Add option to disable redundant_discardable_let in SwiftUI view bod…

…ies (#5929)

CHANGELOG.md

@@ -43,6 +43,10 @@
   [dk-talks](https://github.com/dk-talks)
   [SimplyDanny](https://github.com/SimplyDanny)
 
+* Add option to disable `redundant_discardable_let` rule in SwiftUI view bodies.  
+  [SimplyDanny](https://github.com/SimplyDanny)
+  [#3855](https://github.com/realm/SwiftLint/issues/3855)
+
 * Add new `redundant_sendable` rule that triggers on `Sendable` conformances of
   types that are implicitly already `Sendable` due to being actor-isolated. It
   is enabled by default.  

Source/SwiftLintBuiltInRules/Rules/RuleConfigurations/RedundantDiscardableLetConfiguration.swift

@@ -0,0 +1,11 @@
+import SwiftLintCore
+
+@AutoConfigParser
+struct RedundantDiscardableLetConfiguration: SeverityBasedRuleConfiguration {
+    typealias Parent = RedundantDiscardableLetRule
+
+    @ConfigurationElement(key: "severity")
+    private(set) var severityConfiguration = SeverityConfiguration<Parent>(.warning)
+    @ConfigurationElement(key: "ignore_swiftui_view_bodies")
+    private(set) var ignoreSwiftUIViewBodies = false
+}

Source/SwiftLintBuiltInRules/Rules/Style/RedundantDiscardableLetRule.swift

@@ -1,8 +1,8 @@
 import SwiftSyntax
 
-@SwiftSyntaxRule(explicitRewriter: true)
+@SwiftSyntaxRule(correctable: true)
 struct RedundantDiscardableLetRule: Rule {
-    var configuration = SeverityConfiguration<Self>(.warning)
+    var configuration = RedundantDiscardableLetConfiguration()
 
     static let description = RuleDescription(
         identifier: "redundant_discardable_let",
@@ -16,10 +16,22 @@ struct RedundantDiscardableLetRule: Rule {
             Example("let _: ExplicitType = foo()"),
             Example("while let _ = SplashStyle(rawValue: maxValue) { maxValue += 1 }"),
             Example("async let _ = await foo()"),
+            Example("""
+                var body: some View {
+                    let _ = foo()
+                    return Text("Hello, World!")
+                }
+                """, configuration: ["ignore_swiftui_view_bodies": true]),
         ],
         triggeringExamples: [
             Example("↓let _ = foo()"),
             Example("if _ = foo() { ↓let _ = bar() }"),
+            Example("""
+                var body: some View {
+                    ↓let _ = foo()
+                    Text("Hello, World!")
+                }
+                """),
         ],
         corrections: [
             Example("↓let _ = foo()"): Example("_ = foo()"),
@@ -29,35 +41,63 @@ struct RedundantDiscardableLetRule: Rule {
 }
 
 private extension RedundantDiscardableLetRule {
+    private enum CodeBlockKind {
+        case normal
+        case view
+    }
+
     final class Visitor: ViolationsSyntaxVisitor<ConfigurationType> {
-        override func visitPost(_ node: VariableDeclSyntax) {
-            if node.hasRedundantDiscardableLetViolation {
-                violations.append(node.positionAfterSkippingLeadingTrivia)
-            }
+        private var codeBlockScopes = Stack<CodeBlockKind>()
+
+        override func visit(_ node: AccessorBlockSyntax) -> SyntaxVisitorContinueKind {
+            codeBlockScopes.push(node.isViewBody ? .view : .normal)
+            return .visitChildren
         }
-    }
 
-    final class Rewriter: ViolationsSyntaxRewriter<ConfigurationType> {
-        override func visit(_ node: VariableDeclSyntax) -> DeclSyntax {
-            guard node.hasRedundantDiscardableLetViolation else {
-                return super.visit(node)
-            }
+        override func visitPost(_: AccessorBlockSyntax) {
+            codeBlockScopes.pop()
+        }
 
-            correctionPositions.append(node.positionAfterSkippingLeadingTrivia)
-            let newNode = node
-                .with(\.bindingSpecifier, .keyword(.let, presence: .missing))
-                .with(\.bindings, node.bindings.with(\.leadingTrivia, node.bindingSpecifier.leadingTrivia))
-            return super.visit(newNode)
+        override func visit(_: CodeBlockSyntax) -> SyntaxVisitorContinueKind {
+            codeBlockScopes.push(.normal)
+            return .visitChildren
+        }
+
+        override func visitPost(_: CodeBlockSyntax) {
+            codeBlockScopes.pop()
+        }
+
+        override func visitPost(_ node: VariableDeclSyntax) {
+            if codeBlockScopes.peek() != .view || !configuration.ignoreSwiftUIViewBodies,
+               node.bindingSpecifier.tokenKind == .keyword(.let),
+               let binding = node.bindings.onlyElement,
+               binding.pattern.is(WildcardPatternSyntax.self),
+               binding.typeAnnotation == nil,
+               !node.modifiers.contains(where: { $0.name.text == "async" }) {
+                violations.append(
+                    ReasonedRuleViolation(
+                        position: node.bindingSpecifier.positionAfterSkippingLeadingTrivia,
+                        correction: .init(
+                            start: node.bindingSpecifier.positionAfterSkippingLeadingTrivia,
+                            end: binding.pattern.positionAfterSkippingLeadingTrivia,
+                            replacement: ""
+                        )
+                    )
+                )
+            }
         }
     }
 }
 
-private extension VariableDeclSyntax {
-    var hasRedundantDiscardableLetViolation: Bool {
-           bindingSpecifier.tokenKind == .keyword(.let)
-        && bindings.count == 1
-        && bindings.first!.pattern.is(WildcardPatternSyntax.self)
-        && bindings.first!.typeAnnotation == nil
-        && modifiers.contains(where: { $0.name.text == "async" }) != true
+private extension AccessorBlockSyntax {
+    var isViewBody: Bool {
+        if let binding = parent?.as(PatternBindingSyntax.self),
+           binding.pattern.as(IdentifierPatternSyntax.self)?.identifier.text == "body",
+           let type = binding.typeAnnotation?.type.as(SomeOrAnyTypeSyntax.self) {
+            return type.someOrAnySpecifier.text == "some"
+                && type.constraint.as(IdentifierTypeSyntax.self)?.name.text == "View"
+                && binding.parent?.parent?.is(VariableDeclSyntax.self) == true
+        }
+        return false
     }
 }

Tests/IntegrationTests/default_rule_configurations.yml

@@ -795,6 +795,7 @@ reduce_into:
     opt-in: true
 redundant_discardable_let:
   severity: warning
+  ignore_swiftui_view_bodies: false
   meta:
     opt-in: false
 redundant_nil_coalescing: