionOrExclamationMark?.tokenKind == .postfixQuestionMark,
+           asExpr.type.is(OptionalTypeSyntax.self) == false,
+           self.operator.as(BinaryOperatorExprSyntax.self)?.operator.tokenKind == .binaryOperator("!="),
+           rightOperand.is(NilLiteralExprSyntax.self) {
+            asExpr
+        } else {
+            nil
+        }
     }
 }