fix: util.root_pattern prioritises pattern order (#2885)

* fix: util.root_pattern prioritises pattern order

Instead of traversing the filesystem upwards once and
returning the first match of all the patterns, it traverses
the filesystem upwards once for each pattern. This means
that the order of the patterns provided matters, and the
highest priority patterns should be put first. Also updated
corresponding tests.

* docs: update util.root_pattern description

doc/lspconfig.txt

@@ -371,7 +371,8 @@ below returns a function that takes as its argument the current buffer path.
 - `util.root_pattern`: function which takes multiple arguments, each 
   corresponding to a different root pattern against which the contents of the
   current directory are matched using |vim.fn.glob()| while traversing up the
-  filesystem.
+  filesystem. Parent directories are traversed once per pattern, in the order
+  the patterns are specified.
 >
    root_dir = util.root_pattern('pyproject.toml', 'requirements.txt')
 <

lua/lspconfig/util.lua

@@ -250,19 +250,22 @@ end
 
 function M.root_pattern(...)
   local patterns = vim.tbl_flatten { ... }
-  local function matcher(path)
+  return function(startpath)
+    startpath = M.strip_archive_subpath(startpath)
     for _, pattern in ipairs(patterns) do
-      for _, p in ipairs(vim.fn.glob(M.path.join(M.path.escape_wildcards(path), pattern), true, true)) do
-        if M.path.exists(p) then
-          return path
+      local match = M.search_ancestors(startpath, function(path)
+        for _, p in ipairs(vim.fn.glob(M.path.join(M.path.escape_wildcards(path), pattern), true, true)) do
+          if M.path.exists(p) then
+            return path
+          end
         end
+      end)
+
+      if match ~= nil then
+        return match
       end
     end
   end
-  return function(startpath)
-    startpath = M.strip_archive_subpath(startpath)
-    return M.search_ancestors(startpath, matcher)
-  end
 end
 
 function M.find_git_ancestor(startpath)

test/lspconfig_spec.lua

@@ -136,7 +136,7 @@ describe('lspconfig', function()
         -- change the working directory to test directory
         vim.api.nvim_command 'cd ./test/test_dir/a'
         local cwd = vim.fn.getcwd()
-        eq(true, cwd == lspconfig.util.root_pattern { 'root_marker.txt', 'a_marker.txt' }(cwd))
+        eq(true, cwd == lspconfig.util.root_pattern { 'a_marker.txt', 'root_marker.txt' }(cwd))
       end)
 
       it('resolves to root_marker.txt', function()