message: Add some debug logging for `cargo fix`
diff: @@ -363,6 +363,7 @@ pub fn fix_maybe_exec_rustc(config: &Config) -> CargoResult<bool> {
  let mut cmd = rustc.build_command();
  args.apply(&mut cmd, config);
  cmd.arg("--error-format=json");
  + debug!("calling rustc for final verification: {:?}", cmd);
  let output = cmd.output().context("failed to spawn rustc")?;
  if output.status.success() {
  @@ -388,6 +389,7 @@ pub fn fix_maybe_exec_rustc(config: &Config) -> CargoResult<bool> {
  if !output.status.success() {
  if env::var_os(BROKEN_CODE_ENV).is_none() {
  for (path, file) in fixes.files.iter() {
  + debug!("reverting {:?} due to errors", path);
  paths::write(path, &file.original_code)?;
  }
  }
  @@ -406,6 +408,7 @@ pub fn fix_maybe_exec_rustc(config: &Config) -> CargoResult<bool> {
  // things like colored output to work correctly.
  cmd.arg(arg);
  }
  + debug!("calling rustc to display remaining diagnostics: {:?}", cmd);
  exit_with(cmd.status().context("failed to spawn rustc")?);
  }
  @@ -541,6 +544,10 @@ fn rustfix_and_fix(
  let mut cmd = rustc.build_command();
  cmd.arg("--error-format=json");
  args.apply(&mut cmd, config);
  + debug!(
  + "calling rustc to collect suggestions and validate previous fixes: {:?}",
  + cmd
  + );
  let output = cmd.output().with_context(|| {
  format!(
  "failed to execute `{}`",
  @@ -605,6 +612,7 @@ fn rustfix_and_fix(
  continue;
  }
  + trace!("adding suggestion for {:?}: {:?}", file_name, suggestion);
  file_map
  .entry(file_name)
  .or_insert_with(Vec::new)
  