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-j should also set --test-threads #17357
Description
In 2018, someone asked for cargo test -jN to also set the number of threads used to run tests. In 2023, we closed that issue. #6265 .
We may have discussed this, but I can't seem to find any record of the discussion. I'd like to re-raise that item for consideration.
Activity
epage commentedon Aug 13, 2026
This has a similar problem as #1983 where forwarding config as arguments may be a breaking change. This could be resolved by switching arguments from conflicting with themself to overriding. The main risks are user confusion if we aren't consistent and later changing an override to an append would be a breaking change.
joshtriplett commentedon Aug 14, 2026
@epage Is there a way we can pass this as an environment variable, such that an explicit argument would override it?
epage commentedon Aug 14, 2026
See rust-lang/testing-devex-team#10 (comment)
joshtriplett commentedon Aug 18, 2026
@epage Fair enough. I think switching the arguments to be overriding rather than conflicting seems fine, then.
weihanglo commentedon Aug 22, 2026
This requires rust-lang/rust changes. See rust-lang/rust#161312. The Cargo side is blocked on libtest harness change.
See also the raw meeting note https://github.com/rust-lang/cargo-team/blob/3e93e0d4a3435c100c3fc497815f8c2e8150807b/meetings/sync-meeting/2026-08-18.md?plain=1#L125-L195.
@rustbot label +S-blocked-external