refactor: Remove strncpy/STRNCPY. (#6008)

Closes #731
References #851

Note: This does not remove some intentional legacy usages of strncpy.
      - memcpy isn't equivalent because it doesn't check the string
        length of `src`, and doesn't zero-out the remainder of `dst`.
      - xstrlcpy isn't equivalent because it doesn't zero-out the
        remainder of `dst`. Some Vim logic depends on that (e.g.
        ex_append which calls vim_strnsave).

Helped-by: Douglas Schneider <ds3@ualberta.ca>
Helped-by: oni-link <knil.ino@gmail.com>
Helped-by: James McCoy <jamessan@jamessan.com>

1 files changed, 5 insertions, 6 deletions

diff --git a/src/nvim/strings.c b/src/nvim/strings.c
index 5b4f23f30e..b38d4f8a58 100644
--- a/src/nvim/strings.c
+++ b/src/nvim/strings.c
@@ -51,15 +51,14 @@ char_u *vim_strsave(const char_u *string)
   return (char_u *)xstrdup((char *)string);
 }
 
-/*
- * Copy up to "len" bytes of "string" into newly allocated memory and
- * terminate with a NUL.
- * The allocated memory always has size "len + 1", also when "string" is
- * shorter.
- */
+/// Copy up to `len` bytes of `string` into newly allocated memory and
+/// terminate with a NUL. The allocated memory always has size `len + 1`, even
+/// when `string` is shorter.
 char_u *vim_strnsave(const char_u *string, size_t len)
   FUNC_ATTR_NONNULL_RET FUNC_ATTR_MALLOC FUNC_ATTR_NONNULL_ALL
 {
+  // strncpy is intentional: some parts of Vim use `string` shorter than `len`
+  // and expect the remainder to be zeroed out.
   return (char_u *)strncpy(xmallocz(len), (char *)string, len);
 }