[Suggestion] Add type declaration for (extra)AllowedFileExtensions etc

[billythekid]

When you add a file extension to the allowed uploads/assets but output {{ file.type }} it can return 'undefined'. I propose that the config setting for allowedFileExtensions and extraAllowedFileExtensions be in the format ['extension'=>'type', … ] where type is optional or make it an array of tuples [['ext','type'],['ext,'type']], whatever implementation you like for backwards compatibility.

for example…

// key=>val style
'extraAllowedFileExtensions' => [
    'pub' => 'publisher', 
    'bz'  => 'compressed'
]

// tuple-style
'extraAllowedFileExtensions' => [
    ['pub', 'publisher'], 
    ['bz', 'compressed'],
]

perhaps this can be extended to include mimetypes too to add to Yii's getMimeTypeByExtension helper that it looks like Craft uses. (Which just maps pre-set values anyway)

[missmatsuko]

I think you can do this now with extraFileKinds.
https://docs.craftcms.com/v3/config/config-settings.html#extrafilekinds

[brandonkelly]

Yep! Added in 3.0.37. (e1d9433)