vim-polyglot/syntax/dockerfile.vim

if !exists('g:polyglot_disabled') || index(g:polyglot_disabled, 'dockerfile') == -1
  
" dockerfile.vim - Syntax highlighting for Dockerfiles
" Maintainer:   Honza Pokorny <https://honza.ca>
" Version:      0.5


if exists("b:current_syntax")
    finish
endif

let b:current_syntax = "dockerfile"

syntax case ignore

syntax match dockerfileKeyword /\v^\s*(ONBUILD\s+)?(ADD|ARG|CMD|COPY|ENTRYPOINT|ENV|EXPOSE|FROM|HEALTHCHECK|LABEL|MAINTAINER|RUN|SHELL|STOPSIGNAL|USER|VOLUME|WORKDIR)\s/
highlight link dockerfileKeyword Keyword

syntax region dockerfileString start=/\v"/ skip=/\v\\./ end=/\v"/
highlight link dockerfileString String

syntax match dockerfileComment "\v^\s*#.*$"
highlight link dockerfileComment Comment

set commentstring=#\ %s

" match "RUN", "CMD", and "ENTRYPOINT" lines, and parse them as shell
let s:current_syntax = b:current_syntax
unlet b:current_syntax
syntax include @SH syntax/sh.vim
let b:current_syntax = s:current_syntax
syntax region shLine matchgroup=dockerfileKeyword start=/\v^\s*(RUN|CMD|ENTRYPOINT)\s/ end=/\v$/ contains=@SH
" since @SH will handle "\" as part of the same line automatically, this "just works" for line continuation too, but with the caveat that it will highlight "RUN echo '" followed by a newline as if it were a block because the "'" is shell line continuation...  not sure how to fix that just yet (TODO)

endif