message: Diagnostics for golden tests
diff: use std::{env, fmt::Write, fs};
  +use anyhow::Context;
  +
  use crate::{assert::Assert, eval::compiler::def::FrozenDef};
  const REGENERATE_VAR_NAME: &str = "STARLARK_RUST_REGENERATE_BC_TESTS";
  @@ -62,7 +64,9 @@ pub(crate) fn bc_golden_test(test_name: &str, program: &str) {
  if env::var(REGENERATE_VAR_NAME).is_ok() {
  fs::write(golden_file_name, &actual).unwrap();
  } else {
  - let expected = fs::read_to_string(golden_file_name).unwrap();
  + let expected = fs::read_to_string(&golden_file_name)
  + .with_context(|| format!("Reading `{golden_file_name}`"))
  + .unwrap();
  assert_eq!(expected, actual);
  }
  }
  