[idea] :QfFilter — narrow quickfix list entries by Lua pattern

[stanfish06]

What

Add a :QfFilter {pattern} user command that filters the current quickfix list in-place, keeping only entries whose message text or filename matches a Lua pattern.

Where

lua/config/options.lua — alongside the existing :Compile command and <leader>co/cc keymaps (around lines 159–169).

Why it matters

The config uses quickfix heavily: :Compile populates it with build or grep output, and <leader>co/cc open/close it. After a large make run or wide vimgrep, the list can contain hundreds of entries. There is no built-in way to narrow it without re-running the original command with a tighter query.

Example use cases:

• :QfFilter error — keep only lines containing "error" after a build
• :QfFilter foo%.c — keep only entries from foo.c
• :QfFilter undefined — isolate one class of linker error from a noisy build

The <leader>cf keymap (mnemonic: close/clear → clean/filter) could be a natural extension point, but the command alone is already useful via cmdline completion.

Recommended action

Add to lua/config/options.lua:

vim.api.nvim_create_user_command("QfFilter", function(opts)
    local pattern = opts.args
    local items = vim.fn.getqflist()
    local filtered = vim.tbl_filter(function(item)
        local text = item.text or ""
        local fname = vim.fn.bufname(item.bufnr) or ""
        return text:find(pattern) ~= nil or fname:find(pattern) ~= nil
    end, items)
    vim.fn.setqflist(filtered, "r")
    if #filtered > 0 then
        vim.cmd("copen")
    else
        vim.notify("QfFilter: no entries match " .. vim.inspect(pattern), vim.log.levels.WARN)
    end
end, { nargs = 1, desc = "Filter quickfix list by Lua pattern" })

A companion :QfRestore that reverts to the last unfiltered list (stored in a module-level variable) would round out the feature.