Test that every expr can be scanned

tests/test_precedence.rs

@@ -49,6 +49,7 @@ use std::fs;
 use std::path::Path;
 use std::process;
 use std::sync::atomic::{AtomicUsize, Ordering};
+use syn::parse::Parser as _;
 
 #[macro_use]
 mod macros;
@@ -57,7 +58,6 @@ mod common;
 mod repo;
 
 #[path = "../src/scan_expr.rs"]
-#[allow(dead_code)]
 mod scan_expr;
 
 #[test]
@@ -119,7 +119,8 @@ fn test_expressions(path: &Path, edition: Edition, exprs: Vec<syn::Expr>) -> (us
 
     rustc_span::create_session_if_not_set_then(edition, |_| {
         for expr in exprs {
-            let source_code = expr.to_token_stream().to_string();
+            let expr_tokens = expr.to_token_stream();
+            let source_code = expr_tokens.to_string();
             let librustc_ast = if let Some(e) = librustc_parse_and_rewrite(&source_code) {
                 e
             } else {
@@ -177,6 +178,16 @@ fn test_expressions(path: &Path, edition: Edition, exprs: Vec<syn::Expr>) -> (us
                 continue;
             }
 
+            if scan_expr::scan_expr.parse2(expr_tokens).is_err() {
+                failed += 1;
+                errorf!(
+                    "\nFAIL {} - failed to scan expr\n{}\n",
+                    path.display(),
+                    source_code,
+                );
+                continue;
+            }
+
             passed += 1;
         }
     });