Add regression test for #106226

src/test/rustdoc-ui/issue-106226.rs

@@ -0,0 +1,3 @@
+// This is a regression test for <https://github.com/rust-lang/rust/issues/106226>.
+type F = [_; ()];
+//~^ ERROR

src/test/rustdoc-ui/issue-106226.stderr

@@ -0,0 +1,9 @@
+error[E0308]: mismatched types
+  --> $DIR/issue-106226.rs:2:14
+   |
+LL | type F = [_; ()];
+   |              ^^ expected `usize`, found `()`
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0308`.