no_std crates do not link to primitives

[Manishearth]

#![no_std]

// Link to [u8]
pub fn foo() -> u8 {}

The link in x()'s return type does not work. The intra-doc link on Foo does work, but that's because we hardcode the std in it, which should be fixed once this is.

Turns out that the "primitive type u8" only lives in std, see https://doc.rust-lang.org/nightly/std/index.html?search=u8

[Manishearth]

We should first get these things to link to std at least. If we decide to add a separate primitive page for libcore as well (I'm not sure if we should), then the following patch makes it work for intra doc links:

diff --git a/src/librustdoc/clean/types.rs b/src/librustdoc/clean/types.rs
index 5c76c840b1d..1eb52c8f7bb 100644
--- a/src/librustdoc/clean/types.rs
+++ b/src/librustdoc/clean/types.rs
@@ -55,6 +55,7 @@ pub struct Crate {
     pub external_traits: Rc<RefCell<FxHashMap<DefId, Trait>>>,
     pub masked_crates: FxHashSet<CrateNum>,
     pub collapsed: bool,
+    pub is_no_std: bool,
 }
 
 #[derive(Clone, Debug)]
@@ -114,8 +115,8 @@ impl Item {
         self.attrs.collapsed_doc_value()
     }
 
-    pub fn links(&self) -> Vec<(String, String)> {
-        self.attrs.links(&self.def_id.krate)
+    pub fn links(&self, is_no_std: bool) -> Vec<(String, String)> {
+        self.attrs.links(&self.def_id.krate, is_no_std)
     }
 
     pub fn is_crate(&self) -> bool {
@@ -598,7 +599,7 @@ impl Attributes {
     /// Gets links as a vector
     ///
     /// Cache must be populated before call
-    pub fn links(&self, krate: &CrateNum) -> Vec<(String, String)> {
+    pub fn links(&self, krate: &CrateNum, is_no_std: bool) -> Vec<(String, String)> {
         use crate::html::format::href;
 
         self.links
@@ -630,12 +631,14 @@ impl Attributes {
                             };
                             // This is a primitive so the url is done "by hand".
                             let tail = fragment.find('#').unwrap_or_else(|| fragment.len());
+                            let std = if is_no_std {"core"} else {"std"};
                             Some((
                                 s.clone(),
                                 format!(
-                                    "{}{}std/primitive.{}.html{}",
+                                    "{}{}{}/primitive.{}.html{}",
                                     url,
                                     if !url.ends_with('/') { "/" } else { "" },
+                                    std,
                                     &fragment[..tail],
                                     &fragment[tail..]
                                 ),
diff --git a/src/librustdoc/clean/utils.rs b/src/librustdoc/clean/utils.rs
index c4e4802db6c..cb6b7d26f7d 100644
--- a/src/librustdoc/clean/utils.rs
+++ b/src/librustdoc/clean/utils.rs
@@ -10,6 +10,7 @@ use crate::core::DocContext;
 
 use itertools::Itertools;
 use rustc_data_structures::fx::FxHashSet;
+use rustc_ast::attr;
 use rustc_hir as hir;
 use rustc_hir::def::{DefKind, Res};
 use rustc_hir::def_id::{DefId, LOCAL_CRATE};
@@ -87,6 +88,7 @@ pub fn krate(mut cx: &mut DocContext<'_>) -> Crate {
         }));
     }
 
+    let is_no_std = attr::contains_name(&krate.item.attrs, sym::no_std);
     Crate {
         name,
         version: None,
@@ -97,6 +99,7 @@ pub fn krate(mut cx: &mut DocContext<'_>) -> Crate {
         external_traits: cx.external_traits.clone(),
         masked_crates,
         collapsed: false,
+        is_no_std,
     }
 }
 
diff --git a/src/librustdoc/html/render.rs b/src/librustdoc/html/render.rs
index 07631093edd..abc6ee5de17 100644
--- a/src/librustdoc/html/render.rs
+++ b/src/librustdoc/html/render.rs
@@ -161,6 +161,7 @@ struct Context {
     id_map: Rc<RefCell<IdMap>>,
     pub shared: Arc<SharedContext>,
     pub cache: Arc<Cache>,
+    pub is_no_std: bool,
 }
 
 crate struct SharedContext {
@@ -556,6 +557,7 @@ pub fn run(
         id_map: Rc::new(RefCell::new(id_map)),
         shared: Arc::new(scx),
         cache: cache.clone(),
+        is_no_std: krate.is_no_std,
     };
 
     // Freeze the cache now that the index has been built. Put an Arc into TLS
@@ -1890,7 +1892,7 @@ fn document_short(
         } else {
             plain_summary_line(Some(s))
         };
-        render_markdown(w, cx, &markdown, item.links(), prefix, is_hidden);
+        render_markdown(w, cx, &markdown, item.links(cx.is_no_std), prefix, is_hidden);
     } else if !prefix.is_empty() {
         write!(
             w,
@@ -1904,7 +1906,7 @@ fn document_short(
 fn document_full(w: &mut Buffer, item: &clean::Item, cx: &Context, prefix: &str, is_hidden: bool) {
     if let Some(s) = cx.shared.maybe_collapsed_doc_value(item) {
         debug!("Doc block: =====\n{}\n=====", s);
-        render_markdown(w, cx, &*s, item.links(), prefix, is_hidden);
+        render_markdown(w, cx, &*s, item.links(cx.is_no_std), prefix, is_hidden);
     } else if !prefix.is_empty() {
         write!(
             w,
@@ -2158,7 +2160,7 @@ fn item_module(w: &mut Buffer, cx: &Context, item: &clean::Item, items: &[clean:
                        </tr>",
                     name = *myitem.name.as_ref().unwrap(),
                     stab_tags = stability_tags(myitem),
-                    docs = MarkdownSummaryLine(doc_value, &myitem.links()).to_string(),
+                    docs = MarkdownSummaryLine(doc_value, &myitem.links(cx.is_no_std)).to_string(),
                     class = myitem.type_(),
                     add = add,
                     stab = stab.unwrap_or_else(String::new),
@@ -3616,7 +3618,7 @@ fn render_impl(
                 "<div class='docblock'>{}</div>",
                 Markdown(
                     &*dox,
-                    &i.impl_item.links(),
+                    &i.impl_item.links(cx.is_no_std),
                     &mut ids,
                     cx.shared.codes,
                     cx.shared.edition,

[GuillaumeGomez]

Linked to #43466

[Manishearth]

It's not linked to that issue, it's an independent bug

[jyn514]

I think we should consider moving primitives into libcore. Otherwise there's not a way to fix this without allowing links to upstream types (#73699), which is another can of worms and I don't think should be tied to this issue.

@Manishearth was concerned that this wouldn't show libstd implementations of libcore traits. A possible workaround here is to duplicate primitives in both libstd and libcore; in libstd they would show the trait implementations, in libcore they wouldn't but links to primitives would still work.

Another thing to consider is that it's not clear this is under rustdoc's control: the metric for whether a primitive type is local or not is

rust/src/librustdoc/html/format.rs

Lines 563 to 564 in 9845075

	match m.primitive_locations.get(&prim) {
	Some(&def_id) if def_id.is_local() => {

but that seems independent of anything rustdoc does. So we should figure out why primitives are currently being seen as local to libstd before we go much further.

[jyn514]

we should figure out why primitives are currently being seen as local to libstd before we go much further

Oh, I think it might be as simple as primitive_docs.rs being in libstd, not libcore. https://github.com/rust-lang/rust/blob/98450757e5fa18ee0be9213d2830c9363b0f5fd3/src/libstd/primitive_docs.rs

[jyn514]

I think we should consider moving primitives into libcore.

Doing this means that intra-doc links to String, etc. won't resolve in either libstd or libcore.

[poliorcetics]

I think I'm hitting this case in #77875.

[jyn514]

Note that because the standard library uses lang items to add impls to primitives in alloc and std, this means the documentation in core will be missing some methods (e.g. #83577)

[camelid]

I think we should consider moving primitives into libcore.

Doing this means that intra-doc links to String, etc. won't resolve in either libstd or libcore.

Hmm, why would that be? IIUC, String wouldn't resolve anyway in core because it's defined in alloc, and it's not a primitive. Why would this change cause links to String to not resolve?

[jyn514]

Hmm, why would that be? IIUC, String wouldn't resolve anyway in core because it's defined in alloc, and it's not a primitive. Why would this change cause links to String to not resolve?

Because right now, the links are written in libstd, which can link to alloc fine. If we changed it to be in libcore, then the links would break, because core doesn't depend on alloc. That's true even if the docs are re-exported into libstd, rustdoc resolves the links relative to the original module.