Specifying static-nobundle on command line causes an internal compiler error

[petrochenkov]

Reproduction:

rustc -l static-nobundle=nonexistent main.rs

---

thread 'rustc' panicked at 'called `Option::unwrap()` on a `None` value', src\libcore\option.rs:345:21
note: Run with `RUST_BACKTRACE=1` environment variable to display a backtrace.

error: internal compiler error: unexpected panic

This happens because code in

rust/src/librustc_metadata/native_libs.rs

Line 166 in c0bbc39

span.unwrap(),

assumes that the span always exists, which is not true for things passed from command line.

[AB1908]

I'm very new to Rust so forgive my naivety. Since span may not exist, I assume we need to change span.unwrap() to span.unwrap_or_else() and provide a default value? From the documentation, I couldn't think of a suitable default value for Span which is expected by feature_gate::emit_feature_err(). I couldn't think of any other changes as per your statement:

assumes that the span always exists, which is not true for things passed from command line.

[Patryk27]

Maybe instead of unwrap_or_else() we could go this way?

if let Some(span) = span {
  feature_gate::emit_feature_err(/* ... */);
} else {
  self.tcx.sess.err("some error message here");
}

(see: processing error messages in the process_command_line function below that register_native_lib)

[AB1908]

Does this mean that we should throw an error when span is empty? From the original description, it seemed to me that having a Span value was optional. If throwing an error is the way to go, then I think your solution is the appropriate solution.

[petrochenkov]

@AB1908
DUMMY_SP is the value that's usually used if the span is unknown or doesn't exist.

[AB1908]

Alright. For future reference, how was I to find that out?

[petrochenkov]

@AB1908
If type has a default value, it's usually defined somewhere around the definition of that type.
In case of Span pub const DUMMY_SP: Span = Span(0); is also defined in right below the span definition pub struct Span(u32); in libsyntax_pos/span_encoding.rs

[AB1908]

Thanks for the hand-holding. I'll try to make the necessary changes and start a PR.