[PATCH 2 of 2 V2] paper: make all source lines have the same minimum height

[Anton Shestakov]

# HG changeset patch
# User Anton Shestakov <av6 at dwimlabs.net>
# Date 1522818888 -28800
#      Wed Apr 04 13:14:48 2018 +0800
# Node ID 7279e5d2e3b27b46b19218f91f19023bce5f6c30
# Parent  41826e0ae22d24a04cc1f4b911a56b787635fa6e
paper: make all source lines have the same minimum height

Empty source lines in paper and coal themes used to have smaller height than
every other line (because of the way line numbers are shown and because they
are using smaller font). This wasn't very noticeable before the follow lines
functionality was added, but after that just using the follow-lines button to
select a block of code with empty lines would demonstrate the fact that empty
lines didn't have enough height - there were white "gaps" in the selection
block.

Since this problem occurs when lines don't have any content inside, let's
create a pseudo-element (it's unselectable because of that) which still doesn't
have any content, but fills up empty lines to 100% of their height because of
display: inline-block. This is the most natural way to solve this annoyance
that I've found so far.

Hardcoding height isn't useful because we can have wrapped lines, in which case
multiple lines of text need to fit into a single <span>.

Setting min-height or line-height doesn't remove the gaps when viewed in
Chromium.

diff --git a/mercurial/templates/static/style-paper.css b/mercurial/templates/static/style-paper.css
--- a/mercurial/templates/static/style-paper.css
+++ b/mercurial/templates/static/style-paper.css
@@ -308,6 +308,11 @@ td.annotate:hover div.annotate-info { di
   float: left;
 }
 
+.sourcelines > span:after {
+  content: '';
+  display: inline-block;
+}
+
 .sourcelines > span:target, tr:target td {
   background-color: #bfdfff;
 }