Don't retain SwiftUI previews by default. Closes #524

CHANGELOG.md

@@ -6,7 +6,7 @@
 
 ##### Enhancements
 
-- None.
+- SwiftUI previews (`PreviewProvider`) are no longer retained by default. Retain them with `--retain-swift-ui-previews`.
 
 ##### Bug Fixes
 

Sources/Frontend/Commands/ScanCommand.swift

@@ -75,6 +75,9 @@ struct ScanCommand: FrontendCommand {
     @Flag(help: "Retain unused protocol function parameters, even if the parameter is unused in all conforming functions")
     var retainUnusedProtocolFuncParams: Bool = defaultConfiguration.$retainUnusedProtocolFuncParams.defaultValue
 
+    @Flag(help: "Retain SwiftUI previews")
+    var retainSwiftUIPreviews: Bool = defaultConfiguration.$retainSwiftUIPreviews.defaultValue
+
     @Flag(help: "Clean existing build artifacts before building")
     var cleanBuild: Bool = defaultConfiguration.$cleanBuild.defaultValue
 
@@ -119,6 +122,7 @@ struct ScanCommand: FrontendCommand {
         configuration.apply(\.$retainObjcAccessible, retainObjcAccessible)
         configuration.apply(\.$retainObjcAnnotated, retainObjcAnnotated)
         configuration.apply(\.$retainUnusedProtocolFuncParams, retainUnusedProtocolFuncParams)
+        configuration.apply(\.$retainSwiftUIPreviews, retainSwiftUIPreviews)
         configuration.apply(\.$disableRedundantPublicAnalysis, disableRedundantPublicAnalysis)
         configuration.apply(\.$externalEncodableProtocols, externalEncodableProtocols)
         configuration.apply(\.$externalTestCaseClasses, externalTestCaseClasses)

Sources/PeripheryKit/SourceGraph/Mutators/SwiftUIRetainer.swift

@@ -3,11 +3,13 @@ import Shared
 
 final class SwiftUIRetainer: SourceGraphMutator {
     private let graph: SourceGraph
-    private static let specialProtocolNames = ["PreviewProvider", "LibraryContentProvider"]
+    private let configuration: Configuration
+    private static let specialProtocolNames = ["LibraryContentProvider"]
     private static let applicationDelegateAdaptorStructNames = ["UIApplicationDelegateAdaptor", "NSApplicationDelegateAdaptor"]
 
     required init(graph: SourceGraph, configuration: Configuration) {
         self.graph = graph
+        self.configuration = configuration
     }
 
     func mutate() {
@@ -18,12 +20,18 @@ final class SwiftUIRetainer: SourceGraphMutator {
     // MARK: - Private
 
     private func retainSpecialProtocolConformances() {
+        var names = Self.specialProtocolNames
+
+        if configuration.retainSwiftUIPreviews {
+            names.append("PreviewProvider")
+        }
+
         graph
             .declarations(ofKinds: [.class, .struct, .enum])
             .lazy
             .filter {
                 $0.related.contains {
-                    self.graph.isExternal($0) && $0.kind == .protocol && Self.specialProtocolNames.contains($0.name ?? "")
+                    self.graph.isExternal($0) && $0.kind == .protocol && names.contains($0.name ?? "")
                 }
             }
             .forEach { graph.markRetained($0) }

Sources/Shared/Configuration.swift

@@ -65,6 +65,9 @@ public final class Configuration {
     @Setting(key: "retain_unused_protocol_func_params", defaultValue: false)
     public var retainUnusedProtocolFuncParams: Bool
 
+    @Setting(key: "retain_swift_ui_previews", defaultValue: false)
+    public var retainSwiftUIPreviews: Bool
+
     @Setting(key: "disable_redundant_public_analysis", defaultValue: false)
     public var disableRedundantPublicAnalysis: Bool
 
@@ -166,6 +169,10 @@ public final class Configuration {
             config[$retainUnusedProtocolFuncParams.key] = retainUnusedProtocolFuncParams
         }
 
+        if $retainSwiftUIPreviews.hasNonDefaultValue {
+            config[$retainSwiftUIPreviews.key] = retainSwiftUIPreviews
+        }
+
         if $disableRedundantPublicAnalysis.hasNonDefaultValue {
             config[$disableRedundantPublicAnalysis.key] = disableRedundantPublicAnalysis
         }
@@ -252,6 +259,8 @@ public final class Configuration {
                 $retainObjcAnnotated.assign(value)
             case $retainUnusedProtocolFuncParams.key:
                 $retainUnusedProtocolFuncParams.assign(value)
+            case $retainSwiftUIPreviews.key:
+                $retainSwiftUIPreviews.assign(value)
             case $disableRedundantPublicAnalysis.key:
                 $disableRedundantPublicAnalysis.assign(value)
             case $verbose.key:
@@ -292,6 +301,7 @@ public final class Configuration {
         $retainObjcAccessible.reset()
         $retainObjcAnnotated.reset()
         $retainUnusedProtocolFuncParams.reset()
+        $retainSwiftUIPreviews.reset()
         $disableRedundantPublicAnalysis.reset()
         $externalEncodableProtocols.reset()
         $externalTestCaseClasses.reset()

Tests/XcodeTests/SwiftUIProjectTest.swift

@@ -20,8 +20,8 @@ class SwiftUIProjectTest: SourceGraphTestCase {
         assertReferenced(.struct("SwiftUIProjectApp"))
     }
 
-    func testRetainsPreviewProvider() {
-        assertReferenced(.struct("ContentView_Previews"))
+    func testDoesNotRetainPreviewProvider() {
+        assertNotReferenced(.struct("ContentView_Previews"))
     }
 
     func testRetainsLibraryContentProvider() {