fix running stdlib doctests in Miri in CI

[RalfJung]

r? @bjorn3

[RalfJung]

This is wired up to run the tests from the separate crates, right?

[bjorn3]

I don't think that is implemented for ./x.py miri. ./x.py test has this code:

rust/src/bootstrap/src/core/build_steps/test.rs

Lines 3111 to 3120 in 9f54abe

	// The core and alloc crates can't directly be tested. We
	// could silently ignore them, but adding their own test
	// crates is less confusing for users. We still keep core and
	// alloc themself for doctests
	if crates.iter().any(|crate_| crate_ == "core") {
	crates.push("coretests".to_owned());
	}
	if crates.iter().any(|crate_| crate_ == "alloc") {
	crates.push("alloctests".to_owned());
	}

But ./x.py miri doesn't.

[RalfJung]

That code also runs for ./x miri though?

[RalfJung]

I tried ./x miri library/core -- mem and it said

     Running tests/lib.rs (build/x86_64-unknown-linux-gnu/stage1-std/x86_64-unknown-linux-gnu/debug/deps/coretests-d8eae4d2db388c62)

running 71 tests
.......................................................................

test result: ok. 71 passed; 0 failed; 0 ignored; 0 measured; 2201 filtered out; finished in 24.46s

     Running benches/lib.rs (build/x86_64-unknown-linux-gnu/stage1-std/x86_64-unknown-linux-gnu/debug/deps/corebenches-41b71a0680fbdcd6)

running 0 tests


test result: ok. 0 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in 29.49ms

   Doc-tests core

running 113 tests
........................................................................................  88/113
.........................

test result: ok. 113 passed; 0 failed; 0 ignored; 0 measured; 5467 filtered out; finished in 2.43s

all doctests ran in 2.50s; merged doctests compilation took 0.04s
   Doc-tests coretests

running 0 tests


test result: ok. 0 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in 12.47µs

	finished in 55.808 seconds

That looks good to me?

[bjorn3]

Indeed. I was looking at build_steps::test::Miri, which is for ./x.py test src/tools/miri, not ./x.py miri.

[RalfJung]

@bors try jobs=miri

[rust-bors]

☀️ Try build successful (CI)
Build commit: d178db9 (d178db9e5a55eda3463e86f358ad4f5d0deccf2f, parent: 23d01cd2412583491621ab1ca4f1b01e37d11e39)

[RalfJung]

That is very strange, I expected the try build to fail since there's a broken doctest...

[RalfJung]

Oh wait, that was the wrong job.

@bors try jobs=aux

[rust-log-analyzer]

The job x86_64-gnu-aux failed! Check out the build log: (web) (plain enhanced) (plain)

Click to see the possible cause of the failure (guessed by this bot)

    |
    = help: this indicates a bug in the program: it performed an invalid operation, and caused Undefined Behavior
    = help: see https://doc.rust-lang.org/nightly/reference/behavior-considered-undefined.html for further information
    = note: BACKTRACE:
    = note: inside `main::_doctest_main_library_core_src_mem_maybe_dangling_rs_39_0` at library/core/src/mem/maybe_dangling.rs:15:13: 15:18
note: inside `main`
   --> library/core/src/mem/maybe_dangling.rs:52:3
    |
 52 | } _doctest_main_library_core_src_mem_maybe_dangling_rs_39_0() }
    |   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
note: inside `<fn() as std::ops::FnOnce<()>>::call_once - shim(fn())`
   --> /checkout/library/core/src/ops/function.rs:250:5
    |
250 |     extern "rust-call" fn call_once(self, args: Args) -> Self::Output;
---
all doctests ran in 505.29s; merged doctests compilation took 0.05s
error: doctest failed, to rerun pass `-p core --doc`
Bootstrap failed while executing `miri --stage 2 library/core library/alloc --doc`
Build completed unsuccessfully in 0:09:46
make: *** [Makefile:56: check-aux] Error 1
  local time: Sun Dec 28 17:08:16 UTC 2025
  network time: Sun, 28 Dec 2025 17:08:16 GMT
##[error]Process completed with exit code 2.
##[group]Run echo "disk usage:"
echo "disk usage:"

[rust-bors]

💔 Test for 8c1f4ee failed: CI. Failed jobs:

• try - x86_64-gnu-aux (web logs, enhanced plaintext logs)

[RalfJung]

Nice. And now it should be fixed.

@bors try jobs=aux

[rust-bors]

☀️ Try build successful (CI)
Build commit: 084978e (084978ecbaddcb161b9963a2408f2382a918b993, parent: 7eadf834b536d0659c7445e2b0970316b55abde4)

[bjorn3]

@bors r+

[bors]

📌 Commit a4b4cd5 has been approved by bjorn3

It is now in the queue for this repository.