From 3992bc18f512f30c37576b010fb1b33455486a3c Mon Sep 17 00:00:00 2001
From: Eric Huss <eric@huss.org>
Date: Mon, 27 Oct 2025 18:17:22 -0700
Subject: [PATCH 1/2] Add a test for a fenced code block with an indent

---
 crates/mdbook-html/src/html/hide_lines.rs                   | 4 ++++
 tests/testsuite/rendering.rs                                | 6 ++++++
 .../rendering/code_blocks_fenced_with_indent/book.toml      | 2 ++
 .../expected/code-blocks-fenced-with-indent.html            | 6 ++++++
 .../rendering/code_blocks_fenced_with_indent/src/SUMMARY.md | 3 +++
 .../src/code-blocks-fenced-with-indent.md                   | 6 ++++++
 6 files changed, 27 insertions(+)
 create mode 100644 tests/testsuite/rendering/code_blocks_fenced_with_indent/book.toml
 create mode 100644 tests/testsuite/rendering/code_blocks_fenced_with_indent/expected/code-blocks-fenced-with-indent.html
 create mode 100644 tests/testsuite/rendering/code_blocks_fenced_with_indent/src/SUMMARY.md
 create mode 100644 tests/testsuite/rendering/code_blocks_fenced_with_indent/src/code-blocks-fenced-with-indent.md

diff --git a/crates/mdbook-html/src/html/hide_lines.rs b/crates/mdbook-html/src/html/hide_lines.rs
index 6852b6c4c5..c81b44d886 100644
--- a/crates/mdbook-html/src/html/hide_lines.rs
+++ b/crates/mdbook-html/src/html/hide_lines.rs
@@ -179,4 +179,8 @@ fn it_partitions_rust_source() {
         ),
         ("\n#![allow(foo)]\n\n#![allow(bar)]\n\n", "let x = 1;")
     );
+    assert_eq!(
+        partition_rust_source("    // Example"),
+        ("    ", "// Example")
+    );
 }
diff --git a/tests/testsuite/rendering.rs b/tests/testsuite/rendering.rs
index d9ceb854f4..1f8590ad33 100644
--- a/tests/testsuite/rendering.rs
+++ b/tests/testsuite/rendering.rs
@@ -223,3 +223,9 @@ Html text was:
 fn html_blocks() {
     BookTest::from_dir("rendering/html_blocks").check_all_main_files();
 }
+
+// Test for a fenced code block that is also indented.
+#[test]
+fn code_block_fenced_with_indent() {
+    BookTest::from_dir("rendering/code_blocks_fenced_with_indent").check_all_main_files();
+}
diff --git a/tests/testsuite/rendering/code_blocks_fenced_with_indent/book.toml b/tests/testsuite/rendering/code_blocks_fenced_with_indent/book.toml
new file mode 100644
index 0000000000..7ed7ab96c1
--- /dev/null
+++ b/tests/testsuite/rendering/code_blocks_fenced_with_indent/book.toml
@@ -0,0 +1,2 @@
+[book]
+title = "code_blocks_fenced_with_indent"
diff --git a/tests/testsuite/rendering/code_blocks_fenced_with_indent/expected/code-blocks-fenced-with-indent.html b/tests/testsuite/rendering/code_blocks_fenced_with_indent/expected/code-blocks-fenced-with-indent.html
new file mode 100644
index 0000000000..e2bdfd2b00
--- /dev/null
+++ b/tests/testsuite/rendering/code_blocks_fenced_with_indent/expected/code-blocks-fenced-with-indent.html
@@ -0,0 +1,6 @@
+<h1 id="code-blocks-fenced-with-indent"><a class="header" href="#code-blocks-fenced-with-indent">Code blocks fenced with indent</a></h1>
+<pre class="playground"><code class="language-rust"><span class="boring">#![allow(unused)]
+</span><span class="boring">    fn main() {
+</span>// This has a first line that is indented.
+    println!("hello");
+<span class="boring">}</span></code></pre>
\ No newline at end of file
diff --git a/tests/testsuite/rendering/code_blocks_fenced_with_indent/src/SUMMARY.md b/tests/testsuite/rendering/code_blocks_fenced_with_indent/src/SUMMARY.md
new file mode 100644
index 0000000000..46b1673b02
--- /dev/null
+++ b/tests/testsuite/rendering/code_blocks_fenced_with_indent/src/SUMMARY.md
@@ -0,0 +1,3 @@
+# Summary
+
+- [Code blocks fenced with indent](./code-blocks-fenced-with-indent.md)
diff --git a/tests/testsuite/rendering/code_blocks_fenced_with_indent/src/code-blocks-fenced-with-indent.md b/tests/testsuite/rendering/code_blocks_fenced_with_indent/src/code-blocks-fenced-with-indent.md
new file mode 100644
index 0000000000..e8722979d0
--- /dev/null
+++ b/tests/testsuite/rendering/code_blocks_fenced_with_indent/src/code-blocks-fenced-with-indent.md
@@ -0,0 +1,6 @@
+# Code blocks fenced with indent
+
+```rust
+    // This has a first line that is indented.
+    println!("hello");
+```

From ddf02e0c0ce3740d27db3f1d89e8ffe19ee7b7bd Mon Sep 17 00:00:00 2001
From: Eric Huss <eric@huss.org>
Date: Mon, 27 Oct 2025 18:38:27 -0700
Subject: [PATCH 2/2] Fix rust fenced code blocks with an indent

This fixes a bug in the Rust code block partitioning that was
incorrectly removing the whitespace from the beginning of a code block.
---
 crates/mdbook-html/src/html/hide_lines.rs             | 11 +++++++++--
 .../expected/code-blocks-fenced-with-indent.html      |  4 ++--
 2 files changed, 11 insertions(+), 4 deletions(-)

diff --git a/crates/mdbook-html/src/html/hide_lines.rs b/crates/mdbook-html/src/html/hide_lines.rs
index c81b44d886..8dbe7b12c5 100644
--- a/crates/mdbook-html/src/html/hide_lines.rs
+++ b/crates/mdbook-html/src/html/hide_lines.rs
@@ -141,7 +141,14 @@ fn partition_rust_source(s: &str) -> (&str, &str) {
     let split_idx = match HEADER_RE.captures(s) {
         Some(caps) => {
             let attributes = &caps[1];
-            attributes.len()
+            if attributes.trim().is_empty() {
+                // Don't include pure whitespace as an attribute. The
+                // whitespace in the regex is intended to handle multiple
+                // attributes *separated* by potential whitespace.
+                0
+            } else {
+                attributes.len()
+            }
         }
         None => 0,
     };
@@ -181,6 +188,6 @@ fn it_partitions_rust_source() {
     );
     assert_eq!(
         partition_rust_source("    // Example"),
-        ("    ", "// Example")
+        ("", "    // Example")
     );
 }
diff --git a/tests/testsuite/rendering/code_blocks_fenced_with_indent/expected/code-blocks-fenced-with-indent.html b/tests/testsuite/rendering/code_blocks_fenced_with_indent/expected/code-blocks-fenced-with-indent.html
index e2bdfd2b00..b4ed1ef491 100644
--- a/tests/testsuite/rendering/code_blocks_fenced_with_indent/expected/code-blocks-fenced-with-indent.html
+++ b/tests/testsuite/rendering/code_blocks_fenced_with_indent/expected/code-blocks-fenced-with-indent.html
@@ -1,6 +1,6 @@
 <h1 id="code-blocks-fenced-with-indent"><a class="header" href="#code-blocks-fenced-with-indent">Code blocks fenced with indent</a></h1>
 <pre class="playground"><code class="language-rust"><span class="boring">#![allow(unused)]
-</span><span class="boring">    fn main() {
-</span>// This has a first line that is indented.
+</span><span class="boring">fn main() {
+</span>    // This has a first line that is indented.
     println!("hello");
 <span class="boring">}</span></code></pre>
\ No newline at end of file