cfg(doc) isn't set in build scripts

[maia-s]

Problem

I want to skip (building and) linking a native library when generating documentation, because it takes a long time and might fail on docs.rs, but cfg(doc) isn't set in build scripts when generating documentation.

Steps

1. Create a build script for a crate:

fn main() {
    #[cfg(doc)]
    panic!("doc");
}

2. Run cargo doc -v
3. The build script is run, but cfg(doc) isn't true

Possible Solution(s)

No response

Notes

No response

Version

cargo 1.81.0 (2dbb1af 2024-08-20)
release: 1.81.0
commit-hash: 2dbb1af
commit-date: 2024-08-20
host: aarch64-apple-darwin
libgit2: 1.8.1 (sys:0.19.0 vendored)
libcurl: 8.7.1 (sys:0.4.73+curl-8.8.0 system ssl:(SecureTransport) LibreSSL/3.3.6)
ssl: OpenSSL 1.1.1w 11 Sep 2023
os: Mac OS 15.0.0 [64-bit]

cargo 1.83.0-nightly (c1fa840 2024-08-29)
release: 1.83.0-nightly
commit-hash: c1fa840
commit-date: 2024-08-29
host: aarch64-apple-darwin
libgit2: 1.8.1 (sys:0.19.0 vendored)
libcurl: 8.7.1 (sys:0.4.74+curl-8.9.0 system ssl:(SecureTransport) LibreSSL/3.3.6)
ssl: OpenSSL 1.1.1w 11 Sep 2023
os: Mac OS 15.0.0 [64-bit]

[weihanglo]

Thank you for the report!

Similar requests have been open

• [cargo doc] build.rs does not cover the use cases very well #3053
• Pass --cfg doc to check builds of dependencies as part of cargo doc/rustdoc #8811
• Cargo doc does not pass --cfg doc for build scripts #8944
• This is a summary I made three months ago, which is about differentiating Cargo command/mode in general: Inform build scripts whether cargo is checking or building #4001 (comment)

At this moment you might need to follow this docs.rs official guide to check whether it is a docs.rs build.

Since this is kinda a dup of those above, I am going to close this. Please let us know if there is a reason to keep this issue open separately. Thanks.