Doctest merging doesn't work at all on stable

[notriddle]

I downloaded the current stable branch, and set up this sample crate to detect if the test is running in merged mode.

//! ```rust
//! let location = std::panic::Location::caller();
//! assert_eq!(location.line(), 11);
//! ```

If I run RUSTC_BOOTSTRAP=1 cargo +stable test it passes. If I drop the bootstrap env, it fails.

rust/src/librustdoc/doctest/runner.rs

Lines 74 to 77 in f4a216d

	#![allow(unused_extern_crates)]
	#![allow(internal_features)]
	#![feature(test)]
	#![feature(rustc_attrs)]

Meta

rustc --version --verbose:

rustc 1.85.0 (4d91de4e4 2025-02-17)
binary: rustc
commit-hash: 4d91de4e48198da2e33413efdcd9cd2cc0c46688
commit-date: 2025-02-17
host: aarch64-apple-darwin
release: 1.85.0
LLVM version: 19.1.7

[aDotInTheVoid]

I can't reproduce this locally:

gh-aDotInTheVoid@dev-desktop-eu-1:~/tmp/merge-may-be-borked$ cat ./Cargo.toml
[package]
name = "merge-may-be-borked"
version = "0.1.0"
edition = "2024"

[dependencies]
gh-aDotInTheVoid@dev-desktop-eu-1:~/tmp/merge-may-be-borked$ cat ./src/lib.rs
//! ```rust
//! let location = std::panic::Location::caller();
//! assert_eq!(location.line(), 11);
//! ```
gh-aDotInTheVoid@dev-desktop-eu-1:~/tmp/merge-may-be-borked$ cargo +stable -vV
cargo 1.85.0 (d73d2caf9 2024-12-31)
release: 1.85.0
commit-hash: d73d2caf9e41a39daf2a8d6ce60ec80bf354d2a7
commit-date: 2024-12-31
host: aarch64-unknown-linux-gnu
libgit2: 1.8.1 (sys:0.19.0 vendored)
libcurl: 8.9.0-DEV (sys:0.4.74+curl-8.9.0 vendored ssl:OpenSSL/1.1.1w)
ssl: OpenSSL 1.1.1w  11 Sep 2023
os: Ubuntu 24.4.0 (noble) [64-bit]
gh-aDotInTheVoid@dev-desktop-eu-1:~/tmp/merge-may-be-borked$ echo $RUSTC_BOOTSTRAP

gh-aDotInTheVoid@dev-desktop-eu-1:~/tmp/merge-may-be-borked$ cargo +stable test -v
       Fresh merge-may-be-borked v0.1.0 (/home/gh-aDotInTheVoid/tmp/merge-may-be-borked)
    Finished `test` profile [unoptimized + debuginfo] target(s) in 0.01s
     Running `/home/gh-aDotInTheVoid/tmp/merge-may-be-borked/target/debug/deps/merge_may_be_borked-89c18792c4538da4`

running 0 tests

test result: ok. 0 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.00s

   Doc-tests merge_may_be_borked
     Running `/home/gh-aDotInTheVoid/.rustup/toolchains/stable-aarch64-unknown-linux-gnu/bin/rustdoc --edition=2024 --crate-type lib --color auto --crate-name merge_may_be_borked --test src/lib.rs --test-run-directory /home/gh-aDotInTheVoid/tmp/merge-may-be-borked -L dependency=/home/gh-aDotInTheVoid/tmp/merge-may-be-borked/target/debug/deps -L dependency=/home/gh-aDotInTheVoid/tmp/merge-may-be-borked/target/debug/deps --extern merge_may_be_borked=/home/gh-aDotInTheVoid/tmp/merge-may-be-borked/target/debug/deps/libmerge_may_be_borked-8b78cf23285ca111.rlib -C embed-bitcode=no --check-cfg 'cfg(docsrs,test)' --check-cfg 'cfg(feature, values())' --error-format human`

running 1 test
test src/lib.rs - (line 1) ... FAILED

failures:

---- src/lib.rs - (line 1) stdout ----
Test executable failed (exit status: 101).

stderr:

thread 'main' panicked at src/lib.rs:4:1:
assertion `left == right` failed
  left: 3
 right: 11
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace



failures:
    src/lib.rs - (line 1)

test result: FAILED. 0 passed; 1 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.19s

error: doctest failed, to rerun pass `--doc`

But I agree something spooky is up with merged doctests.