error: mixing `-Zsanitizer` will cause an ABI mismatch - when running doctests

[gendx]

I tried these commands (following the sanitizer tutorial) on the code at https://github.com/gendx/paralight/tree/791d03a794b3c2089186979687065d107532fc93:

export RUSTFLAGS="-Zsanitizer=thread"
export RUSTDOCFLAGS="-Zsanitizer=thread"
cargo +nightly test --release -Zbuild-std --target=x86_64-unknown-linux-gnu

I expected to see this happen: tests should run with thread sanitizer enabled.

Instead, this happened: regular tests ran fine, but doc tests failed to compile with the following error. In particular, "help: set -Zsanitizer=thread in this crate" is strange given that I've set RUSTDOCFLAGS="-Zsanitizer=thread".

error: mixing `-Zsanitizer` will cause an ABI mismatch in crate `paralight`
 --> src/lib.rs:9:1
  |
9 | #![doc = include_str!("../README.md")]
  | ^
  |
  = help: the `-Zsanitizer` flag modifies the ABI so Rust crates compiled with different values of this flag cannot be used together safely
  = note: unset `-Zsanitizer` in this crate is incompatible with `-Zsanitizer=thread` in dependency `std`
  = help: set `-Zsanitizer=thread` in this crate or unset `-Zsanitizer` in `std`
  = help: if you are sure this will not cause problems, you may use `-Cunsafe-allow-abi-mismatch=sanitizer` to silence this error

I suspect this might be related to #138736 or more broadly the work tracked in #138453.

Meta

rustc +nightly --version --verbose:

rustc 1.91.0-nightly (5eda692e7 2025-09-11)
binary: rustc
commit-hash: 5eda692e73f37dcbe2437ce878db7bb71f323e74
commit-date: 2025-09-11
host: x86_64-unknown-linux-gnu
release: 1.91.0-nightly
LLVM version: 21.1.1

[iorizu]

The CI for the crate triomphe fails for this exact reason also. I've tested various versions and the one that introduces the failure is nightly 2025-09-06 (rustc 6c699a372). That version contains #138736.

$ git log --first-parent --oneline af00ff2ce..6c699a372
6c699a37235 Auto merge of #146255 - fmease:rollup-1v0kp8i, r=fmease
99317ef14d0 Auto merge of #146121 - Muscraft:filter-suggestion-parts, r=petrochenkov
9cd272dc853 Auto merge of #146044 - estebank:issue-88727, r=chenyukang
c559c4a7418 Auto merge of #146224 - tgross35:rollup-1bgjms3, r=tgross35
ad85bc524b1 Auto merge of #144737 - petrochenkov:extprelcache, r=davidtwco
91edc3ebccc Auto merge of #146218 - flip1995:clippy-subtree-update, r=Manishearth
b3cfb8faf84 Auto merge of #138736 - azhogin:azhogin/sanitizers-target-modificators, r=rcvalle

af00ff2ce is the commit hash of nightly 2025-09-05.

That PR (and the error) says that adding -Cunsafe-allow-abi-mismatch=sanitizer will fix the issue, but it feels like that shouldn't be necessary. Assuming that the issue is that the std lib is being built with -Zsanitizer=thread set and the doctests are being built with -Zsanitizer unset, shouldn't it be the case that the RUSTDOCFLAGS='-Zsanitizer=thread' env variables force the tests to be built with the sanitizer option set? If not, that feels like a bug.

[Darksonn]

Similar to #144521. Probably has a similar to fix to #144523.

[Darksonn]

cc @rcvalle @azhogin