The span of this error is useful:

error[E0282]: type annotations needed
  |
# |     println!("{:?}", []);
  |                      ^^ cannot infer type
  |

However, in a slightly more complicated println, the same error points at the entire macro invocation:

error[E0282]: type annotations needed
  |
# |     println!("{:?} {a} {a:?}", [], a = 1 + 1);
  |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ cannot infer type
  |

It should have just pointed at [] (or perhaps {:?}), rather than the entire macro call.

The simple println results in this case in format_args lowering:

The more complicated println results in this case in format_args lowering:

It'd be nice if both cases would cause any type/trait errors to be reported on the argument (or placeholders), instead of on the span of the entire macro invocation.

I'm not sure if this requires changes in rustc_ast_lowering, or in the code that reports the type errors.