[FEATURE] if helper inline form

FEATURES.md

@@ -86,3 +86,11 @@ for a detailed explanation.
 
   Enables HTMLBars compiler to interpret `<x-foo></x-foo>` as a component
   invocation (instead of a standard HTML5 style element).
+
+* `ember-htmlbars-inline-if-helper`
+
+  Enables the use of the if helper in inline form. The truthy 
+  and falsy values are passed as params, instead of using the block form.
+
+  Added in [#9718](https://github.com/emberjs/ember.js/pull/9718).
+

features.json

@@ -18,7 +18,8 @@
     "ember-testing-pause-test": true,
     "ember-htmlbars": null,
     "ember-htmlbars-block-params": null,
-    "ember-htmlbars-component-generation": null
+    "ember-htmlbars-component-generation": null,
+    "ember-htmlbars-inline-if-helper": null
   },
   "debugStatements": [
     "Ember.warn",

packages/ember-htmlbars/lib/helpers/if_unless.js

@@ -8,6 +8,7 @@ import { bind } from "ember-htmlbars/helpers/binding";
 
 import { get } from "ember-metal/property_get";
 import { isArray } from "ember-metal/utils";
+import ConditionalStream from "ember-views/streams/conditional_stream";
 
 function shouldDisplayIfHelperContent(result) {
   var truthy = result && get(result, 'isTruthy');
@@ -89,13 +90,21 @@ function unboundIfHelper(params, hash, options, env) {
   @return {String} HTML string
 */
 function ifHelper(params, hash, options, env) {
-  Ember.assert("You must pass exactly one argument to the if helper", params.length === 1);
-  Ember.assert("You must pass a block to the if helper", !!options.render);
-
-  options.helperName = options.helperName || ('if ');
+  Ember.assert("If helper in block form expect exactly one argument", !options.render || params.length === 1);
+  if (Ember.FEATURES.isEnabled('ember-htmlbars-inline-if-helper')) {
+    if (!options.render) {
+      Ember.assert("If helper in inline form expects between two and three arguments", params.length === 2 || params.length === 3);
+      var condition = params[0];
+      var truthy = params[1];
+      var falsy = params[2];
+      return new ConditionalStream(condition, truthy, falsy);
+    }
+  }
 
   options.inverse = options.inverse || function(){ return ''; };
 
+  options.helperName = options.helperName || ('if ');
+
   if (env.data.isUnbound) {
     return env.helpers.unboundIf.helperFunction.call(this, params, hash, options, env);
   } else {

packages/ember-htmlbars/tests/helpers/if_unless_test.js

@@ -665,3 +665,174 @@ test('edge case: rerender appearance of inner virtual view', function() {
 
   equal(Ember.$('#qunit-fixture').text(), 'test');
 });
+
+if (Ember.FEATURES.isEnabled('ember-htmlbars-inline-if-helper')) {
+  test("`if` helper with inline form: renders the second argument when conditional is truthy", function() {
+    view = EmberView.create({
+      conditional: true,
+      template: compile('{{if view.conditional "truthy" "falsy"}}')
+    });
+
+    appendView(view);
+
+    equal(view.$().text(), 'truthy');
+  });
+
+  test("`if` helper with inline form: renders the third argument when conditional is falsy", function() {
+    view = EmberView.create({
+      conditional: false,
+      template: compile('{{if view.conditional "truthy" "falsy"}}')
+    });
+
+    appendView(view);
+
+    equal(view.$().text(), 'falsy');
+  });
+
+  test("`if` helper with inline form: can omit the falsy argument", function() {
+    view = EmberView.create({
+      conditional: true,
+      template: compile('{{if view.conditional "truthy"}}')
+    });
+
+    appendView(view);
+
+    equal(view.$().text(), 'truthy');
+  });
+
+  test("`if` helper with inline form: can omit the falsy argument and renders nothing when conditional is falsy", function() {
+    view = EmberView.create({
+      conditional: false,
+      template: compile('{{if view.conditional "truthy"}}')
+    });
+
+    appendView(view);
+
+    equal(view.$().text(), '');
+  });
+
+  test("`if` helper with inline form: truthy and falsy arguments are changed if conditional changes", function() {
+    view = EmberView.create({
+      conditional: true,
+      template: compile('{{if view.conditional "truthy" "falsy"}}')
+    });
+
+    appendView(view);
+
+    equal(view.$().text(), 'truthy');
+
+    run(function() {
+      view.set('conditional', false);
+    });
+
+    equal(view.$().text(), 'falsy');
+  });
+
+  test("`if` helper with inline form: can use truthy param as binding", function() {
+    view = EmberView.create({
+      truthy: 'ok',
+      conditional: true,
+      template: compile('{{if view.conditional view.truthy}}')
+    });
+
+    appendView(view);
+
+    equal(view.$().text(), 'ok');
+
+    run(function() {
+      view.set('truthy', 'yes');
+    });
+
+    equal(view.$().text(), 'yes');
+  });
+
+  test("`if` helper with inline form: can use falsy param as binding", function() {
+    view = EmberView.create({
+      truthy: 'ok',
+      falsy: 'boom',
+      conditional: false,
+      template: compile('{{if view.conditional view.truthy view.falsy}}')
+    });
+
+    appendView(view);
+
+    equal(view.$().text(), 'boom');
+
+    run(function() {
+      view.set('falsy', 'no');
+    });
+
+    equal(view.$().text(), 'no');
+  });
+
+  test("`if` helper with inline form: raises when using more than three arguments", function() {
+    view = EmberView.create({
+      conditional: true,
+      template: compile('{{if one two three four}}')
+    });
+
+    expectAssertion(function() {
+      appendView(view);
+    }, 'If helper in inline form expects between two and three arguments');
+  });
+
+  test("`if` helper with inline form: raises when using less than two arguments", function() {
+    view = EmberView.create({
+      conditional: true,
+      template: compile('{{if one}}')
+    });
+
+    expectAssertion(function() {
+      appendView(view);
+    }, 'If helper in inline form expects between two and three arguments');
+  });
+
+  test("`if` helper with inline form: works when used in a sub expression", function() {
+    view = EmberView.create({
+      conditional: true,
+      innerConditional: true,
+      template: compile('{{if view.conditional (if view.innerConditional "truthy" )}}')
+    });
+
+    appendView(view);
+
+    equal(view.$().text(), 'truthy');
+  });
+
+  test("`if` helper with inline form: updates if condition changes in a sub expression", function() {
+    view = EmberView.create({
+      conditional: true,
+      innerConditional: true,
+      template: compile('{{if view.conditional (if view.innerConditional "innerTruthy" "innerFalsy")}}')
+    });
+
+    appendView(view);
+
+    equal(view.$().text(), 'innerTruthy');
+
+    run(function() {
+      view.set('innerConditional', false);
+    });
+
+    equal(view.$().text(), 'innerFalsy');
+  });
+
+  test("`if` helper with inline form: can use truthy param as binding in a sub expression", function() {
+    view = EmberView.create({
+      conditional: true,
+      innerConditional: true,
+      innerTruthy: "innerTruthy",
+      template: compile('{{if view.conditional (if view.innerConditional view.innerTruthy)}}')
+    });
+
+    appendView(view);
+
+    equal(view.$().text(), 'innerTruthy');
+
+    run(function() {
+      view.set('innerTruthy', 'innerOk');
+    });
+
+    equal(view.$().text(), 'innerOk');
+  });
+}

packages/ember-views/lib/streams/conditional_stream.js

@@ -0,0 +1,52 @@
+import Stream from "ember-metal/streams/stream";
+import { read } from "ember-metal/streams/read";
+import { create as o_create } from "ember-metal/platform";
+
+function ConditionalStream(test, consequent, alternate) {
+  this._super(conditionalValueFn);
+  this.oldTest = undefined;
+  this.test = test;
+  this.consequent = consequent;
+  this.alternate = alternate;
+
+  if (test && test.isStream) {
+    test.subscribe(this.notify, this);
+  }
+}
+
+ConditionalStream.prototype = o_create(Stream.prototype);
+ConditionalStream.prototype._super = Stream;
+
+ConditionalStream.prototype._unsubscribe = function(value) {
+  if (value && value.isStream) {
+    value.unsubscribe(this.notify, this);
+  }
+};
+
+ConditionalStream.prototype._subscribe = function(value) {
+  if (value && value.isStream) {
+    value.subscribe(this.notify, this);
+  }
+};
+
+function conditionalValueFn() {
+  var test = !!read(this.test);
+
+  if (test !== this.oldTest) {
+    if (this.oldTest) {
+      this._unsubscribe(this.consequent);
+    } else {
+      this._unsubscribe(this.alternate);
+    }
+    if (test) {
+      this._subscribe(this.consequent);
+    } else {
+      this._subscribe(this.alternate);
+    }
+    this.oldTest = test;
+  }
+
+  return test ? read(this.consequent) : read(this.alternate);
+}
+
+export default ConditionalStream;