core: Check for TERM=dumb in show_status()

We shouldn't try to use any ANSI escape sequences if TERM=dumb.
Also, the "\r\n" we output can get interpreted as a double newline
(for example by Github Actions), so let's output just "\n" when
TERM=dumb to clean up the CI logs.

src/basic/log.c

@@ -434,6 +434,8 @@ static int write_to_console(
                 const char *func,
                 const char *buffer) {
 
+        static int dumb = -1;
+
         char location[256],
              header_time[FORMAT_TIMESTAMP_MAX],
              prefix[1 + DECIMAL_STR_MAX(int) + 2],
@@ -445,6 +447,9 @@ static int write_to_console(
         if (console_fd < 0)
                 return 0;
 
+        if (dumb < 0)
+                dumb = getenv_terminal_is_dumb();
+
         if (LOG_PRI(level) > log_target_max_level[LOG_TARGET_CONSOLE])
                 return 0;
 
@@ -491,8 +496,9 @@ static int write_to_console(
         /* When writing to a TTY we output an extra '\r' (i.e. CR) first, to generate CRNL rather than just
          * NL. This is a robustness thing in case the TTY is currently in raw mode (specifically: has the
          * ONLCR flag off). We want that subsequent output definitely starts at the beginning of the line
-         * again, after all. If the TTY is not in raw mode the extra CR should not hurt. */
-        iovec[n++] = IOVEC_MAKE_STRING(check_console_fd_is_tty() ? "\r\n" : "\n");
+         * again, after all. If the TTY is not in raw mode the extra CR should not hurt. If we're writing to
+         * a dumb terminal, only write NL as CRNL might be interpreted as a double newline. */
+        iovec[n++] = IOVEC_MAKE_STRING(check_console_fd_is_tty() && !dumb ? "\r\n" : "\n");
 
         if (writev(console_fd, iovec, n) < 0) {
 

src/basic/terminal-util.c

@@ -1296,7 +1296,7 @@ static bool on_dev_null(void) {
         return cached_on_dev_null;
 }
 
-static bool getenv_terminal_is_dumb(void) {
+bool getenv_terminal_is_dumb(void) {
         const char *e;
 
         e = getenv("TERM");

src/basic/terminal-util.h

@@ -172,6 +172,7 @@ void columns_lines_cache_reset(int _unused_ signum);
 void reset_terminal_feature_caches(void);
 
 bool on_tty(void);
+bool getenv_terminal_is_dumb(void);
 bool terminal_is_dumb(void);
 ColorMode get_color_mode(void);
 bool underline_enabled(void);