A filter that seems close enough is the bibexport filter at 
https://raw.githubusercontent.com/pandoc/lua-filters/master/bibexport/bibexport.lua 
which I reproduce below:

```
local utils = require 'pandoc.utils'
local List = require 'pandoc.List'

local citation_id_set = {}

local type = utils.type or type

-- Collect all citation IDs.
function Cite (c)
  local cs = c.citations
  for i = 1, #cs do
    citation_id_set[cs[i].id or cs[i].citationId] = true
  end
end

--- Return a list of citation IDs
function citation_ids ()
  local citations = {};
  for cid, _ in pairs(citation_id_set) do
    citations[#citations + 1] = cid
  end
  return citations
end

--- stringify meta inline elements. Pandoc prior to version 2.8
-- didn't properly tag MetaInline values, so making it necessary to use an
-- auxiliary Span.
local stringifyMetaInlines = function (el)
  return el.t
    and utils.stringify(el)
    or utils.stringify(pandoc.Span(el))
end

function bibdata (bibliography)
  function bibname (bibitem)
    return type(bibitem) == 'string'
      and bibitem:gsub('%.bib$', '')
      -- bibitem is assumed to be a list of inlines or MetaInlines element
      or stringifyMetaInlines(bibitem):gsub('%.bib$', '')
  end

  local bibs = (type(bibliography) == 'List' or bibliography.t == 
'MetaList')
    and List.map(bibliography, bibname)
    or {bibname(bibliography)}
  return table.concat(bibs, ',')
end

function aux_content(bibliography)
  local cites = citation_ids()
  table.sort(cites)
  local citations = table.concat(cites, ',')
  return table.concat(
    {
      '\\bibstyle{alpha}',
      '\\bibdata{' .. bibdata(bibliography) .. '}',
      '\\citation{' .. citations .. '}',
      '',
    },
    '\n'
  )
end

function write_dummy_aux (bibliography, auxfile)
  local filename
  if type(auxfile) == 'string' then
    filename = auxfile
  elseif type(auxfile) == 'table' or type(auxfile) == 'Inlines' then
    -- assume list of inlines
    filename = utils.stringify(pandoc.Span(auxfile))
  else
    filename = 'bibexport.aux'
  end
  local fh = io.open(filename, 'w')
  fh:write(aux_content(bibliography))
  fh:close()
  io.stdout:write('Aux written to ' .. filename .. '\n')
  return filename
end

function Pandoc (doc)
  local meta = doc.meta
  if not meta.bibliography then
    return nil
  else
    -- create a dummy .aux file
    local auxfile_name = write_dummy_aux(meta.bibliography, meta.auxfile)
    os.execute('bibexport ' .. auxfile_name)
    io.stdout:write('Output written to bibexport.bib\n')
    return nil
  end
end
```

We already have something that will collect the whole bibliography. How do 
we go from this to actually using this to replace Cites with special 
attributes? E.g. [@Citekey]{.title} or with a suffix [@Citekey-]? This last 
one (the suffix) I was able to dig down until I could locate it in the 
Pandoc AST using Paru for Ruby, but not using Lua. (At first, I thought Lua 
would be easier, but the underlying Haskell architecture and the AST model 
are still very foreign to me.)

Thanks,
B.

On Monday, January 30, 2023 at 2:41:35 PM UTC-3 John MacFarlane wrote:

> In a Lua filter you could probably just use pandoc.read with the format 
> "bibtex" or "biblatex".
>
>
> > On Jan 30, 2023, at 9:21 AM, Bastien DUMONT <bastien...-VwIFZPTo/vqsTnJN9+BGXg@public.gmane.org> 
> wrote:
> > 
> > Do you mean a function that parses the .bib file directly? I really 
> think that it would be easier to convert the .bib file to a CSL JSON file 
> and import it via a JSON parser.
> > 
> > Le Monday 30 January 2023 à 08:49:36AM, Bernardo C. D. A. Vasconcelos a 
> écrit :
> >> Thanks for the feedback, Bastien! 
> >> Can you think of a similar example script that contains the function to 
> parse
> >> the bib data? I searched for it online to no avail.
> >> On Saturday, January 28, 2023 at 7:35:40 PM UTC-3 Bastien Dumont wrote:
> >> 
> >> I think that it would be better to run it before citeproc, since you 
> don't
> >> want citeproc output (unless you want to still benefit from the "ibid./
> >> cited" feature). Citeproc would not help you so much here because it 
> does
> >> not tag the different parts of a formatted citation. On the other hand,
> >> parsing the bib file would be rather simple if it is in the CSL JSON
> >> format: then you would just have to use one of the JSON modules for Lua 
> to
> >> import your bibliographic references into a Lua table. If you use 
> Bib(La)
> >> TeX, you can convert a .bib file to a .json with `pandoc -f bibtex (or
> >> biblatex) -t csljson myfile.bib -o myfile.json`.
> >> 
> >> Le Saturday 28 January 2023 à 02:07:54PM, Bernardo C. D. A. Vasconcelos 
> a
> >> écrit :
> >>> An HTML equivalent of these commands was proposed in Github, but there
> >> was no
> >>> feasible way for it to be implemented as part of Citeproc. I suggested 
> a
> >> Lua
> >>> filter to achieve this and John said it sounded doable. 
> >>> 
> >>> I learned some Lua and experimented, but I didn't come close enough to
> >> have
> >>> something worth sharing. In short: I imagined something like `[@Ref]
> >>> {.citetitle}` and `[@Ref]{.citeauthor}`. So this would imply: parsing 
> the
> >> bib
> >>> data and saving it to a Lua table (stuck here); filtering spans; 
> checking
> >> the
> >>> type and performing the replacement (not clear to me either what the
> >> correct
> >>> way would be to replace the id with the data or if this would have to 
> run
> >>> before/after citeproc).
> >>> 
> >>> Any pointers would be much appreciated.
> >>> 
> >>> --
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> >> email
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> >>> To view this discussion on the web visit [2][1]
> https://groups.google.com/
> >> d/msgid/
> >>> pandoc-discuss/51e71797-b029-4438-be64-6a8a15dd500an%[2]
> >> 40googlegroups.com.
> >>> 
> >>> References:
> >>> 
> >>> [1] mailto:pandoc-discus...-/JYPxA39Uh5TLH3MbocFFw@public.gmane.org
> >>> [2] [3]https://groups.google.com/d/msgid/pandoc-discuss/
> >> 51e71797-b029-4438-be64-6a8a15dd500an%
> 40googlegroups.com?utm_medium=email&
> >> utm_source=footer
> >> 
> >> 
> >> --
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> >> to [4]pandoc-discus...-/JYPxA39Uh5TLH3MbocFF+G/Ez6ZCGd0@public.gmane.org
> >> To view this discussion on the web visit [5]
> https://groups.google.com/d/msgid/
> >> pandoc-discuss/4865a325-42c0-4245-b992-b4fbdeab576en%40googlegroups.com
> .
> >> 
> >> References:
> >> 
> >> [1] https://groups.google.com/d/msgid/
> >> [2] http://40googlegroups.com/
> >> [3] 
> https://groups.google.com/d/msgid/pandoc-discuss/51e71797-b029-4438-be64-6a8a15dd500an%40googlegroups.com?utm_medium=email&utm_source=footer
> >> [4] mailto:pandoc-discus...-/JYPxA39Uh5TLH3MbocFFw@public.gmane.org
> >> [5] 
> https://groups.google.com/d/msgid/pandoc-discuss/4865a325-42c0-4245-b992-b4fbdeab576en%40googlegroups.com?utm_medium=email&utm_source=footer
> > 
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> > To view this discussion on the web visit 
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> .
>
>

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