time-util: add timestamp output style that shows dates only, no times

src/basic/time-util.c

@@ -326,14 +326,15 @@ char *format_timestamp_style(
                 return snprintf_ok(buf, l, "@" USEC_FMT, t / USEC_PER_SEC);  /* round down µs → s */
         }
 
-        utc = IN_SET(style, TIMESTAMP_UTC, TIMESTAMP_US_UTC);
+        utc = IN_SET(style, TIMESTAMP_UTC, TIMESTAMP_US_UTC, TIMESTAMP_DATE);
         us = IN_SET(style, TIMESTAMP_US, TIMESTAMP_US_UTC);
 
-        if (l < (size_t) (3 +                  /* week day */
-                          1 + 10 +             /* space and date */
-                          1 + 8 +              /* space and time */
-                          (us ? 1 + 6 : 0) +   /* "." and microsecond part */
-                          1 + (utc ? 3 : 1) +  /* space and shortest possible zone */
+        if (l < (size_t) (3 +                   /* week day */
+                          1 + 10 +              /* space and date */
+                          style == TIMESTAMP_DATE ? 0 :
+                          (1 + 8 +              /* space and time */
+                           (us ? 1 + 6 : 0) +   /* "." and microsecond part */
+                           1 + (utc ? 3 : 1)) + /* space and shortest possible zone */
                           1))
                 return NULL; /* Not enough space even for the shortest form. */
 
@@ -344,6 +345,7 @@ char *format_timestamp_style(
                         [TIMESTAMP_US]     = "--- XXXX-XX-XX XX:XX:XX.XXXXXX",
                         [TIMESTAMP_UTC]    = "--- XXXX-XX-XX XX:XX:XX UTC",
                         [TIMESTAMP_US_UTC] = "--- XXXX-XX-XX XX:XX:XX.XXXXXX UTC",
+                        [TIMESTAMP_DATE]   = "--- XXXX-XX-XX",
                 };
 
                 assert(l >= strlen(xxx[style]) + 1);
@@ -359,6 +361,14 @@ char *format_timestamp_style(
         assert((size_t) tm.tm_wday < ELEMENTSOF(weekdays));
         memcpy(buf, weekdays[tm.tm_wday], 4);
 
+        if (style == TIMESTAMP_DATE) {
+                /* Special format string if only date should be shown. */
+                if (strftime(buf + 3, l - 3, " %Y-%m-%d", &tm) <= 0)
+                        return NULL; /* Doesn't fit */
+
+                return buf;
+        }
+
         /* Add the main components */
         if (strftime(buf + 3, l - 3, " %Y-%m-%d %H:%M:%S", &tm) <= 0)
                 return NULL; /* Doesn't fit */

src/basic/time-util.h

@@ -35,6 +35,7 @@ typedef enum TimestampStyle {
         TIMESTAMP_UTC,
         TIMESTAMP_US_UTC,
         TIMESTAMP_UNIX,
+        TIMESTAMP_DATE,
         _TIMESTAMP_STYLE_MAX,
         _TIMESTAMP_STYLE_INVALID = -EINVAL,
 } TimestampStyle;