Respect ignore_swiftui_view_bodies option in view builders and preview macros/providers (#6075)

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

Author: kaseken

CHANGELOG.md

@@ -33,6 +33,12 @@
   [JP Simard](https://github.com/jpsim)
   [Matt Pennig](https://github.com/pennig)
 
+* Fix false positives of `redundant_discardable_let` rule in `@ViewBuilder` functions,
+  `#Preview` macro bodies and preview providers when `ignore_swiftui_view_bodies` is
+  enabled.  
+  [kaseken](https://github.com/kaseken)
+  [#6063](https://github.com/realm/SwiftLint/issues/6063)
+
 ### Bug Fixes
 
 * Improved error reporting when SwiftLint exits, because of an invalid configuration file

Source/SwiftLintBuiltInRules/Rules/Style/RedundantDiscardableLetRule.swift

@@ -22,6 +22,25 @@ struct RedundantDiscardableLetRule: Rule {
                     return Text("Hello, World!")
                 }
                 """, configuration: ["ignore_swiftui_view_bodies": true]),
+            Example("""
+                @ViewBuilder
+                func bar() -> some View {
+                    let _ = foo()
+                    Text("Hello, World!")
+                }
+                """, configuration: ["ignore_swiftui_view_bodies": true]),
+            Example("""
+                #Preview {
+                    let _ = foo()
+                    Text("Hello, World!")
+                }
+                """, configuration: ["ignore_swiftui_view_bodies": true]),
+            Example("""
+                static var previews: some View {
+                    let _ = foo()
+                    Text("Hello, World!")
+                }
+                """, configuration: ["ignore_swiftui_view_bodies": true]),
         ],
         triggeringExamples: [
             Example("↓let _ = foo()"),
@@ -32,10 +51,74 @@ struct RedundantDiscardableLetRule: Rule {
                     Text("Hello, World!")
                 }
                 """),
+            Example("""
+                @ViewBuilder
+                func bar() -> some View {
+                    ↓let _ = foo()
+                    return Text("Hello, World!")
+                }
+                """),
+            Example("""
+                #Preview {
+                    ↓let _ = foo()
+                    return Text("Hello, World!")
+                }
+                """),
+            Example("""
+                static var previews: some View {
+                    ↓let _ = foo()
+                    Text("Hello, World!")
+                }
+                """),
+            Example("""
+                var notBody: some View {
+                    ↓let _ = foo()
+                    Text("Hello, World!")
+                }
+                """, configuration: ["ignore_swiftui_view_bodies": true], excludeFromDocumentation: true),
+            Example("""
+                var body: some NotView {
+                    ↓let _ = foo()
+                    Text("Hello, World!")
+                }
+                """, configuration: ["ignore_swiftui_view_bodies": true], excludeFromDocumentation: true),
         ],
         corrections: [
             Example("↓let _ = foo()"): Example("_ = foo()"),
             Example("if _ = foo() { ↓let _ = bar() }"): Example("if _ = foo() { _ = bar() }"),
+            Example("""
+                var body: some View {
+                    ↓let _ = foo()
+                    Text("Hello, World!")
+                }
+                """): Example("""
+                    var body: some View {
+                        _ = foo()
+                        Text("Hello, World!")
+                    }
+                    """),
+            Example("""
+                #Preview {
+                    ↓let _ = foo()
+                    return Text("Hello, World!")
+                }
+                """): Example("""
+                    #Preview {
+                        _ = foo()
+                        return Text("Hello, World!")
+                    }
+                    """),
+            Example("""
+                var body: some View {
+                    let _ = foo()
+                    return Text("Hello, World!")
+                }
+                """, configuration: ["ignore_swiftui_view_bodies": true]): Example("""
+                    var body: some View {
+                        let _ = foo()
+                        return Text("Hello, World!")
+                    }
+                    """),
         ]
     )
 }
@@ -50,23 +133,32 @@ private extension RedundantDiscardableLetRule {
         private var codeBlockScopes = Stack<CodeBlockKind>()
 
         override func visit(_ node: AccessorBlockSyntax) -> SyntaxVisitorContinueKind {
-            codeBlockScopes.push(node.isViewBody ? .view : .normal)
+            codeBlockScopes.push(node.isViewBody || node.isPreviewProviderBody ? .view : .normal)
             return .visitChildren
         }
 
         override func visitPost(_: AccessorBlockSyntax) {
             codeBlockScopes.pop()
         }
 
-        override func visit(_: CodeBlockSyntax) -> SyntaxVisitorContinueKind {
-            codeBlockScopes.push(.normal)
+        override func visit(_ node: CodeBlockSyntax) -> SyntaxVisitorContinueKind {
+            codeBlockScopes.push(node.isViewBuilderFunctionBody ? .view : .normal)
             return .visitChildren
         }
 
         override func visitPost(_: CodeBlockSyntax) {
             codeBlockScopes.pop()
         }
 
+        override func visit(_ node: ClosureExprSyntax) -> SyntaxVisitorContinueKind {
+            codeBlockScopes.push(node.isPreviewMacroBody ? .view : .normal)
+            return .visitChildren
+        }
+
+        override func visitPost(_: ClosureExprSyntax) {
+            codeBlockScopes.pop()
+        }
+
         override func visitPost(_ node: VariableDeclSyntax) {
             if codeBlockScopes.peek() != .view || !configuration.ignoreSwiftUIViewBodies,
                node.bindingSpecifier.tokenKind == .keyword(.let),
@@ -94,10 +186,45 @@ private extension AccessorBlockSyntax {
         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 type.isView && binding.parent?.parent?.is(VariableDeclSyntax.self) == true
         }
         return false
     }
+
+    var isPreviewProviderBody: Bool {
+        guard let binding = parent?.as(PatternBindingSyntax.self),
+              binding.pattern.as(IdentifierPatternSyntax.self)?.identifier.text == "previews",
+              let bindingList = binding.parent?.as(PatternBindingListSyntax.self),
+              let variableDecl = bindingList.parent?.as(VariableDeclSyntax.self),
+              variableDecl.modifiers.contains(keyword: .static),
+              variableDecl.bindingSpecifier.tokenKind == .keyword(.var),
+              let type = binding.typeAnnotation?.type.as(SomeOrAnyTypeSyntax.self) else {
+            return false
+        }
+
+        return type.isView
+    }
+}
+
+private extension CodeBlockSyntax {
+    var isViewBuilderFunctionBody: Bool {
+        guard let functionDecl = parent?.as(FunctionDeclSyntax.self),
+              functionDecl.attributes.contains(attributeNamed: "ViewBuilder") else {
+            return false
+        }
+        return functionDecl.signature.returnClause?.type.as(SomeOrAnyTypeSyntax.self)?.isView ?? false
+    }
+}
+
+private extension ClosureExprSyntax {
+    var isPreviewMacroBody: Bool {
+        parent?.as(MacroExpansionExprSyntax.self)?.macroName.text == "Preview"
+    }
+}
+
+private extension SomeOrAnyTypeSyntax {
+    var isView: Bool {
+        someOrAnySpecifier.text == "some" &&
+            constraint.as(IdentifierTypeSyntax.self)?.name.text == "View"
+    }
 }