Updated default visibility in foreach for posts to all

closes https://github.com/TryGhost/Team/issues/485

In order to loop over all posts, we currently need to pass a visibility="all" flag to a foreach as default for all items in current `visibility` helper is set to `public`. For a post, this behaviour is unintuitive, and inconsistent with the API. Instead, the default visibility should be "all" for the posts. The update allows themes to get all posts directly without passing in visibility -

```
{{#get "posts"}}
    {{#foreach posts}}
        //Loops over all posts, not just `public`
    {{/foreach}}
{{/get}}
```

core/frontend/helpers/foreach.js

@@ -3,7 +3,7 @@
 //
 // Block helper designed for looping through posts
 const _ = require('lodash');
-const {logging, i18n, hbs} = require('../services/proxy');
+const {logging, i18n, hbs, checks} = require('../services/proxy');
 const {Utils: hbsUtils, handlebars: {createFrame}} = hbs;
 const ghostHelperUtils = require('@tryghost/helpers').utils;
 
@@ -15,9 +15,16 @@ module.exports = function foreach(items, options) {
     if (hbsUtils.isFunction(items)) {
         items = items.call(this);
     }
-
+    let visibility = options.hash.visibility;
+    if (_.isArray(items) && items.length > 0 && checks.isPost(items[0])) {
+        visibility = visibility || 'all';
+    } else if (_.isObject(items) && _.isArray(Object.values(items))) {
+        if (Object.values(items).length > 0 && checks.isPost(Object.values(items)[0])) {
+            visibility = visibility || 'all';
+        }
+    }
     // Exclude items which should not be visible in the theme
-    items = ghostHelperUtils.visibility.filter(items, options.hash.visibility);
+    items = ghostHelperUtils.visibility.filter(items, visibility);
 
     // Initial values set based on parameters sent through. If nothing sent, set to defaults
     const {fn, inverse, hash, data, ids} = options;

test/unit/helpers/foreach_spec.js

@@ -260,12 +260,28 @@ describe('{{#foreach}} helper', function () {
             }
         };
 
+        const objectHashWithVis = {
+            posts: {
+                first: {title: 'first', visibility: 'members', slug: 'first', html: ''},
+                second: {title: 'second'},
+                third: {title: 'third'},
+                fourth: {title: 'fourth'},
+                fifth: {title: 'fifth'}
+            }
+        };
+
         const arrayHash = {
             posts: [
                 {title: 'first'}, {title: 'second'}, {title: 'third'}, {title: 'fourth'}, {title: 'fifth'}
             ]
         };
 
+        const arrayHashWithVis = {
+            posts: [
+                {title: 'first', visibility: 'members', slug: 'first', html: ''}, {title: 'second'}, {title: 'third'}, {title: 'fourth'}, {title: 'fifth'}
+            ]
+        };
+
         const arrayHash2 = {goodbyes: [{text: 'goodbye'}, {text: 'Goodbye'}, {text: 'GOODBYE'}], world: 'world'};
 
         const objectHash2 = {
@@ -386,6 +402,13 @@ describe('{{#foreach}} helper', function () {
             shouldCompileToExpected(templateString, objectHash, expected);
         });
 
+        it('foreach with limit 3 and post with members visibility', function () {
+            const templateString = '<ul>{{#foreach posts limit="3"}}<li>{{title}}</li>{{else}}not this{{/foreach}}</ul>';
+            const expected = '<ul><li>first</li><li>second</li><li>third</li></ul>';
+            shouldCompileToExpected(templateString, arrayHashWithVis, expected);
+            shouldCompileToExpected(templateString, objectHashWithVis, expected);
+        });
+
         it('foreach with from 2', function () {
             const templateString = '<ul>{{#foreach posts from="2"}}<li>{{title}}</li>{{else}}not this{{/foreach}}</ul>';
             const expected = '<ul><li>second</li><li>third</li><li>fourth</li><li>fifth</li></ul>';