chore: Fix docs.rs build failure

[Bravo555]

kstring fails to build on docs.rs because feature doc_auto_cfg was removed from nightly in 1.92.0.
Replace it with doc_cfg.

Fix can be verified using RUSTFLAGS="--cfg docsrs" cargo +nightly-2025-11-28 check

[epage]

For verifying this, you recommend

$ RUSTFLAGS="--cfg docsrs" cargo +nightly-2025-11-28 check

In your Cargo.toml, you have:

[package.metadata.docs.rs]
all-features = true
rustc-args = ["--cfg", "docsrs"]
rustdoc-args = ["--cfg", "docsrs", "--generate-link-to-definition"]

Is there a reason you are using RUSTFLAGS / rustc-args for this? RUSTFLAGS applies to you and all of your dependencies. RUSTDOCFLAGS / rustdoc-args applies to just the packages being documented.

The reason I'm pushing back on this is because this maintains a brittle state where your ability to be documented is dependent on whether a nightly feature was broken in any of your dependencies that uses it. So far when I've asked about this for any of my packages, no one has had a need for me to merge a fix and publish it. Yes, I'll eventually need to fix this but it is fixed in my repo template and will be propagated here next time I update from the template.

[Bravo555]

Is there a reason you are using RUSTFLAGS / rustc-args for this? RUSTFLAGS applies to you and all of your dependencies. RUSTDOCFLAGS / rustdoc-args applies to just the packages being documented.

The reason I'm pushing back on this is because this maintains a brittle state where your ability to be documented is dependent on whether a nightly feature was broken in any of your dependencies that uses it. So far when I've asked about this for any of my packages, no one has had a need for me to merge a fix and publish it.

I see, the problem was with gstreamer-rs reapplying the docsrs feature to dependencies when building, which they seem to have already fixed when I made this issue and now it fails to build for a different reason. So the problem was not in kstring and I just didn't understand how docsrs build process works. Sorry for making noise!

I'll close the issue since it's not blocking anything and you are aware of the feature rename and have the fix ready in the template. Thanks for the clarification!

[epage]

Note that docs.rs automatically adding that cfg is relatively new (from the summer?) and people are likely not to have heard of it.