update comment as requested. also change outdated b references in other comments

Author: IntegralPilot

compiler/rustc_builtin_macros/src/test.rs

@@ -207,22 +207,22 @@ pub(crate) fn expand_test_or_bench(
     };
 
     let test_fn = if is_bench {
-        // A simple ident for a lambda, using the user's function name within it to avoid collisions.
+        // A collision-resistant ident for a lambda, using the user's function name within it to avoid collisions.
         let bencher_param =
             Ident::from_str_and_span(&format!("__bench_{}", fn_.ident.name), attr_sp);
         cx.expr_call(
             sp,
             cx.expr_path(test_path("StaticBenchFn")),
             thin_vec![
                 // #[coverage(off)]
-                // |b| self::test::assert_test_result(
+                // |__bench_fn_name| self::test::assert_test_result(
                 coverage_off(cx.lambda1(
                     sp,
                     cx.expr_call(
                         sp,
                         cx.expr_path(test_path("assert_test_result")),
                         thin_vec![
-                            // super::$test_fn(b)
+                            // super::$test_fn(__bench_fn_name)
                             cx.expr_call(
                                 ret_ty_sp,
                                 cx.expr_path(cx.path(sp, vec![fn_.ident])),