Pass compiler (error) output in json (--message-format=json-diagnostic-rendered-ansi)

[vlad20012]

Hello!

We're looking at cargo nextest integration into RustRover alongside with cargo test.

One caveat is that cargo nextest does not support Cargo's --message-format option (which works with cargo build or cargo test --no-run).

RustRover then uses the structured compiler output to show compilation errors/warnings in a structured way.

Screencast.from.2026-01-21.22-12-30.mp4

Any possibility of adding a similar feature? Don't confuse with an existing --message-format nextest option 😅

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More details

When running tests from RustRover, actually 2 commands are executed sequentially:

1. cargo test --no-run --message-format=json-diagnostic-rendered-ansi
2. cargo test -- --format=json

The first one compiles the binaries and produce compiler diagnostics (errors/warnings) if any.
The second one actually runs the tests using the default test framework.

In the case of cargo nextest run, it looks like we can do the same trick, splitting the invocation into 2 commands:

1. cargo nextest run --no-run
2. cargo nextest run --message-format=libtest-json-plus

The problem here is that in the case of cargo nextest run --no-run, there isn't an equivalent of Cargo's --message-format=json-diagnostic-rendered-ansi.

We could workaround it by invoking cargo test --no-run --message-format=json-diagnostic-rendered-ansi under the hood instead of cargo nextest run --no-run. But this option implies transforming the whole command line from cargo nextest to cargo test on RustRover side, which would be too huge maintenance burden

[sunshowers]

Thanks -- honestly I'd been dreading this due to the complexity, but it wasn't too bad in the end. See #2985.

[sunshowers]

Could you try cargo-nextest 0.9.123-b.4? It has a new --cargo-message-format option.

[vlad20012]

Amazing, thank you!
Just tested 0.9.123-b.4 with --cargo-message-format=json-diagnostic-rendered-ansi - it works flawlessly on our side and fits the integration perfectly.

Really appreciate how quickly this was addressed, and hats off for tackling what looked like a nasty bit of complexity 🙌

[sunshowers]

This is now out in cargo-nextest 0.9.123. By the way if and when RustRover ships nextest support, I'd love a PR to https://nexte.st/docs/integrations/.

[vlad20012]

That would be our pleasure!