fix: Revert optional feature syntax

[KeyWeeUsr]

Hey 👋

I read the guide but I'm not sure whether this revert would justify creating a separate issue, so I made a PR instead. Feel free to close/convert if needed.

What does this PR try to solve?

I'm experiencing an issue when vendoring caused by 132fe86 (package-name?/feature specifically). I'm not sure whether this is a bug in Cargo potentially opened elsewhere, however I reverted the problematic parts locally this way. The commit also contains a POC which might also be useful as a CI test for vendoring in case such change happens again in the future, so it's caught before releasing.

POC below:

FROM rust:alpine
WORKDIR /tmp

RUN apk add git
RUN git clone --depth=1 https://github.com/rust-lang/log vendor/log
RUN git clone --depth=1 https://github.com/rust-cli/env_logger vendor/env_logger

RUN <<EOR
cat<<EOF > vendor/env_logger/fix.patch
diff --git a/crates/env_filter/Cargo.toml b/crates/env_filter/Cargo.toml
--- a/crates/env_filter/Cargo.toml
+++ b/crates/env_filter/Cargo.toml
@@ -28,11 +28,11 @@ pre-release-replacements = [
 [features]
 default = ["std", "regex"]
 regex = ["dep:regex"]
-std = ["log/std", "regex?/std"]
+std = ["log/std"]

 [dependencies]
 log = { version = "0.4.29" }
-regex = { version = "1.12.3", optional = true, default-features=false, features=["perf"] }
+regex = { version = "1.12.3", optional = true, default-features=false, features=["std", "perf"] }

 [dev-dependencies]
 snapbox = "1.0"
EOF

cd vendor/env_logger&&git apply fix.patch
EOR

RUN cat vendor/env_logger/crates/env_filter/Cargo.toml
RUN <<EOR
mkdir src
echo "fn main() {}" > src/main.rs

cat<<EOF > Cargo.toml
[package]
name = "bug"
edition = "2024"

[dependencies]
env_logger = { version = "0.11.11", default-features = false, features = [] }
log = { version = "0.4.34", default-features = false }
# note: happens even if not specified here
env_filter = { version = "2.0.0", default-features = false, features = [] }

[patch.crates-io]
env_logger = { path = "vendor/env_logger" }
env_filter = { path = "vendor/env_logger/crates/env_filter" }
log = { path = "vendor/log" }
EOF
EOR

RUN <<EOR
rustc --version
cargo --version
cargo build --offline --no-default-features --verbose
EOR

Notes to reviewers

POC above and in the commit message.
LLM involvement: Zero

[epage]

I can't imagine what this would be the root cause for, rather than a workaround. I'd prefer to focus on the root cause. The only vendor issue I'm aware of is rust-lang/cargo#10801.

Going to close this in favor of whereever the root cause Issue is opened.

Note that If reverting somethìng, then likely this isn' t so straightforward that you can skip an issue. An Issue would have better encouraged describing the problem, more than the PR template does.

[KeyWeeUsr]

@epage I believe that's the bug I'm experiencing! Thanks