fix(eval): writestring() handling of null #39328

Problem:
- write_blob, write_string dereference args which may be NULL.
- `writefile(v:_null_blob, …)` fails.

Solution:
- Fix the annotation.
- Handle null blob.

Co-authored-by: zeertzjq <zeertzjq@outlook.com>

1 files changed, 8 insertions, 1 deletions

diff --git a/test/functional/vimscript/writefile_spec.lua b/test/functional/vimscript/writefile_spec.lua
index f406e5a469..b784868a7b 100644
--- a/test/functional/vimscript/writefile_spec.lua
+++ b/test/functional/vimscript/writefile_spec.lua
@@ -65,6 +65,13 @@ describe('writefile()', function()
     eq('\n', read_file(fname))
   end)
 
+  it('writes a null blob to a file', function()
+    eq(0, fn.writefile({ 'line1' }, fname, 'b'))
+    eq('line1', read_file(fname))
+    command(('call writefile(v:_null_blob, "%s")'):format(fname))
+    eq('', read_file(fname))
+  end)
+
   it('appends to a file', function()
     eq(nil, read_file(fname))
     eq(0, fn.writefile({ 'abc', 'def', 'ghi' }, fname))
@@ -100,7 +107,7 @@ describe('writefile()', function()
     eq('a\0', read_file(fname))
   end)
 
-  it('writes Lua strings to a file', function()
+  it('writes Lua (binary) strings to a file', function()
     eq(0, exec_lua([[return vim.fn.writefile('foo\0bar', ..., 'b')]], fname))
     eq('foo\0bar', read_file(fname))
   end)