Add prefer_asset_symbols rule (#6261)

Co-authored-by: Danny Mösch <[email protected]>

Author: danglingP0inter

CHANGELOG.md

@@ -39,6 +39,13 @@
   * `sorted_imports`
   <!-- Keep empty line to have the contributors on a separate line. -->
   [SimplyDanny](https://github.com/SimplyDanny)
+  
+* Add new `prefer_asset_symbols` rule that suggests using asset symbols over
+  string-based image initialization to avoid typos and enable compile-time
+  checking. This rule detects `UIImage(named:)` and `SwiftUI.Image(_:)` calls
+  with string literals and suggests using asset symbols instead.  
+  [danglingP0inter](https://github.com/danglingP0inter)
+  [#5939](https://github.com/realm/SwiftLint/issues/5939)
 
 ### Bug Fixes
 

Source/SwiftLintBuiltInRules/Models/BuiltInRules.swift

@@ -149,6 +149,7 @@ public let builtInRules: [any Rule.Type] = [
     OverrideInExtensionRule.self,
     PatternMatchingKeywordsRule.self,
     PeriodSpacingRule.self,
+    PreferAssetSymbolsRule.self,
     PreferConditionListRule.self,
     PreferKeyPathRule.self,
     PreferNimbleRule.self,

Source/SwiftLintBuiltInRules/Rules/Idiomatic/PreferAssetSymbolsRule.swift

@@ -0,0 +1,101 @@
+import SwiftLintCore
+import SwiftSyntax
+
+@SwiftSyntaxRule(optIn: true)
+struct PreferAssetSymbolsRule: Rule {
+    var configuration = SeverityConfiguration<Self>(.warning)
+
+    static let description = RuleDescription(
+        identifier: "prefer_asset_symbols",
+        name: "Prefer Asset Symbols",
+        description: "Prefer using asset symbols over string-based image initialization",
+        rationale: """
+            `UIKit.UIImage(named:)` and `SwiftUI.Image(_:)` bear the risk of bugs due to typos in their string \
+            arguments. Since Xcode 15, Xcode generates codes for images in the Asset Catalog. Usage of these codes \
+            and system icons from SF Symbols avoid typos and allow for compile-time checking.
+            """,
+        kind: .idiomatic,
+        minSwiftVersion: .fiveDotNine,
+        nonTriggeringExamples: [
+            // UIKit - using asset symbols
+            Example("UIImage(resource: .someImage)"),
+            Example("UIImage(systemName: \"trash\")"),
+            // SwiftUI - using asset symbols  
+            Example("Image(.someImage)"),
+            Example("Image(systemName: \"trash\")"),
+            // Dynamic strings (variables or interpolated)
+            Example("UIImage(named: imageName)"),
+            Example("UIImage(named: \"image_\\(suffix)\")"),
+            Example("Image(imageName)"),
+            Example("Image(\"image_\\(suffix)\")"),
+        ],
+        triggeringExamples: [
+            // UIKit examples
+            Example("↓UIImage(named: \"some_image\")"),
+            Example("↓UIImage(named: \"some image\")"),
+            Example("↓UIImage.init(named: \"someImage\")"),
+            // UIKit with bundle parameters
+            Example("↓UIImage(named: \"someImage\", in: Bundle.main, compatibleWith: nil)"),
+            Example("↓UIImage(named: \"someImage\", in: .main)"),
+            // SwiftUI examples  
+            Example("↓Image(\"some_image\")"),
+            Example("↓Image(\"some image\")"),
+            Example("↓Image.init(\"someImage\")"),
+            // SwiftUI with bundle parameters
+            Example("↓Image(\"someImage\", bundle: Bundle.main)"),
+            Example("↓Image(\"someImage\", bundle: .main)"),
+        ]
+    )
+}
+
+private extension PreferAssetSymbolsRule {
+    final class Visitor: ViolationsSyntaxVisitor<ConfigurationType> {
+        override func visitPost(_ node: FunctionCallExprSyntax) {
+            // Check for UIImage(named:) or SwiftUI Image(_:) calls
+            if isImageInit(node: node, className: "UIImage", argumentLabel: "named") ||
+               isImageInit(node: node, className: "Image", argumentLabel: nil) {
+                violations.append(node.positionAfterSkippingLeadingTrivia)
+            }
+        }
+
+        private func isImageInit(node: FunctionCallExprSyntax, className: String, argumentLabel: String?) -> Bool {
+            // Check if this is the specified class or class.init call using syntax tree matching
+            guard isImageCall(node.calledExpression, className: className) else {
+                return false
+            }
+
+            // Check if the first argument has the expected label and is a string literal
+            guard let firstArgument = node.arguments.first,
+                  firstArgument.label?.text == argumentLabel,
+                  let stringLiteral = firstArgument.expression.as(StringLiteralExprSyntax.self),
+                  stringLiteral.isConstantString else {
+                return false
+            }
+
+            return true
+        }
+
+        private func isImageCall(_ expression: ExprSyntax, className: String) -> Bool {
+            // Match ClassName directly
+            if let identifierExpr = expression.as(DeclReferenceExprSyntax.self) {
+                return identifierExpr.baseName.text == className
+            }
+
+            // Match ClassName.init
+            if let memberAccessExpr = expression.as(MemberAccessExprSyntax.self),
+               let baseExpr = memberAccessExpr.base?.as(DeclReferenceExprSyntax.self),
+               baseExpr.baseName.text == className,
+               memberAccessExpr.declName.baseName.text == "init" {
+                return true
+            }
+
+            return false
+        }
+    }
+}
+
+private extension StringLiteralExprSyntax {
+    var isConstantString: Bool {
+        segments.allSatisfy { $0.is(StringSegmentSyntax.self) }
+    }
+}

Tests/GeneratedTests/GeneratedTests_06.swift

@@ -139,20 +139,20 @@ final class PeriodSpacingRuleGeneratedTests: SwiftLintTestCase {
     }
 }
 
-final class PreferConditionListRuleGeneratedTests: SwiftLintTestCase {
+final class PreferAssetSymbolsRuleGeneratedTests: SwiftLintTestCase {
     func testWithDefaultConfiguration() {
-        verifyRule(PreferConditionListRule.description)
+        verifyRule(PreferAssetSymbolsRule.description)
     }
 }
 
-final class PreferKeyPathRuleGeneratedTests: SwiftLintTestCase {
+final class PreferConditionListRuleGeneratedTests: SwiftLintTestCase {
     func testWithDefaultConfiguration() {
-        verifyRule(PreferKeyPathRule.description)
+        verifyRule(PreferConditionListRule.description)
     }
 }
 
-final class PreferNimbleRuleGeneratedTests: SwiftLintTestCase {
+final class PreferKeyPathRuleGeneratedTests: SwiftLintTestCase {
     func testWithDefaultConfiguration() {
-        verifyRule(PreferNimbleRule.description)
+        verifyRule(PreferKeyPathRule.description)
     }
 }

Tests/GeneratedTests/GeneratedTests_07.swift

@@ -7,6 +7,12 @@
 @testable import SwiftLintCore
 import TestHelpers
 
+final class PreferNimbleRuleGeneratedTests: SwiftLintTestCase {
+    func testWithDefaultConfiguration() {
+        verifyRule(PreferNimbleRule.description)
+    }
+}
+
 final class PreferSelfInStaticReferencesRuleGeneratedTests: SwiftLintTestCase {
     func testWithDefaultConfiguration() {
         verifyRule(PreferSelfInStaticReferencesRule.description)
@@ -150,9 +156,3 @@ final class RedundantSelfInClosureRuleGeneratedTests: SwiftLintTestCase {
         verifyRule(RedundantSelfInClosureRule.description)
     }
 }
-
-final class RedundantSendableRuleGeneratedTests: SwiftLintTestCase {
-    func testWithDefaultConfiguration() {
-        verifyRule(RedundantSendableRule.description)
-    }
-}

Tests/GeneratedTests/GeneratedTests_08.swift

@@ -7,6 +7,12 @@
 @testable import SwiftLintCore
 import TestHelpers
 
+final class RedundantSendableRuleGeneratedTests: SwiftLintTestCase {
+    func testWithDefaultConfiguration() {
+        verifyRule(RedundantSendableRule.description)
+    }
+}
+
 final class RedundantSetAccessControlRuleGeneratedTests: SwiftLintTestCase {
     func testWithDefaultConfiguration() {
         verifyRule(RedundantSetAccessControlRule.description)
@@ -150,9 +156,3 @@ final class SwitchCaseAlignmentRuleGeneratedTests: SwiftLintTestCase {
         verifyRule(SwitchCaseAlignmentRule.description)
     }
 }
-
-final class SwitchCaseOnNewlineRuleGeneratedTests: SwiftLintTestCase {
-    func testWithDefaultConfiguration() {
-        verifyRule(SwitchCaseOnNewlineRule.description)
-    }
-}

Tests/GeneratedTests/GeneratedTests_09.swift

@@ -7,6 +7,12 @@
 @testable import SwiftLintCore
 import TestHelpers
 
+final class SwitchCaseOnNewlineRuleGeneratedTests: SwiftLintTestCase {
+    func testWithDefaultConfiguration() {
+        verifyRule(SwitchCaseOnNewlineRule.description)
+    }
+}
+
 final class SyntacticSugarRuleGeneratedTests: SwiftLintTestCase {
     func testWithDefaultConfiguration() {
         verifyRule(SyntacticSugarRule.description)
@@ -150,9 +156,3 @@ final class UnusedControlFlowLabelRuleGeneratedTests: SwiftLintTestCase {
         verifyRule(UnusedControlFlowLabelRule.description)
     }
 }
-
-final class UnusedDeclarationRuleGeneratedTests: SwiftLintTestCase {
-    func testWithDefaultConfiguration() {
-        verifyRule(UnusedDeclarationRule.description)
-    }
-}

Tests/GeneratedTests/GeneratedTests_10.swift

@@ -7,6 +7,12 @@
 @testable import SwiftLintCore
 import TestHelpers
 
+final class UnusedDeclarationRuleGeneratedTests: SwiftLintTestCase {
+    func testWithDefaultConfiguration() {
+        verifyRule(UnusedDeclarationRule.description)
+    }
+}
+
 final class UnusedEnumeratedRuleGeneratedTests: SwiftLintTestCase {
     func testWithDefaultConfiguration() {
         verifyRule(UnusedEnumeratedRule.description)

Tests/IntegrationTests/default_rule_configurations.yml

@@ -857,6 +857,11 @@ period_spacing:
   meta:
     opt-in: true
     correctable: true
+prefer_asset_symbols:
+  severity: warning
+  meta:
+    opt-in: true
+    correctable: false
 prefer_condition_list:
   severity: warning
   meta: