fix extra newlines when copying from diff in Firefox (#7288)

* fix extra newlines when copying from diff

See https://bugzilla.mozilla.org/show_bug.cgi?id=1273836

Basically, the <pre><code> seems to add a forced newline that is not
possible to get rid of via CSS, so I replaced it with just a <code>.

Secondly, .lines-type-marker also forced a newline in the copied text,
but that was possible to get rid of via user-select.

Safari still has a extraneous newline in the copied text of unknown
origin, but this should not block stop this PR.

* simplify .line-type-marker

* fix selector

* remove erronous ^^^

* Fix empty split diff

* Fix arc-theme-green

* fix add comment

* ensure line-num is copied too

* Update templates/repo/diff/box.tmpl

Co-Authored-By: zeripath <art27@cantab.net>

* attempt to fix safari via removing <code>

* remove useless whitespace at the end of 'class'

* remove inter-tag whitespace for code <td>s

* more inter-tag removal

* final inter-tag removal

* attempt to fix empty line copy

* move and comment getLineContent

* fix golint

* make background grey for missing added code

3 files changed, 12 insertions, 10 deletions

diff --git a/public/less/_base.less b/public/less/_base.less
index 13ae1ad665..213ae2d2e6 100644
--- a/public/less/_base.less
+++ b/public/less/_base.less
@@ -160,7 +160,8 @@ a {
 }
 
 pre,
-code {
+code,
+.mono {
     font: 12px @monospaced-fonts, monospace;
 
     &.raw {
diff --git a/public/less/_repository.less b/public/less/_repository.less
index 8d38faf50c..681296b74d 100644
--- a/public/less/_repository.less
+++ b/public/less/_repository.less
@@ -1362,10 +1362,6 @@
                 border-top: 0;
             }
 
-            pre {
-                margin: 0;
-            }
-
             .lines-num {
                 border-color: #d4d4d5;
                 border-right-width: 1px;
@@ -1405,7 +1401,7 @@
                         background-color: #99ff99;
                     }
 
-                    .lines-num[data-line-num]::before {
+                    [data-line-num]::before {
                         content: attr(data-line-num);
                         text-align: right;
                     }
@@ -1413,9 +1409,10 @@
                     .lines-type-marker {
                         width: 10px;
                         min-width: 10px;
+                        user-select: none;
                     }
 
-                    .line-type-marker[data-type-marker]::before {
+                    [data-type-marker]::before {
                         content: attr(data-type-marker);
                         text-align: right;
                         display: inline-block;
@@ -1448,7 +1445,7 @@
                 // light gray for empty lines before / after commit
                 &.add-code td:nth-child(1),
                 &.add-code td:nth-child(2),
-                &.del-code td:nth-child(3),
+                &.add-code td:nth-child(3),
                 &.del-code td:nth-child(4),
                 &.del-code td:nth-child(5),
                 &.del-code td:nth-child(6) {
diff --git a/public/less/themes/arc-green.less b/public/less/themes/arc-green.less
index d2fe2982d7..463a979434 100644
--- a/public/less/themes/arc-green.less
+++ b/public/less/themes/arc-green.less
@@ -1115,12 +1115,15 @@ a.ui.labels .label:hover {
 .repository .diff-file-box .code-diff-split tbody tr.add-code td:nth-child(1),
 .repository .diff-file-box .code-diff-split tbody tr.add-code td:nth-child(2),
 .repository .diff-file-box .code-diff-split tbody tr.del-code td:nth-child(3),
-.repository .diff-file-box .code-diff-split tbody tr.del-code td:nth-child(4) {
+.repository .diff-file-box .code-diff-split tbody tr.del-code td:nth-child(4),
+.repository .diff-file-box .code-diff-split tbody tr.del-code td:nth-child(5),
+.repository .diff-file-box .code-diff-split tbody tr.del-code td:nth-child(6) {
     background-color: #2a2e3a;
 }
 
-.repository .diff-file-box .code-diff-split tbody tr.add-code td:nth-child(3),
 .repository .diff-file-box .code-diff-split tbody tr.add-code td:nth-child(4),
+.repository .diff-file-box .code-diff-split tbody tr.add-code td:nth-child(5),
+.repository .diff-file-box .code-diff-split tbody tr.add-code td:nth-child(6),
 .repository .diff-file-box .code-diff-split tbody tr td.add-code {
     background-color: #283e2d !important;
     border-color: #314a37 !important;
@@ -1128,6 +1131,7 @@ a.ui.labels .label:hover {
 
 .repository .diff-file-box .code-diff-split tbody tr.del-code td:nth-child(1),
 .repository .diff-file-box .code-diff-split tbody tr.del-code td:nth-child(2),
+.repository .diff-file-box .code-diff-split tbody tr.del-code td:nth-child(3),
 .repository .diff-file-box .code-diff-split tbody tr td.del-code {
     background-color: #3c2626 !important;
     border-color: #634343 !important;