From 217546c2a056be7a95d029b3265bce66bd79cee4 Mon Sep 17 00:00:00 2001
From: Martin Geisler <mgeisler@google.com>
Date: Wed, 29 Jun 2022 10:31:44 +0200
Subject: [PATCH] Trim trailing whitespace in Rust code blocks
MIME-Version: 1.0
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Content-Transfer-Encoding: 8bit

Before, a code block would always end with a final newline. The
newline was added unconditionally by `hide_lines`.

When the code block is syntax highlighted by highlight.js, this is not
a problem, no empty line is added for a final trailing `\n` character.
However, when the code block is editable and thus handled by the ACE
editor, a trailing newline _is_ significant. I believe this issue is
most closely described by https://github.com/ajaxorg/ace/issues/2083
in the upstream repository.

The effect of the way ACE handles newlines is that a code block like

    <pre>
      Some code
    </pre>

will create an editor with _two_ lines, not just one.

By trimming trailing whitespace, we ensure that we don’t accidentally
create more lines in the ACE editor than necessary.
---
 src/renderer/html_handlebars/hbs_renderer.rs | 49 +++++++++++---------
 1 file changed, 26 insertions(+), 23 deletions(-)

diff --git a/src/renderer/html_handlebars/hbs_renderer.rs b/src/renderer/html_handlebars/hbs_renderer.rs
index 26f1432c..6debd669 100644
--- a/src/renderer/html_handlebars/hbs_renderer.rs
+++ b/src/renderer/html_handlebars/hbs_renderer.rs
@@ -903,13 +903,16 @@ fn hide_lines(content: &str) -> String {
     }
 
     let mut result = String::with_capacity(content.len());
-    for line in content.lines() {
+    let mut lines = content.lines().peekable();
+    while let Some(line) = lines.next() {
+        // Don't include newline on the last line.
+        let newline = if lines.peek().is_none() { "" } else { "\n" };
         if let Some(caps) = BORING_LINES_REGEX.captures(line) {
             if &caps[2] == "#" {
                 result += &caps[1];
                 result += &caps[2];
                 result += &caps[3];
-                result += "\n";
+                result += newline;
                 continue;
             } else if &caps[2] != "!" && &caps[2] != "[" {
                 result += "<span class=\"boring\">";
@@ -918,13 +921,13 @@ fn hide_lines(content: &str) -> String {
                     result += &caps[2];
                 }
                 result += &caps[3];
-                result += "\n";
+                result += newline;
                 result += "</span>";
                 continue;
             }
         }
         result += line;
-        result += "\n";
+        result += newline;
     }
     result
 }
@@ -1004,19 +1007,19 @@ mod tests {
     fn add_playground() {
         let inputs = [
           ("<code class=\"language-rust\">x()</code>",
-           "<pre class=\"playground\"><code class=\"language-rust\"><span class=\"boring\">#![allow(unused)]\n</span><span class=\"boring\">fn main() {\n</span>x()\n<span class=\"boring\">}\n</span></code></pre>"),
+           "<pre class=\"playground\"><code class=\"language-rust\"><span class=\"boring\">#![allow(unused)]\n</span><span class=\"boring\">fn main() {\n</span>x()\n<span class=\"boring\">}</span></code></pre>"),
           ("<code class=\"language-rust\">fn main() {}</code>",
-           "<pre class=\"playground\"><code class=\"language-rust\">fn main() {}\n</code></pre>"),
+           "<pre class=\"playground\"><code class=\"language-rust\">fn main() {}</code></pre>"),
           ("<code class=\"language-rust editable\">let s = \"foo\n # bar\n\";</code>",
-           "<pre class=\"playground\"><code class=\"language-rust editable\">let s = \"foo\n<span class=\"boring\"> bar\n</span>\";\n</code></pre>"),
+           "<pre class=\"playground\"><code class=\"language-rust editable\">let s = \"foo\n<span class=\"boring\"> bar\n</span>\";</code></pre>"),
           ("<code class=\"language-rust editable\">let s = \"foo\n ## bar\n\";</code>",
-           "<pre class=\"playground\"><code class=\"language-rust editable\">let s = \"foo\n # bar\n\";\n</code></pre>"),
+           "<pre class=\"playground\"><code class=\"language-rust editable\">let s = \"foo\n # bar\n\";</code></pre>"),
           ("<code class=\"language-rust editable\">let s = \"foo\n # bar\n#\n\";</code>",
-           "<pre class=\"playground\"><code class=\"language-rust editable\">let s = \"foo\n<span class=\"boring\"> bar\n</span><span class=\"boring\">\n</span>\";\n</code></pre>"),
+           "<pre class=\"playground\"><code class=\"language-rust editable\">let s = \"foo\n<span class=\"boring\"> bar\n</span><span class=\"boring\">\n</span>\";</code></pre>"),
           ("<code class=\"language-rust ignore\">let s = \"foo\n # bar\n\";</code>",
-           "<code class=\"language-rust ignore\">let s = \"foo\n<span class=\"boring\"> bar\n</span>\";\n</code>"),
+           "<code class=\"language-rust ignore\">let s = \"foo\n<span class=\"boring\"> bar\n</span>\";</code>"),
           ("<code class=\"language-rust editable\">#![no_std]\nlet s = \"foo\";\n #[some_attr]</code>",
-           "<pre class=\"playground\"><code class=\"language-rust editable\">#![no_std]\nlet s = \"foo\";\n #[some_attr]\n</code></pre>"),
+           "<pre class=\"playground\"><code class=\"language-rust editable\">#![no_std]\nlet s = \"foo\";\n #[some_attr]</code></pre>"),
         ];
         for (src, should_be) in &inputs {
             let got = add_playground_pre(
@@ -1034,13 +1037,13 @@ mod tests {
     fn add_playground_edition2015() {
         let inputs = [
           ("<code class=\"language-rust\">x()</code>",
-           "<pre class=\"playground\"><code class=\"language-rust edition2015\"><span class=\"boring\">#![allow(unused)]\n</span><span class=\"boring\">fn main() {\n</span>x()\n<span class=\"boring\">}\n</span></code></pre>"),
+           "<pre class=\"playground\"><code class=\"language-rust edition2015\"><span class=\"boring\">#![allow(unused)]\n</span><span class=\"boring\">fn main() {\n</span>x()\n<span class=\"boring\">}</span></code></pre>"),
           ("<code class=\"language-rust\">fn main() {}</code>",
-           "<pre class=\"playground\"><code class=\"language-rust edition2015\">fn main() {}\n</code></pre>"),
+           "<pre class=\"playground\"><code class=\"language-rust edition2015\">fn main() {}</code></pre>"),
           ("<code class=\"language-rust edition2015\">fn main() {}</code>",
-           "<pre class=\"playground\"><code class=\"language-rust edition2015\">fn main() {}\n</code></pre>"),
+           "<pre class=\"playground\"><code class=\"language-rust edition2015\">fn main() {}</code></pre>"),
           ("<code class=\"language-rust edition2018\">fn main() {}</code>",
-           "<pre class=\"playground\"><code class=\"language-rust edition2018\">fn main() {}\n</code></pre>"),
+           "<pre class=\"playground\"><code class=\"language-rust edition2018\">fn main() {}</code></pre>"),
         ];
         for (src, should_be) in &inputs {
             let got = add_playground_pre(
@@ -1058,13 +1061,13 @@ mod tests {
     fn add_playground_edition2018() {
         let inputs = [
           ("<code class=\"language-rust\">x()</code>",
-           "<pre class=\"playground\"><code class=\"language-rust edition2018\"><span class=\"boring\">#![allow(unused)]\n</span><span class=\"boring\">fn main() {\n</span>x()\n<span class=\"boring\">}\n</span></code></pre>"),
+           "<pre class=\"playground\"><code class=\"language-rust edition2018\"><span class=\"boring\">#![allow(unused)]\n</span><span class=\"boring\">fn main() {\n</span>x()\n<span class=\"boring\">}</span></code></pre>"),
           ("<code class=\"language-rust\">fn main() {}</code>",
-           "<pre class=\"playground\"><code class=\"language-rust edition2018\">fn main() {}\n</code></pre>"),
+           "<pre class=\"playground\"><code class=\"language-rust edition2018\">fn main() {}</code></pre>"),
           ("<code class=\"language-rust edition2015\">fn main() {}</code>",
-           "<pre class=\"playground\"><code class=\"language-rust edition2015\">fn main() {}\n</code></pre>"),
+           "<pre class=\"playground\"><code class=\"language-rust edition2015\">fn main() {}</code></pre>"),
           ("<code class=\"language-rust edition2018\">fn main() {}</code>",
-           "<pre class=\"playground\"><code class=\"language-rust edition2018\">fn main() {}\n</code></pre>"),
+           "<pre class=\"playground\"><code class=\"language-rust edition2018\">fn main() {}</code></pre>"),
         ];
         for (src, should_be) in &inputs {
             let got = add_playground_pre(
@@ -1082,13 +1085,13 @@ mod tests {
     fn add_playground_edition2021() {
         let inputs = [
             ("<code class=\"language-rust\">x()</code>",
-             "<pre class=\"playground\"><code class=\"language-rust edition2021\"><span class=\"boring\">#![allow(unused)]\n</span><span class=\"boring\">fn main() {\n</span>x()\n<span class=\"boring\">}\n</span></code></pre>"),
+             "<pre class=\"playground\"><code class=\"language-rust edition2021\"><span class=\"boring\">#![allow(unused)]\n</span><span class=\"boring\">fn main() {\n</span>x()\n<span class=\"boring\">}</span></code></pre>"),
             ("<code class=\"language-rust\">fn main() {}</code>",
-             "<pre class=\"playground\"><code class=\"language-rust edition2021\">fn main() {}\n</code></pre>"),
+             "<pre class=\"playground\"><code class=\"language-rust edition2021\">fn main() {}</code></pre>"),
             ("<code class=\"language-rust edition2015\">fn main() {}</code>",
-             "<pre class=\"playground\"><code class=\"language-rust edition2015\">fn main() {}\n</code></pre>"),
+             "<pre class=\"playground\"><code class=\"language-rust edition2015\">fn main() {}</code></pre>"),
             ("<code class=\"language-rust edition2018\">fn main() {}</code>",
-             "<pre class=\"playground\"><code class=\"language-rust edition2018\">fn main() {}\n</code></pre>"),
+             "<pre class=\"playground\"><code class=\"language-rust edition2018\">fn main() {}</code></pre>"),
         ];
         for (src, should_be) in &inputs {
             let got = add_playground_pre(