eval: delimit string with NUL byte (#6467)

A recent refactor left cpy without a NUL terminator, simplify the code
instead of patching over it.

Instead of plain memcpy, it'd be better to employ harder to misuse string
functions made for this purpose like xstrlcpy(), but path_tail() takes
char_u arguments and returns them, leading to a lot of ugly casting.

Fixes #6431.

1 files changed, 4 insertions, 6 deletions

diff --git a/src/nvim/eval.c b/src/nvim/eval.c
index 7ab07fe6a2..1636b490d5 100644
--- a/src/nvim/eval.c
+++ b/src/nvim/eval.c
@@ -13416,14 +13416,12 @@ static void f_resolve(typval_T *argvars, typval_T *rettv, FunPtr fptr)
           q = (char *)path_tail((char_u *)p);
         }
         if (q > p && !path_is_absolute_path((const char_u *)buf)) {
-          // Symlink is relative to directory of argument.
+          // Symlink is relative to directory of argument. Replace the
+          // symlink with the resolved name in the same directory.
           const size_t p_len = strlen(p);
           const size_t buf_len = strlen(buf);
-          cpy = xmalloc(p_len + buf_len + 1);
-          memcpy(cpy, p, p_len);
-          memcpy(path_tail((char_u *)cpy), buf, buf_len + 1);
-          xfree(p);
-          p = cpy;
+          p = xrealloc(p, p_len + buf_len + 1);
+          memcpy(path_tail((char_u *)p), buf, buf_len + 1);
         } else {
           xfree(p);
           p = xstrdup(buf);