feature: unsupported message for $idents (#293)

crates/syn-solidity/src/ident/mod.rs

@@ -5,7 +5,7 @@ use std::fmt;
 use syn::{
     ext::IdentExt,
     parse::{Parse, ParseStream},
-    Result,
+    Result, Token,
 };
 
 mod path;
@@ -105,6 +105,7 @@ impl SolIdent {
 
     /// Parses any identifier including keywords.
     pub fn parse_any(input: ParseStream<'_>) -> Result<Self> {
+        check_dollar(input)?;
         input.call(Ident::parse_any).map(Self)
     }
 
@@ -121,3 +122,11 @@ impl SolIdent {
         }
     }
 }
+
+fn check_dollar(input: ParseStream<'_>) -> Result<()> {
+    if input.peek(Token![$]) {
+        Err(input.error("Solidity identifiers starting with `$` are unsupported. This is a known limitation of syn-solidity."))
+    } else {
+        Ok(())
+    }
+}

crates/syn-solidity/tests/ident.rs

@@ -16,3 +16,13 @@ fn ident_path() {
 fn ident_path_trailing() {
     let _e = syn::parse_str::<SolPath>("a.b.").unwrap_err();
 }
+
+#[test]
+fn ident_dollar() {
+    let id: Result<SolIdent, _> = syn::parse_str("$hello");
+    assert!(id.is_err());
+    assert!(id
+        .unwrap_err()
+        .to_string()
+        .contains("Solidity identifiers starting with `$` are unsupported."));
+}