Error reporting: investigate the possibility of reporting where error ocurred in the template in dev mode

[sdegueldre]

Eg, for an invalid loop expression, give line and column number of the t-foreach in the original xml, possibly with a short snippet of the offending code

Error while rendering template:
<div t-name="Greeter" class="greeter" t-on-click="toggle">
    <div t-foreach="test" t-key="2"/>
--------------------^ invalid loop expression at in template Greeter:2:20
</div>