Add regression tests for intra-doc links

Author: GuillaumeGomez

tests/rustdoc-ui/intra-doc/hidden-check.rs

@@ -0,0 +1,14 @@
+// This test ensures that `doc(hidden)` items intra-doc links are checked whereas private
+// items are ignored.
+
+//@ compile-flags: -Zunstable-options --document-hidden-items
+
+#![deny(rustdoc::broken_intra_doc_links)]
+
+/// [not::exist]
+//~^ ERROR unresolved link to `not::exist`
+#[doc(hidden)]
+pub struct X;
+
+/// [not::exist]
+struct Y;

tests/rustdoc-ui/intra-doc/hidden-check.stderr

@@ -0,0 +1,14 @@
+error: unresolved link to `not::exist`
+  --> $DIR/hidden-check.rs:8:6
+   |
+LL | /// [not::exist]
+   |      ^^^^^^^^^^ no item named `not` in scope
+   |
+note: the lint level is defined here
+  --> $DIR/hidden-check.rs:6:9
+   |
+LL | #![deny(rustdoc::broken_intra_doc_links)]
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error: aborting due to 1 previous error
+

tests/rustdoc-ui/intra-doc/private-check.rs

@@ -0,0 +1,14 @@
+// This test ensures that private items intra-doc links are checked whereas `doc(hidden)`
+// items are ignored.
+
+//@ compile-flags: -Zunstable-options --document-private-items
+
+#![deny(rustdoc::broken_intra_doc_links)]
+
+/// [not::exist]
+#[doc(hidden)]
+pub struct X;
+
+/// [not::exist]
+//~^ ERROR unresolved link to `not::exist`
+struct Y;

tests/rustdoc-ui/intra-doc/private-check.stderr

@@ -0,0 +1,14 @@
+error: unresolved link to `not::exist`
+  --> $DIR/private-check.rs:12:6
+   |
+LL | /// [not::exist]
+   |      ^^^^^^^^^^ no item named `not` in scope
+   |
+note: the lint level is defined here
+  --> $DIR/private-check.rs:6:9
+   |
+LL | #![deny(rustdoc::broken_intra_doc_links)]
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error: aborting due to 1 previous error
+