Auto merge of #113958 - lukas-code:doc-links, r=GuillaumeGomez,petrochenkov

fix intra-doc links on nested `use` and `extern crate` items

This PR fixes two rustdoc ICEs that happen if there are any intra-doc links on nested `use` or `extern crate` items, for example:
```rust
/// Re-export [`fmt`] and [`io`].
pub use std::{fmt, io}; // "nested" use = use with braces

/// Re-export [`std`].
pub extern crate std;
```

Nested use items were incorrectly considered private and therefore didn't have their intra-doc links resolved. I fixed this by always resolving intra-doc links for nested `use` items that are declared `pub`.

<details>

During AST->HIR lowering, nested `use` items are desugared like this:
```rust
pub use std::{}; // "list stem"
pub use std::fmt;
pub use std::io;
```
Each of these HIR nodes has it's own effective visibility and the list stem is always considered private.
To check the effective visibility of an AST node, the AST node is mapped to a HIR node with `Resolver::local_def_id`, which returns the (private) list stem for nested use items.

</details>

For `extern crate`, there was a hack in rustdoc that stored the `DefId` of the crate itself in the cleaned item, instead of the `DefId` of the `extern crate` item. This made rustdoc look at the resolved links of the extern crate's crate root instead of the `extern crate` item. I've removed this hack and instead translate the `DefId` in the appropriate places.

As as side effect of fixing `extern crate`, i've turned
```rust
#[doc(masked)]
extern crate self as _;
```
into a no-op instead of hiding all trait impls. Proper verification for `doc(masked)` is included as a bonus.

fixes #113896

Author: bors

compiler/rustc_metadata/src/rmeta/encoder.rs

@@ -2244,13 +2244,12 @@ pub fn provide(providers: &mut Providers) {
             tcx.resolutions(())
                 .doc_link_resolutions
                 .get(&def_id)
-                .expect("no resolutions for a doc link")
+                .unwrap_or_else(|| span_bug!(tcx.def_span(def_id), "no resolutions for a doc link"))
         },
         doc_link_traits_in_scope: |tcx, def_id| {
-            tcx.resolutions(())
-                .doc_link_traits_in_scope
-                .get(&def_id)
-                .expect("no traits in scope for a doc link")
+            tcx.resolutions(()).doc_link_traits_in_scope.get(&def_id).unwrap_or_else(|| {
+                span_bug!(tcx.def_span(def_id), "no traits in scope for a doc link")
+            })
         },
         traits: |tcx, LocalCrate| {
             let mut traits = Vec::new();

compiler/rustc_passes/messages.ftl

@@ -211,6 +211,17 @@ passes_doc_keyword_not_mod =
 passes_doc_keyword_only_impl =
     `#[doc(keyword = "...")]` should be used on impl blocks
 
+passes_doc_masked_not_extern_crate_self =
+    this attribute cannot be applied to an `extern crate self` item
+    .label = not applicable on `extern crate self` items
+    .extern_crate_self_label = `extern crate self` defined here
+
+passes_doc_masked_only_extern_crate =
+    this attribute can only be applied to an `extern crate` item
+    .label = only applicable on `extern crate` items
+    .not_an_extern_crate_label = not an `extern crate` item
+    .note = read <https://doc.rust-lang.org/unstable-book/language-features/doc-masked.html> for more information
+
 passes_doc_test_literal = `#![doc(test(...)]` does not take a literal
 
 passes_doc_test_takes_list =

compiler/rustc_passes/src/check_attr.rs

@@ -878,6 +878,44 @@ impl CheckAttrVisitor<'_> {
         }
     }
 
+    fn check_doc_masked(
+        &self,
+        attr: &Attribute,
+        meta: &NestedMetaItem,
+        hir_id: HirId,
+        target: Target,
+    ) -> bool {
+        if target != Target::ExternCrate {
+            self.tcx.emit_spanned_lint(
+                INVALID_DOC_ATTRIBUTES,
+                hir_id,
+                meta.span(),
+                errors::DocMaskedOnlyExternCrate {
+                    attr_span: meta.span(),
+                    item_span: (attr.style == AttrStyle::Outer)
+                        .then(|| self.tcx.hir().span(hir_id)),
+                },
+            );
+            return false;
+        }
+
+        if self.tcx.extern_mod_stmt_cnum(hir_id.owner).is_none() {
+            self.tcx.emit_spanned_lint(
+                INVALID_DOC_ATTRIBUTES,
+                hir_id,
+                meta.span(),
+                errors::DocMaskedNotExternCrateSelf {
+                    attr_span: meta.span(),
+                    item_span: (attr.style == AttrStyle::Outer)
+                        .then(|| self.tcx.hir().span(hir_id)),
+                },
+            );
+            return false;
+        }
+
+        true
+    }
+
     /// Checks that an attribute is *not* used at the crate level. Returns `true` if valid.
     fn check_attr_not_crate_level(
         &self,
@@ -1048,6 +1086,17 @@ impl CheckAttrVisitor<'_> {
                             is_valid = false;
                         }
 
+                        sym::masked
+                            if !self.check_doc_masked(
+                                attr,
+                                meta,
+                                hir_id,
+                                target,
+                            ) =>
+                        {
+                            is_valid = false;
+                        }
+
                         // no_default_passes: deprecated
                         // passes: deprecated
                         // plugins: removed, but rustdoc warns about it itself

compiler/rustc_passes/src/errors.rs

@@ -267,6 +267,25 @@ pub struct DocInlineOnlyUse {
     pub item_span: Option<Span>,
 }
 
+#[derive(LintDiagnostic)]
+#[diag(passes_doc_masked_only_extern_crate)]
+#[note]
+pub struct DocMaskedOnlyExternCrate {
+    #[label]
+    pub attr_span: Span,
+    #[label(passes_not_an_extern_crate_label)]
+    pub item_span: Option<Span>,
+}
+
+#[derive(LintDiagnostic)]
+#[diag(passes_doc_masked_not_extern_crate_self)]
+pub struct DocMaskedNotExternCrateSelf {
+    #[label]
+    pub attr_span: Span,
+    #[label(passes_extern_crate_self_label)]
+    pub item_span: Option<Span>,
+}
+
 #[derive(Diagnostic)]
 #[diag(passes_doc_attr_not_crate_level)]
 pub struct DocAttrNotCrateLevel<'a> {

compiler/rustc_resolve/src/late.rs

@@ -549,6 +549,7 @@ enum MaybeExported<'a> {
     Ok(NodeId),
     Impl(Option<DefId>),
     ImplItem(Result<DefId, &'a Visibility>),
+    NestedUse(&'a Visibility),
 }
 
 impl MaybeExported<'_> {
@@ -559,7 +560,9 @@ impl MaybeExported<'_> {
                 trait_def_id.as_local()
             }
             MaybeExported::Impl(None) => return true,
-            MaybeExported::ImplItem(Err(vis)) => return vis.kind.is_pub(),
+            MaybeExported::ImplItem(Err(vis)) | MaybeExported::NestedUse(vis) => {
+                return vis.kind.is_pub();
+            }
         };
         def_id.map_or(true, |def_id| r.effective_visibilities.is_exported(def_id))
     }
@@ -2284,7 +2287,7 @@ impl<'a: 'ast, 'b, 'ast, 'tcx> LateResolutionVisitor<'a, 'b, 'ast, 'tcx> {
     fn resolve_item(&mut self, item: &'ast Item) {
         let mod_inner_docs =
             matches!(item.kind, ItemKind::Mod(..)) && rustdoc::inner_docs(&item.attrs);
-        if !mod_inner_docs && !matches!(item.kind, ItemKind::Impl(..)) {
+        if !mod_inner_docs && !matches!(item.kind, ItemKind::Impl(..) | ItemKind::Use(..)) {
             self.resolve_doc_links(&item.attrs, MaybeExported::Ok(item.id));
         }
 
@@ -2428,6 +2431,12 @@ impl<'a: 'ast, 'b, 'ast, 'tcx> LateResolutionVisitor<'a, 'b, 'ast, 'tcx> {
             }
 
             ItemKind::Use(ref use_tree) => {
+                let maybe_exported = match use_tree.kind {
+                    UseTreeKind::Simple(_) | UseTreeKind::Glob => MaybeExported::Ok(item.id),
+                    UseTreeKind::Nested(_) => MaybeExported::NestedUse(&item.vis),
+                };
+                self.resolve_doc_links(&item.attrs, maybe_exported);
+
                 self.future_proof_import(use_tree);
             }
 

src/librustdoc/clean/mod.rs

@@ -2643,15 +2643,12 @@ fn clean_extern_crate<'tcx>(
         }
     }
 
-    // FIXME: using `from_def_id_and_kind` breaks `rustdoc/masked` for some reason
-    vec![Item {
-        name: Some(name),
-        attrs: Box::new(Attributes::from_ast(attrs)),
-        item_id: crate_def_id.into(),
-        kind: Box::new(ExternCrateItem { src: orig_name }),
-        cfg: attrs.cfg(cx.tcx, &cx.cache.hidden_cfg),
-        inline_stmt_id: Some(krate_owner_def_id),
-    }]
+    vec![Item::from_def_id_and_parts(
+        krate_owner_def_id,
+        Some(name),
+        ExternCrateItem { src: orig_name },
+        cx,
+    )]
 }
 
 fn clean_use_statement<'tcx>(

src/librustdoc/clean/utils.rs

@@ -38,11 +38,15 @@ pub(crate) fn krate(cx: &mut DocContext<'_>) -> Crate {
             for it in &module.items {
                 // `compiler_builtins` should be masked too, but we can't apply
                 // `#[doc(masked)]` to the injected `extern crate` because it's unstable.
-                if it.is_extern_crate()
-                    && (it.attrs.has_doc_flag(sym::masked)
-                        || cx.tcx.is_compiler_builtins(it.item_id.krate()))
-                {
+                if cx.tcx.is_compiler_builtins(it.item_id.krate()) {
                     cx.cache.masked_crates.insert(it.item_id.krate());
+                } else if it.is_extern_crate()
+                    && it.attrs.has_doc_flag(sym::masked)
+                    && let Some(def_id) = it.item_id.as_def_id()
+                    && let Some(local_def_id) = def_id.as_local()
+                    && let Some(cnum) = cx.tcx.extern_mod_stmt_cnum(local_def_id)
+                {
+                    cx.cache.masked_crates.insert(cnum);
                 }
             }
         }

src/librustdoc/html/format.rs

@@ -18,7 +18,7 @@ use rustc_data_structures::captures::Captures;
 use rustc_data_structures::fx::FxHashSet;
 use rustc_hir as hir;
 use rustc_hir::def::DefKind;
-use rustc_hir::def_id::DefId;
+use rustc_hir::def_id::{DefId, LOCAL_CRATE};
 use rustc_metadata::creader::{CStore, LoadedMacro};
 use rustc_middle::ty;
 use rustc_middle::ty::TyCtxt;
@@ -662,6 +662,14 @@ pub(crate) fn href_with_root_path(
             // documented on their parent's page
             tcx.parent(did)
         }
+        DefKind::ExternCrate => {
+            // Link to the crate itself, not the `extern crate` item.
+            if let Some(local_did) = did.as_local() {
+                tcx.extern_mod_stmt_cnum(local_did).unwrap_or(LOCAL_CRATE).as_def_id()
+            } else {
+                did
+            }
+        }
         _ => did,
     };
     let cache = cx.cache();

src/librustdoc/passes/collect_intra_doc_links.rs

@@ -14,7 +14,7 @@ use rustc_hir::def::{DefKind, Namespace, PerNS};
 use rustc_hir::def_id::{DefId, CRATE_DEF_ID};
 use rustc_hir::Mutability;
 use rustc_middle::ty::{Ty, TyCtxt};
-use rustc_middle::{bug, ty};
+use rustc_middle::{bug, span_bug, ty};
 use rustc_resolve::rustdoc::{has_primitive_or_keyword_docs, prepare_to_doc_link_resolution};
 use rustc_resolve::rustdoc::{strip_generics_from_path, MalformedGenerics};
 use rustc_session::lint::Lint;
@@ -402,7 +402,12 @@ impl<'a, 'tcx> LinkCollector<'a, 'tcx> {
             // `doc_link_resolutions` is missing a `path_str`, that means that there are valid links
             // that are being missed. To fix the ICE, change
             // `rustc_resolve::rustdoc::attrs_to_preprocessed_links` to cache the link.
-            .unwrap_or_else(|| panic!("no resolution for {:?} {:?} {:?}", path_str, ns, module_id))
+            .unwrap_or_else(|| {
+                span_bug!(
+                    self.cx.tcx.def_span(item_id),
+                    "no resolution for {path_str:?} {ns:?} {module_id:?}",
+                )
+            })
             .and_then(|res| res.try_into().ok())
             .or_else(|| resolve_primitive(path_str, ns));
         debug!("{} resolved to {:?} in namespace {:?}", path_str, result, ns);
@@ -963,6 +968,7 @@ fn preprocessed_markdown_links(s: &str) -> Vec<PreprocessedMarkdownLink> {
 }
 
 impl LinkCollector<'_, '_> {
+    #[instrument(level = "debug", skip_all)]
     fn resolve_links(&mut self, item: &Item) {
         if !self.cx.render_options.document_private
             && let Some(def_id) = item.item_id.as_def_id()

tests/rustdoc-ui/intra-doc/broken-link-in-unused-doc-string.rs

@@ -0,0 +1,16 @@
+// Test that we don't ICE with broken links that don't show up in the docs.
+
+// check-pass
+// edition: 2021
+
+/// [1]
+//~^ WARN unresolved link to `1`
+//~| WARN unresolved link to `1`
+pub use {std, core};
+
+/// [2]
+pub use {};
+
+/// [3]
+//~^ WARN unresolved link to `3`
+pub extern crate alloc;

tests/rustdoc-ui/intra-doc/broken-link-in-unused-doc-string.stderr

@@ -0,0 +1,27 @@
+warning: unresolved link to `3`
+  --> $DIR/broken-link-in-unused-doc-string.rs:14:6
+   |
+LL | /// [3]
+   |      ^ no item named `3` in scope
+   |
+   = help: to escape `[` and `]` characters, add '\' before them like `\[` or `\]`
+   = note: `#[warn(rustdoc::broken_intra_doc_links)]` on by default
+
+warning: unresolved link to `1`
+  --> $DIR/broken-link-in-unused-doc-string.rs:6:6
+   |
+LL | /// [1]
+   |      ^ no item named `1` in scope
+   |
+   = help: to escape `[` and `]` characters, add '\' before them like `\[` or `\]`
+
+warning: unresolved link to `1`
+  --> $DIR/broken-link-in-unused-doc-string.rs:6:6
+   |
+LL | /// [1]
+   |      ^ no item named `1` in scope
+   |
+   = help: to escape `[` and `]` characters, add '\' before them like `\[` or `\]`
+
+warning: 3 warnings emitted
+

tests/rustdoc-ui/lints/invalid-doc-attr.rs

@@ -1,5 +1,10 @@
 #![crate_type = "lib"]
 #![deny(warnings)]
+#![feature(doc_masked)]
+
+#![doc(masked)]
+//~^ ERROR this attribute can only be applied to an `extern crate` item
+//~| WARN is being phased out
 
 #[doc(test(no_crate_inject))]
 //~^ ERROR can only be applied at the crate level
@@ -30,3 +35,13 @@ pub mod bar {
 //~^^ ERROR conflicting doc inlining attributes
 //~|  HELP remove one of the conflicting attributes
 pub use bar::baz;
+
+#[doc(masked)]
+//~^ ERROR this attribute can only be applied to an `extern crate` item
+//~| WARN is being phased out
+pub struct Masked;
+
+#[doc(masked)]
+//~^ ERROR this attribute cannot be applied to an `extern crate self` item
+//~| WARN is being phased out
+pub extern crate self as reexport;