feat(tags): implement yield tag

src/Tags/YieldTag.js

@@ -0,0 +1,93 @@
+'use strict'
+
+/*
+ * edge
+ *
+ * (c) Harminder Virk <virk@adonisjs.com>
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+*/
+
+const BaseTag = require('./BaseTag')
+
+class YieldTag extends BaseTag {
+  /**
+   * Tag name to be used for registering
+   * the tag
+   *
+   * @method tagName
+   *
+   * @return {String}
+   */
+  get tagName () {
+    return 'yield'
+  }
+
+  /**
+   * Whether or not the tag is block level
+   * tag. Which is yes in this case.
+   *
+   * @method isBlock
+   *
+   * @return {Boolean}
+   */
+  get isBlock () {
+    return true
+  }
+
+  /**
+   * Compiles the yield body
+   *
+   * @method compile
+   *
+   * @param  {Object} parser
+   * @param  {Object} lexer
+   * @param  {Object} buffer
+   * @param  {String} options.body
+   * @param  {Array} options.childs
+   * @param  {Number} options.lineno
+   *
+   * @return {void}
+   */
+  compile (parser, lexer, buffer, { body, childs, lineno }) {
+    const parsedStatement = lexer.parseRaw(body).toStatement()
+
+    /**
+     * If there is no fallback content, just write it
+     */
+    if (!childs.length) {
+      buffer.writeToOutput(`$\{${parsedStatement}}`)
+      return
+    }
+
+    /**
+     * Otherwise wrap the value inside an if clause and
+     * output the fallback content when actual value
+     * does not exists.
+     */
+    buffer.writeLine(`if (${parsedStatement}) {`)
+    buffer.indent()
+    buffer.writeToOutput(`$\{${parsedStatement}}`)
+    buffer.dedent()
+
+    /**
+     * Else statement for fallback content
+     */
+    buffer.writeLine('} else {')
+    buffer.indent()
+    childs.forEach((child) => parser.parseLine(child))
+    buffer.dedent()
+    buffer.writeLine('}')
+  }
+
+  /**
+   * Does not need anything special at runtime
+   *
+   * @method run
+   */
+  run () {
+  }
+}
+
+module.exports = YieldTag

src/Tags/index.js

@@ -17,5 +17,6 @@ module.exports = {
   includeTag: new (require('./IncludeTag'))(),
   componentTag: new (require('./ComponentTag'))(),
   slotTag: new (require('./SlotTag'))(),
-  sectionTag: new (require('./SectionTag'))()
+  sectionTag: new (require('./SectionTag'))(),
+  yieldTag: new (require('./YieldTag'))()
 }

test/unit/tags/yield.spec.js

@@ -0,0 +1,57 @@
+'use strict'
+
+/*
+ * edge
+ *
+ * (c) Harminder Virk <virk@adonisjs.com>
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+*/
+
+const test = require('japa')
+const Template = require('../../../src/Template')
+const dedent = require('dedent-js')
+
+test.group('Tags | Yield ', (group) => {
+  group.before(() => {
+    require('../../../test-helpers/transform-tags')(this, require('../../../src/Tags'))
+  })
+
+  test('compile simple yield statement', (assert) => {
+    const statement = dedent`
+    @!yield(username)
+    `
+    const template = new Template(this.tags)
+    const output = template.compileString(statement)
+    assert.equal(output, dedent`
+    return (function templateFn () {
+      let out = new String()
+      out += \`\${this.context.resolve('username')}\\n\`
+      return out
+    }).bind(this)()
+    `)
+  })
+
+  test('compile simple yield statement with fallback content', (assert) => {
+    const statement = dedent`
+    @yield(username)
+      <h2> Hello anonymous </h2>
+    @endyield
+    `
+    const template = new Template(this.tags)
+    const output = template.compileString(statement)
+
+    assert.equal(output, dedent`
+    return (function templateFn () {
+      let out = new String()
+      if (this.context.resolve('username')) {
+        out += \`\${this.context.resolve('username')}\\n\`
+      } else {
+        out += \`  <h2> Hello anonymous </h2>\\n\`
+      }
+      return out
+    }).bind(this)()
+    `)
+  })
+})