nvim: fix handling of tabs/spaces for shfmt formatter

config/nvim/lua/fschauen/plugins/formatter.lua

@@ -1,3 +1,26 @@
+local shfmt = function()
+  local indent = 0 -- Assume tabs initially.
+  if vim.opt.expandtab:get() then
+    local shiftwidth = vim.opt.shiftwidth:get()
+    if shiftwidth == 0 then
+      indent = vim.opt.tabstop:get()
+    else
+      indent = shiftwidth
+    end
+  end
+
+  return {
+    exe = "shfmt",
+    -- stylua: ignore start
+    args = {
+      "--indent", indent,   -- 0 for tabs, >0 for number of spaces.
+      "--keep-padding",     -- Keep column alignment paddings.
+    },
+    -- stylua: ignore end
+    stdin = true,
+  }
+end
+
 return {
   "mhartington/formatter.nvim",
 
@@ -28,7 +51,7 @@ return {
         lua      = { builtin.lua.stylua },
         markdown = { builtin.markdown.prettier },
         python   = {}, -- TODO: pick one
-        sh       = { builtin.sh.shfmt },
+        sh       = { shfmt() },
         zsh      = { builtin.zsh.beautysh },
         -- stylua: ignore end
       },