Add experimental unused import analysis.

.periphery.linux.yml

@@ -6,3 +6,4 @@ targets:
 - PeripheryTests
 - SPMTests
 - AccessibilityTests
+enable_unused_import_analysis: true

.periphery.yml

@@ -8,3 +8,4 @@ targets:
 - XcodeTests
 - SPMTests
 - AccessibilityTests
+enable_unused_import_analysis: true

CHANGELOG.md

@@ -6,7 +6,7 @@
 
 ##### Enhancements
 
-- None.
+- Add experimental unused import analysis.
 
 ##### Bug Fixes
 

Sources/Frontend/Commands/ScanCommand.swift

@@ -54,6 +54,9 @@ struct ScanCommand: FrontendCommand {
     @Flag(help: "Disable identification of redundant public accessibility")
     var disableRedundantPublicAnalysis: Bool = defaultConfiguration.$disableRedundantPublicAnalysis.defaultValue
 
+    @Flag(help: "Enable identification of unused imports (experimental)")
+    var enableUnusedImportAnalysis: Bool = defaultConfiguration.$enableUnusedImportsAnalysis.defaultValue
+
     @Flag(help: "Retain properties that are assigned, but never used")
     var retainAssignOnlyProperties: Bool = defaultConfiguration.$retainAssignOnlyProperties.defaultValue
 
@@ -127,6 +130,7 @@ struct ScanCommand: FrontendCommand {
         configuration.apply(\.$retainUnusedProtocolFuncParams, retainUnusedProtocolFuncParams)
         configuration.apply(\.$retainSwiftUIPreviews, retainSwiftUIPreviews)
         configuration.apply(\.$disableRedundantPublicAnalysis, disableRedundantPublicAnalysis)
+        configuration.apply(\.$enableUnusedImportsAnalysis, enableUnusedImportAnalysis)
         configuration.apply(\.$externalEncodableProtocols, externalEncodableProtocols)
         configuration.apply(\.$externalTestCaseClasses, externalTestCaseClasses)
         configuration.apply(\.$verbose, verbose)

Sources/Frontend/main.swift

@@ -1,6 +1,5 @@
 import Foundation
 import ArgumentParser
-import PeripheryKit
 import Shared
 
 Logger.configureBuffering()

Sources/PeripheryKit/Indexer/Declaration.swift

@@ -109,10 +109,29 @@ final class Declaration {
             }
         }
 
+        var extensionKind: Kind? {
+            switch self {
+            case .class:
+                return .extensionClass
+            case .struct:
+                return .extensionStruct
+            case .enum:
+                return .extensionEnum
+            case .protocol:
+                return .extensionProtocol
+            default:
+                return nil
+            }
+        }
+
         var isExtensionKind: Bool {
             rawValue.hasPrefix("extension")
         }
 
+        var isExtendableKind: Bool {
+            isConcreteTypeDeclarableKind
+        }
+
         var isConformableKind: Bool {
             isDiscreteConformableKind || isExtensionKind
         }
@@ -125,6 +144,10 @@ final class Declaration {
             return [.class, .struct, .enum]
         }
 
+        var isConcreteTypeDeclarableKind: Bool {
+            Self.concreteTypeDeclarableKinds.contains(self)
+        }
+
         static var concreteTypeDeclarableKinds: Set<Kind> {
             return [.class, .struct, .enum, .typealias]
         }
@@ -147,6 +170,8 @@ final class Declaration {
 
         var displayName: String? {
             switch self {
+            case .module:
+                return "imported module"
             case .class:
                 return "class"
             case .protocol:

Sources/PeripheryKit/Indexer/SourceFile.swift

@@ -2,8 +2,6 @@ import Foundation
 import SystemPackage
 
 class SourceFile {
-    typealias ImportStatement = (parts: [String], isTestable: Bool)
-
     let path: FilePath
     let modules: Set<String>
     var importStatements: [ImportStatement] = []

Sources/PeripheryKit/Indexer/SwiftIndexer.swift

@@ -240,6 +240,14 @@ public final class SwiftIndexer: Indexer {
             multiplexingSyntaxVisitor.visit()
 
             sourceFile.importStatements = importSyntaxVisitor.importStatements
+
+            if configuration.enableUnusedImportsAnalysis {
+                for stmt in sourceFile.importStatements {
+                    if stmt.isExported {
+                        graph.addExportedModule(stmt.module, exportedBy: sourceFile.modules)
+                    }
+                }
+            }
 
             associateLatentReferences()
             associateDanglingReferences()
@@ -266,6 +274,10 @@ public final class SwiftIndexer: Indexer {
                 }
             }
 
+            if configuration.enableUnusedImportsAnalysis {
+                graph.addIndexedModules(modules)
+            }
+
             let sourceFile = SourceFile(path: file, modules: modules)
             self.sourceFile = sourceFile
             return sourceFile

Sources/PeripheryKit/Indexer/XibParser.swift

@@ -1,7 +1,6 @@
 import Foundation
 import AEXML
 import SystemPackage
-import Shared
 
 final class XibParser {
     private let path: FilePath

Sources/PeripheryKit/SPM/SPMProjectDriver.swift

@@ -74,7 +74,10 @@ extension SPMProjectDriver: ProjectDriver {
             storePaths = [FilePath(package.path).appending(".build/debug/index/store")]
         }
 
-        try SwiftIndexer(sourceFiles: sourceFiles, graph: graph, indexStorePaths: storePaths).perform()
+        try SwiftIndexer(
+            sourceFiles: sourceFiles,
+            graph: graph,
+            indexStorePaths: storePaths).perform()
 
         graph.indexingComplete()
     }

Sources/PeripheryKit/ScanResultBuilder.swift

@@ -1,10 +1,11 @@
 import Foundation
-import Shared
 
 public struct ScanResultBuilder {
     public static func build(for graph: SourceGraph) -> [ScanResult] {
         let assignOnlyProperties = graph.assignOnlyProperties
-        let removableDeclarations = graph.unusedDeclarations.subtracting(assignOnlyProperties)
+        let removableDeclarations = graph.unusedDeclarations
+            .subtracting(assignOnlyProperties)
+            .union(graph.unusedModuleImports)
         let redundantProtocols = graph.redundantProtocols.filter { !removableDeclarations.contains($0.0) }
         let redundantPublicAccessibility = graph.redundantPublicAccessibility.filter { !removableDeclarations.contains($0.0) }
 

Sources/PeripheryKit/SourceGraph/Mutators/RedundantExplicitPublicAccessibilityMarker.swift

@@ -159,8 +159,8 @@ final class RedundantExplicitPublicAccessibilityMarker: SourceGraphMutator {
         let referenceFiles = graph.references(to: decl).map { $0.location.file }
 
         let referenceModules = referenceFiles.flatMapSet { file -> Set<String> in
-            let importsDeclModuleTestable = file.importStatements.contains(where: { (parts, isTestable) in
-                isTestable && !Set(parts).isDisjoint(with: decl.location.file.modules)
+            let importsDeclModuleTestable = file.importStatements.contains(where: {
+                $0.isTestable && decl.location.file.modules.contains($0.module)
             })
 
             if !importsDeclModuleTestable {

Sources/PeripheryKit/SourceGraph/Mutators/UnusedImportMarker.swift

@@ -0,0 +1,82 @@
+import Foundation
+import Shared
+
+/// Marks unused import statements (experimental).
+///
+/// A module import is unused when the source file contains no references to it, and no other
+/// imported modules either export it, or extend declarations declared by it.
+///
+/// Testing TODO:
+/// * Exports, including nested exports
+/// * Public declaration extended by another module
+final class UnusedImportMarker: SourceGraphMutator {
+    private let graph: SourceGraph
+    private let configuration: Configuration
+
+    required init(graph: SourceGraph, configuration: Configuration) {
+        self.graph = graph
+        self.configuration = configuration
+    }
+
+    func mutate() throws {
+        guard configuration.enableUnusedImportsAnalysis else { return }
+
+        var referencedModulesByFile = [SourceFile: Set<String>]()
+
+        // Build a mapping of source files and the modules they reference.
+        for ref in graph.allReferences {
+            guard let decl = graph.explicitDeclaration(withUsr: ref.usr) else { continue }
+            // Record directly referenced modules and also identify any modules that extended
+            // the declaration. These extensions may provide members/conformances that aren't
+            // referenced directly but which are still required.
+            let referencedModules = decl.location.file.modules.union(modulesExtending(decl))
+            referencedModulesByFile[ref.location.file, default: []].formUnion(referencedModules)
+        }
+
+        // For each source file, determine whether its imports are unused.
+        for (file, referencedModules) in referencedModulesByFile {
+            let unreferencedImports = file.importStatements
+                .filter {
+                    // Only consider modules that have been indexed as we need to see which modules
+                    // they export.
+                    graph.indexedModules.contains($0.module) &&
+                    !referencedModules.contains($0.module)
+                }
+
+            for unreferencedImport in unreferencedImports {
+                // In the simple case, a module is unused if it's not referenced. However, it's
+                // possible the module exports other referenced modules.
+                guard !referencedModules.contains(where: {
+                    graph.isModule($0, exportedBy: unreferencedImport.module)
+                }) else { continue }
+
+                graph.markUnusedModuleImport(unreferencedImport)
+            }
+        }
+    }
+
+    // MARK: - Private
+
+    private var extendedDeclCache: [Declaration: Set<String>] = [:]
+
+    /// Identifies any modules that extend the given declaration.
+    private func modulesExtending(_ decl: Declaration) -> Set<String> {
+        guard decl.kind.isExtendableKind else { return [] }
+
+        if let modules = extendedDeclCache[decl] {
+            return modules
+        }
+
+        let modules: Set<String> = graph.references(to: decl)
+            .flatMapSet {
+                guard let parent = $0.parent,
+                      parent.kind == decl.kind.extensionKind,
+                      parent.name == decl.name
+                else { return [] }
+
+                return parent.location.file.modules
+            }
+        extendedDeclCache[decl] = modules
+        return modules
+    }
+}

Sources/PeripheryKit/SourceGraph/SourceGraph.swift

@@ -17,10 +17,13 @@ public final class SourceGraph {
     private(set) var assetReferences: Set<AssetReference> = []
     private(set) var mainAttributedDeclarations: Set<Declaration> = []
     private(set) var allReferencesByUsr: [String: Set<Reference>] = [:]
+    private(set) var indexedModules: Set<String> = []
+    private(set) var unusedModuleImports: Set<Declaration> = []
 
     private var potentialAssignOnlyProperties: Set<Declaration> = []
     private var allDeclarationsByKind: [Declaration.Kind: Set<Declaration>] = [:]
     private var allExplicitDeclarationsByUsr: [String: Declaration] = [:]
+    private var moduleToExportingModules: [String: Set<String>] = [:]
 
     private let lock = UnfairLock()
 
@@ -150,12 +153,6 @@ public final class SourceGraph {
         declaration.usrs.forEach { allExplicitDeclarationsByUsr.removeValue(forKey: $0) }
     }
 
-    func add(_ reference: Reference) {
-        withLock {
-            addUnsafe(reference)
-        }
-    }
-
     func addUnsafe(_ reference: Reference) {
         _ = allReferences.insert(reference)
         allReferencesByUsr[reference.usr, default: []].insert(reference)
@@ -173,9 +170,9 @@ public final class SourceGraph {
             } else {
                 _ = declaration.references.insert(reference)
             }
-        }
 
-        add(reference)
+            addUnsafe(reference)
+        }
     }
 
     func remove(_ reference: Reference) {
@@ -215,6 +212,48 @@ public final class SourceGraph {
         explicitDeclaration(withUsr: reference.usr) == nil
     }
 
+    func addIndexedModules(_ modules: Set<String>) {
+        withLock {
+            indexedModules.formUnion(modules)
+        }
+    }
+
+    func addExportedModule(_ module: String, exportedBy exportingModules: Set<String>) {
+        withLock {
+            moduleToExportingModules[module, default: []].formUnion(exportingModules)
+        }
+    }
+
+    func isModule(_ module: String, exportedBy exportingModule: String) -> Bool {
+        withLock {
+            isModuleUnsafe(module, exportedBy: exportingModule)
+        }
+    }
+
+    private func isModuleUnsafe(_ module: String, exportedBy exportingModule: String) -> Bool {
+        let exportingModules = moduleToExportingModules[module, default: []]
+
+        if exportingModules.contains(exportingModule) {
+            // The module is exported directly.
+            return true
+        }
+
+        // Recursively check if the module is exported transitively.
+        return exportingModules.contains { nestedExportingModule in
+            return isModuleUnsafe(nestedExportingModule, exportedBy: exportingModule) &&
+            isModuleUnsafe(module, exportedBy: nestedExportingModule)
+        }
+    }
+
+    func markUnusedModuleImport(_ statement: ImportStatement) {
+        withLock {
+            let usr = "\(statement.location.description)-\(statement.module)"
+            let decl = Declaration(kind: .module, usrs: [usr], location: statement.location)
+            decl.name = statement.module
+            unusedModuleImports.insert(decl)
+        }
+    }
+
     func inheritedTypeReferences(of decl: Declaration, seenDeclarations: Set<Declaration> = []) -> [Reference] {
         var references: [Reference] = []
 

Sources/PeripheryKit/SourceGraph/SourceGraphMutatorRunner.swift

@@ -7,6 +7,9 @@ public final class SourceGraphMutatorRunner {
     }
 
     private let mutators: [SourceGraphMutator.Type] = [
+        // Must come before all others as we need to observe all references prior to any mutations.
+        UnusedImportMarker.self,
+
         // Must come before ExtensionReferenceBuilder.
         AccessibilityCascader.self,
         ObjCAccessibleRetainer.self,
@@ -44,7 +47,7 @@ public final class SourceGraphMutatorRunner {
         AssignOnlyPropertyReferenceEliminator.self,
 
         UsedDeclarationMarker.self,
-        RedundantProtocolMarker.self
+        RedundantProtocolMarker.self,
     ]
 
     private let graph: SourceGraph