Allow generic parameters in intra-doc links

The contents of the generics will be mostly ignored (except for warning
if fully-qualified syntax is used, which is currently unsupported in
intra-doc links - see issue #74563).

* Allow links like `Vec<T>`, `Result<T, E>`, and `Option<Box<T>>`
* Allow links like `Vec::<T>::new()`
* Warn on
  * Unbalanced angle brackets (e.g. `Vec<T` or `Vec<T>>`)
  * Missing type to apply generics to (`<T>` or `<Box<T>>`)
  * Use of fully-qualified syntax (`<Vec as IntoIterator>::into_iter`)
  * Invalid path separator (`Vec:<T>:new`)
  * Too many angle brackets (`Vec<<T>>`)
  * Empty angle brackets (`Vec<>`)

Note that this implementation *does* allow some constructs that aren't
valid in the actual Rust syntax, for example `Box::<T>new()`. That may
not be supported in rustdoc in the future; it is an implementation
detail.

3 files changed, 122 insertions, 1 deletions

diff --git a/src/test/rustdoc-ui/intra-link-errors.rs b/src/test/rustdoc-ui/intra-link-errors.rs
index ef928ae02f3..81e42643ae8 100644
--- a/src/test/rustdoc-ui/intra-link-errors.rs
+++ b/src/test/rustdoc-ui/intra-link-errors.rs
@@ -2,7 +2,7 @@
 //~^ NOTE lint level is defined
 
 // FIXME: this should say that it was skipped (maybe an allowed by default lint?)
-/// [<invalid syntax>]
+/// [invalid intra-doc syntax!!]
 
 /// [path::to::nonexistent::module]
 //~^ ERROR unresolved link
diff --git a/src/test/rustdoc-ui/intra-link-malformed-generics.rs b/src/test/rustdoc-ui/intra-link-malformed-generics.rs
new file mode 100644
index 00000000000..9c54092146f
--- /dev/null
+++ b/src/test/rustdoc-ui/intra-link-malformed-generics.rs
@@ -0,0 +1,19 @@
+#![deny(broken_intra_doc_links)]
+
+//! [Vec<] //~ ERROR
+//! [Vec<Box<T] //~ ERROR
+//! [Vec<Box<T>] //~ ERROR
+//! [Vec<Box<T>>>] //~ ERROR
+//! [Vec<T>>>] //~ ERROR
+//! [<Vec] //~ ERROR
+//! [Vec::<] //~ ERROR
+//! [<T>] //~ ERROR
+//! [<invalid syntax>] //~ ERROR
+//! [Vec:<T>:new()] //~ ERROR
+//! [Vec<<T>>] //~ ERROR
+//! [Vec<>] //~ ERROR
+//! [Vec<<>>] //~ ERROR
+
+// FIXME(#74563) support UFCS
+//! [<Vec as IntoIterator>::into_iter] //~ ERROR
+//! [<Vec<T> as IntoIterator>::iter] //~ ERROR
diff --git a/src/test/rustdoc-ui/intra-link-malformed-generics.stderr b/src/test/rustdoc-ui/intra-link-malformed-generics.stderr
new file mode 100644
index 00000000000..fe5d4cd1bbf
--- /dev/null
+++ b/src/test/rustdoc-ui/intra-link-malformed-generics.stderr
@@ -0,0 +1,102 @@
+error: unresolved link to `Vec<`
+  --> $DIR/intra-link-malformed-generics.rs:3:6
+   |
+LL | //! [Vec<]
+   |      ^^^^ unbalanced angle brackets
+   |
+note: the lint level is defined here
+  --> $DIR/intra-link-malformed-generics.rs:1:9
+   |
+LL | #![deny(broken_intra_doc_links)]
+   |         ^^^^^^^^^^^^^^^^^^^^^^
+
+error: unresolved link to `Vec<Box<T`
+  --> $DIR/intra-link-malformed-generics.rs:4:6
+   |
+LL | //! [Vec<Box<T]
+   |      ^^^^^^^^^ unbalanced angle brackets
+
+error: unresolved link to `Vec<Box<T>`
+  --> $DIR/intra-link-malformed-generics.rs:5:6
+   |
+LL | //! [Vec<Box<T>]
+   |      ^^^^^^^^^^ unbalanced angle brackets
+
+error: unresolved link to `Vec<Box<T>>>`
+  --> $DIR/intra-link-malformed-generics.rs:6:6
+   |
+LL | //! [Vec<Box<T>>>]
+   |      ^^^^^^^^^^^^ unbalanced angle brackets
+
+error: unresolved link to `Vec<T>>>`
+  --> $DIR/intra-link-malformed-generics.rs:7:6
+   |
+LL | //! [Vec<T>>>]
+   |      ^^^^^^^^ unbalanced angle brackets
+
+error: unresolved link to `<Vec`
+  --> $DIR/intra-link-malformed-generics.rs:8:6
+   |
+LL | //! [<Vec]
+   |      ^^^^ unbalanced angle brackets
+
+error: unresolved link to `Vec::<`
+  --> $DIR/intra-link-malformed-generics.rs:9:6
+   |
+LL | //! [Vec::<]
+   |      ^^^^^^ unbalanced angle brackets
+
+error: unresolved link to `<T>`
+  --> $DIR/intra-link-malformed-generics.rs:10:6
+   |
+LL | //! [<T>]
+   |      ^^^ missing type for generic parameters
+
+error: unresolved link to `<invalid syntax>`
+  --> $DIR/intra-link-malformed-generics.rs:11:6
+   |
+LL | //! [<invalid syntax>]
+   |      ^^^^^^^^^^^^^^^^ missing type for generic parameters
+
+error: unresolved link to `Vec:<T>:new`
+  --> $DIR/intra-link-malformed-generics.rs:12:6
+   |
+LL | //! [Vec:<T>:new()]
+   |      ^^^^^^^^^^^^^ has invalid path separator
+
+error: unresolved link to `Vec<<T>>`
+  --> $DIR/intra-link-malformed-generics.rs:13:6
+   |
+LL | //! [Vec<<T>>]
+   |      ^^^^^^^^ too many angle brackets
+
+error: unresolved link to `Vec<>`
+  --> $DIR/intra-link-malformed-generics.rs:14:6
+   |
+LL | //! [Vec<>]
+   |      ^^^^^ empty angle brackets
+
+error: unresolved link to `Vec<<>>`
+  --> $DIR/intra-link-malformed-generics.rs:15:6
+   |
+LL | //! [Vec<<>>]
+   |      ^^^^^^^ too many angle brackets
+
+error: unresolved link to `<Vec as IntoIterator>::into_iter`
+  --> $DIR/intra-link-malformed-generics.rs:18:6
+   |
+LL | //! [<Vec as IntoIterator>::into_iter]
+   |      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ fully-qualified syntax is unsupported
+   |
+   = note: see https://github.com/rust-lang/rust/issues/74563 for more information
+
+error: unresolved link to `<Vec<T> as IntoIterator>::iter`
+  --> $DIR/intra-link-malformed-generics.rs:19:6
+   |
+LL | //! [<Vec<T> as IntoIterator>::iter]
+   |      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ fully-qualified syntax is unsupported
+   |
+   = note: see https://github.com/rust-lang/rust/issues/74563 for more information
+
+error: aborting due to 15 previous errors
+