This test documents the current behavior
when using both `-Zbuild-analysis` and `--message-format=json`.

When both `-Zbuild-analysis` and `--message-format=json` are enabled,
emit a `build-started` JSON message to stdout containing the `run_id`.
This allows external tools to associate the JSON output stream
with the corresponding log file in `~/.cargo/log/{run_id}.jsonl`.
While a better design of JSON message and structured logging is needed,
this provides a temporary workaround for those needing the old
`--timings=json` flag
Closes rust-lang#16576

Open