Syntax highlighting ENV and ARG references

[pn-santos]

It would be nice (if possible) to highlight the text associated with a Dockerfile's ENV and ARG references in a different color.

[rcjsuen]

Interestingly enough, if you select the dockerfile language on the Monaco Editor website, the ENV variables are indeed getting highlighted. So the Monaco Dockerfile grammar definition is arguably a little bit better than the TextMate Dockerfile grammar definition.

[StephenWeatherford]

Closing for now due to lack of interest. If anybody thinks this would be very important to them, please let us know! Thanks.

[rcjsuen]

If semantic highlighting gets added to the LSP I may be able to help with this. See microsoft/language-server-protocol#513.