Keep first letter capitalisation from buffer source

[degnbol]

When writing normal prose one might start a sentence with a word already found in the buffer, but the capitalisation will be lost on completion. Or the other way around, the buffer word was used first in a sentence and the completion forces capitalisation.
For these scenarios it can be useful to keep the capitalisation. The following might be a useful config recipe for others writing prose:

sources = {
    providers = {
        buffer = {
            -- keep case of first char
            transform_items = function (a, items)
                local keyword = a.get_keyword()
                local correct, case
                if keyword:match('^%l') then
                    correct = '^%u%l+$'
                    case = string.lower
                elseif keyword:match('^%u') then
                    correct = '^%l+$'
                    case = string.upper
                else
                    return items
                end
                -- avoid duplicates from the corrections
                local seen = {}
                local out = {}
                for _, item in ipairs(items) do
                    local raw = item.insertText
                    if raw:match(correct) then
                        local text = case(raw:sub(1,1)) .. raw:sub(2)
                        item.insertText = text
                        item.label = text
                    end
                    if not seen[item.insertText] then
                        seen[item.insertText] = true
                        table.insert(out, item)
                    end
                end
                return out
            end
        }
    }
}

[Saghen]

Added it to the recipes, thanks! https://cmp.saghen.dev/recipes#keep-first-letter-capitalization-on-buffer-source