nvim/lua/init.lua

vim.o.foldmethod = 'expr'
vim.o.foldexpr = 'nvim_treesitter#foldexpr()'

vim.diagnostic.config({
    virtual_text = false,
    signs = true,
    underline = false,
    update_in_insert = false,
    severity_sort = true,
    float = {
        border = "single",
        source = "always" -- Or "if_many"
    }
})

local signs = {Error = "● ", Warn = "● ", Hint = "● ", Info = "● "}
for type, icon in pairs(signs) do
    local hl = "DiagnosticSign" .. type
    vim.fn.sign_define(hl, {text = icon, texthl = hl, numhl = hl})
end

local border = {
    {"┌", "FloatBorder"}, {"─", "FloatBorder"}, {"┐", "FloatBorder"},
    {"│", "FloatBorder"}, {"┘", "FloatBorder"}, {"─", "FloatBorder"},
    {"└", "FloatBorder"}, {"│", "FloatBorder"}
}

vim.lsp.handlers["textDocument/hover"] =
    vim.lsp.with(vim.lsp.handlers.hover, {border = "single"})
vim.lsp.handlers["textDocument/signatureHelp"] =
    vim.lsp.with(vim.lsp.handlers.signature_help, {border = "single"})

local orig_util_open_floating_preview = vim.lsp.util.open_floating_preview
function vim.lsp.util.open_floating_preview(contents, syntax, opts, ...)
    opts = opts or {}
    opts.border = opts.border or border
    return orig_util_open_floating_preview(contents, syntax, opts, ...)
end