Problem

The panic setting is ignored for benchmarks since (by default) they link libtest which is compiled with panic = "unwind". This would otherwise lead to confusing errors at link time when "abort" is used (#3166, #3175).

However, it is possible to disable the default harness for a benchmark (which means libtest is no longer linked):

[[bench]]
name = "my_bench"
harness = false

(this is common when using external benchmarking frameworks such as criterion)

The ability to disable unwinding when benchmarking is useful since the inclusion of unwinding machinery can affect performance.

Proposed Solution

Allow panic = "abort" when harness = false.

Cargo currently always prints a warning when the bench profile contains panic = "abort". With this proposal that warning would only be printed when building/running a benchmark where the setting is ignored. (Note: currently running a benchmark with a different profile, e.g. cargo bench --profile release that has panic = "abort" will ignore the panic setting but not print any warning)

Notes

No response