get unstable-api compiling again

Author: KodrAus

tools/unstable-api/Cargo.toml

@@ -8,6 +8,12 @@ edition = "2018"
 version = "1"
 features = ["full", "extra-traits", "visit"]
 
+[dependencies.quote]
+version = "1"
+
+[dependencies.proc-macro2]
+version = "1"
+
 [dependencies.structopt]
 version = "0.3"
 

tools/unstable-api/src/visit/mod.rs

@@ -1,9 +1,10 @@
 use anyhow::{anyhow, ensure, Context, Error};
 use syn::{
-    export::{Span, ToTokens, TokenStream2 as TokenStream},
     ext::IdentExt,
     visit::{self, Visit},
 };
+use quote::ToTokens;
+use proc_macro2::{Span, TokenStream};
 
 use std::{fs, fmt, path::PathBuf};