Auto merge of #60065 - QuietMisdreavus:async-move-doctests, r=ollie27

rustdoc: set the default edition when pre-parsing a doctest

Fixes https://github.com/rust-lang/rust/issues/59313 (possibly more? i think we've had issues with parsing edition-specific syntax in doctests at some point)

When handling a doctest, rustdoc needs to parse it beforehand, so that it can see whether it declares a `fn main` or `extern crate my_crate` explicitly. However, while doing this, rustdoc doesn't set the "default edition" used by the parser like the regular compilation runs do. This caused a problem when parsing a doctest with an `async move` block in it, since it was expecting the `move` keyword to start a closure, not a block.

This PR changes the `rustdoc::test::make_test` function to set the parser's default edition while looking for a main function and `extern crate` statement. However, to do this, `make_test` needs to know what edition to set. Since this is also used during the HTML rendering process (to make playground URLs), now the HTML renderer needs to know about the default edition. Upshot: rendering standalone markdown files can now accept a "default edition" for their doctests with the `--edition` flag! (I'm pretty sure i waffled around how to set that a long time ago when we first added the `--edition` flag... `>_>`)

I'm posting this before i stop for the night so that i can write this description while it's still in my head, but before this merges i want to make sure that (1) the `rustdoc-ui/failed-doctest-output` test still works (i expect it doesn't), and (2) i add a test with the sample from the linked issue.

src/librustdoc/html/render.rs

@@ -47,6 +47,7 @@ use std::rc::Rc;
 use errors;
 use serialize::json::{ToJson, Json, as_json};
 use syntax::ast;
+use syntax::edition::Edition;
 use syntax::ext::base::MacroKind;
 use syntax::source_map::FileName;
 use syntax::feature_gate::UnstableFeatures;
@@ -108,6 +109,8 @@ struct Context {
     /// publicly reused items to redirect to the right location.
     pub render_redirect_pages: bool,
     pub codes: ErrorCodes,
+    /// The default edition used to parse doctests.
+    pub edition: Edition,
     /// The map used to ensure all generated 'id=' attributes are unique.
     id_map: Rc<RefCell<IdMap>>,
     pub shared: Arc<SharedContext>,
@@ -514,7 +517,8 @@ pub fn run(mut krate: clean::Crate,
            options: RenderOptions,
            passes: FxHashSet<String>,
            renderinfo: RenderInfo,
-           diag: &errors::Handler) -> Result<(), Error> {
+           diag: &errors::Handler,
+           edition: Edition) -> Result<(), Error> {
     // need to save a copy of the options for rendering the index page
     let md_opts = options.clone();
     let RenderOptions {
@@ -604,6 +608,7 @@ pub fn run(mut krate: clean::Crate,
         dst,
         render_redirect_pages: false,
         codes: ErrorCodes::from(UnstableFeatures::from_environment().is_nightly_build()),
+        edition,
         id_map: Rc::new(RefCell::new(id_map)),
         shared: Arc::new(scx),
     };
@@ -1128,7 +1133,7 @@ themePicker.onblur = handleThemeButtonsBlur;
             md_opts.output = cx.dst.clone();
             md_opts.external_html = (*cx.shared).layout.external_html.clone();
 
-            crate::markdown::render(index_page, md_opts, diag);
+            crate::markdown::render(index_page, md_opts, diag, cx.edition);
         } else {
             let dst = cx.dst.join("index.html");
             let mut w = BufWriter::new(try_err!(File::create(&dst), &dst));
@@ -2553,7 +2558,7 @@ fn render_markdown(w: &mut fmt::Formatter<'_>,
            if is_hidden { " hidden" } else { "" },
            prefix,
            Markdown(md_text, &links, RefCell::new(&mut ids),
-           cx.codes))
+           cx.codes, cx.edition))
 }
 
 fn document_short(
@@ -2918,7 +2923,7 @@ fn short_stability(item: &clean::Item, cx: &Context) -> Vec<String> {
 
         if let Some(note) = note {
             let mut ids = cx.id_map.borrow_mut();
-            let html = MarkdownHtml(&note, RefCell::new(&mut ids), error_codes);
+            let html = MarkdownHtml(&note, RefCell::new(&mut ids), error_codes, cx.edition);
             message.push_str(&format!(": {}", html));
         }
         stability.push(format!("<div class='stab deprecated'>{}</div>", message));
@@ -2967,7 +2972,7 @@ fn short_stability(item: &clean::Item, cx: &Context) -> Vec<String> {
             message = format!(
                 "<details><summary>{}</summary>{}</details>",
                 message,
-                MarkdownHtml(&unstable_reason, RefCell::new(&mut ids), error_codes)
+                MarkdownHtml(&unstable_reason, RefCell::new(&mut ids), error_codes, cx.edition)
             );
         }
 
@@ -4197,7 +4202,8 @@ fn render_impl(w: &mut fmt::Formatter<'_>, cx: &Context, i: &Impl, link: AssocIt
         if let Some(ref dox) = cx.shared.maybe_collapsed_doc_value(&i.impl_item) {
             let mut ids = cx.id_map.borrow_mut();
             write!(w, "<div class='docblock'>{}</div>",
-                   Markdown(&*dox, &i.impl_item.links(), RefCell::new(&mut ids), cx.codes))?;
+                   Markdown(&*dox, &i.impl_item.links(), RefCell::new(&mut ids),
+                            cx.codes, cx.edition))?;
         }
     }