Really we’d need rustc to support some kind of AOP technique that lets you inject code at every call site somehow. That way you write the extra context info in a single macro that gets applied transparently for you.
That being said, SNAFU’s approach seems better in the interim. Just add a Location (and presumably there’s a backtrace option too) to your error type and it’s captured automatically without any macros.
There is [0].
However, I'm not personally a fan of backtraces (or the lightweight location information, really). I'd much rather provide what I call a "semantic backtrace", which is where almost every Result-returning function is annotated by the programmer with a unique `.context(...)` call. This often results in a better error to the user ("couldn't connect to the server <because> couldn't get the URL <because> couldn't open the config file <because> couldn't open file ..."). The programmer can identify the location of the error due to the uniqueness of each context.
Backtraces are an easier way of getting similar information, but much less useful to the end user. I'd rather people prioritize the end user over the developer, so that's what I try to encourage in SNAFU.
That being said, plenty of people want location / backtrace information, so SNAFU tries to support those as well.
[0]: https://docs.rs/snafu/latest/snafu/struct.Backtrace.html
Also, most users are non-technical. So semantic backtraces that are visible only end up helping a small, more technical subset of your customer base (even if your customer base is developers in my experience). You do want to be able to have a way to link a semantic backtrace to a specific error instance that a customer observed though.
Maybe `cargo fmt` could be extended to add such annotations automatically? That way, it wouldn't be "magic", since the macros would be spelled out in the code, but the manual work of adding them would be eliminated.