Groupidentity not validated, improve documentation about requiredness of template.json fields

[jannikbuschke]

Using the same groupIdentity in two different templates, but not providing any tags, its possible to pack a nuget template and publish it. I.e. there are no warnings or errors shown.
However when trying to create one of theses templates, via dotnet new the following error is shown:
Couldn't find an installed template that matches the input, searching online for one that does...
(no user input is triggered).

Steps to reproduce

Create two templates with same groupIdentity but no tags.

Possible solutions

Improve the documentation https://github.com/dotnet/templating/wiki/Reference-for-template.json. It is unclear that groupIdentity and tags should be used together (I also just assume this by my observations). It is also unclear if groupIdentity is a required property or not. This is also true for all other properties. Ideally there should be a column, that states for each property the requiredness.

Also when creating the template and some point the should happen some validation. I.e. when running nuget pack or nuget push

[vlada-shubina]

Using groupIdentity is still poorly documented. It's worth to create a separate article explaining:

• groupIdentity concept and its uniqueness
• precedence and identity withing the template group
• how to use groupIdentity to create the template group for templates in different languages
• how to use groupIdentity to create the template group for templates with different choice parameters values (as 1st party templates do for framework)

[seangwright]

I recently used groupIdentity and tags.language to expose 2 completely different templates under the same shortName by letting consumers of the template specify the -lang option when using the template.

I don't know if this is the intended use, but it would be great to have this area of templating documented.