Add a docs link to the “Unable to find” warnings

[chasenlehara]

@frank-dspeed commented on Mon Jul 24 2017

Hi, when I write something like:
<h3 class="userCard-userName">{{currentPerson.firstname}} {{currentPerson.lastname}}</h3>
I have a warning in console:
WARN: can-stache/src/expression.js: Unable to find key or helper "currentPerson.imageUrl".
It doesn't break anything, but annoys a bit. Besides currentPerson is in viewModel, what exactly wrong with {{currentPerson}} notation, because I think I have the same warning in other places when show some info on the page.

The Warning could stay as is but we add https://canjs.com/faq#expression-warnings

The content would be something like:
This warning happens sometimes when you do not try to read it (imgUrl) in a stache Template but its set on a property of defineMap as property

Based on this, I think it would be useful if we added docs to canjs.com with common scenarios where this might happen and how to fix it, then include a link to those docs wherever this kind of warning appears.

[chasenlehara]

This search shows all(?) of the “unable to find” warnings: https://github.com/search?q=org%3Acanjs+%22Unable+to+find%22&type=Code

I think helper, key, and partial are the three main types we make warnings for. Here’s a CodePen with some examples: https://codepen.io/chasenlehara/pen/mZbYPN?editors=1011

For each place we generate warnings, I think it’d be helpful to include a link to the docs on what the error means and how it can be fixed. Here are some examples of warnings where we link to the docs: https://github.com/search?o=desc&q=org%3Acanjs+%22https%3A%2F%2Fcanjs.com%22+warn&s=indexed&type=Code

Here are some common issues:

• All three types: misspellings
• Helpers & partials: defined in a separate file that hasn’t been imported
• Keys: not defined on the VM or not defined on an object (e.g. the obj object not having prop defined on it so obj.prop gives a warning)

I’m not sure where these docs should go… some ideas:

1. A “common warnings” section in the main can-stache docs: https://canjs.com/doc/can-stache.html

2. A warnings section in the API pages for {{expression}} and {{> partialName}}.

3. A warnings section in each of the KeyLookup expressions and Helper expressions docs.

4. …?