All the things 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 might like to indicate you is that we have now a brand new render technique. Up 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:"Whats up Leaf Tau!")
return req.view.render("index", context)
}
}
We will use an Encodable object and cross it round as a context variable. It is a handy approach of offering values for our Leaf variables. Earlier than we proceed I’ve to let you know that each one of it will 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 may say at first sight. Nicely, the factor is that this new technique supplies type-safe values for our templates and that is simply the tip of the iceberg. You must 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)])
}
}
In case you take a better have a look at this comparable instance, you discover out that the context object and the values are representable by varied sorts, but when we attempt to use an interpolated string, we have now to be just a little bit extra sort 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 function is available in Tau. You should utilize the static LeafData helper strategies to ship your values as given sorts. 🔨
The from parameter could be a LeafSource key, in case you are utilizing a number of template places or file sources then you may render a view utilizing a particular one, ignoring the supply loading order. There may be 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 should utilize to set predefined choices. You possibly can disable the cache mechanism with the .caching(.bypass) worth or the built-in warning message by means of .missingVariableThrows(false) if a variable just isn’t 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 through .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 afterward.
It is usually potential to disable Leaf cache globally by means of the LeafRenderer.Context property:
if !app.setting.isRelease {
LeafRenderer.Choice.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 may change any of the settings at utility setup time, however they’re locked as quickly as a LeafRenderer is created. 🔒
Context and knowledge illustration
You possibly can conform to the LeafDataRepresentable protocol to submit a customized sort as a context worth. You simply need to implement one leafData property.
struct Person {
let id: UUID?
let e mail: String
let birthYear: Int?
let isAdmin: Bool
}
extension Person: 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 may see there are many LeafData helper strategies to characterize Swift sorts. Each single sort has built-in non-obligatory assist, so you may ship nil values with out spending extra effort on worth checks or nil coalescing.
app.get() { req -> EventLoopFuture<View> in
let consumer = Person(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. Luckily that sort may be expressed utilizing a dictionary the place keys are strings and values are LeafData sorts, so it will scale back the quantity of code that it’s a must to sort.
Constants, variables, nil coalescing
Now let’s transfer away just a little bit from Swift and speak concerning the new options in Leaf. In Leaf Tau you may outline variables utilizing template information with actual dictionary and array assist. 🥳
#var(x = 2)
<p>2 + 2 = #(x + 2)</p>
<hr>
#let(consumer = ["name": "Guest"])
<p>Whats up #(consumer.identify)</p>
<hr>
#(non-obligatory ?? "fallback")
Identical to in Swift, we will create variables and constants with any of the supported sorts. Whenever you inline a template variables may be accessed in each templates, that is fairly helpful as a result of you do not have to repeat the identical code time and again, however you should utilize variables and reuse chunks of Leaf code in a clear and environment friendly approach. Let me present you the way this works.
It is usually potential to make use of the coalescing operator to supply fallback values for nil variables.
Outline, Consider, Inline
One of many greatest debate in Leaf is the entire template hierarchy system. In Tau, your complete method is rebuilt below the hood (the entire thing is extra highly effective now), however from the end-user perspective only some key phrases have modified.
Inline
Prolong 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 wish to carry out different operations (comparable 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("residence", as: uncooked)
</physique>
</html>
<!-- residence.leaf -->
<h1>Whats up Leaf Tau!</h1>
As you may see we’re merely placing the content material of the house template into the physique part of the index template.
Now it is extra attention-grabbing once we skip the uncooked half and we inline an everyday template that incorporates 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: "residence", 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 strive 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>
<!-- residence.leaf -->
<h1>Whats up Leaf Tau!</h1>
#inline("index")
Wait a minute… this code just isn’t going to work. Within the residence template first we print the physique variable, then we inline the index template and print its contents. That is not what we would like. I wish 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 afterward 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 straight 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 should utilize the `#bodyBlock()` syntax #)
</physique>
</html>
On this template we will consider the bodyBlock and afterward we’ll be capable to 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 residence 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 accountable for constructing a block variable referred to as bodyBlock that’s callable and we will consider it afterward. 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 total content material of the index template into the house template) which is able to print out the title context variable and evaluates the bodyBlock. The bodyBlock might be obtainable 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>Whats up, world!</h2>
<p>I am a multi-line block definition</p>
#endblock
<!-- consider -->
#consider(resultBlock)
#bodyBlock()
I am actually comfortable about these adjustments, as a result of Leaf is heading into the best route, and people individuals who haven’t used the pre-released Leaf 4 variations but these adjustments will not trigger that a lot hassle. This new method follows extra like the unique Leaf 3 habits.
Goodbye tags. Whats up entities!
Nothing is a tag anymore, however they’re separated to the next issues:
- Blocks (e.g. #for, #whereas, #if, #elseif, #else)
- Features (e.g. #Date, #Timestamp, and many others.)
- Strategies (e.g. .depend(), .isEmpty, and many others.)
Now you can create your very personal features, strategies and even blocks. 🔥
public struct Whats up: LeafFunction, StringReturn, Invariant {
public static var callSignature: [LeafCallParameter] { [.string] }
public func consider(_ params: LeafCallValues) -> LeafData {
guard let identify = params[0].string else {
return .error("`Whats up` have to be referred to as with a string parameter.")
}
return .string("Whats up (identify)!")
}
}
public func configure(_ app: Software) throws {
LeafConfiguration.entities.use(Whats up(), asFunction: "Whats up")
}
Now you should utilize this perform in your templates like this:
#Whats up("Leaf Tau")
You possibly can occasion overload the identical perform with totally 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("`Whats up` 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(Whats up(), asFunction: "Whats up")
LeafConfiguration.entities.use(HelloPrefix(), asFunction: "Whats up")
}
This manner you should utilize a number of variations of the identical performance.
#Whats up("Leaf Tau")
#Whats up(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 personal Leaf entities (extensions) through protocols. You do not have to recollect all of them, as a result of there may be 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 unintended effects.
You possibly can register these entities as[Function|Method|Block] by means of the entities property. It should take some time till you get conversant in them, however thankfully Leaf 4 comes with fairly a superb 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 nearly forgot to say that for those who want particular entry to the app or req property it’s a must to outline an unsafe entity, which might be thought of as a foul follow, however thankfully we have now one thing else to exchange the necessity for accessing these items…
Scopes
If you should 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 {
strive req.leaf.context.register(mills: req.customLeafVars, toScope: "req")
strive req.leaf.context.register(mills: req.utility.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 brief, you may put LeafData values right into a customized scope, the good factor about this method is that they are often lazy, so Leaf will solely compute the corresponding values if when are getting used. The query is, how will 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>
You must know that self is an alias to $context, and you’ll entry your personal context variables utilizing the $ signal. You may also construct your personal LeafContextPublisher object that may use to change the scope.
ultimate 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")
strive context.register(object: versionInfo, toScope: "api")
return req.leaf.render(template: "residence", context: context)
}
}
What if you wish to lengthen a scope? No downside, 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")
strive context.register(object: versionInfo, toScope: "api")
strive context.register(mills: versionInfo.extendedVariables, toScope: "api")
return req.leaf.render(template: "residence", context: context)
There may be an app and req scope obtainable by default, so you may lengthen these by means of an extension that may return a [String: LeafDataGenerator] variable.
Abstract
As you may 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 assist you throughout the migration course of, and I consider 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 extra native constructions, Leaf variables and the redesigned hierarchy system will assist us to design much more highly effective reusable templates. By means of entity and the scope API we will deliver Leaf to a very new stage. 🍃
