[humanize] pad out duration to align fields

Fixes #933

src/base/humanize.time.cc

@@ -192,6 +192,9 @@ duration::to_string() const
                  amount,
                  curr_interval->symbol);
         retval.insert(0, segment);
+        if (remaining > 0 && amount < 10 && curr_interval->symbol[0]) {
+            retval.insert(0, "0");
+        }
     }
 
     if (neg) {

src/base/humanize.time.tests.cc

@@ -106,7 +106,10 @@ TEST_CASE("duration to_string")
     std::string val;
 
     val = humanize::time::duration::from_tv({25 * 60 * 60, 123000}).to_string();
-    CHECK(val == "1d1h0m0s");
+    CHECK(val == "1d01h00m00s");
+    val = humanize::time::duration::from_tv({25 * 60 * 60 + 25 * 60, 123000})
+              .to_string();
+    CHECK(val == "1d01h25m00s");
     val = humanize::time::duration::from_tv({10, 123000}).to_string();
     CHECK(val == "10s123");
     val = humanize::time::duration::from_tv({10, 0}).to_string();

src/internals/sql-ref.rst

@@ -1528,7 +1528,7 @@ humanize_duration(*secs*)
     .. code-block::  custsqlite
 
       ;SELECT humanize_duration(15 * 60)
-      15m0s
+      15m00s
 
     To format a sub-second value: