fix(expert): implement root_dir instead #4054

Copy the approach from `lsp/elixirls.lua` to support monorepos.

fix #4052

1 files changed, 15 insertions, 1 deletions

diff --git a/lsp/expert.lua b/lsp/expert.lua
index e30afd4b..971e3de4 100644
--- a/lsp/expert.lua
+++ b/lsp/expert.lua
@@ -3,10 +3,24 @@
 --- https://github.com/elixir-lang/expert
 ---
 --- Expert is the official language server implementation for the Elixir programming language.
+---
+--- 'root_dir' is chosen like this: if two or more directories containing `mix.exs` were found when
+--- searching directories upward, the second one (higher up) is chosen, with the assumption that it
+--- is the root of an umbrella app. Otherwise the directory containing the single mix.exs that was
+--- found is chosen.
 
 ---@type vim.lsp.Config
 return {
   filetypes = { 'elixir', 'eelixir', 'heex', 'surface' },
-  root_markers = { '.git', 'mix.exs' },
   cmd = { 'expert' },
+  root_dir = function(bufnr, on_dir)
+    local fname = vim.api.nvim_buf_get_name(bufnr)
+    --- Elixir workspaces may have `mix.exs` files, e.g. for an "umbrella" layout or monorepo. So we
+    --- specify `limit=2` and treat the highest one (if any) as the root of an umbrella app.
+    local matches = vim.fs.find({ 'mix.exs' }, { upward = true, limit = 2, path = fname })
+    local child_or_root_path, maybe_umbrella_path = unpack(matches)
+    local root_dir = vim.fs.dirname(maybe_umbrella_path or child_or_root_path)
+
+    on_dir(root_dir)
+  end,
 }