Backtraces

An error event carries a backtrace when one is captured. The layer captures it with std::backtrace::Backtrace::capture() at the place the event is logged, so a capture costs nothing unless RUST_BACKTRACE or RUST_LIB_BACKTRACE enables it:

RUST_BACKTRACE=1 PROJECT_ID=<your-google-project-id> cargo run --example errors-error-reporting --features logs-api

Set one of the two variables in the environment of the deployed service to get backtraces in Error Reporting. The layer never forces a capture, so without them the entry has no backtrace.

The backtrace is rendered with Display, as std::backtrace frames, and follows the first line of message. Error Reporting has accepted Rust std::backtrace frames since 2026-08-13, see its release notes, and groups errors by their top frames. The trace is placed in message only, never in stack_trace, because Error Reporting reads stack_trace before message and the first present wins, which would hide the first line.

Error Reporting’s release note asks for debug symbols to be enabled. In a release build, debug = "line-tables-only" in [profile.release] keeps the file and line numbers of the frames.