bug: fatal error when `nvim-web-devicons` is installed but an icon is unavailable for the current file

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Neovim version (nvim -v)

0.9.5

Operating system/version

Arch Linux (up-to-date 2024-02-22)

Describe the bug

When icons = true in Trouble's config, but an icon is not available for a filetype/extension, the Trouble window will fail to open with:

E5108: Error executing lua .../.repro/plugins/trouble.nvim/lua/trouble/view.lua:368: Error executing lua: .../.repro/plugins/trouble.nvim/lua/trouble/text.lua:22: attempt to index local 'str' (a nil value)

when there are diagnostics.

I believe this is because gsub is called here (text.lua L22) on str without a nil check, but get_icons called here (renderer.lua L108) can still return nil as the ok check in its definition here (renderer L13) only checks whether devicons is installed, not if it can actually return an icon for the given require("nvim-web-devicons").get_icon.

Steps To Reproduce

nvim -u repro.lua test.py
Type something that generates a diagnostic, such as def: only and exiting insert mode
Open the trouble window (:TroubleToggle)

Expected Behavior

Ideally, Trouble should simply not render an icon for that file, like icons = false.

example

Repro

-- DO NOT change the paths and don't remove the colorscheme
local root = vim.fn.fnamemodify("./.repro", ":p")

-- set stdpaths to use .repro
for _, name in ipairs({ "config", "data", "state", "cache" }) do
  vim.env[("XDG_%s_HOME"):format(name:upper())] = root .. "/" .. name
end

-- bootstrap lazy
local lazypath = root .. "/plugins/lazy.nvim"
if not vim.loop.fs_stat(lazypath) then
  vim.fn.system({ "git", "clone", "--filter=blob:none", "https://github.com/folke/lazy.nvim.git", lazypath, })
end
vim.opt.runtimepath:prepend(lazypath)

-- install plugins
local plugins = {
  "folke/tokyonight.nvim",
  "folke/trouble.nvim",
  -- add any other plugins here
  {
    "nvim-tree/nvim-web-devicons",
    opts = {
      override_by_extension = {
        ["py"] = {},
      }
    }
  },

  -- To generate diagnostics
  "neovim/nvim-lspconfig",
  {
    dir = "",
    name = "lspconfig-jedils",
    ft = "python",
    dependencies = "neovim/nvim-lspconfig",
    config = function(_, opts)
      require "lspconfig".jedi_language_server.setup(opts)
    end
  }
}
require("lazy").setup(plugins, {
  root = root .. "/plugins",
})

vim.cmd.colorscheme("tokyonight")
-- add anything else here

folke / trouble.nvim