New compiler warning for v.c after upgrade to Fedora-28

[tavmem]

cc -g -pthread -O0 -g3 -DDEBUG -Wall -c -o src/v.t.o src/v.c
src/v.c: In function ‘enumerate_charvec’:
src/v.c:335:3: warning: ‘strncpy’ output truncated before terminating nul copying 3 bytes from a string of the same length [-Wstringop-truncation]
strncpy(kC(p),"ls ", 3);
^~~~~~~~~~~~~~~~~~~~~~~

This warning occurs with the -DDEBUG option when compiling k_test.

[tavmem]

This compiler warning first shows up in the first of 2 commits 444c19b made on Feb 9, 2018.
The title of this commit is "fix warnings using -Wall with gcc & remove some trailing blanks".

[tavmem]

The reason that this warning first shows up in the commit 444c19b of Feb 9, 2018 is that beginning with that commit 'Makefile' specifies the display of all Warning messages:

-DEVFLAGS = -O0 -g3 -DDEBUG -Wunused -Wreturn-type -Wimplicit-int #-Wall
+DEVFLAGS = -O0 -g3 -DDEBUG -Wunused -Wreturn-type -Wimplicit-int -Wall

[tavmem]

The code currently causing the warning message exists at least as far back as the commit 41e48b6 made on Nov 24, 2011:

static K enumerate_charvec(C *pth)
{
  K z;
  I len=strlen(pth);
  K p=newK(-3,len+3);
  strncpy(kC(p),"ls ", 3);
  strncpy(kC(p)+3,pth,len);
  z = popen_charvec(kC(p));
  cd(p);
  R z;
}

[tavmem]

@bakul wrote:

This code change seems wrong.
man strcat
man strncat
The original code is also wrong unless newK allocates an extra element for the array as strncat tacks on a terminating nul char.

[tavmem]

@bakul also wrote:

s is assigned a literal string. strcat(s,pth) will append the contents of pth at the end of s. This is an undefined operation as per the C standard (and does indeed crash a simple example program for me) as it will overwrite whatever was statically allocated after the literal "ls ".

The original code is fine. I don't know what the compiler was bitching about, but a better change may be to replace original lines 333-336 with

I len=strlen(pth)+3;
K p=newK(-3,len);
snprintf(kC(p),len,"ls %s", pth);

Thanks !!