fix(text): indent() ignores `expandtab` when indent unchanged #40932

Problem:
After expanding tabs with the `expandtab` option, if the old indent
matches the requested one, `vim.text.indent()` returns the input
unchanged.
The optimization path assumes that if old_indent == size, the input
wouldn't be changed, which is not correct when old_indent is formed by
expanded tabs.

Solution:
Apply the optimization only when `expandtab` is not set.

1 files changed, 2 insertions, 0 deletions

diff --git a/test/functional/lua/text_spec.lua b/test/functional/lua/text_spec.lua
index a4a41dc862..9e80f81bc5 100644
--- a/test/functional/lua/text_spec.lua
+++ b/test/functional/lua/text_spec.lua
@@ -47,6 +47,8 @@ describe('vim.text', function()
         { ' \n  \nfoo\n\nbar\nbaz\n    \n', 1 },
         { vim.text.indent(0, '  \n   \n foo\n\n bar\n baz\n     \n') }
       )
+      -- Tabs expand when old indent matches new indent #40932.
+      eq({ '  a', 2 }, { vim.text.indent(2, '\t a', { expandtab = 1 }) })
     end)
 
     it('real-world cases', function()