Ccls language server not attached to a c++ project

Language Server Protocol (LSP)
1

I have set up neovim lsp support with ccls language server for c++ projects, but it does not work.
The following is the output of :LspInfo command, together with my configuration.

The output of :LspInfo:
image

my configuration about lsp support is:

Plug 'neovim/nvim-lspconfig'
Plug 'hrsh7th/cmp-nvim-lsp'
Plug 'hrsh7th/cmp-buffer'
Plug 'hrsh7th/cmp-path'
Plug 'hrsh7th/cmp-cmdline'
Plug 'hrsh7th/nvim-cmp'

lua require('lsp-comp')

and the lsp-comp.lua is:

-- Setup nvim-cmp.
local cmp = require'cmp'

cmp.setup({
  snippet = {
    -- REQUIRED - you must specify a snippet engine
    expand = function(args)
      vim.fn["vsnip#anonymous"](args.body) -- For `vsnip` users.
      -- require('luasnip').lsp_expand(args.body) -- For `luasnip` users.
      -- require('snippy').expand_snippet(args.body) -- For `snippy` users.
      -- vim.fn["UltiSnips#Anon"](args.body) -- For `ultisnips` users.
    end,
  },
  mapping = {
    ['<C-b>'] = cmp.mapping(cmp.mapping.scroll_docs(-4), { 'i', 'c' }),
    ['<C-f>'] = cmp.mapping(cmp.mapping.scroll_docs(4), { 'i', 'c' }),
    ['<C-Space>'] = cmp.mapping(cmp.mapping.complete(), { 'i', 'c' }),
    ['<C-y>'] = cmp.config.disable, -- Specify `cmp.config.disable` if you want to remove the default `<C-y>` mapping.
    ['<C-e>'] = cmp.mapping({
      i = cmp.mapping.abort(),
      c = cmp.mapping.close(),
    }),
    ['<CR>'] = cmp.mapping.confirm({ select = true }), -- Accept currently selected item. Set `select` to `false` to only confirm explicitly selected items.
  },
  sources = cmp.config.sources({
    { name = 'nvim_lsp' },
    { name = 'vsnip' }, -- For vsnip users.
    -- { name = 'luasnip' }, -- For luasnip users.
    -- { name = 'ultisnips' }, -- For ultisnips users.
    -- { name = 'snippy' }, -- For snippy users.
  }, {
    { name = 'buffer' },
  })
})

-- Set configuration for specific filetype.
cmp.setup.filetype('gitcommit', {
  sources = cmp.config.sources({
    { name = 'cmp_git' }, -- You can specify the `cmp_git` source if you were installed it.
  }, {
    { name = 'buffer' },
  })
})

-- Use buffer source for `/` (if you enabled `native_menu`, this won't work anymore).
cmp.setup.cmdline('/', {
  sources = {
    { name = 'buffer' }
  }
})

-- Use cmdline & path source for ':' (if you enabled `native_menu`, this won't work anymore).
cmp.setup.cmdline(':', {
  sources = cmp.config.sources({
    { name = 'path' }
  }, {
    { name = 'cmdline' }
  })
})

-- Use cmdline & path source for ':' (if you enabled `native_menu`, this won't work anymore).
--cmp.setup.cmdline(':', {
--  sources = cmp.config.sources(
--  {
--    { name = 'path' }
--  }
--  --,
--  --{
--  --  { name = 'cmdline' }
--  --}
--  )
--})

-- Setup lspconfig.
-- Mappings.
-- See `:help vim.diagnostic.*` for documentation on any of the below functions
local opts = { noremap=true, silent=true }
vim.api.nvim_set_keymap('n', '<space>e', '<cmd>lua vim.diagnostic.open_float()<CR>', opts)
vim.api.nvim_set_keymap('n', '[d', '<cmd>lua vim.diagnostic.goto_prev()<CR>', opts)
vim.api.nvim_set_keymap('n', ']d', '<cmd>lua vim.diagnostic.goto_next()<CR>', opts)
vim.api.nvim_set_keymap('n', '<space>q', '<cmd>lua vim.diagnostic.setloclist()<CR>', opts)

-- Use an on_attach function to only map the following keys
-- after the language server attaches to the current buffer
local on_attach = function(client, bufnr)
  -- Enable completion triggered by <c-x><c-o>
  vim.api.nvim_buf_set_option(bufnr, 'omnifunc', 'v:lua.vim.lsp.omnifunc')

  -- Mappings.
  -- See `:help vim.lsp.*` for documentation on any of the below functions
  vim.api.nvim_buf_set_keymap(bufnr, 'n', 'gD', '<cmd>lua vim.lsp.buf.declaration()<CR>', opts)
  vim.api.nvim_buf_set_keymap(bufnr, 'n', 'gd', '<cmd>lua vim.lsp.buf.definition()<CR>', opts)
  vim.api.nvim_buf_set_keymap(bufnr, 'n', 'K', '<cmd>lua vim.lsp.buf.hover()<CR>', opts)
  vim.api.nvim_buf_set_keymap(bufnr, 'n', 'gi', '<cmd>lua vim.lsp.buf.implementation()<CR>', opts)
  vim.api.nvim_buf_set_keymap(bufnr, 'n', '<C-k>', '<cmd>lua vim.lsp.buf.signature_help()<CR>', opts)
  vim.api.nvim_buf_set_keymap(bufnr, 'n', '<space>wa', '<cmd>lua vim.lsp.buf.add_workspace_folder()<CR>', opts)
  vim.api.nvim_buf_set_keymap(bufnr, 'n', '<space>wr', '<cmd>lua vim.lsp.buf.remove_workspace_folder()<CR>', opts)
  vim.api.nvim_buf_set_keymap(bufnr, 'n', '<space>wl', '<cmd>lua print(vim.inspect(vim.lsp.buf.list_workspace_folders()))<CR>', opts)
  vim.api.nvim_buf_set_keymap(bufnr, 'n', '<space>D', '<cmd>lua vim.lsp.buf.type_definition()<CR>', opts)
  vim.api.nvim_buf_set_keymap(bufnr, 'n', '<space>rn', '<cmd>lua vim.lsp.buf.rename()<CR>', opts)
  vim.api.nvim_buf_set_keymap(bufnr, 'n', '<space>ca', '<cmd>lua vim.lsp.buf.code_action()<CR>', opts)
  vim.api.nvim_buf_set_keymap(bufnr, 'n', 'gr', '<cmd>lua vim.lsp.buf.references()<CR>', opts)
  vim.api.nvim_buf_set_keymap(bufnr, 'n', '<space>wf', '<cmd>lua vim.lsp.buf.formatting()<CR>', opts)
end

local capabilities = require('cmp_nvim_lsp').update_capabilities(vim.lsp.protocol.make_client_capabilities())

-- Use a loop to conveniently call 'setup' on multiple servers and
-- map buffer local keybindings when the language server attaches
local servers = { 'pyright', 'ccls', 'solargraph' }
for _, lsp in pairs(servers) do
  require('lspconfig')[lsp].setup {
    on_attach = on_attach,
    flags = {
      -- This will be the default in neovim 0.7+
      debounce_text_changes = 150,
    },
    capabilities = capabilities
  }
end

Could anyone help me, please?