rustdoc: never link to unnamable items

src/librustdoc/html/format.rs

@@ -367,6 +367,8 @@ pub(crate) enum HrefError {
     Private,
     // Not in external cache, href link should be in same page
     NotInExternalCache,
+    /// Refers to an unnamable item, such as one defined within a function or const block.
+    UnnamableItem,
 }
 
 // Panics if `syms` is empty.
@@ -509,7 +511,13 @@ fn url_parts(
             builder.extend(module_fqp.iter().copied());
             Ok(builder)
         }
-        ExternalLocation::Local => Ok(href_relative_parts(module_fqp, relative_to)),
+        ExternalLocation::Local => {
+            if module_fqp.iter().any(|sym| sym.as_str() == "_") {
+                Err(HrefError::UnnamableItem)
+            } else {
+                Ok(href_relative_parts(module_fqp, relative_to))
+            }
+        }
         ExternalLocation::Unknown => Err(HrefError::DocumentationNotBuilt),
     }
 }

tests/rustdoc/reexport/auxiliary/wrap-unnamable-type.rs

@@ -0,0 +1,12 @@
+pub trait Assoc {
+    type Ty;
+}
+
+pub struct Foo(<Foo as crate::Assoc>::Ty);
+
+const _: () = {
+    impl crate::Assoc for Foo {
+        type Ty = Bar;
+    }
+    pub struct Bar;
+};

tests/rustdoc/reexport/wrapped-unnamble-type-143222.rs

@@ -0,0 +1,12 @@
+//@ compile-flags: -Z normalize-docs --document-private-items -Zunstable-options --show-type-layout
+//@ aux-build:wrap-unnamable-type.rs
+//@ build-aux-docs
+
+#![crate_name = "foo"]
+
+extern crate wrap_unnamable_type as helper;
+//extern crate helper;
+//@ has 'foo/struct.Foo.html'
+//@ !hasraw - '_/struct.Bar.html'
+#[doc(inline)]
+pub use helper::Foo;