Detect misusage of handlebars

[kirrg001]

Steps to reproduce:

1. Add e.g. {{#if img_url feature_image}} in your post.hbs
2. Navigate to any post

TypeError: [post.hbs] Cannot read property 'includeZero' of undefined
    at Object.<anonymous> (/ghost/node_modules/express-hbs/node_modules/handlebars/dist/cjs/handlebars/helpers/if.js:16:22)

The if helper is an inbuilt helper of Handlebars. People sometimes misuse this helper.
Would be great to detect that in gscan.

• add a warning in our instructions and double check docs
• add detection in gscan

[ErisDS]

As far as I know, the only reason we're seeing this happen is because the output from gscan about changing instances of image tell them to do a straight swap to img_url feature_image.

I've never seen people do this before 1.0 - and all of them were following instructions from gscan.

Therefore, before we add an extra check, I think the first task is to fix the instructions?

[kirrg001]

As far as I know, the only reason we're seeing this happen is because the output from gscan about changing instances of image tell them to do a straight swap to img_url feature_image.

100%.

I'll added subtasks to the issue.

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Another case is if you are using the {{pagination}} helper wrong.
e.g. if the helper is not used within a post context object. Then Ghost would complain and throw pagination data is not an object or is a function error. This error message should be improved. Docs should be improved as well.