diff -r 0131b7b44c32 -r d85258458623 src/Pure/Tools/phabricator.scala
--- a/src/Pure/Tools/phabricator.scala	Thu Dec 19 17:29:35 2019 +0100
+++ b/src/Pure/Tools/phabricator.scala	Thu Dec 19 22:13:47 2019 +0100
@@ -243,7 +243,7 @@
 
     if (mercurial_source.nonEmpty) {
       for { name <- List("mercurial", "mercurial-common") if Linux.package_installed(name) } {
-        error("Cannot install Mercurial from source:" +
+        error("Cannot install Mercurial from source:\n" +
           "package package " + quote(name) + " already installed")
       }
       mercurial_setup(mercurial_source, progress = progress)