varlinkctl: respect $COLUMNS when rebreaking lines and we are not connected to a TTY

Let's provide a mechanism to select the number of screen columns for
rebreaking comments in Varlink IDL connected to a TTY, by honouring the
$COLUMNS env var then too. Previously we'd only honour when connected to
a TTY, but it's also useful otherwise for rebreaking ridiculously long
comments, hence honour it in this case too.

src/basic/terminal-util.c

@@ -944,24 +944,35 @@ int fd_columns(int fd) {
         return ws.ws_col;
 }
 
+int getenv_columns(void) {
+        int r;
+
+        const char *e = getenv("COLUMNS");
+        if (!e)
+                return -ENXIO;
+
+        unsigned c;
+        r = safe_atou_bounded(e, 1, USHRT_MAX, &c);
+        if (r < 0)
+                return r;
+
+        return (int) c;
+}
+
 unsigned columns(void) {
-        const char *e;
-        int c;
 
         if (cached_columns > 0)
                 return cached_columns;
 
-        c = 0;
-        e = getenv("COLUMNS");
-        if (e)
-                (void) safe_atoi(e, &c);
-
-        if (c <= 0 || c > USHRT_MAX) {
+        int c = getenv_columns();
+        if (c < 0) {
                 c = fd_columns(STDOUT_FILENO);
-                if (c <= 0)
+                if (c < 0)
                         c = 80;
         }
 
+        assert(c > 0);
+
         cached_columns = c;
         return cached_columns;
 }

src/basic/terminal-util.h

@@ -95,6 +95,7 @@ void reset_dev_console_fd(int fd, bool switch_to_text);
 int lock_dev_console(void);
 int make_console_stdio(void);
 
+int getenv_columns(void);
 int fd_columns(int fd);
 unsigned columns(void);
 int fd_lines(int fd);