What's new in Leaf 4 (Tau)?

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2020/10/20

Every part you need to know concerning the upcoming Leaf template engine replace and how you can migrate your Vapor / Swift codebase.

Vapor

Utilizing Leaf 4 Tau

Earlier than we dive in, let’s make a brand new Vapor venture with the next package deal definition.


import PackageDescription

let package deal = Package deal(
    identify: "myProject",
    platforms: [
       .macOS(.v10_15)
    ],
    dependencies: [
        
        .package(url: "https://github.com/vapor/vapor.git", from: "4.30.0"),
        .package(url: "https://github.com/vapor/leaf", .exact("4.0.0-tau.1")),
        .package(url: "https://github.com/vapor/leaf-kit", .exact("1.0.0-tau.1.1")),
    ],
    targets: [
        .target(name: "App", dependencies: [
            .product(name: "Vapor", package: "vapor"),
            .product(name: "Leaf", package: "leaf"),
        ]),
        .goal(identify: "Run", dependencies: ["App"]),
        .testTarget(identify: "AppTests", dependencies: [
            .target(name: "App"),
            .product(name: "XCTVapor", package: "vapor"),
        ])
    ]
)

The very very first thing I would like to indicate you is that now we have a brand new render technique. Prior to now we have been in a position to make use of the req.view.render perform to render our template information. Take into account the next actually easy index.leaf file with two context variables that we’ll give show actual quickly.

<!DOCTYPE html>
<html>
    <head>
        <meta charset="utf-8">
        <meta identify="viewport" content material="width=device-width, initial-scale=1">
        <title>#(title)</title>
    </head>
    <physique>
        #(physique)
    </physique>
</html>

Now in our Vapor codebase we may use one thing like this to render the template.

import Vapor
import Leaf

public func configure(_ app: Software) throws {

    app.views.use(.leaf)

    app.get() { req -> EventLoopFuture<View> in
        struct Context: Encodable {
            let title: String
            let physique: String
        }
        let context = Context(title: "Leaf 4", physique:"Good day Leaf Tau!")
        return req.view.render("index", context)
    }
}

We are able to use an Encodable object and cross it round as a context variable. It is a handy method of offering values for our Leaf variables. Earlier than we proceed I’ve to inform you that each one of this may proceed to work in Leaf Tau and you do not have to make use of the brand new strategies. 👍

New render strategies

So let me present you the very same factor utilizing the brand new API.

import Vapor
import Leaf

public func configure(_ app: Software) throws {

    app.views.use(.leaf)

    app.get() { req -> EventLoopFuture<View> in
        let context: LeafRenderer.Context = [
            "title": "Leaf 4",
            "body": "Hello Leaf Tau!",
        ]
        return req.leaf.render(template: "index", context: context)
    }
}

That is not a giant deal you would say at first sight. Nicely, the factor is that this new technique gives type-safe values for our templates and that is simply the tip of the iceberg. It’s best to overlook concerning the view property on the request object, since Leaf began to outgrow the view layer in Vapor.

import Vapor
import Leaf

public func configure(_ app: Software) throws {

    app.views.use(.leaf)

    app.get() { req -> EventLoopFuture<View> in
        let identify = "Leaf Tau"
        let context: LeafRenderer.Context = [
            "title": "Leaf 4",
            "body": .string("Hello (name)!"),
        ]
        return req.leaf.render(template: "index",
                               from: "default",
                               context: context,
                               choices: [.caching(.bypass)])
    }
}

Should you take a better have a look at this comparable instance, you discover out that the context object and the values are representable by numerous sorts, but when we attempt to use an interpolated string, now we have to be a bit of bit extra kind particular. A LeafRenderer.Context object is considerably a [String: LeafData] alias the place LeafData has a number of static strategies to initialize the built-in fundamental Swift sorts for Leaf. That is the place the type-safety characteristic is available in Tau. You should utilize the static LeafData helper strategies to ship your values as given sorts. 🔨

The from parameter generally is a LeafSource key, in case you are utilizing a number of template places or file sources then you possibly can render a view utilizing a selected one, ignoring the supply loading order. There’s one other render technique with out the from parameter that’ll use the default search order of sources.

There’s a new argument that you need to use to set predefined choices. You possibly can disable the cache mechanism with the .caching(.bypass) worth or the built-in warning message via .missingVariableThrows(false) if a variable is just not outlined in your template, however you are attempting to make use of it. You possibly can replace the timeout utilizing .timeout(Double) or the encoding by way of .encoding(.utf8) and grant entry to some nasty entities by together with the .grantUnsafeEntityAccess(true) worth plus there’s a embeddedASTRawLimit choice. Extra about this in a while.

Additionally it is attainable to disable Leaf cache globally via the LeafRenderer.Context property:

if !app.setting.isRelease {
    LeafRenderer.Possibility.caching = .bypass
}

If the cache is disabled Leaf will re-parse template information each time you attempt to render one thing. Something that may be configured globally for LeafKit is marked with the @LeafRuntimeGuard property wrapper, you possibly can change any of the settings at software setup time, however they’re locked as quickly as a LeafRenderer is created. 🔒

Context and information illustration

You possibly can conform to the LeafDataRepresentable protocol to submit a customized kind as a context worth. You simply need to implement one leafData property.

struct Consumer {
    let id: UUID?
    let e mail: String
    let birthYear: Int?
    let isAdmin: Bool
}
extension Consumer: LeafDataRepresentable {
    var leafData: LeafData {
        .dictionary([
            "id": .string(id?.uuidString),
            "email": .string(email),
            "birthYear": .int(birthYear),
            "isAdmin": .bool(isAdmin),
            "permissions": .array(["read", "write"]),
            "empty": .nil(.string),
        ])
    }
}

As you possibly can see there are many LeafData helper strategies to symbolize Swift sorts. Each single kind has built-in non-compulsory help, so you possibly can ship nil values with out spending further effort on worth checks or nil coalescing.

app.get() { req -> EventLoopFuture<View> in
    let consumer = Consumer(id: .init(),
                e mail: "[email protected]",
                birthYear: 1980,
                isAdmin: false)

    return req.leaf.render(template: "profile", context: [
        "user": user.leafData,
    ])
}

You possibly can assemble a LeafDataRepresentable object, however you continue to have to make use of the LeafRenderer.Context as a context worth. Thankfully that kind could be expressed utilizing a dictionary the place keys are strings and values are LeafData sorts, so this may cut back the quantity of code that it’s important to kind.

Constants, variables, nil coalescing

Now let’s transfer away a bit of bit from Swift and speak concerning the new options in Leaf. In Leaf Tau you possibly can outline variables utilizing template information with actual dictionary and array help. 🥳

#var(x = 2)
<p>2 + 2 = #(x + 2)</p>
<hr>
#let(consumer = ["name": "Guest"])
<p>Good day #(consumer.identify)</p>
<hr>
#(non-compulsory ?? "fallback")

Similar to in Swift, we will create variables and constants with any of the supported sorts. Once you inline a template variables could be accessed in each templates, that is fairly useful as a result of you do not have to repeat the identical code repeatedly, however you need to use variables and reuse chunks of Leaf code in a clear and environment friendly method. Let me present you the way this works.

Additionally it is attainable to make use of the coalescing operator to offer fallback values for nil variables.

Outline, Consider, Inline

One of many largest debate in Leaf is the entire template hierarchy system. In Tau, your entire strategy is rebuilt below the hood (the entire thing is extra highly effective now), however from the end-user perspective just a few key phrases have modified.

Inline

Lengthen is now changed with the brand new inline block. The inline technique actually places the content material of a template into one other. You possibly can even use uncooked values for those who do not need to carry out different operations (akin to evaluating Leaf variables and tags) on the inlined template.

<!-- index.leaf -->
<!DOCTYPE html>
<html>
    <head>
        <meta charset="utf-8">
        <meta identify="viewport" content material="width=device-width, initial-scale=1">
        <title>Leaf 4</title>
    </head>
    <physique>
        #inline("house", as: uncooked)
    </physique>
</html>

<!-- house.leaf -->
<h1>Good day Leaf Tau!</h1>

As you possibly can see we’re merely placing the content material of the house template into the physique part of the index template.

Now it is extra fascinating once we skip the uncooked half and we inline an everyday template that accommodates different expressions. We’re going to flip issues just a bit bit and render the house template as a substitute of the index.

app.get() { req -> EventLoopFuture<View> in
    req.leaf.render(template: "house", context: [
        "title": "Leaf 4",
        "body": "Hello Leaf Tau!",
    ])
}

So how can I reuse my index template? Ought to I merely print the physique variable and see what occurs? Nicely, we will attempt that…

<!DOCTYPE html>
<html>
    <head>
        <meta charset="utf-8">
        <meta identify="viewport" content material="width=device-width, initial-scale=1">
        <title>#(title)</title>
    </head>
    <physique>
        #(physique)
    </physique>
</html>

<!-- house.leaf -->
<h1>Good day Leaf Tau!</h1>
#inline("index")

Wait a minute… this code is just not going to work. Within the house template first we print the physique variable, then we inline the index template and print its contents. That is not what we wish. I need to use the contents of the house template and place it in between the physique tags. 💪

Consider

Meet consider, a perform that may consider a Leaf definition. You possibly can consider this as a block variable definition in Swift. You possibly can create a variable with a given identify and in a while name that variable (consider) utilizing parentheses after the identify of the variable. Now you are able to do the identical skinny in Leaf through the use of the consider key phrase or instantly calling the block like a perform.

<!DOCTYPE html>
<html>
    <head>
        <meta charset="utf-8">
        <meta identify="viewport" content material="width=device-width, initial-scale=1">
        <title>#(title)</title>
    </head>
    <physique>
        #consider(bodyBlock) (# or you need to use the `#bodyBlock()` syntax #)
    </physique>
</html>

On this template we will consider the bodyBlock and in a while we’ll be capable of outline it some place else.

Outline

Definitions. Lastly arrived to the final element that we’ll have to compose templates. Now we will create our physique block within the house template.

#outline(bodyBlock):
<h1>#(physique)</h1>
#enddefine

#inline("index")

Now for those who reload the browser (Leaf cache have to be disabled) every little thing ought to work as it’s anticipated. Magic… or science, no matter, be at liberty to decide on one. 💫

Particular thanks goes to tdotclare who labored day and evening to make Leaf higher. 🙏

So what is going on on right here? The #outline(bodyBlock) part is answerable for constructing a block variable referred to as bodyBlock that’s callable and we will consider it in a while. We merely print out the physique context variable inside this block, the physique variable is a context variable coming from Swift, that is fairly easy. Subsequent we inline the index template (think about copy-pasting complete content material of the index template into the house template) which can print out the title context variable and evaluates the bodyBlock. The bodyBlock will probably be accessible since we have simply outlined it earlier than our inline assertion. Straightforward peasy. 😝

<!-- var, let -->
#var(x = 10)
#let(foo = "bar")

<!-- outline -->
#outline(resultBlock = x + 1)
#outline(bodyBlock):
    <h2>Good day, world!</h2>
    <p>I am a multi-line block definition</p>
#endblock

<!-- consider -->
#consider(resultBlock)
#bodyBlock()

I am actually glad about these modifications, as a result of Leaf is heading into the proper course, and people individuals who haven’t used the pre-released Leaf 4 variations but these modifications will not trigger that a lot bother. This new strategy follows extra like the unique Leaf 3 conduct.

Goodbye tags. Good day entities!

Nothing is a tag anymore, however they’re separated to the next issues:

Blocks (e.g. #for, #whereas, #if, #elseif, #else)

Capabilities (e.g. #Date, #Timestamp, and so forth.)

Strategies (e.g. .depend(), .isEmpty, and so forth.)

Now you can create your very personal capabilities, strategies and even blocks. 🔥

public struct Good day: LeafFunction, StringReturn, Invariant {
    public static var callSignature: [LeafCallParameter] { [.string] }

    public func consider(_ params: LeafCallValues) -> LeafData {
        guard let identify = params[0].string else {
            return .error("`Good day` have to be referred to as with a string parameter.")
        }
        return .string("Good day (identify)!")
    }
}

public func configure(_ app: Software) throws {

    LeafConfiguration.entities.use(Good day(), asFunction: "Good day")
    
}

Now you need to use this perform in your templates like this:

#Good day("Leaf Tau")

You possibly can occasion overload the identical perform with completely different argument labels

public struct HelloPrefix: LeafFunction, StringReturn, Invariant {

    public static var callSignature: [LeafCallParameter] { [
        .string(labeled: "name"),
        .string(labeled: "prefix", optional: true, defaultValue: "Hello")]
    }

    public func consider(_ params: LeafCallValues) -> LeafData {
        guard let identify = params[0].string else {
            return .error("`Good day` have to be referred to as with a string parameter.")
        }
        let prefix = params[1].string!
        return .string("(prefix) (identify)!")
    }
}

public func configure(_ app: Software) throws {


    LeafConfiguration.entities.use(Good day(), asFunction: "Good day")
    LeafConfiguration.entities.use(HelloPrefix(), asFunction: "Good day")

    
}

This manner you need to use a number of variations of the identical performance.

#Good day("Leaf Tau")
#Good day(identify: "Leaf Tau", prefix: "Hello")

This is one other instance of a customized Leaf technique:

public struct DropLast: LeafNonMutatingMethod, StringReturn, Invariant {
    public static var callSignature: [LeafCallParameter] { [.string] }

    public func consider(_ params: LeafCallValues) -> LeafData {
        .string(String(params[0].string!.dropLast()))
    }
}

public func configure(_ app: Software) throws {

    LeafConfiguration.entities.use(DropLast(), asMethod: "dropLast")
    
}

You possibly can outline your individual Leaf entities (extensions) by way of protocols. You do not have to recollect all of them, as a result of there’s various them, however that is the sample that you need to search for Leaf*[Method|Function|Block] for the return sorts: [type]Return. If you do not know invariant is a perform that produces the identical output for a given enter and it has no negative effects.

You possibly can register these entities as[Function|Method|Block] via the entities property. It is going to take some time till you get aware of them, however fortuitously Leaf 4 comes with fairly an excellent set of built-in entities, hopefully the official documentation will cowl most of them. 😉

public struct Path: LeafUnsafeEntity, LeafFunction, StringReturn {
    public var unsafeObjects: UnsafeObjects? = nil

    public static var callSignature: [LeafCallParameter] { [] }

    public func consider(_ params: LeafCallValues) -> LeafData {
        guard let req = req else { return .error("Wants unsafe entry to Request") }
        return .string(req.url.path)
    }
}


public func configure(_ app: Software) throws {

    LeafConfiguration.entities.use(Path(), asFunction: "Path")

    
}

Oh, I virtually forgot to say that for those who want particular entry to the app or req property it’s important to outline an unsafe entity, which will probably be thought of as a foul observe, however fortuitously now we have one thing else to interchange the necessity for accessing this stuff…

Scopes

If that you must cross particular issues to your Leaf templates it is possible for you to to outline customized scopes.

extension Request {
    var customLeafVars: [String: LeafDataGenerator] {
        [
            "url": .lazy([
                        "isSecure": LeafData.bool(self.url.scheme?.contains("https")),
                        "host": LeafData.string(self.url.host),
                        "port": LeafData.int(self.url.port),
                        "path": LeafData.string(self.url.path),
                        "query": LeafData.string(self.url.query)
                    ]),
        ]
    }
}
extension Software {
    var customLeafVars: [String: LeafDataGenerator] {
        [
            "isDebug": .lazy(LeafData.bool(!self.environment.isRelease && self.environment != .production))
        ]
    }
}

struct ScopeExtensionMiddleware: Middleware {

    func reply(to req: Request, chainingTo subsequent: Responder) -> EventLoopFuture<Response> {
        do {
            attempt req.leaf.context.register(turbines: req.customLeafVars, toScope: "req")
            attempt req.leaf.context.register(turbines: req.software.customLeafVars, toScope: "app")
        }
        catch {
            return req.eventLoop.makeFailedFuture(error)
        }
        return subsequent.reply(to: req)
    }
}

public func configure(_ app: Software) throws {

    app.middleware.use(ScopeExtensionMiddleware())

    
}

Lengthy story quick, you possibly can put LeafData values right into a customized scope, the great factor about this strategy is that they are often lazy, so Leaf will solely compute the corresponding values if when are getting used. The query is, how can we entry the scope? 🤔

<ul>
    <li><b>ctx:</b>: #($context)</li>
    <li><b>self:</b>: #(self)</li>
    <li><b>req:</b>: #($req)</li>
    <li><b>app:</b>: #($app)</li>
</ul>

It’s best to know that self is an alias to $context, and you may entry your individual context variables utilizing the $ signal. You can even construct your individual LeafContextPublisher object that may use to change the scope.

last class VersionInfo: LeafContextPublisher {

    let main: Int
    let minor: Int
    let patch: Int
    let flags: String?

    init(main: Int, minor: Int, patch: Int, flags: String? = nil) {
        self.main = main
        self.minor = minor
        self.patch = patch
        self.flags = flags
    }

    var versionInfo: String {
        let model = "(main).(minor).(patch)"
        if let flags = flags {
            return model + "-" + flags
        }
        return model
    }

    lazy var leafVariables: [String: LeafDataGenerator] = [
        "version": .lazy([
            "major": LeafData.int(self.major),
            "minor": LeafData.int(self.minor),
            "patch": LeafData.int(self.patch),
            "flags": LeafData.string(self.flags),
            "string": LeafData.string(self.versionInfo),
        ])
    ]
}

public func configure(_ app: Software) throws {

    app.views.use(.leaf)

    app.middleware.use(LeafCacheDropperMiddleware())

    app.get(.catchall) { req -> EventLoopFuture<View> in
        var context: LeafRenderer.Context = [
            "title": .string("Leaf 4"),
            "body": .string("Hello Leaf Tau!"),
        ]
        let versionInfo = VersionInfo(main: 1, minor: 0, patch: 0, flags: "rc.1")
        attempt context.register(object: versionInfo, toScope: "api")
        return req.leaf.render(template: "house", context: context)
    }

    

}

What if you wish to lengthen a scope? No drawback, you are able to do that by registering a generator

extension VersionInfo {

    var extendedVariables: [String: LeafDataGenerator] {[
        "isRelease": .lazy(self.major > 0)
    ]}
}



let versionInfo = VersionInfo(main: 1, minor: 0, patch: 0, flags: "rc.1")
attempt context.register(object: versionInfo, toScope: "api")
attempt context.register(turbines: versionInfo.extendedVariables, toScope: "api")
return req.leaf.render(template: "house", context: context)

There’s an app and req scope accessible by default, so you possibly can lengthen these via an extension that may return a [String: LeafDataGenerator] variable.

Abstract

As you possibly can see Leaf improved quite a bit in comparison with the earlier variations. Even within the beta / rc interval of the 4th main model of this async template engine introduced us so many nice stuff.

Hopefully this text will allow you to in the course of the migration course of, and I imagine that it is possible for you to to make the most of most of those built-in functionalities. The model new render and context mechanism offers us extra flexibility with out the necessity of declaring further native constructions, Leaf variables and the redesigned hierarchy system will help us to design much more highly effective reusable templates. By entity and the scope API we will convey Leaf to a totally new stage. 🍃

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What’s new in Leaf 4 (Tau)?