Hi!

Thanks for the patch!

It’s strange, but Tarantool happens to handle this case correctly?

% echo 'error({}); print(42)' | ./src/tarantool -e 'debug.debug()' 
lua_debug> (null)
lua_debug> %                                                                                                                                                                                                                                                              % echo $?
0

Surely, with the patch applied I see the following, as expected:

% echo 'error({}); print(42)' | ./src/tarantool -e 'debug.debug()'
lua_debug> (error object is not a string)
lua_debug> %                                                                                                                                                                                                                                                              % 


Is it relevant at all?

regards,
Sergos


> On 30 Dec 2021, at 14:45, Sergey Kaplun <skaplun@tarantool.org> wrote:
> 
> From: Mike Pall <mike>
> 
> (cherry picked from f5b0fff5a990004375ad43aa6e6c4a11a8b6eb7e)
> 
> `lua_tostring()` returns NULL for non-string and non-number objects.
> Returned value is passed to `fputs()` without check, so that leads to
> crash in case of NULL.
> 
> This patch adds the corresponding check. "(error object is not a
> string)" is returned in the aforementioned case.
> 
> Sergey Kaplun:
> * added the description and the test for the problem
> 
> Part of tarantool/tarantool#6548
> ---
> 
> Related issue: https://github.com/tarantool/tarantool/issues/6548
> Branch: https://github.com/tarantool/luajit/tree/skaplun/gh-noticket-debug-debug-non-string-err
> Tarantool branch: https://github.com/tarantool/tarantool/tree/skaplun/gh-noticket-debug-debug-non-string-err-full-ci
> 
> src/lib_debug.c                               |  3 ++-
> .../debug-non-string-error.test.lua           | 26 +++++++++++++++++++
> 2 files changed, 28 insertions(+), 1 deletion(-)
> create mode 100644 test/tarantool-tests/debug-non-string-error.test.lua
> 
> diff --git a/src/lib_debug.c b/src/lib_debug.c
> index 8fdfda03..c8f61a43 100644
> --- a/src/lib_debug.c
> +++ b/src/lib_debug.c
> @@ -369,7 +369,8 @@ LJLIB_CF(debug_debug)
>       return 0;
>     if (luaL_loadbuffer(L, buffer, strlen(buffer), "=(debug command)") ||
> 	lua_pcall(L, 0, 0, 0)) {
> -      fputs(lua_tostring(L, -1), stderr);
> +      const char *s = lua_tostring(L, -1);
> +      fputs(s ? s : "(error object is not a string)", stderr);
>       fputs("\n", stderr);
>     }
>     lua_settop(L, 0);  /* remove eventual returns */
> diff --git a/test/tarantool-tests/debug-non-string-error.test.lua b/test/tarantool-tests/debug-non-string-error.test.lua
> new file mode 100644
> index 00000000..9151dd1a
> --- /dev/null
> +++ b/test/tarantool-tests/debug-non-string-error.test.lua
> @@ -0,0 +1,26 @@
> +local tap = require('tap')
> +
> +local test = tap.test('debug-non-string-error')
> +test:plan(1)
> +
> +local i = 0
> +while arg[i] do i = i - 1 end
> +local luabin = arg[i + 1]
> +
> +local magic = 42
> +-- XXX: Need \n before print to be interpreted as independend
> +-- command.
> +local cmd = ([[
> +  echo 'error({});
> +  print(%d)' | %s -e 'debug.debug()' 2>&1
> +]]):format(magic, luabin)
> +
> +local proc = io.popen(cmd)
> +local res = proc:read('*all'):gsub('%s+$', '')
> +local ldb = 'lua_debug> '
> +local errmsg = '(error object is not a string)'
> +-- XXX: lines aren't broken by '\n', so need 2 `ldb`.
> +local expected = ldb .. errmsg .. '\n' .. ldb .. ldb .. magic
> +test:ok(res == expected, 'handle non-string error in debug.debug()')
> +
> +os.exit(test:check() and 0 or 1)
> -- 
> 2.34.1
>