Test rustdoc encountering proc_macro_derive in a non-proc-macro crate

tests/rustdoc-ui/proc_macro_bug.rs

@@ -0,0 +1,12 @@
+// regression test for failing to pass `--crate-type proc-macro` to rustdoc
+// when documenting a proc macro crate https://github.com/rust-lang/rust/pull/107291
+
+extern crate proc_macro;
+
+use proc_macro::TokenStream;
+
+#[proc_macro_derive(DeriveA)]
+//~^ ERROR the `#[proc_macro_derive]` attribute is only usable with crates of the `proc-macro` crate type
+pub fn a_derive(input: TokenStream) -> TokenStream {
+    input
+}

tests/rustdoc-ui/proc_macro_bug.stderr

@@ -0,0 +1,8 @@
+error: the `#[proc_macro_derive]` attribute is only usable with crates of the `proc-macro` crate type
+  --> $DIR/proc_macro_bug.rs:8:1
+   |
+LL | #[proc_macro_derive(DeriveA)]
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error: aborting due to previous error
+