feature: Pick command

[milisims]

Did you check the docs?

• I have read all the snacks.nvim docs

Is your feature request related to a problem? Please describe.

I use the vim cmdline far more often than specialized keymaps, and I use a lot of commandline abbreviations. For example, if I want to pick files from a specific directory, I have to write out lua Snacks.picker.files({ cwd = ... }), and while that's expressive and a better programmatic interface than the commandline, it would be nice to just have one abbreviation for something like Pick files where I could just write cwd=... after.

Describe the solution you'd like

A Pick command with useful completions. Sources followed by options, something like:
Pick files cwd=dir\ with\ escaped\ spaces layout=ivy hidden=true

Describe alternatives you've considered

Currently I'm using this. It completes booleans, 'focus', 'layout', and 'cwd', but any key in opts that is not a table will be completed as a key.

Using fargs lets escaped whitespace work without any effort, but requires no spaces per key/value. I like this solution overall.

      callback = function(cmd)
        local opts = { source = cmd.fargs[1] }

        for i = 2, #cmd.fargs do
          local k, v = cmd.fargs[i]:match('^(%w+)=(.*)$') -- escaping ws works
          if not k then
            error('Invalid argument: ' .. cmd.fargs[i])
          end
          if v == 'true' then
            opts[k] = true
          elseif v == 'false' then
            opts[k] = false
          else
            opts[k] = vim.fn.expandcmd(v) -- lets $ENV , %:p, etc work
          end
        end

        Snacks.picker.pick(opts)
      end

      -- arglead, cmdline, cursorpos
      complete = function(arglead, cmdline, _)
        if cmdline == 'Pick ' then
          return vim.tbl_keys(Snacks.picker.config.get().sources --[[@as table]])
        end

        local opts = Snacks.picker.config.get({ source = cmdline:match('Pick (%S+)') })

        local opt = arglead:match('^(%w+)=')
        if not opt then
          local ret = { 'cwd=' }
          local skip = { enabled = true, source = true }

          for k, v in pairs(opts) do
            if not skip[k] and type(v) ~= 'table' then
              table.insert(ret, k .. '=')
            end
          end
          return ret
        end

        if opt == 'focus' then
          return { 'input', 'list' }
        elseif opt == 'finder' then
          return vim
            .iter(Snacks.picker.config.get().sources)
            :map(function(_, v)
              return type(v.finder) == 'string' and v.finder or nil
            end)
            :totable()
        elseif opt == 'layout' then
          return vim.tbl_keys(Snacks.picker.config.get().layouts)
        elseif opt == 'cwd' then
          return vim.fn.getcompletion(arglead:sub(#opt + 2), 'dir', true)
        elseif type(opts[opt]) == 'boolean' then
          return { 'true', 'false' }
        end
      end

Additional context

No response