perf: speed up writing pbxproj files

Sources/XcodeProj/Extensions/String+md5.swift

@@ -27,22 +27,34 @@ import Foundation
 
 extension String {
     var md5: String {
-        guard let data = data(using: .utf8, allowLossyConversion: true) else {
-            return self
-        }
         #if canImport(CryptoKit)
             if #available(OSX 10.15, iOS 13.0, *) {
-                return Insecure.MD5.hash(data: data)
-                    .withUnsafeBytes { Array($0) }.hexString
-            } else {
-                return data.slowMD5
+                // Hashes the UTF-8 bytes in place and writes the hex digits straight into the result, without the
+                // intermediate `Data`, byte array, and hex buffer.
+                var string = self
+                let digest = string.withUTF8 { Insecure.MD5.hash(data: UnsafeRawBufferPointer($0)) }
+                return digest.withUnsafeBytes { bytes in
+                    String(unsafeUninitializedCapacity: bytes.count * 2) { hex in
+                        for (offset, byte) in bytes.enumerated() {
+                            hex[offset * 2] = hexDigit(byte >> 4)
+                            hex[offset * 2 + 1] = hexDigit(byte & 0xF)
+                        }
+                        return bytes.count * 2
+                    }
+                }
             }
-        #else
-            return data.slowMD5
         #endif
+        guard let data = data(using: .utf8, allowLossyConversion: true) else {
+            return self
+        }
+        return data.slowMD5
     }
 }
 
+private func hexDigit(_ value: UInt8) -> UInt8 {
+    (value > 9) ? (charA + value - 10) : (char0 + value)
+}
+
 private let charA = UInt8(UnicodeScalar("a").value)
 private let char0 = UInt8(UnicodeScalar("0").value)
 
@@ -54,18 +66,14 @@ private extension DataProtocol {
 
         for _ in regions {
             for i in self {
-                hexChars[Int(offset * 2)] = itoh((i >> 4) & 0xF)
-                hexChars[Int(offset * 2 + 1)] = itoh(i & 0xF)
+                hexChars[Int(offset * 2)] = hexDigit((i >> 4) & 0xF)
+                hexChars[Int(offset * 2 + 1)] = hexDigit(i & 0xF)
                 offset += 1
             }
         }
 
         return String(bytes: hexChars, encoding: .utf8)!
     }
-
-    func itoh(_ value: UInt8) -> UInt8 {
-        (value > 9) ? (charA + value - 10) : (char0 + value)
-    }
 }
 
 private extension Data {

Sources/XcodeProj/Objects/BuildPhase/PBXBuildFile.swift

@@ -186,7 +186,8 @@ final class PBXBuildPhaseFile: PlistSerializable, Equatable {
     }
 
     func plistKeyAndValue(proj _: PBXProj, reference: String) throws -> (key: CommentedString, value: PlistValue) {
-        var dictionary: [CommentedString: PlistValue] = [:]
+        // Room for every key below, so the dictionary isn't regrown while it's filled.
+        var dictionary = [CommentedString: PlistValue](minimumCapacity: 6)
         dictionary["isa"] = .string(CommentedString(PBXBuildFile.isa))
         if let fileReference = buildFile.fileReference {
             let fileElement: PBXFileElement? = fileReference.getObject()

Sources/XcodeProj/Objects/Project/PBXObject.swift

@@ -57,7 +57,8 @@ public class PBXObject: Hashable, Decodable, Equatable, AutoEquatable {
 
     /// Object isa (type id)
     public static var isa: String {
-        String(describing: self)
+        // What `String(describing: self)` prints for a class, without the reflection it goes through first.
+        _typeName(self, qualified: false)
     }
 
     public static func == (lhs: PBXObject,

Sources/XcodeProj/Objects/Project/PBXObjectReference.swift

@@ -7,7 +7,12 @@ class PBXObjectReference: NSObject, Comparable, NSCopying {
     private(set) var temporary: Bool
 
     /// String reference.
-    private(set) var value: String
+    private(set) var value: String {
+        didSet { valueHash = value.hashValue }
+    }
+
+    /// The hash of `value`, which dictionaries keyed by references ask for again every time they move an entry.
+    private var valueHash: Int
 
     /// Weak reference to the objects instance that contains the project objects.
     weak var objects: PBXObjects?
@@ -20,13 +25,15 @@ class PBXObjectReference: NSObject, Comparable, NSCopying {
     /// - Parameter reference: reference.
     init(_ reference: String, objects: PBXObjects) {
         value = reference
+        valueHash = reference.hashValue
         temporary = false
         self.objects = objects
     }
 
     /// Initializes a temporary reference
     init(objects: PBXObjects? = nil) {
         value = "TEMP_\(UUID().uuidString)"
+        valueHash = value.hashValue
         temporary = true
         self.objects = objects
     }
@@ -36,6 +43,7 @@ class PBXObjectReference: NSObject, Comparable, NSCopying {
     /// - Parameter reference: reference.
     init(_ reference: String) {
         value = reference
+        valueHash = reference.hashValue
         temporary = false
     }
 
@@ -44,14 +52,16 @@ class PBXObjectReference: NSObject, Comparable, NSCopying {
     /// - Parameter objectReference: object reference to be initialized from.
     required init(_ objectReference: PBXObjectReference) {
         value = objectReference.value
+        valueHash = objectReference.valueHash
         temporary = objectReference.temporary
     }
 
     /// Fixes its value making it permanent.
     ///
     /// - Parameter value: value.
     func fix(_ value: String) {
-        let object = objects?.delete(reference: self)
+        // The referenced object's type says which collection holds it, which saves probing every collection.
+        let object = object.flatMap { objects?.remove(reference: self, typeOf: $0) } ?? objects?.delete(reference: self)
         self.value = value
         temporary = false
         if let object {
@@ -71,7 +81,7 @@ class PBXObjectReference: NSObject, Comparable, NSCopying {
 
     /// Hash value.
     override var hash: Int {
-        value.hashValue
+        valueHash
     }
 
     func copy(with _: NSZone? = nil) -> Any {

Sources/XcodeProj/Objects/Project/PBXObjects.swift

@@ -208,40 +208,70 @@ class PBXObjects: Equatable {
         }
         let objectReference: PBXObjectReference = object.reference
         objectReference.objects = self
+        update(object, reference: objectReference, inserting: true)
+    }
+
+    /// Removes the object stored under `reference` from the collection that objects of `object`'s type belong to.
+    /// Unlike `delete(reference:)`, it doesn't probe every collection.
+    ///
+    /// - Returns: the removed object, or nil when that collection has nothing under `reference`.
+    func remove(reference: PBXObjectReference, typeOf object: PBXObject) -> PBXObject? {
+        lock.lock()
+        defer { lock.unlock() }
+        return update(object, reference: reference, inserting: false)
+    }
+
+    /// Inserts `object` under `reference` into the collection its type belongs to, or removes what that collection
+    /// stores under `reference`, so `add` and `remove` always agree on the collection.
+    @discardableResult private func update(
+        _ object: PBXObject,
+        reference: PBXObjectReference,
+        inserting: Bool
+    ) -> PBXObject? {
+        func update<T: PBXObject>(_ objects: inout [PBXObjectReference: T], _ object: T) -> PBXObject? {
+            if inserting {
+                objects[reference] = object
+                return object
+            }
+            return objects.removeValue(forKey: reference)
+        }
 
         switch object {
         // subclasses of PBXGroup; must be tested before PBXGroup
-        case let object as PBXVariantGroup: _variantGroups[objectReference] = object
-        case let object as XCVersionGroup: _versionGroups[objectReference] = object
+        case let object as PBXVariantGroup: return update(&_variantGroups, object)
+        case let object as XCVersionGroup: return update(&_versionGroups, object)
         // everything else
-        case let object as PBXBuildFile: _buildFiles[objectReference] = object
-        case let object as PBXAggregateTarget: _aggregateTargets[objectReference] = object
-        case let object as PBXLegacyTarget: _legacyTargets[objectReference] = object
-        case let object as PBXContainerItemProxy: _containerItemProxies[objectReference] = object
-        case let object as PBXCopyFilesBuildPhase: _copyFilesBuildPhases[objectReference] = object
-        case let object as PBXGroup: _groups[objectReference] = object
-        case let object as XCConfigurationList: _configurationLists[objectReference] = object
-        case let object as XCBuildConfiguration: _buildConfigurations[objectReference] = object
-        case let object as PBXTargetDependency: _targetDependencies[objectReference] = object
-        case let object as PBXSourcesBuildPhase: _sourcesBuildPhases[objectReference] = object
-        case let object as PBXShellScriptBuildPhase: _shellScriptBuildPhases[objectReference] = object
-        case let object as PBXResourcesBuildPhase: _resourcesBuildPhases[objectReference] = object
-        case let object as PBXFrameworksBuildPhase: _frameworksBuildPhases[objectReference] = object
-        case let object as PBXHeadersBuildPhase: _headersBuildPhases[objectReference] = object
-        case let object as PBXNativeTarget: _nativeTargets[objectReference] = object
-        case let object as PBXFileReference: _fileReferences[objectReference] = object
-        case let object as PBXProject: _projects[objectReference] = object
-        case let object as PBXReferenceProxy: _referenceProxies[objectReference] = object
-        case let object as PBXRezBuildPhase: _carbonResourcesBuildPhases[objectReference] = object
-        case let object as PBXBuildRule: _buildRules[objectReference] = object
-        case let object as XCRemoteSwiftPackageReference: _remoteSwiftPackageReferences[objectReference] = object
-        case let object as XCLocalSwiftPackageReference: _localSwiftPackageReferences[objectReference] = object
-        case let object as XCSwiftPackageProductDependency: _swiftPackageProductDependencies[objectReference] = object
-        case let object as PBXFileSystemSynchronizedRootGroup: _fileSystemSynchronizedRootGroups[objectReference] = object
-        case let object as PBXFileSystemSynchronizedBuildFileExceptionSet: _fileSystemSynchronizedBuildFileExceptionSets[objectReference] = object
+        case let object as PBXBuildFile: return update(&_buildFiles, object)
+        case let object as PBXAggregateTarget: return update(&_aggregateTargets, object)
+        case let object as PBXLegacyTarget: return update(&_legacyTargets, object)
+        case let object as PBXContainerItemProxy: return update(&_containerItemProxies, object)
+        case let object as PBXCopyFilesBuildPhase: return update(&_copyFilesBuildPhases, object)
+        case let object as PBXGroup: return update(&_groups, object)
+        case let object as XCConfigurationList: return update(&_configurationLists, object)
+        case let object as XCBuildConfiguration: return update(&_buildConfigurations, object)
+        case let object as PBXTargetDependency: return update(&_targetDependencies, object)
+        case let object as PBXSourcesBuildPhase: return update(&_sourcesBuildPhases, object)
+        case let object as PBXShellScriptBuildPhase: return update(&_shellScriptBuildPhases, object)
+        case let object as PBXResourcesBuildPhase: return update(&_resourcesBuildPhases, object)
+        case let object as PBXFrameworksBuildPhase: return update(&_frameworksBuildPhases, object)
+        case let object as PBXHeadersBuildPhase: return update(&_headersBuildPhases, object)
+        case let object as PBXNativeTarget: return update(&_nativeTargets, object)
+        case let object as PBXFileReference: return update(&_fileReferences, object)
+        case let object as PBXProject: return update(&_projects, object)
+        case let object as PBXReferenceProxy: return update(&_referenceProxies, object)
+        case let object as PBXRezBuildPhase: return update(&_carbonResourcesBuildPhases, object)
+        case let object as PBXBuildRule: return update(&_buildRules, object)
+        case let object as XCRemoteSwiftPackageReference: return update(&_remoteSwiftPackageReferences, object)
+        case let object as XCLocalSwiftPackageReference: return update(&_localSwiftPackageReferences, object)
+        case let object as XCSwiftPackageProductDependency: return update(&_swiftPackageProductDependencies, object)
+        case let object as PBXFileSystemSynchronizedRootGroup: return update(&_fileSystemSynchronizedRootGroups, object)
+        case let object as PBXFileSystemSynchronizedBuildFileExceptionSet: return update(&_fileSystemSynchronizedBuildFileExceptionSets, object)
         case let object as PBXFileSystemSynchronizedGroupBuildPhaseMembershipExceptionSet:
-            _fileSystemSynchronizedGroupBuildPhaseMembershipExceptionSet[objectReference] = object
-        default: fatalError("Unhandled PBXObject type for \(object), this is likely a bug / todo")
+            return update(&_fileSystemSynchronizedGroupBuildPhaseMembershipExceptionSet, object)
+        default:
+            // Objects of these types are never added, so there is nothing to remove.
+            guard inserting else { return nil }
+            fatalError("Unhandled PBXObject type for \(object), this is likely a bug / todo")
         }
     }
 
@@ -430,17 +460,15 @@ extension PBXObjects {
     // This is used to decode build files. (we need the name of the build phase)
     // Otherwise, we would have to go through all the build phases for each file.
     var buildPhaseFile: [PBXObjectReference: PBXBuildPhaseFile] {
-        let values: [[PBXBuildPhaseFile]] = buildPhases.values.map { buildPhase in
-            let files = buildPhase.files
-            let buildPhaseFile: [PBXBuildPhaseFile] = files?.compactMap { (file: PBXBuildFile) -> PBXBuildPhaseFile in
-                PBXBuildPhaseFile(
-                    buildFile: file,
-                    buildPhase: buildPhase
-                )
-            } ?? []
-            return buildPhaseFile
+        // A build file listed by several phases maps to the first of them. Visiting the phases and files backwards lets
+        // each entry be overwritten without checking it first, so the first occurrence is the one that stays.
+        var buildPhaseFile = [PBXObjectReference: PBXBuildPhaseFile](minimumCapacity: buildFiles.count)
+        for buildPhase in buildPhases.values.reversed() {
+            for file in (buildPhase.files ?? []).reversed() {
+                buildPhaseFile[file.reference] = PBXBuildPhaseFile(buildFile: file, buildPhase: buildPhase)
+            }
         }
-        return Dictionary(values.flatMap { $0 }.map { ($0.buildFile.reference, $0) }, uniquingKeysWith: { first, _ in first })
+        return buildPhaseFile
     }
 
     /// Runs the given closure for each of the objects that are part of the project.

Sources/XcodeProj/Objects/Project/PBXProjEncoder.swift

@@ -374,9 +374,11 @@ final class PBXProjEncoder {
             }
         }
 
-        let joinedArray: [String] = resultArray.flatMap { $0 }
         // should check multiline
-        output.append(contentsOf: joinedArray)
+        // Appended element by element, which saves flattening them into a temporary array first.
+        for lines in resultArray {
+            output.append(contentsOf: lines)
+        }
         write(string: "/* End \(section) section */", to: &output)
         writeNewLine(stateHolder: &stateHolder, to: &output)
     }

Sources/XcodeProj/Utils/ReferenceGenerator.swift

@@ -16,6 +16,8 @@ protocol ReferenceGenerating: AnyObject {
 final class ReferenceGenerator: ReferenceGenerating {
     let outputSettings: PBXOutputSettings
     var references: Set<String> = []
+    /// The type name and reference acronym of each object type, which only depend on the type.
+    private var typeNamesAndAcronyms: [ObjectIdentifier: (typeName: String, acronym: String)] = [:]
 
     init(outputSettings: PBXOutputSettings) {
         self.outputSettings = outputSettings
@@ -386,14 +388,7 @@ extension ReferenceGenerator {
             if let context = object.context {
                 identifiers.append(context)
             }
-            let typeName = String(describing: type(of: object))
-
-            // Get acronym to be used as prefix for the reference.
-            // PBXFileReference is turned to FR.
-            let acronym = typeName
-                .replacingOccurrences(of: "PBX", with: "")
-                .replacingOccurrences(of: "XC", with: "")
-                .filter { String($0).lowercased() != String($0) }
+            let (typeName, acronym) = typeNameAndAcronym(of: object)
 
             var reference = ""
             var counter = 0
@@ -410,6 +405,21 @@ extension ReferenceGenerator {
         }
     }
 
+    private func typeNameAndAcronym(of object: some PBXObject) -> (typeName: String, acronym: String) {
+        let objectType = type(of: object)
+        if let cached = typeNamesAndAcronyms[ObjectIdentifier(objectType)] { return cached }
+        let typeName = String(describing: objectType)
+
+        // Get acronym to be used as prefix for the reference.
+        // PBXFileReference is turned to FR.
+        let acronym = typeName
+            .replacingOccurrences(of: "PBX", with: "")
+            .replacingOccurrences(of: "XC", with: "")
+            .filter { String($0).lowercased() != String($0) }
+        typeNamesAndAcronyms[ObjectIdentifier(objectType)] = (typeName, acronym)
+        return (typeName, acronym)
+    }
+
     private func generateReferenceFrom(acronym: String,
                                        typeName: String,
                                        identifiers: [String],