feat(gopls): refactor root_dir identification #3942

Refactor the logic on how to identify the root_dir for gopls. This will
provide a viable solution to the issue where multiple gopls lsp client
instances are started, causing adverse effects in certain areas like
diagnostics, lsp functionality (such as `go to definition`,
workspace-enabled projects). The identification for required directories
are based on golang-specific environment variables which are set by
default.

1 files changed, 72 insertions, 19 deletions

diff --git a/lsp/gopls.lua b/lsp/gopls.lua
index fd22ff0d..0b4c59f6 100644
--- a/lsp/gopls.lua
+++ b/lsp/gopls.lua
@@ -4,13 +4,80 @@
 ---
 --- Google's lsp server for golang.
 
+--- @class go_dir_custom_args
+---
+--- @field envvar_id string
+---
+--- @field custom_subdir string?
+
 local mod_cache = nil
+local std_lib = nil
+
+---@param custom_args go_dir_custom_args
+---@param on_complete fun(dir: string | nil)
+local function identify_go_dir(custom_args, on_complete)
+  local cmd = { 'go', 'env', custom_args.envvar_id }
+  vim.system(cmd, { text = true }, function(output)
+    local res = vim.trim(output.stdout or '')
+    if output.code == 0 and res ~= '' then
+      if custom_args.custom_subdir and custom_args.custom_subdir ~= '' then
+        res = res .. custom_args.custom_subdir
+      end
+      on_complete(res)
+    else
+      vim.schedule(function()
+        vim.notify(
+          ('[gopls] identify ' .. custom_args.envvar_id .. ' dir cmd failed with code %d: %s\n%s'):format(
+            output.code,
+            vim.inspect(cmd),
+            output.stderr
+          )
+        )
+      end)
+      on_complete(nil)
+    end
+  end)
+end
+
+---@return string?
+local function get_std_lib_dir()
+  if std_lib and std_lib ~= '' then
+    return std_lib
+  end
+
+  identify_go_dir({ envvar_id = 'GOROOT', custom_subdir = '/src' }, function(dir)
+    if dir then
+      std_lib = dir
+    end
+  end)
+  return std_lib
+end
+
+---@return string?
+local function get_mod_cache_dir()
+  if mod_cache and mod_cache ~= '' then
+    return mod_cache
+  end
+
+  identify_go_dir({ envvar_id = 'GOMODCACHE' }, function(dir)
+    if dir then
+      mod_cache = dir
+    end
+  end)
+  return mod_cache
+end
 
 ---@param fname string
 ---@return string?
-local function get_root(fname)
+local function get_root_dir(fname)
   if mod_cache and fname:sub(1, #mod_cache) == mod_cache then
-    local clients = vim.lsp.get_clients { name = 'gopls' }
+    local clients = vim.lsp.get_clients({ name = 'gopls' })
+    if #clients > 0 then
+      return clients[#clients].config.root_dir
+    end
+  end
+  if std_lib and fname:sub(1, #std_lib) == std_lib then
+    local clients = vim.lsp.get_clients({ name = 'gopls' })
     if #clients > 0 then
       return clients[#clients].config.root_dir
     end
@@ -23,23 +90,9 @@ return {
   filetypes = { 'go', 'gomod', 'gowork', 'gotmpl' },
   root_dir = function(bufnr, on_dir)
     local fname = vim.api.nvim_buf_get_name(bufnr)
+    get_mod_cache_dir()
+    get_std_lib_dir()
     -- see: https://github.com/neovim/nvim-lspconfig/issues/804
-    if mod_cache then
-      on_dir(get_root(fname))
-      return
-    end
-    local cmd = { 'go', 'env', 'GOMODCACHE' }
-    vim.system(cmd, { text = true }, function(output)
-      if output.code == 0 then
-        if output.stdout then
-          mod_cache = vim.trim(output.stdout)
-        end
-        on_dir(get_root(fname))
-      else
-        vim.schedule(function()
-          vim.notify(('[gopls] cmd failed with code %d: %s\n%s'):format(output.code, cmd, output.stderr))
-        end)
-      end
-    end)
+    on_dir(get_root_dir(fname))
   end,
 }