string-util: imply NULL termination of strextend() argument list

The trailing NULL in the argument list is now implied (similar to
what we already have in place in strjoin()).

src/basic/cgroup-util.c

@@ -1619,7 +1619,7 @@ int cg_slice_to_path(const char *unit, char **ret) {
                 if (!escaped)
                         return -ENOMEM;
 
-                if (!strextend(&s, escaped, "/", NULL))
+                if (!strextend(&s, escaped, "/"))
                         return -ENOMEM;
 
                 dash = strchr(dash+1, '-');
@@ -1629,7 +1629,7 @@ int cg_slice_to_path(const char *unit, char **ret) {
         if (!e)
                 return -ENOMEM;
 
-        if (!strextend(&s, e, NULL))
+        if (!strextend(&s, e))
                 return -ENOMEM;
 
         *ret = TAKE_PTR(s);

src/basic/fs-util.c

@@ -934,7 +934,7 @@ int chase_symlinks(const char *path, const char *original_root, unsigned flags,
                         /* Preserve the trailing slash */
 
                         if (flags & CHASE_TRAIL_SLASH)
-                                if (!strextend(&done, "/", NULL))
+                                if (!strextend(&done, "/"))
                                         return -ENOMEM;
 
                         break;
@@ -1005,7 +1005,7 @@ int chase_symlinks(const char *path, const char *original_root, unsigned flags,
                                 if (streq_ptr(done, "/"))
                                         *done = '\0';
 
-                                if (!strextend(&done, first, todo, NULL))
+                                if (!strextend(&done, first, todo))
                                         return -ENOMEM;
 
                                 exists = false;
@@ -1098,7 +1098,7 @@ int chase_symlinks(const char *path, const char *original_root, unsigned flags,
                         if (streq(done, "/"))
                                 *done = '\0';
 
-                        if (!strextend(&done, first, NULL))
+                        if (!strextend(&done, first))
                                 return -ENOMEM;
                 }
 

src/basic/string-util.c

@@ -791,10 +791,10 @@ char *strip_tab_ansi(char **ibuf, size_t *_isz, size_t highlight[2]) {
         return *ibuf;
 }
 
-char *strextend_with_separator(char **x, const char *separator, ...) {
-        bool need_separator;
+char *strextend_with_separator_internal(char **x, const char *separator, ...) {
         size_t f, l, l_separator;
-        char *r, *p;
+        bool need_separator;
+        char *nr, *p;
         va_list ap;
 
         assert(x);
@@ -818,7 +818,7 @@ char *strextend_with_separator(char **x, const char *separator, ...) {
                 if (need_separator)
                         n += l_separator;
 
-                if (n > ((size_t) -1) - l) {
+                if (n >= SIZE_MAX - l) {
                         va_end(ap);
                         return NULL;
                 }
@@ -830,11 +830,12 @@ char *strextend_with_separator(char **x, const char *separator, ...) {
 
         need_separator = !isempty(*x);
 
-        r = realloc(*x, l+1);
-        if (!r)
+        nr = realloc(*x, l+1);
+        if (!nr)
                 return NULL;
 
-        p = r + f;
+        *x = nr;
+        p = nr + f;
 
         va_start(ap, separator);
         for (;;) {
@@ -853,12 +854,11 @@ char *strextend_with_separator(char **x, const char *separator, ...) {
         }
         va_end(ap);
 
-        assert(p == r + l);
+        assert(p == nr + l);
 
         *p = 0;
-        *x = r;
 
-        return r + l;
+        return p;
 }
 
 char *strrep(const char *s, unsigned n) {

src/basic/string-util.h

@@ -189,9 +189,10 @@ char *strreplace(const char *text, const char *old_string, const char *new_strin
 
 char *strip_tab_ansi(char **ibuf, size_t *_isz, size_t highlight[2]);
 
-char *strextend_with_separator(char **x, const char *separator, ...) _sentinel_;
+char *strextend_with_separator_internal(char **x, const char *separator, ...) _sentinel_;
 
-#define strextend(x, ...) strextend_with_separator(x, NULL, __VA_ARGS__)
+#define strextend_with_separator(x, separator, ...) strextend_with_separator_internal(x, separator, __VA_ARGS__, NULL)
+#define strextend(x, ...) strextend_with_separator_internal(x, NULL, __VA_ARGS__, NULL)
 
 char *strrep(const char *s, unsigned n);