Add Equatable and Hashable property retention (#1126)

Co-authored-by: Ian Leitch <ian@leitch.io>

Author: horia-openai

CHANGELOG.md

@@ -6,6 +6,7 @@
 
 ##### Enhancements
 
+- Added the `--retain-equatable-properties` and `--retain-hashable-properties` options to retain all properties on `Equatable` and `Hashable` types.
 - Expose a stable `@periphery//bazel:generated` package group so Bazel projects can grant visibility to Periphery's generated scan target and use `--bazel-check-visibility` safely.
 - Added a `--bazel-query` option to override the default Bazel top-level target query.
 

README.md

@@ -31,6 +31,7 @@
     - [Unused Imports](#unused-imports)
     - [Objective-C](#objective-c)
     - [Codable](#codable)
+    - [Equatable and Hashable](#equatable-and-hashable)
     - [XCTestCase](#xctestcase)
     - [Interface Builder](#interface-builder)
     - [SPI (System Programming Interface)](#spi-system-programming-interface)
@@ -312,6 +313,10 @@ Swift synthesizes additional code for `Codable` types that is not visible to Per
 
 If `Codable` conformance is declared by a protocol in an external module not scanned by Periphery, you can instruct Periphery to identify the protocols as `Codable` with `--external-codable-protocols "ExternalProtocol"`.
 
+### Equatable and Hashable
+
+Swift synthesizes additional code for `Equatable` and `Hashable` types that is not visible to Periphery and can result in false positives for properties not directly referenced from non-synthesized code. If your project contains many such types, you can retain all properties on `Equatable` types with `--retain-equatable-properties`, or all properties on `Hashable` types with `--retain-hashable-properties`. The `Equatable` option also retains properties on `Hashable` types because `Hashable` refines `Equatable`.
+
 ### XCTestCase
 
 Any class that inherits `XCTestCase` is automatically retained along with its test methods. However, when a class inherits `XCTestCase` indirectly via another class, e.g., `UnitTestCase`, and that class resides in a target that isn't scanned by Periphery, you need to use the `--external-test-case-classes UnitTestCase` option to instruct Periphery to treat `UnitTestCase` as an `XCTestCase` subclass.

Sources/BUILD.bazel

@@ -68,6 +68,7 @@ swift_library(
         "SourceGraph/Mutators/DynamicMemberRetainer.swift",
         "SourceGraph/Mutators/EntryPointAttributeRetainer.swift",
         "SourceGraph/Mutators/EnumCaseReferenceBuilder.swift",
+        "SourceGraph/Mutators/EquatableHashablePropertyRetainer.swift",
         "SourceGraph/Mutators/ExtensionReferenceBuilder.swift",
         "SourceGraph/Mutators/ExternalOverrideRetainer.swift",
         "SourceGraph/Mutators/ExternalTypeProtocolConformanceReferenceRemover.swift",

Sources/Configuration/Configuration.swift

@@ -95,6 +95,12 @@ public final class Configuration {
     @Setting(key: "retain_encodable_properties", defaultValue: false)
     public var retainEncodableProperties: Bool
 
+    @Setting(key: "retain_equatable_properties", defaultValue: false)
+    public var retainEquatableProperties: Bool
+
+    @Setting(key: "retain_hashable_properties", defaultValue: false)
+    public var retainHashableProperties: Bool
+
     @Setting(key: "verbose", defaultValue: false)
     public var verbose: Bool
 
@@ -226,7 +232,8 @@ public final class Configuration {
         $externalEncodableProtocols, $externalCodableProtocols, $externalTestCaseClasses, $verbose, $quiet, $color,
         $disableUpdateCheck, $strict, $indexStorePath,
         $skipBuild, $skipSchemesValidation, $cleanBuild, $buildArguments, $xcodeListArguments, $relativeResults,
-        $jsonPackageManifestPath, $retainCodableProperties, $retainEncodableProperties, $baseline, $writeBaseline,
+        $jsonPackageManifestPath, $retainCodableProperties, $retainEncodableProperties, $retainEquatableProperties,
+        $retainHashableProperties, $baseline, $writeBaseline,
         $writeResults, $genericProjectConfig, $bazel, $bazelFilter, $bazelQuery, $bazelIndexStore, $bazelCheckVisibility,
     ]
 

Sources/Frontend/Commands/ScanCommand.swift

@@ -105,6 +105,12 @@ struct ScanCommand: ParsableCommand {
     @Flag(help: "Retain properties on Encodable types only")
     var retainEncodableProperties: Bool = defaultConfiguration.$retainEncodableProperties.defaultValue
 
+    @Flag(help: "Retain properties on Equatable types, including Hashable types")
+    var retainEquatableProperties: Bool = defaultConfiguration.$retainEquatableProperties.defaultValue
+
+    @Flag(help: "Retain properties on Hashable types")
+    var retainHashableProperties: Bool = defaultConfiguration.$retainHashableProperties.defaultValue
+
     @Flag(help: "Clean existing build artifacts before building")
     var cleanBuild: Bool = defaultConfiguration.$cleanBuild.defaultValue
 
@@ -217,6 +223,8 @@ struct ScanCommand: ParsableCommand {
         configuration.apply(\.$relativeResults, relativeResults)
         configuration.apply(\.$retainCodableProperties, retainCodableProperties)
         configuration.apply(\.$retainEncodableProperties, retainEncodableProperties)
+        configuration.apply(\.$retainEquatableProperties, retainEquatableProperties)
+        configuration.apply(\.$retainHashableProperties, retainHashableProperties)
         configuration.apply(\.$jsonPackageManifestPath, jsonPackageManifestPath)
         configuration.apply(\.$baseline, baseline)
         configuration.apply(\.$writeBaseline, writeBaseline)

Sources/SourceGraph/Mutators/EquatableHashablePropertyRetainer.swift

@@ -0,0 +1,37 @@
+import Configuration
+import Foundation
+import Shared
+
+final class EquatableHashablePropertyRetainer: SourceGraphMutator {
+    private let graph: SourceGraph
+    private let configuration: Configuration
+
+    required init(graph: SourceGraph, configuration: Configuration, swiftVersion _: SwiftVersion) {
+        self.graph = graph
+        self.configuration = configuration
+    }
+
+    func mutate() {
+        for decl in graph.declarations(ofKinds: Declaration.Kind.discreteConformableKinds) {
+            guard decl.kind != .class, shouldRetainProperties(of: decl) else { continue }
+
+            for decl in decl.declarations {
+                guard decl.kind == .varInstance else { continue }
+
+                graph.markRetained(decl)
+            }
+        }
+    }
+
+    private func shouldRetainProperties(of decl: Declaration) -> Bool {
+        if configuration.retainEquatableProperties, graph.isEquatable(decl) {
+            return true
+        }
+
+        if configuration.retainHashableProperties, graph.isHashable(decl) {
+            return true
+        }
+
+        return false
+    }
+}

Sources/SourceGraph/SourceGraph.swift

@@ -403,4 +403,18 @@ public final class SourceGraph {
             [.protocol, .typealias].contains($0.declarationKind) && encodableTypes.contains($0.name)
         }
     }
+
+    func isEquatable(_ decl: Declaration) -> Bool {
+        let equatableTypes = ["Equatable", "Hashable"]
+
+        return inheritedTypeReferences(of: decl).contains {
+            [.protocol, .typealias].contains($0.declarationKind) && equatableTypes.contains($0.name)
+        }
+    }
+
+    func isHashable(_ decl: Declaration) -> Bool {
+        inheritedTypeReferences(of: decl).contains {
+            [.protocol, .typealias].contains($0.declarationKind) && $0.name == "Hashable"
+        }
+    }
 }

Sources/SourceGraph/SourceGraphMutatorRunner.swift

@@ -44,6 +44,7 @@ public final class SourceGraphMutatorRunner {
         PropertyWrapperRetainer.self,
         ResultBuilderRetainer.self,
         CodablePropertyRetainer.self,
+        EquatableHashablePropertyRetainer.self,
         ExternalOverrideRetainer.self,
 
         AncestralReferenceEliminator.self,

Tests/Fixtures/Sources/RetentionFixtures/testRetainsEquatableProperties.swift

@@ -0,0 +1,29 @@
+import Foundation
+
+public struct FixtureStruct222: Equatable {
+    let unused: Int
+
+    init(unused: Int) {
+        self.unused = unused
+    }
+}
+
+public struct FixtureStruct223: Hashable {
+    let unused: Int
+
+    init(unused: Int) {
+        self.unused = unused
+    }
+}
+
+public final class FixtureClass222: Equatable {
+    let unused: Int
+
+    init(unused: Int) {
+        self.unused = unused
+    }
+
+    public static func == (lhs: FixtureClass222, rhs: FixtureClass222) -> Bool {
+        true
+    }
+}

Tests/Fixtures/Sources/RetentionFixtures/testRetainsHashableProperties.swift

@@ -0,0 +1,9 @@
+import Foundation
+
+public struct FixtureStruct224: Hashable {
+    let unused: Int
+
+    init(unused: Int) {
+        self.unused = unused
+    }
+}