No backtrace on windows with current rustc stable

[TheBlueMatt]

Currently rustc beta in our CI is giving us backtraces like this with simple cargo tests (with Cargo.toml set for opt-level = 1):

0: <unknown>
   1: <unknown>
   2: <unknown>
   3: <unknown>
   4: <unknown>
   5: <unknown>
   6: <unknown>
   7: <unknown>
   8: <unknown>
   9: <unknown>
  10: <unknown>
  11: <unknown>
  12: <unknown>
  13: <unknown>
  14: BaseThreadInitThunk
  15: RtlUserThreadStart

[ChrisDenton]

Hm, I wonder if that's due to a change in debug information being generated. Does it work if you use debuginfo="line-tables-only"? EDIT: Oh the Cargo.toml would be debug = "line-tables-only"

[TheBlueMatt]

I tried RUSTFLAGS="-C debuginfo=line-tables-only" cargo test --features backtrace and it seems to still fail with the same backtrace.

[workingjubilee]

@TheBlueMatt What about nightly?

[ChrisDenton]

The reasons I can think of for a lack of symbols is:

• debug info is not being generated
• debug info is being removed somehow
• the pdb file is not being found for some reason
• there's a bug in the dbghelp code

The last case I think is the most unlikely because that should show up in our CI. The other cases are more likely caused by either a rustc or CI issue, in which case it should be reported on the rust-lang/rust repository. A possibly relevant PR I see is #121297

[workingjubilee]

Oh yeah, the beta is a really recent nightly, right.

[workingjubilee]

Confirmed in rust-lang/backtrace-rs#594 that our CI for Windows is now broken, likely due to rustc changes. Transferring this to rust-lang/rust accordingly.