Add #[doc(hidden)] attribute on compiler generated proc-macro module.

Stops unavoidable `missing_docs` warning/error on proc-macro crates.
Resolves #42008.

1 files changed, 16 insertions, 0 deletions

diff --git a/src/test/ui/proc-macro/no-missing-docs.rs b/src/test/ui/proc-macro/no-missing-docs.rs
new file mode 100644
index 00000000000..e5a5f8beb45
--- /dev/null
+++ b/src/test/ui/proc-macro/no-missing-docs.rs
@@ -0,0 +1,16 @@
+//! Verify that the `decls` module implicitly added by the compiler does not cause `missing_docs`
+//! warnings.
+
+// compile-pass
+// force-host
+// no-prefer-dynamic
+
+#![crate_type = "proc-macro"]
+#![deny(missing_docs)]
+
+extern crate proc_macro;
+use proc_macro::*;
+
+/// Foo1.
+#[proc_macro]
+pub fn foo1(input: TokenStream) -> TokenStream { input }