From 544bde3accf33370d1ac1b3306abb23bdbb2d01a Mon Sep 17 00:00:00 2001
From: zeertzjq <zeertzjq@outlook.com>
Date: Wed, 17 Dec 2025 06:46:22 +0800
Subject: [PATCH] vim-patch:9.1.1987: assert_equal() prepends unnecessary ':'
 when typed

Problem:  assert_equal() prepends unnecessary ':' when typed
          (after 9.0.1758).
Solution: Don't change a NULL stacktrace to an empty string (zeertzjq).

closes: vim/vim#18936

https://github.com/vim/vim/commit/c4b3aefd0d5f81693e7098f224d3e4bfe24a7aa7
---
 src/nvim/runtime.c               |  5 ++++-
 test/old/testdir/test_assert.vim | 13 +++++++++++++
 2 files changed, 17 insertions(+), 1 deletion(-)

diff --git a/src/nvim/runtime.c b/src/nvim/runtime.c
index 90f48333b2..9152f132ce 100644
--- a/src/nvim/runtime.c
+++ b/src/nvim/runtime.c
@@ -229,7 +229,10 @@ char *estack_sfile(estack_arg_T which)
     }
   }
 
-  ga_append(&ga, NUL);
+  // Only NUL-terminate when not returning NULL.
+  if (ga.ga_data != NULL) {
+    ga_append(&ga, NUL);
+  }
   return (char *)ga.ga_data;
 }
 
diff --git a/test/old/testdir/test_assert.vim b/test/old/testdir/test_assert.vim
index fa63af687d..03d3cab771 100644
--- a/test/old/testdir/test_assert.vim
+++ b/test/old/testdir/test_assert.vim
@@ -386,6 +386,19 @@ func Test_assert_fails_in_timer()
   call StopVimInTerminal(buf)
 endfunc
 
+" Check that a typed assert_equal() doesn't prepend an unnecessary ':'.
+func Test_assert_equal_typed()
+  let after =<< trim END
+    call feedkeys(":call assert_equal(0, 1)\<CR>", 't')
+    call feedkeys(":call writefile(v:errors, 'Xerrors')\<CR>", 't')
+    call feedkeys(":qa!\<CR>", 't')
+  END
+  call assert_equal(1, RunVim([], after, ''))
+  call assert_equal(['Expected 0 but got 1'], readfile('Xerrors'))
+
+  call delete('Xerrors')
+endfunc
+
 func Test_assert_beeps()
   new
   call assert_equal(0, assert_beeps('normal h'))