From 9653b601b2c5ac554e6adedf98d2ac173eb61985 Mon Sep 17 00:00:00 2001
From: Joshua Nelson <jyn514@gmail.com>
Date: Thu, 4 Feb 2021 18:10:33 -0500
Subject: [PATCH] Enable 'task list' markdown extension

- Add documentation about task lists
---
 .../rustdoc/src/how-to-write-documentation.md | 20 +++++++++++++++++++
 src/librustdoc/html/markdown.rs               |  5 ++++-
 src/test/rustdoc/task-lists.rs                | 13 ++++++++++++
 3 files changed, 37 insertions(+), 1 deletion(-)
 create mode 100644 src/test/rustdoc/task-lists.rs

diff --git a/src/doc/rustdoc/src/how-to-write-documentation.md b/src/doc/rustdoc/src/how-to-write-documentation.md
index 41736e5ee3a..b3664cb9940 100644
--- a/src/doc/rustdoc/src/how-to-write-documentation.md
+++ b/src/doc/rustdoc/src/how-to-write-documentation.md
@@ -221,6 +221,25 @@ This example will render similarly to this:
 See the specification for the [GitHub Tables extension][tables] for more
 details on the exact syntax supported.
 
+### Task lists
+
+Task lists can be used as a checklist of items that have been completed.
+Example:
+
+```md
+- [x] Complete task
+- [ ] IncComplete task
+```
+
+This will render as
+
+<ul>
+    <li><input type="checkbox"></li>
+    <li><input type="checkbox" checked></li>
+</ul>
+
+See the specification for the [task list extension] for more details.
+
 [`backtrace`]: https://docs.rs/backtrace/0.3.50/backtrace/
 [commonmark markdown specification]: https://commonmark.org/
 [commonmark quick reference]: https://commonmark.org/help/
@@ -234,3 +253,4 @@ details on the exact syntax supported.
 [`std::env`]: https://doc.rust-lang.org/stable/std/env/index.html#functions
 [strikethrough]: https://github.github.com/gfm/#strikethrough-extension-
 [tables]: https://github.github.com/gfm/#tables-extension-
+[task list extension]: https://github.github.com/gfm/#task-list-items-extension-
diff --git a/src/librustdoc/html/markdown.rs b/src/librustdoc/html/markdown.rs
index bdb92844f07..a81fd55f6f1 100644
--- a/src/librustdoc/html/markdown.rs
+++ b/src/librustdoc/html/markdown.rs
@@ -48,7 +48,10 @@ mod tests;
 
 /// Options for rendering Markdown in the main body of documentation.
 pub(crate) fn opts() -> Options {
-    Options::ENABLE_TABLES | Options::ENABLE_FOOTNOTES | Options::ENABLE_STRIKETHROUGH
+    Options::ENABLE_TABLES
+        | Options::ENABLE_FOOTNOTES
+        | Options::ENABLE_STRIKETHROUGH
+        | Options::ENABLE_TASKLISTS
 }
 
 /// A subset of [`opts()`] used for rendering summaries.
diff --git a/src/test/rustdoc/task-lists.rs b/src/test/rustdoc/task-lists.rs
new file mode 100644
index 00000000000..c2e7dd60f22
--- /dev/null
+++ b/src/test/rustdoc/task-lists.rs
@@ -0,0 +1,13 @@
+// ignore-tidy-linelength
+// FIXME: this doesn't test as much as I'd like; ideally it would have these query too:
+  // has task_lists/index.html '//li/input[@type="checkbox" and disabled]/following-sibling::text()' 'a'
+  // has task_lists/index.html '//li/input[@type="checkbox"]/following-sibling::text()' 'b'
+// Unfortunately that requires LXML, because the built-in xml module doesn't support all of xpath.
+
+// @has task_lists/index.html '//ul/li/input[@type="checkbox"]' ''
+// @has task_lists/index.html '//ul/li/input[@disabled]' ''
+// @has task_lists/index.html '//ul/li' 'a'
+// @has task_lists/index.html '//ul/li' 'b'
+//! This tests 'task list' support, a common markdown extension.
+//! - [ ] a
+//! - [x] b