Rust analyzer highlighting with nvim-lsp

Start by reproducing the Rust Analyzer documentation highlighting in Neovim 0.5 with nvim-lsp and nvim-completion, using the reported after/ftplugin/rust.vim configuration. Compare which Rust documentation tokens receive Markdown highlights and which do not; the issue says attempts in before/ftplugin/markdown.vim and before/syntax/markdown.vim had no effect. Done means identifying and fixing the missing highlighting behavior.

• rust.vim version: Downloaded October,15th 2020

Steps to reproduce:

• Running latest neovim 0.5
• Using nvim-lsp and nvim-completion

Rust analyzer documentation gets treat as markdown and is mostly able to highlighted as markdown

However as you can see somethings are not able to highlighted with markdown highlights

I am using this in my after/ftplugin/rust.vim

function s:rustdoclsphilight()
	if &background ==# 'dark'
		let l:color = '#5d4d7a'
	else
		let l:color = '#e2e0ea'
	endif
	exec 'hi markdownItalic guibg='.l:color
	exec 'hi markdownAutomaticLink guibg='.l:color
	exec 'hi markdownBlockquote guibg='.l:color
	exec 'hi markdownBold guibg='.l:color
	exec 'hi markdownBoldDelimiter guibg='.l:color
	exec 'hi markdownBoldItalic guibg='.l:color
	exec 'hi markdownBoldItalicDelimiter guibg='.l:color
	exec 'hi markdownCode guibg='.l:color
	exec 'hi markdownCodeBlock guibg='.l:color
	exec 'hi markdownCodeDelimiter guibg='.l:color
	exec 'hi markdownError guibg='.l:color
	exec 'hi markdownEscape guibg='.l:color
	exec 'hi markdownFootnote guibg='.l:color
	exec 'hi markdownFootnoteDefinition guibg='.l:color
	exec 'hi markdownH1 guibg='.l:color
	exec 'hi markdownH2 guibg='.l:color
	exec 'hi markdownH3 guibg='.l:color
	exec 'hi markdownH4 guibg='.l:color
	exec 'hi markdownH5 guibg='.l:color
	exec 'hi markdownH6 guibg='.l:color
	exec 'hi markdownHeadingDelimiter guibg='.l:color
	exec 'hi markdownHeadingRule guibg='.l:color
	exec 'hi markdownId guibg='.l:color
	exec 'hi markdownIdDeclaration guibg='.l:color
	exec 'hi markdownIdDelimiter guibg='.l:color
	exec 'hi markdownItalic guibg='.l:color
	exec 'hi markdownItalicDelimiter guibg='.l:color
	exec 'hi markdownLineBreak guibg='.l:color
	exec 'hi markdownLineStart guibg='.l:color
	exec 'hi markdownLink guibg='.l:color
	exec 'hi markdownLinkDelimiter guibg='.l:color
	exec 'hi markdownLinkText guibg='.l:color
	exec 'hi markdownLinkTextDelimiter guibg='.l:color
	exec 'hi markdownListMarker guibg='.l:color
	exec 'hi markdownOrderedListMarker guibg='.l:color
	exec 'hi markdownRule guibg='.l:color
	exec 'hi markdownUrl guibg='.l:color
	exec 'hi markdownUrlDelimiter guibg='.l:color
	exec 'hi markdownUrlTitle guibg='.l:color
	exec 'hi markdownUrlTitleDelimiter guibg='.l:color
	exec 'hi markdownUrlValid guibg='.l:color
endfunction!

call <SID>rustdoclsphilight()

I have tried adding syn keyword blocks in before/ftplugin/markdown.vim and before/syntax/markdown.vim but it doesn't seem to change anything.