[Static Themes] Unsupported image formats are not detected by the linter at static theme submission

[AlexandraMoga]

STR:

1. Log in to AMO -dev
2. Submit a static theme and make sure to incude an unsupported image format under 'images' in your manifest - i.e. a .tif file
3. Observe the validation results

Actual result:
There are no errors generated when a static theme package contains an unsupported image format

Expected result:
The linter should detect when an image format doesn't match the static theme requirements specified in the guideline - ST guideline

Notes:

• when a theme with an unsupported image file is submitted, a preview will be generated but the image file can't be inspected in Rev Tools and the image is not applied in the browser when the theme is installed
• here is an example:
  Rev Tools
  https://reviewers.addons-dev.allizom.org/en-US/reviewers/review/st-theme-zip-a
  Listing page
  https://addons-dev.allizom.org/en-US/firefox/addon/st-theme-zip-a/
• reproduced on AMO -dev with FF60, WIn10x64

[eviljeff]

see https://bugzilla.mozilla.org/show_bug.cgi?id=1500501

[eviljeff]

From #2243 (comment)

There is already validation for the icons property happening in src/parsers/manifestjson.js -> validateIcon which also validates the images by actually opening the first part of them and reading their size.

So that functionality can be re-used for this purpose. See validateIcons for a bit more information on this, all that should be generalized into a validateImage function that has the ability to check arbitrary sizes (for icons) as well.

This may not necessarily a good first bug but given that most of the functionality is already there and needs to be restructured it may as well be.

[muffinresearch]

@rpl hi - would you have the bandwidth to help out with this?

[AlexandraMoga]

@rpl Hi, I guess this can be tested when a new linter version will be released. Do you know when this is going to happen?
Thanks