This seems like it would be useful to have as a configuration option. We could create a new configuration sub-table for repo-map options e.g.:

{
  repo_map = {
    ignore_patterns = { "%.git", "%.worktree", "__pycache__", "node_modules" }, -- ignore files matching these patterns when building the repo map
  }
}

With this approach, I think it's debatable whether vendor should be added to the default configuration in this case. It's not as standard as node_modules or __pycache__; some users may actually want to include things inside of vendor directories. Users who do want to ignore it can opt-in.

If you decide to take this approach, in order to decouple parse_gitignore from repo-map specifics, maybe we should not set the default ignore_patterns directly inside of parse_gitignore, but extend the returned table inside of RepoMap._build_repo_map:

function M.parse_gitignore(gitignore_path)
  local ignore_patterns = {}
  local negate_patterns = {}
  --- ... snip ...
  return ignore_patterns, negate_patterns
end

function RepoMap._build_repo_map(project_root, file_ext)
  local output = {}
  local gitignore_path = project_root .. "/.gitignore"
  local ignore_patterns, negate_patterns = Utils.parse_gitignore(gitignore_path)
  vim.list_extend(ignore_patterns, Config.repo_map.ignore_patterns)
  -- maybe we should support configurable negate_patterns too?
  -- ... snip ...
end

Thanks for the feedback @b0o. Seems like a reasonable approach. I'll look into implementing this over the next couple of days.

‌‌‌‌‌@brewinski Thank you for your PR and @b0o's suggestions! I'll merge this PR first, and then you can submit a new PR to make it configurable.