With "+" the strings are separate expressions, and format() is called on the last string before concatenation. (So substitution does not happen.) Without "+" the string literals are merged first by the parser, so format() is called on the complete string.

Should I make a JIRA for this?

Author: Daniel Darabos <darabos.daniel@gmail.com>

Closes #7288 from darabos/patch-2 and squashes the following commits:

be0d3b7 [Daniel Darabos] Correctly print hostname in error

(cherry picked from commit 5687f765)
Signed-off-by: Kousuke Saruta <sarutak@oss.nttdata.co.jp>