Major refactoring

The additions to `_config.yml` go together with the changes to `code.scss`,
to facilitate adjusttments by users. See `docs/linenos-test` for the details.
The CSS code has been significantly refactored and simplified,
and seems to produce sensible results (at least on Safari and Firefox).

_config.yml

@@ -99,6 +99,11 @@ ga_tracking_anonymize_ip: true # Use GDPR compliant Google Analytics settings (t
 plugins:
   - jekyll-seo-tag
 
+kramdown:
+  syntax_highlighter_opts:
+    block:
+      line_numbers: false
+
 compress_html:
   clippings: all
   comments: all
@@ -106,3 +111,5 @@ compress_html:
   startings: []
   blanklines: false
   profile: false
+  # ignore:
+  #   envs: all

_sass/code.scss

@@ -38,55 +38,58 @@ code {
 // No kramdown line_numbers: fences and Liquid highlighting look the same.
 // Kramdown line_numbers = true: fences have a wider gutter than with Liquid?
 
-pre.highlight,
+// ```[LANG]...```
-figure.highlight {
+div.highlighter-rouge {
   padding: $sp-3;
   margin-top: 0;
-  margin-bottom: 0;
-  background-color: $code-background-color;
-  border-radius: $border-radius;
-  -webkit-overflow-scrolling: touch;
-
-  code {
-    padding: 0;
-    border: 0;
-  }
-}
-
-// Using Liquid tags for highlighting, optionally with linenos
-
-// Without linenos: figure.highlight > pre > code > div > span*
-
-figure.highlight,
-div.highlight {
-  padding: 0;
-  margin-top: 0;
   margin-bottom: $sp-3;
   background-color: $code-background-color;
   border-radius: $border-radius;
+  box-shadow: none;
   -webkit-overflow-scrolling: touch;
 
-  pre {
+  div.highlight,
-    padding: $sp-3;
+  pre.highlight,
-    margin-top: 0;
+  code {
-    margin-bottom: 0;
+    padding: 0;
+    margin: 0;
+    border: 0;
   }
 }
 
-// With linenos or kramdown line_numbers option:
+// {% highlight LANG [linenos] %}...{% endhighlight %}:
+figure.highlight {
+  padding: $sp-3;
+  margin-top: 0;
+  margin-bottom: $sp-3;
+  background-color: $code-background-color;
+  border-radius: $border-radius;
+  box-shadow: none;
+  -webkit-overflow-scrolling: touch;
 
-figure.highlight > pre > code,
+  pre,
-figure.highlight > code,
+  code {
-div.highlight > pre > code,
+    padding: 0;
-div.highlight > code {
+    margin: 0;
-  td,
+    border: 0;
+  }
+}
+
+// ```[LANG]...```, kramdown line_numbers = true,
+// {% highlight LANG linenos %}...{% endhighlight %}:
+.highlight .table-wrapper {
+  padding: 0;
+  margin: 0;
+  border: 0;
+  box-shadow: none;
+
+  tr > td,
   td > pre {
     @include fs-2;
     min-width: 0;
     padding: 0;
+    border: 0;
     background-color: $code-background-color;
-    border-bottom: 0;
-    border-left: 0;
   }
 
   td.gl {
@@ -94,38 +97,9 @@ div.highlight > code {
   }
 
   pre {
-    margin-top: 0;
+    margin: 0;
     line-height: 2;
   }
-
-  tbody > tr > td {
-    padding-bottom: 0;
-    border-bottom: 0;
-  }
-}
-
-// Jekyll 4.1.1: figure.highlight > pre > code > div > table > ...
-
-figure.highlight > pre > code .table-wrapper,
-div.highlight > pre > code .table-wrapper {
-  padding: 0;
-  margin-bottom: 0;
-  border: 0;
-  box-shadow: none;
-}
-
-// Using fix_linenos: figure.highlight > code > div > table > ...
-
-figure.highlight > code .table-wrapper,
-div.highlight > code .table-wrapper {
-  padding: $sp-3;
-  margin-bottom: 0;
-  border: 0;
-  box-shadow: none;
-}
-
-.highlighter-rouge {
-  margin-bottom: $sp-3;
 }
 
 .highlight .c {

docs/linenos-test.md

@@ -4,17 +4,80 @@ title: Markdown line number test
 nav_order: 999
 ---
 
-```
+# Configuration options
-Some unknown code in fences
+
-```
+The default settings for HTML compression are incompatible with the HTML
+produced by Jekyll (4.1.1 or earlier) for line numbers from highlighted code
+-- both when using Kramdown code fences and when using Liquid highlight tags.
+
+To avoid non-conforming HTML and unsatisfactory layout, HTML compression
+can be turned off by using the following configuration option:
 
-Some of the code examples below require the following setting in `_config.yml`:
 ```yaml
 compress_html:
   ignore:
     envs: all
 ```
 
+When using Kramdown code fences, line numbers are turned on globally by the
+following configuration option:
+
+```yaml
+kramdown:
+  syntax_highlighter_opts:
+    block:
+      line_numbers: false
+```
+
+Line numbers can then be suppressed locally using Liquid tags (_without_ the
+`linenos` option) instead of fences:
+
+```
+{% raw %}{% highlight some_language %}
+Some code
+{% endhighlight %}{% endraw %}
+```
+
+# Workarounds
+
+To use HTML compression together with line numbers, all highlighted code
+needs to be wrapped using one of the following workarounds.
+(The variable name `some_var` can be changed to avoid clashes; it can also
+be replaced by `code` -- but note that `code=code` cannot be removed).
+
+## Code fences
+
+````
+{% raw %}{% capture some_var %}
+```some_language
+Some code
+```
+{% endcapture %}
+{% assign some_var = some_var | markdownify %}
+{% include fix_linenos.html code=some_var %}{% endraw %}
+````
+
+## Liquid highlighting
+
+```
+{% raw %}{% capture some_var %}
+{% highlight some_language linenos %}
+Some code
+{% endhighlight %}
+{% endcapture %}
+{% include fix_linenos.html code=some_var %}{% endraw %}
+```
+
+_Credit:_ The original version of the above workaround was suggested by
+Dmitry Hrabrov at
+<https://github.com/penibelst/jekyll-compress-html/issues/71#issuecomment-188144901>.
+
+# Examples
+
+```
+Some unknown code in fences
+```
+
 ```js
 // Javascript code with syntax highlighting in fences
 var fun = function lang(l) {
@@ -48,6 +111,10 @@ end
 {% include fix_linenos.html code=code %}
 {% assign code = nil %}
 
+With the default configuration options, the following example illustrates
+the incorrect formatting arising from the incompatibility of HTML compression
+and the non-conforming HTML produced by Jekyll for line numbers:
+
 {% highlight ruby linenos %}
 # Ruby code with syntax highlighting and unfixed line numbers using Liquid
 GitHubPages::Dependencies.gems.each do |gem, version|