Now I am become Delete, the destroyer of codes.
- Installation
- How To Use
- Analysis
- Comment Commands
- Xcode Integration
- Excluding Files
- Continuous Integration
- Build Systems
- Platforms
- Troubleshooting
- Known Bugs
- Sponsors
brew install peripherymint install peripheryapp/peripherybazel_dep(name = "periphery", version = "<version>")
use_repo(use_extension("@periphery//bazel:generated.bzl", "generated"), "periphery_generated")bazel run @periphery -- scan --bazelThe scan command is Periphery's primary function. To begin a guided setup, change to your project directory and run:
periphery scan --setupThe guided setup will detect your project type and configure a few options. After answering a few questions, Periphery will print out the full scan command and execute it.
The guided setup is only intended for introductory purposes, once you are familiar with Periphery you can try some more advanced options, all of which can be seen with periphery help scan.
To get the most from Periphery, it’s important to understand how it works. Periphery first builds your project; it does this to generate the “index store”. The index store contains detailed information about the declarations (class, struct, func, etc.) in your project and their references to other declarations. Using this store, Periphery builds an in-memory graph of the relational structure of your project, supplementing it with additional information obtained by parsing each source file. Next, the graph is mutated to make it more suitable for detecting unused code, e.g. marking your project’s entry points. Finally, the graph is traversed from its roots to identify unreferenced declarations.
Tip
The index store only contains information about source files in the build targets compiled during the build phase. If a given class is only referenced in a source file that was not compiled, then Periphery will identify the class as unused. It’s important to ensure you build all the targets you expect to contain references. For an Xcode project, this is controlled using the
-—schemesoption. For a Swift package, all targets are built automatically.
If your project consists of one or more standalone frameworks that do not also contain some kind of application that consumes their interfaces, you need to tell Periphery to assume that all public declarations are used with the --retain-public option.
For projects that are mixed Objective-C & Swift, it's highly recommended you read about the implications this can have on your results.
Once you've settled upon the appropriate options for your project, you may wish to persist them in a YAML configuration file. The simplest way to achieve this is to run Periphery with the --verbose option. Near the beginning of the output you will see the [configuration:begin] section with your configuration formatted as YAML below. Copy & paste the configuration into .periphery.yml in the root of your project folder. You can now simply run periphery scan and the YAML configuration will be used.
The goal of Periphery is to report instances of unused declarations. A declaration is a class, struct, protocol, function, property, constructor, enum, typealias, associatedtype, etc. As you'd expect, Periphery can identify simple unreferenced declarations, e.g. a class that is no longer used anywhere in your codebase.
Periphery can also identify more advanced instances of unused code. The following section explains these in detail.
Periphery can identify unused function parameters. Instances of unused parameters can also be identified in protocols and their conforming declarations, as well as parameters in overridden methods. Both of these scenarios are explained further below.
An unused parameter of a protocol function will only be reported as unused if the parameter is also unused in all implementations.
protocol Greeter {
func greet(name: String)
func farewell(name: String) // 'name' is unused
}
class InformalGreeter: Greeter {
func greet(name: String) {
print("Sup " + name + ".")
}
func farewell(name: String) { // 'name' is unused
print("Cya.")
}
}Tip
You can ignore all unused parameters from protocols and conforming functions with the
--retain-unused-protocol-func-paramsoption.
Similar to protocols, parameters of overridden functions are only reported as unused if they're also unused in the base function and all overriding functions.
class BaseGreeter {
func greet(name: String) {
print("Hello.")
}
func farewell(name: String) { // 'name' is unused
print("Goodbye.")
}
}
class InformalGreeter: BaseGreeter {
override func greet(name: String) {
print("Sup " + name + ".")
}
override func farewell(name: String) { // 'name' is unused
print("Cya.")
}
}Unused parameters of protocols or classes defined in foreign modules (e.g. Foundation) are always ignored since you do not have access to modify the base function declaration.
Unused parameters of functions that simply call fatalError are also ignored. Such functions are often unimplemented required initializers in subclasses.
class Base {
let param: String
required init(param: String) {
self.param = param
}
}
class Subclass: Base {
init(custom: String) {
super.init(param: custom)
}
required init(param: String) {
fatalError("init(param:) has not been implemented")
}
}A protocol which is conformed to by an object is not truly used unless it's also used as an existential type, or to specialize a generic method/class. Periphery is able to identify such redundant protocols whether they are conformed to by one, or even multiple objects.
protocol MyProtocol { // 'MyProtocol' is redundant
func someMethod()
}
class MyClass1: MyProtocol { // 'MyProtocol' conformance is redundant
func someMethod() {
print("Hello from MyClass1!")
}
}
class MyClass2: MyProtocol { // 'MyProtocol' conformance is redundant
func someMethod() {
print("Hello from MyClass2!")
}
}
let myClass1 = MyClass1()
myClass1.someMethod()
let myClass2 = MyClass2()
myClass2.someMethod()Here we can see that despite both implementations of someMethod are called, at no point does an object take on the type of MyProtocol. Therefore the protocol itself is redundant, and there's no benefit from MyClass1 or MyClass2 conforming to it. We can remove MyProtocol along with each redundant conformance, and just keep someMethod in each class.
Just like a normal method or property of a object, individual properties and methods declared by your protocol can also be identified as unused.
protocol MyProtocol {
var usedProperty: String { get }
var unusedProperty: String { get } // 'unusedProperty' is unused
}
class MyConformingClass: MyProtocol {
var usedProperty: String = "used"
var unusedProperty: String = "unused" // 'unusedProperty' is unused
}
class MyClass {
let conformingClass: MyProtocol
init() {
conformingClass = MyConformingClass()
}
func perform() {
print(conformingClass.usedProperty)
}
}
let myClass = MyClass()
myClass.perform()Here we can see that MyProtocol is itself used, and cannot be removed. However, since unusedProperty is never called on MyConformingClass, Periphery can identify that the declaration of unusedProperty in MyProtocol is also unused and can be removed along with the unused implementation of unusedProperty.
Along with being able to identify unused enumerations, Periphery can also identify individual unused enum cases. Plain enums that are not raw representable, i.e. that don't have a String, Character, Int, or floating-point value type can be reliably identified. However, enumerations that do have a raw value type can be dynamic, and therefore must be assumed to be used.
Let's clear this up with a quick example:
enum MyEnum: String {
case myCase
}
func someFunction(value: String) {
if let myEnum = MyEnum(rawValue: value) {
somethingImportant(myEnum)
}
}There's no direct reference to the myCase case, so it's reasonable to expect it might no longer be needed, however, if it were removed we can see that somethingImportant would never be called if someFunction were passed the value of "myCase".
Properties that are assigned but never used are identified as such, e.g:
class MyClass {
var assignOnlyProperty: String // 'assignOnlyProperty' is assigned, but never used
init(value: String) {
self.assignOnlyProperty = value
}
}In some cases this may be the intended behavior, therefore you have a few options available to silence such results:
- Retain individual properties using Comment Commands.
- Retain all assign-only properties by their type with
--retain-assign-only-property-types. Given types must match their exact usage in the property declaration (sans optional question mark), e.g.String,[String],Set<String>. Periphery is unable to resolve inferred property types, therefore in some instances, you may need to add explicit type annotations to your properties. - Disable assign-only property analysis entirely with
--retain-assign-only-properties.
Declarations that are marked public yet are not referenced from outside their home module, are identified as having redundant public accessibility. In this scenario, the public annotation can be removed from the declaration. Removing redundant public accessibility has a couple of benefits:
- It helps reduce the public surface area of your modules.
- In Whole Module Compilation mode, Swift can infer
finalby automatically discovering all potentially overriding declarations.finalclasses are better optimized by the compiler.
This analysis can be disabled with --disable-redundant-public-analysis.
Periphery can detect unused imports of targets it has scanned, i.e. those specified with the --targets argument. It cannot detect unused imports of other targets because the Swift source files are unavailable and uses of @_exported cannot be observed. @_exported is problematic because it changes the public interface of a target such that the declarations exported by the target are no longer necessarily declared by the imported target. For example, the Foundation target exports Dispatch, among other targets. If any given source file imports Foundation and references DispatchQueue but no other declarations from Foundation, then the Foundation import cannot be removed as it would also make the DispatchQueue type unavailable. To avoid false positives, therefore, Periphery only detects unused imports of targets it has scanned.
Periphery will likely produce false positives for targets with mixed Swift and Objective-C, as Periphery cannot scan the Objective-C files. It is recommended therefore to disable unused import detection for projects with a significant amount of Objective-C, or manually exclude the mixed language targets from the results.
Periphery cannot analyze Objective-C code since types may be dynamically typed.
By default, Periphery does not assume that declarations accessible by the Objective-C runtime are in use. If your project is a mix of Swift & Objective-C, you can enable this behavior with the --retain-objc-accessible option. Swift declarations that are accessible by the Objective-C runtime are those that are explicitly annotated with @objc or @objcMembers, and classes that inherit NSObject either directly or indirectly via another class.
Alternatively, the --retain-objc-annotated can be used to only retain declarations that are explicitly annotated with @objc or @objcMembers. Types that inherit NSObject are not retained unless they have explicit annotations. This option may uncover more unused code, but with the caveat that some of the results may be incorrect if the declaration is used in Objective-C code. To resolve these incorrect results you must add an @objc annotation to the declaration.
Swift synthesizes additional code for Codable 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 Codable types with --retain-codable-properties. Alternatively, you can retain properties only on Encodable types with --retain-encodable-properties.
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".
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.
If your project contains Interface Builder files (such as storyboards and XIBs), Periphery will take these into account when identifying unused declarations. However, Periphery currently only identifies unused classes. This limitation exists because Periphery does not yet fully parse Interface Builder files (see issue #212). Due to Periphery's design principle of avoiding false positives, it is assumed that if a class is referenced in an Interface Builder file, all of its IBOutlets and IBActions are used, even if they might not be in reality. This approach will be revised to accurately identify unused IBActions and IBOutlets once Periphery gains the capability to parse Interface Builder files.
For whatever reason, you may want to keep some unused code. Source code comment commands can be used to ignore specific declarations and exclude them from the results.
An ignore comment command can be placed directly on the line above any declaration to ignore it, and all descendent declarations:
// periphery:ignore
class MyClass {}You can also ignore specific unused function parameters:
// periphery:ignore:parameters unusedOne,unusedTwo
func someFunc(used: String, unusedOne: String, unusedTwo: String) {
print(used)
}The // periphery:ignore:all command can be placed at the top of the source file to ignore the entire contents of the file. Note that the comment must be placed above any code, including import statements.
Comment commands also support trailing comments following a hyphen so that you can include an explanation on the same line:
// periphery:ignore - explanation of why this is necessary
class MyClass {}Before setting up Xcode integration, we highly recommend you first get Periphery working in a terminal, as you will be using the same command via Xcode.
Select your project in the Project Navigator and click the + button at the bottom left of the Targets section. Select Cross-platform and choose Aggregate. Hit Next.
Choose a name for the new target, e.g. "Periphery" or "Unused Code".
In the Build Phases section click the + button to add a new Run Script phase.
In the shell script window enter the Periphery command. Be sure to include the --format xcode option.
You're ready to roll. You should now see the new scheme in the dropdown. Select it and hit run.
Tip
If you'd like others on your team to be able to use the scheme, you'll need to mark it as Shared. This can be done by selecting Manage Schemes... and selecting the Shared checkbox next to the new scheme. The scheme definition can now be checked into source control.
Both exclusion options described below accept a Bash v4 style path glob, either absolute or relative to your project directory. You can delimit multiple globs with a space, e.g. --option "Sources/Single.swift" "**/Generated/*.swift" "**/*.{xib,storyboard}".
To exclude the results from certain files, pass the --report-exclude <globs> option to the scan command.
Excluding files from the indexing phase means that any declarations and references contained within the files will not be seen by Periphery. Periphery will behave as if the files do not exist.
To exclude files from being indexed, there are a few options:
- Use
--exclude-targets "TargetA" "TargetB"to exclude all source files in the chosen targets. - Use
--exclude-teststo exclude all test targets. - Use
--index-exclude "file.swift" "path/*.swift"to exclude individual source files.
To retain all declarations in files, pass the --retain-files <globs> option to the scan command. This option is equivalent to adding a // periphery:ignore:all comment command at the top of each file.
When integrating Periphery into a CI pipeline, you can potentially skip the build phase if your pipeline has already done so, e.g. to run tests. This can be achieved using the --skip-build option. However, you also need to tell Periphery the location of the index store using --index-store-path. This location is dependent on your project type.
Note that when using --skip-build and --index-store-path it's vital that the index store contains data for all of the targets you specify via --targets. For example, if your pipeline previously built the targets 'App' and 'Lib', the index store will only contain data for the files in those targets. You cannot then instruct Periphery to scan additional targets, e.g 'Extension', or 'UnitTests'.
The index store generated by xcodebuild exists in DerivedData at a location dependent on your project, e.g ~/Library/Developer/Xcode/DerivedData/YourProject-abc123/Index/DataStore. For Xcode 14 and later, the Index directory can be found as Index.noindex, which suppresses Spotlight indexing.
By default, Periphery looks for the index store at .build/debug/index/store. Therefore, if you intend to run Periphery directly after calling swift test, you can omit the --index-store-path option and Periphery will use the index store created when the project was built for testing. However, if this isn't the case, then you must provide Periphery the location of the index store with --index-store-path.
Periphery can analyze projects using other build systems, though it cannot drive them automatically like SPM, Xcode and Bazel. Instead, you need to specify the location of indexstore and other resource files. The format is as follows:
{
"indexstores": [
"path/to/file.indexstore"
],
"test_targets": [
"MyTests"
],
"plists": [
"path/to/file.plist"
],
"xibs": [
"path/to/file.xib",
"path/to/file.storyboard"
],
"xcdatamodels": [
"path/to/file.xcdatamodel"
],
"xcmappingmodels": [
"path/to/file.xcmappingmodel"
]
}Tip
Relative paths are assumed to be relative to the current directory.
You can then invoke Periphery as follows:
periphery scan --generic-project-config config.jsonTip
Both options support multiple paths.
Periphery supports both macOS and Linux. macOS supports both Xcode and Swift Package Manager (SPM) projects, whereas only SPM projects are supported on Linux.
It's possible for the index store to become corrupt, or out of sync with the source file. This can happen, for example, if you forcefully terminate (^C) a scan. To rectify this, you can pass the --clean-build flag to the scan command to force removal of existing build artifacts.
When Periphery builds your project it uses the default build configuration, which is typically 'debug'. If you use preprocessor macros to conditionally compile code, Periphery will only have visibility into the branches that are compiled. In the example below, releaseName will be reported as unused as it is only referenced within the non-debug branch of the macro.
struct BuildInfo {
let debugName = "debug"
let releaseName = "release" // 'releaseName' is unused
var name: String {
#if DEBUG
debugName
#else
releaseName
#endif
}
}You have a few options to workaround this:
- Use Comment Commands to explicitly ignore
releaseName. - Filter the results to remove known instances.
- Run Periphery once for each build configuration and merge the results. You can pass arguments to the underlying build by specifying them after
--, e.g.periphery scan ... -- -configuration release.
Periphery uses swift build to compile a Swift package which will fail if the Swift package is platform-specific (e.g. to iOS).
As a workaround, you can manually build the Swift package with xcodebuild and then use the --skip-build and --index-store-path options to target the index store previously produced by xcodebuild.
Example:
# 1. Use xcodebuild
xcodebuild -scheme MyScheme -destination 'platform=iOS Simulator,OS=16.2,name=iPhone 14' -derivedDataPath '../dd' clean build
# 2. Use produced index store for scanning
periphery scan --skip-build --index-store-path '../dd/Index.noindex/DataStore/'Due to some underlying bugs in Swift, Periphery may in some instances report incorrect results.
| ID | Title |
|---|---|
| 56541 | Index store does not relate static property getter used as subscript key |
| 56327 | Index store does not relate objc optional protocol method implemented in subclass |
| 56189 | Index store should relate appendInterpolation from string literals |
| 56165 | Index store does not relate constructor via literal notation |
Periphery is passion project that takes a huge amount of effort to maintain and develop. If you find Periphery useful, please consider sponsoring through GitHub Sponsors.
Special thanks goes to the following generous sponsors:
SaGa Corp develops unique technology for financial players and their customers.
Emerge Tools is a suite of revolutionary products designed to supercharge mobile apps and the teams that build them.
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