Fix bad intra-doc-link preprocessing

compiler/rustc_resolve/src/rustdoc.rs

@@ -393,13 +393,15 @@ pub fn has_primitive_or_keyword_or_attribute_docs(attrs: &[impl AttributeExt]) -
 }
 
 /// Simplified version of the corresponding function in rustdoc.
-/// If the rustdoc version returns a successful result, this function must return the same result.
-/// Otherwise this function may return anything.
 fn preprocess_link(link: &str) -> Box<str> {
+    // IMPORTANT: To be kept in sync with the corresponding function in rustdoc.
+    // Namely, whenever the rustdoc function returns a successful result for a
+    // given input, this function *MUST* return the same result!
+
     let link = link.replace('`', "");
     let link = link.split('#').next().unwrap();
     let link = link.trim();
-    let link = link.rsplit('@').next().unwrap();
+    let link = link.split_once('@').map_or(link, |(_, rhs)| rhs);
     let link = link.strip_suffix("()").unwrap_or(link);
     let link = link.strip_suffix("{}").unwrap_or(link);
     let link = link.strip_suffix("[]").unwrap_or(link);

src/librustdoc/passes/collect_intra_doc_links.rs

@@ -938,14 +938,18 @@ pub(crate) struct PreprocessedMarkdownLink(
 
 /// Returns:
 /// - `None` if the link should be ignored.
-/// - `Some(Err)` if the link should emit an error
-/// - `Some(Ok)` if the link is valid
+/// - `Some(Err(_))` if the link should emit an error
+/// - `Some(Ok(_))` if the link is valid
 ///
 /// `link_buffer` is needed for lifetime reasons; it will always be overwritten and the contents ignored.
 fn preprocess_link(
     ori_link: &MarkdownLink,
     dox: &str,
 ) -> Option<Result<PreprocessingInfo, PreprocessingError>> {
+    // IMPORTANT: To be kept in sync with the corresponding function in `rustc_resolve::rustdoc`.
+    // Namely, whenever this function successfully returns a preprocessed link for a given input,
+    // the rustc counterpart *MUST* return the same link!
+
     // certain link kinds cannot have their path be urls,
     // so they should not be ignored, no matter how much they look like urls.
     // e.g. [https://example.com/] is not a link to example.com.

tests/rustdoc-ui/intra-doc/malformed-paths.rs

@@ -0,0 +1,17 @@
+// This test ensures that (syntactically) malformed paths will not crash rustdoc.
+#![deny(rustdoc::broken_intra_doc_links)]
+
+// This is a regression test for <https://github.com/rust-lang/rust/issues/140026>.
+//! [`Type::`]
+//~^ ERROR
+
+// This is a regression test for <https://github.com/rust-lang/rust/issues/147981>
+//! [`struct@Type@field`]
+//~^ ERROR
+
+//! [Type&content]
+//~^ ERROR
+//! [`Type::field%extra`]
+//~^ ERROR
+
+pub struct Type { pub field: () }

tests/rustdoc-ui/intra-doc/malformed-paths.stderr

@@ -0,0 +1,36 @@
+error: unresolved link to `Type::`
+  --> $DIR/malformed-paths.rs:5:7
+   |
+LL | //! [`Type::`]
+   |       ^^^^^^ the struct `Type` has no field or associated item named ``
+   |
+note: the lint level is defined here
+  --> $DIR/malformed-paths.rs:2:9
+   |
+LL | #![deny(rustdoc::broken_intra_doc_links)]
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error: unresolved link to `Type@field`
+  --> $DIR/malformed-paths.rs:9:7
+   |
+LL | //! [`struct@Type@field`]
+   |       ^^^^^^^^^^^^^^^^^ no item named `Type@field` in scope
+   |
+   = help: to escape `[` and `]` characters, add '\' before them like `\[` or `\]`
+
+error: unresolved link to `Type&content`
+  --> $DIR/malformed-paths.rs:12:6
+   |
+LL | //! [Type&content]
+   |      ^^^^^^^^^^^^ no item named `Type&content` in scope
+   |
+   = help: to escape `[` and `]` characters, add '\' before them like `\[` or `\]`
+
+error: unresolved link to `Type::field%extra`
+  --> $DIR/malformed-paths.rs:14:7
+   |
+LL | //! [`Type::field%extra`]
+   |       ^^^^^^^^^^^^^^^^^ the struct `Type` has no field or associated item named `field%extra`
+
+error: aborting due to 4 previous errors
+