LSP: Refine formatting tabSize #11834

Use the logic explained in the softtabstop help section for defining
the tabSize parameter in formatting requests. This means that:

 - if softtabstop is 0, tabstop is used
 - if softtabstop < 0, shiftwidth is used
 - if softtabstop > 0, softtabstop is used

When inserting spaces instead of tabs, softtabstop is used in vim.
Therefor it would be more logical to use it when formatting instead
of the current tabstop.

1 files changed, 4 insertions, 2 deletions

diff --git a/runtime/lua/vim/lsp/buf.lua b/runtime/lua/vim/lsp/buf.lua
index a6a05fb095..19deb5df45 100644
--- a/runtime/lua/vim/lsp/buf.lua
+++ b/runtime/lua/vim/lsp/buf.lua
@@ -68,8 +68,9 @@ end
 
 function M.formatting(options)
   validate { options = {options, 't', true} }
+  local sts = vim.bo.softtabstop;
   options = vim.tbl_extend('keep', options or {}, {
-    tabSize = vim.bo.tabstop;
+    tabSize = (sts > 0 and sts) or (sts < 0 and vim.bo.shiftwidth) or vim.bo.tabstop;
     insertSpaces = vim.bo.expandtab;
   })
   local params = {
@@ -85,8 +86,9 @@ function M.range_formatting(options, start_pos, end_pos)
     start_pos = {start_pos, 't', true};
     end_pos = {end_pos, 't', true};
   }
+  local sts = vim.bo.softtabstop;
   options = vim.tbl_extend('keep', options or {}, {
-    tabSize = vim.bo.tabstop;
+    tabSize = (sts > 0 and sts) or (sts < 0 and vim.bo.shiftwidth) or vim.bo.tabstop;
     insertSpaces = vim.bo.expandtab;
   })
   local A = list_extend({}, start_pos or api.nvim_buf_get_mark(0, '<'))