Fix: Ensure filetype is set for Go templates

[PaulDugdale]

*.tmpl is already detected and a filetype is already set here:
https://github.com/vim/vim/blob/e0e3917554327f2524066f89fbbef9c83c1535da/runtime/filetype.vim#L744

Using setfiletype prevents this from being overridden, and the filetype is left as "template" and not set to "gohtmltmpl" as intended.

[bhcleek]

I'm not sure we should override what Vim is doing with the filetype. 🤔

[PaulDugdale]

Thanks! Here's some more info...

With the vim-go plugin installed, I expect the syntax and indentation to work correctly on Go text/html template files.
This isn't the case, the standard Vim html syntax/indentation will be used.

The problem is that there is already a template filetype in vim, that is a simple wrapper around the html filetype.

Because of this, and the fact thatsetfiletype is used, the gotexttmpl and gohtmltmpl filetypes will never be used unless they are forced in your .vimrc

This used to work until this change

[bhcleek]

My concern is that there may be a lot of people that do edit html template files and that use .tmpl as an extension for those files. Since vim-go sets the template filetype based on a wildcard pattern (as opposed to a specific file name like go.sum uses), I'm reluctant to unconditionally override.

I think I'd prefer a solution that changes vim-go to use setfiletype with a different extension (e.g. *.go.tmpl, *.gotmpl, etc.) or that users that really want this put the au BufRead,BufNewFile *.tmpl set filetype gohtmltmpl in their own vimrc file.

[PaulDugdale]

I understand the concerns, but I respectfully disagree...

The .tmpl has been given "official" blessing in both the Golang examples, and the Golang team maintained VSCode extension, so I think it's better to use .tmpl than an alternate extension.
I also think that leaving it in it's current state will break syntax/indentation for more users than changing it would. It's a very common extension inside of Go, and a very unusual one outside of it.

[bhcleek]

Since the default filetype for .tmpl files is template and since it seems to be a subset of what vim-go uses for the the .tmpl, this change is appears to be purely additive and reasonably safe. I'm not super keen on doing this unconditionally, but let's see if anyone complains.