Implement a new View Engine for the Jet template parser as requested at: https://github.com/kataras/iris/issues/1281

Former-commit-id: 3e00bdfbf1f3998a1744c390c12fd70430ac0320

_examples/view/template_jet_0/README.md

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+# Jet Engine Example
+
+This example is a fork of <https://github.com/CloudyKit/jet/tree/master/examples/todos> to work with Iris, so you can
+notice the differences side by side.
+
+Read more at: https://github.com/kataras/iris/issues/1281
+
+> The Iris Jet View Engine fixes some bugs that the underline [jet template parser](https://github.com/CloudyKit/jet) currently has.
+
+
+Continue by learning how you can [serve embedded templates](../template_jet_1_embedded).

_examples/view/template_jet_0/main.go

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+// Package main shows how to use jet template parser with ease using the Iris built-in Jet view engine.
+// This example is customized fork of https://github.com/CloudyKit/jet/tree/master/examples/todos, so you can
+// notice the differences side by side.
+package main
+
+import (
+	"bytes"
+	"encoding/base64"
+	"fmt"
+	"os"
+	"reflect"
+	"strings"
+
+	"github.com/kataras/iris"
+	"github.com/kataras/iris/view"
+)
+
+type tTODO struct {
+	Text string
+	Done bool
+}
+
+type doneTODOs struct {
+	list map[string]*tTODO
+	keys []string
+	len  int
+	i    int
+}
+
+func (dt *doneTODOs) New(todos map[string]*tTODO) *doneTODOs {
+	dt.len = len(todos)
+	for k := range todos {
+		dt.keys = append(dt.keys, k)
+	}
+	dt.list = todos
+	return dt
+}
+
+// Range satisfies the jet.Ranger interface and only returns TODOs that are done,
+// even when the list contains TODOs that are not done.
+func (dt *doneTODOs) Range() (reflect.Value, reflect.Value, bool) {
+	for dt.i < dt.len {
+		key := dt.keys[dt.i]
+		dt.i++
+		if dt.list[key].Done {
+			return reflect.ValueOf(key), reflect.ValueOf(dt.list[key]), false
+		}
+	}
+	return reflect.Value{}, reflect.Value{}, true
+}
+
+func (dt *doneTODOs) Render(r *view.JetRuntime) {
+	r.Write([]byte(fmt.Sprintf("custom renderer")))
+}
+
+// Render implements jet.Renderer interface
+func (t *tTODO) Render(r *view.JetRuntime) {
+	done := "yes"
+	if !t.Done {
+		done = "no"
+	}
+	r.Write([]byte(fmt.Sprintf("TODO: %s (done: %s)", t.Text, done)))
+}
+
+func main() {
+	//
+	// Type aliases:
+	// view.JetRuntimeVars = jet.VarMap
+	// view.JetRuntime = jet.Runtime
+	// view.JetArguments = jet.Arguments
+	//
+	// Iris also gives you the ability to put runtime variables
+	// from middlewares as well, by:
+	// view.AddJetRuntimeVars(ctx, vars)
+	// or tmpl.AddRuntimeVars(ctx, vars)
+	//
+	// The Iris Jet fixes the issue when custom jet.Ranger and custom jet.Renderer are not actually work at all,
+	// hope that this is a temp issue on the jet parser itself and authors will fix it soon
+	// so we can remove the "hacks" we've putted for those to work as expected.
+
+	app := iris.New()
+	tmpl := iris.Jet("./views", ".jet") // <--
+	tmpl.Reload(true)                   // remove in production.
+	tmpl.AddFunc("base64", func(a view.JetArguments) reflect.Value {
+		a.RequireNumOfArguments("base64", 1, 1)
+
+		buffer := bytes.NewBuffer(nil)
+		fmt.Fprint(buffer, a.Get(0))
+
+		return reflect.ValueOf(base64.URLEncoding.EncodeToString(buffer.Bytes()))
+	})
+	app.RegisterView(tmpl) // <--
+
+	var todos = map[string]*tTODO{
+		"example-todo-1": {Text: "Add an show todo page to the example project", Done: true},
+		"example-todo-2": {Text: "Add an add todo page to the example project"},
+		"example-todo-3": {Text: "Add an update todo page to the example project"},
+		"example-todo-4": {Text: "Add an delete todo page to the example project", Done: true},
+	}
+
+	app.Get("/", func(ctx iris.Context) {
+		ctx.View("todos/index.jet", todos) // <--
+		// Note that the `ctx.View` already logs the error if logger level is allowing it and returns the error.
+	})
+
+	app.Get("/todo", func(ctx iris.Context) {
+		id := ctx.URLParam("id")
+		todo, ok := todos[id]
+		if !ok {
+			ctx.Redirect("/")
+			return
+		}
+
+		ctx.View("todos/show.jet", todo)
+	})
+	app.Get("/all-done", func(ctx iris.Context) {
+		vars := make(view.JetRuntimeVars) // <-- or keep use the jet.VarMap, decision up to you, it refers to the same type.
+		vars.Set("showingAllDone", true)
+		view.AddJetRuntimeVars(ctx, vars) // <--
+		ctx.View("todos/index.jet", (&doneTODOs{}).New(todos))
+	})
+
+	port := os.Getenv("PORT")
+	if len(port) == 0 {
+		port = ":8080"
+	} else if !strings.HasPrefix(":", port) {
+		port = ":" + port
+	}
+
+	app.Run(iris.Addr(port))
+}

_examples/view/template_jet_0/views/layouts/application.jet

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+<!DOCTYPE html>
+<html lang="en">
+  <head>
+    <meta charset="UTF-8">
+    <title>{{ isset(title) ? title : "" }}</title>
+  </head>
+  <body>
+    {{block documentBody()}}{{end}}
+  </body>
+</html>

_examples/view/template_jet_0/views/todos/index.jet

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+{{extends "layouts/application.jet"}}
+
+{{block button(label, href="javascript:void(0)")}}
+  <a href="{{ href }}">{{ label }}</a>
+{{end}}
+
+{{block ul()}}
+  <ul>
+    {{yield content}}
+  </ul>
+{{end}}
+
+{{block documentBody()}}
+  <h1>List of TODOs</h1>
+
+  {{if isset(showingAllDone) && showingAllDone}}
+    <p>Showing only TODOs that are done</p>
+  {{else}}
+    <p><a href="/all-done">Show only TODOs that are done</a></p>
+  {{end}}
+
+  {{yield ul() content}}
+    {{range id, value := .}}
+      <li {{if value.Done}}style="color:red;text-decoration: line-through;"{{end}}>
+        <a href="/todo?id={{ id }}">{{ value.Text }}</a>
+        {{yield button(label="UP", href="/update/?id="+base64(id))}} - {{yield button(href="/delete/?id="+id, label="DL")}}
+      </li>
+    {{end}}
+  {{end}}
+{{end}}

_examples/view/template_jet_0/views/todos/show.jet

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+{{extends "layouts/application.jet"}}
+
+{{block documentBody()}}
+  <h1>Show TODO</h1>
+  <p>This uses a custom renderer by implementing the jet.Renderer interface.
+  <p>
+    {{.}}
+  </p>
+{{end}}