Add a test for proc macro generating $ IDENT

Author: petrochenkov

src/test/ui/proc-macro/auxiliary/generate-dollar-ident.rs

@@ -0,0 +1,17 @@
+// force-host
+// no-prefer-dynamic
+
+#![feature(proc_macro_hygiene)]
+#![feature(proc_macro_quote)]
+#![crate_type = "proc-macro"]
+
+extern crate proc_macro;
+use proc_macro::*;
+
+#[proc_macro]
+pub fn dollar_ident(input: TokenStream) -> TokenStream {
+    let black_hole = input.into_iter().next().unwrap();
+    quote! {
+        $black_hole!($$var);
+    }
+}

src/test/ui/proc-macro/generate-dollar-ident.rs

@@ -0,0 +1,18 @@
+// Proc macros can generate token sequence `$ IDENT`
+// without it being recognized as an unknown macro variable.
+
+// check-pass
+// aux-build:generate-dollar-ident.rs
+
+extern crate generate_dollar_ident;
+use generate_dollar_ident::*;
+
+macro_rules! black_hole {
+    ($($tt:tt)*) => {};
+}
+
+black_hole!($var);
+
+dollar_ident!(black_hole);
+
+fn main() {}