Add support for Rust edition 2018 in playpens (#1086)

* Add support for Rust edition 2018 in playpens

* Add Rust edition support to rustdoc

* Run rustfmt

* Fix enum variant reference

3 files changed, 94 insertions, 15 deletions

diff --git a/src/book/mod.rs b/src/book/mod.rs
index 8d69eea2..29d2dc3d 100644
--- a/src/book/mod.rs
+++ b/src/book/mod.rs
@@ -27,7 +27,7 @@ use crate::preprocess::{
 use crate::renderer::{CmdRenderer, HtmlHandlebars, MarkdownRenderer, RenderContext, Renderer};
 use crate::utils;
 
-use crate::config::Config;
+use crate::config::{Config, RustEdition};
 
 /// The object used to manage and build a book.
 pub struct MDBook {
@@ -262,11 +262,17 @@ impl MDBook {
                     let mut tmpf = utils::fs::create_file(&path)?;
                     tmpf.write_all(ch.content.as_bytes())?;
 
-                    let output = Command::new("rustdoc")
-                        .arg(&path)
-                        .arg("--test")
-                        .args(&library_args)
-                        .output()?;
+                    let mut cmd = Command::new("rustdoc");
+
+                    cmd.arg(&path).arg("--test").args(&library_args);
+
+                    if let Some(html_cfg) = self.config.html_config() {
+                        if html_cfg.playpen.edition == RustEdition::E2018 {
+                            cmd.args(&["--edition", "2018"]);
+                        }
+                    }
+
+                    let output = cmd.output()?;
 
                     if !output.status.success() {
                         bail!(ErrorKind::Subprocess(
diff --git a/src/config.rs b/src/config.rs
index fae3da84..4c8624a6 100644
--- a/src/config.rs
+++ b/src/config.rs
@@ -513,6 +513,8 @@ pub struct Playpen {
     pub copy_js: bool,
     /// Display line numbers on playpen snippets. Default: `false`.
     pub line_numbers: bool,
+    /// Rust edition to use for the code. Default: `2015`.
+    pub edition: RustEdition,
 }
 
 impl Default for Playpen {
@@ -522,10 +524,66 @@ impl Default for Playpen {
             copyable: true,
             copy_js: true,
             line_numbers: false,
+            edition: RustEdition::E2015,
         }
     }
 }
 
+#[derive(Debug, Clone, PartialEq)]
+/// The edition of Rust used in a playpen code snippet
+pub enum RustEdition {
+    /// The 2018 edition of Rust
+    E2018,
+    /// The 2015 edition of Rust
+    E2015,
+}
+
+impl Default for RustEdition {
+    fn default() -> Self {
+        RustEdition::E2015
+    }
+}
+
+impl Serialize for RustEdition {
+    fn serialize<S>(&self, serializer: S) -> std::result::Result<S::Ok, S::Error>
+    where
+        S: Serializer,
+    {
+        match self {
+            RustEdition::E2015 => serializer.serialize_str("2015"),
+            RustEdition::E2018 => serializer.serialize_str("2018"),
+        }
+    }
+}
+
+impl<'de> Deserialize<'de> for RustEdition {
+    fn deserialize<D>(de: D) -> std::result::Result<Self, D::Error>
+    where
+        D: Deserializer<'de>,
+    {
+        use serde::de::Error;
+
+        let raw = Value::deserialize(de)?;
+
+        let edition = match raw {
+            Value::String(s) => s,
+            _ => {
+                return Err(D::Error::custom("Rust edition should be a string"));
+            }
+        };
+
+        let edition = match edition.as_str() {
+            "2018" => RustEdition::E2018,
+            "2015" => RustEdition::E2015,
+            _ => {
+                return Err(D::Error::custom("Unknown Rust edition"));
+            }
+        };
+
+        Ok(edition)
+    }
+}
+
 /// Configuration of the search functionality of the HTML renderer.
 #[derive(Debug, Clone, PartialEq, Serialize, Deserialize)]
 #[serde(default, rename_all = "kebab-case")]
@@ -630,6 +688,7 @@ mod tests {
         [output.html.playpen]
         editable = true
         editor = "ace"
+        edition = "2018"
 
         [preprocessor.first]
 
@@ -658,6 +717,7 @@ mod tests {
             copyable: true,
             copy_js: true,
             line_numbers: false,
+            edition: RustEdition::E2018,
         };
         let html_should_be = HtmlConfig {
             curly_quotes: true,
diff --git a/src/renderer/html_handlebars/hbs_renderer.rs b/src/renderer/html_handlebars/hbs_renderer.rs
index 0be92562..aa2bdcc9 100644
--- a/src/renderer/html_handlebars/hbs_renderer.rs
+++ b/src/renderer/html_handlebars/hbs_renderer.rs
@@ -1,5 +1,5 @@
 use crate::book::{Book, BookItem};
-use crate::config::{Config, HtmlConfig, Playpen};
+use crate::config::{Config, HtmlConfig, Playpen, RustEdition};
 use crate::errors::*;
 use crate::renderer::html_handlebars::helpers;
 use crate::renderer::{RenderContext, Renderer};
@@ -608,14 +608,27 @@ fn add_playpen_pre(html: &str, playpen_config: &Playpen) -> String {
             let classes = &caps[2];
             let code = &caps[3];
 
-            if classes.contains("language-rust") {
-                if (!classes.contains("ignore") && !classes.contains("noplaypen"))
-                    || classes.contains("mdbook-runnable")
-                {
-                    // wrap the contents in an external pre block
-                    format!(
-                        "<pre class=\"playpen\"><code class=\"{}\">{}</code></pre>",
-                        classes,
+
+            if (classes.contains("language-rust")
+                && !classes.contains("ignore")
+                && !classes.contains("noplaypen"))
+                || classes.contains("mdbook-runnable")
+            {
+                let mut classes = classes.to_string();
+                match playpen_config.edition {
+                    RustEdition::E2018 => classes += " edition2018",
+                    _ => (),
+                }
+
+                // wrap the contents in an external pre block
+                format!(
+                    "<pre class=\"playpen\"><code class=\"{}\">{}</code></pre>",
+                    classes,
+                    {
+                        let content: Cow<'_, str> = if playpen_config.editable
+                            && classes.contains("editable")
+                            || text.contains("fn main")
+                            || text.contains("quick_main!")
                         {
                             let content: Cow<'_, str> = if playpen_config.editable
                                 && classes.contains("editable")