Expose {{concat}} helper publicly.

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

@@ -1,7 +1,18 @@
-/** @private
-  This private helper is used by the legacy class bindings AST transformer
-  to concatenate class names together.
+/**
+  Concatenates input params together.
+
+  Example:
+
+  ```handlebars
+  {{some-component name=(concat firstName " " lastName)}}
+
+  {{! would pass name="<first name value> <last name value>" to the component}}
+  ```
+
+  @public
+  @method concat
+  @for Ember.HTMLBars
 */
-export default function concat(params, hash) {
-  return params.join(hash.separator);
+export default function concat(params) {
+  return params.join('');
 }

packages/ember-htmlbars/lib/main.js

@@ -51,7 +51,7 @@ if (Ember.FEATURES.isEnabled('ember-htmlbars-each-in')) {
 }
 registerHelper('-bind-attr-class', bindAttrClassHelper);
 registerHelper('-normalize-class', normalizeClassHelper);
-registerHelper('-concat', concatHelper);
+registerHelper('concat', concatHelper);
 registerHelper('-join-classes', joinClassesHelper);
 registerHelper('-legacy-each-with-controller', legacyEachWithControllerHelper);
 registerHelper('-legacy-each-with-keyword', legacyEachWithKeywordHelper);

packages/ember-htmlbars/tests/helpers/concat-test.js

@@ -0,0 +1,87 @@
+import run from "ember-metal/run_loop";
+import { Registry } from "ember-runtime/system/container";
+import Component from "ember-views/views/component";
+import compile from "ember-template-compiler/system/compile";
+
+import { runAppend, runDestroy } from "ember-runtime/tests/utils";
+
+var component, registry, container;
+
+QUnit.module("ember-htmlbars: {{concat}} helper", {
+  setup() {
+    registry = new Registry();
+    container = registry.container();
+    registry.optionsForType('helper', { instantiate: false });
+  },
+
+  teardown() {
+    runDestroy(container);
+    runDestroy(component);
+  }
+});
+
+QUnit.test('concats provided params', function() {
+  component = Component.create({
+    container,
+
+    template: compile(`{{concat "foo" " " "bar" " " "baz"}}`)
+  });
+
+  runAppend(component);
+
+  equal(component.$().text(), 'foo bar baz');
+});
+
+QUnit.test('updates for bound params', function() {
+  component = Component.create({
+    container,
+
+    firstParam: 'one',
+    secondParam: 'two',
+
+    template: compile(`{{concat firstParam secondParam}}`)
+  });
+
+  runAppend(component);
+
+  equal(component.$().text(), 'onetwo');
+
+  run(function() {
+    component.set('firstParam', 'three');
+  });
+
+  equal(component.$().text(), 'threetwo');
+
+  run(function() {
+    component.set('secondParam', 'four');
+  });
+
+  equal(component.$().text(), 'threefour');
+});
+
+QUnit.test('can be used as a sub-expression', function() {
+  function eq([ actual, expected ]) {
+    return actual === expected;
+  }
+  eq.isHTMLBars = true;
+  registry.register('helper:x-eq', eq);
+
+  component = Component.create({
+    container,
+
+    firstParam: 'one',
+    secondParam: 'two',
+
+    template: compile(`{{#if (x-eq (concat firstParam secondParam) "onetwo")}}Truthy!{{else}}False{{/if}}`)
+  });
+
+  runAppend(component);
+
+  equal(component.$().text(), 'Truthy!');
+
+  run(function() {
+    component.set('firstParam', 'three');
+  });
+
+  equal(component.$().text(), 'False');
+});

packages/ember-template-compiler/lib/plugins/transform-old-class-binding-syntax.js

@@ -31,6 +31,7 @@ TransformOldClassBindingSyntax.prototype.transform = function TransformOldClassB
 
     if (classPair) {
       classValue.push(classPair.value);
+      classValue.push(b.string(' '));
     } else {
       classPair = b.pair('class', null);
       node.hash.pairs.push(classPair);
@@ -54,8 +55,8 @@ TransformOldClassBindingSyntax.prototype.transform = function TransformOldClassB
       }
     });
 
-    let hash = b.hash([b.pair('separator', b.string(' '))]);
-    classPair.value = b.sexpr(b.string('-concat'), classValue, hash);
+    let hash = b.hash();
+    classPair.value = b.sexpr(b.string('concat'), classValue, hash);
   });
 
   return ast;
@@ -97,6 +98,7 @@ function buildSexprs(microsyntax, sexprs, b) {
     }
 
     sexprs.push(sexpr);
+    sexprs.push(b.string(' '));
   }
 }
 

packages/ember-views/lib/system/build-component-template.js

@@ -180,7 +180,7 @@ function normalizeComponentAttributes(component, isAngleBracket, attrs) {
     var existingStyle = normalized.style;
 
     if (existingStyle) {
-      normalized.style = ['subexpr', '-concat', [existingStyle, hiddenStyle], ['separator', ' ']];
+      normalized.style = ['subexpr', 'concat', [existingStyle, ' ', hiddenStyle], [ ]];
     } else {
       normalized.style = hiddenStyle;
     }