`-Znext-solver=globally` not working when generating documentation

[nazar-pc]

error: could not compile ab-merkle-tree (lib) due to 1 previous error

Caused by:
process didn't exit successfully: /home/nazar-pc/.rustup/toolchains/nightly-2026-06-05-x86_64-unknown-linux-gnu/bin/rustc --crate-name ab_merkle_tree --edition=2024 crates/shared/ab-merkle-tree/src/lib.rs --error-format=json --json=diagnostic-rendered-ansi,artifacts,future-incompat --diagnostic-width=459 --crate-type lib --emit=dep-info,metadata -C embed-bitcode=no -C debuginfo=2 '--warn=clippy::restriction' '--warn=clippy::pedantic' --allow=unexpected_cfgs --check-cfg 'cfg(target_arch, values("spirv"))' --cfg 'feature="alloc"' --cfg 'feature="blake3"' --cfg 'feature="no-panic"' --check-cfg 'cfg(docsrs,test)' --check-cfg 'cfg(feature, values("alloc", "blake3", "no-panic"))' -C metadata=eb08b49561c7a8b2 -C extra-filename=-416f2ac9fa87de93 --out-dir ../target/debug/deps -C incremental=../target/debug/incremental -L dependency=../target/debug/deps --extern ab_blake3=../target/debug/deps/libab_blake3-26a309518180e962.rmeta --extern blake3=../target/debug/deps/libblake3-8c9d0896b35d6bea.rmeta --extern no_panic=../target/debug/deps/libno_panic-97b8f8fee7a6cabc.so -Znext-solver=globally -Zmin-recursion-limit=256 --verbose -L native=../target/debug/build/blake3-51ae43493c8acac9/out -L native=../target/debug/build/blake3-51ae43493c8acac9/out (exit status: 1)
warning: build failed, waiting for other jobs to finish...

error: `generic_const_args` requires -Znext-solver=globally to be enabled
  --> crates/shared/ab-merkle-tree/src/lib.rs:36:5
   |
36 |     generic_const_args,
   |     ^^^^^^^^^^^^^^^^^^
   |
   = help: enable all of these features

The crate is clearly compiled with cargo doc and clearly has -Znext-solver=globally in RUSTFLAGS, yet it complains that -Znext-solver=globally is not enabled.

Meta

rustc --version --verbose:

rustc 1.98.0-nightly (e7815e522 2026-06-04)
binary: rustc
commit-hash: e7815e522ecc746592fee32f50478f521333b503
commit-date: 2026-06-04
host: x86_64-unknown-linux-gnu
release: 1.98.0-nightly
LLVM version: 22.1.6

[nazar-pc]

I believe I'm having an identical issue with Miri too, this is a blocker for me

[fmease]

The crate is clearly compiled with cargo doc and clearly has -Znext-solver=globally in RUSTFLAGS, yet it complains that -Znext-solver=globally is not enabled.

Have you tried setting RUSTDOCFLAGS=-Znext-solver instead?

[nazar-pc]

I just did and got this ICE:

thread 'rustc' panicked at /rustc-dev/e7815e522ecc746592fee32f50478f521333b503/compiler/rustc_trait_selection/src/traits/select/mod.rs:261:9:
assertion failed: !self.infcx.next_trait_solver()
stack backtrace:
   0:     0x7f814727291b - <std[a2c4e7691074cc7]::backtrace::Backtrace>::create
   1:     0x7f8147272865 - <std[a2c4e7691074cc7]::backtrace::Backtrace>::force_capture
   2:     0x7f814608397d - std[a2c4e7691074cc7]::panicking::update_hook::<alloc[704292d5d5e17f2b]::boxed::Box<rustc_driver_impl[7d60d181532479ee]::install_ice_hook::{closure#1}>>::{closure#0}
   3:     0x7f81472864a2 - std[a2c4e7691074cc7]::panicking::panic_with_hook
   4:     0x7f8147268bb4 - std[a2c4e7691074cc7]::panicking::panic_handler::{closure#0}
   5:     0x7f814725d0a9 - std[a2c4e7691074cc7]::sys::backtrace::__rust_end_short_backtrace::<std[a2c4e7691074cc7]::panicking::panic_handler::{closure#0}, !>
   6:     0x7f814726a5ed - __rustc[dcf84ea68fc7090c]::rust_begin_unwind
   7:     0x7f8143f3f53c - core[fe3f0cb4d355ec52]::panicking::panic_fmt
   8:     0x7f8144701022 - core[fe3f0cb4d355ec52]::panicking::panic
   9:     0x7f8147e6cc30 - <rustc_trait_selection[7f9285f483b1d843]::traits::select::SelectionContext>::poly_select::{closure#0}
  10:     0x7f8146fb211a - <rustc_trait_selection[7f9285f483b1d843]::traits::auto_trait::AutoTraitFinder>::evaluate_predicates
  11:     0x55da86ab26f3 - <rustc_trait_selection[7f9285f483b1d843]::traits::auto_trait::AutoTraitFinder>::find_auto_trait_generics::<rustdoc[efd1ab9c578d77eb]::clean::types::Generics, rustdoc[efd1ab9c578d77eb]::clean::auto_trait::synthesize_auto_trait_impl::{closure#0}>
  12:     0x55da86dbae53 - rustdoc[efd1ab9c578d77eb]::clean::auto_trait::synthesize_auto_trait_impl
  13:     0x55da86dc1f10 - rustdoc[efd1ab9c578d77eb]::clean::utils::synthesize_auto_trait_and_blanket_impls
  14:     0x55da86e18715 - <rustdoc[efd1ab9c578d77eb]::passes::collect_trait_impls::SyntheticImplCollector as rustdoc[efd1ab9c578d77eb]::visit::DocVisitor>::visit_item
  15:     0x55da86e18529 - <rustdoc[efd1ab9c578d77eb]::passes::collect_trait_impls::SyntheticImplCollector as rustdoc[efd1ab9c578d77eb]::visit::DocVisitor>::visit_item
  16:     0x55da86dcf850 - rustdoc[efd1ab9c578d77eb]::passes::collect_trait_impls::collect_trait_impls
  17:     0x55da86d74cfc - rustdoc[efd1ab9c578d77eb]::core::run_global_ctxt
  18:     0x55da86c88a41 - rustdoc[efd1ab9c578d77eb]::main_args::{closure#2}::{closure#0}
  19:     0x55da86c800fd - rustc_interface[e9bf703edc77c76f]::interface::run_compiler::<(), rustdoc[efd1ab9c578d77eb]::main_args::{closure#2}>::{closure#1}
  20:     0x55da86ba49e6 - std[a2c4e7691074cc7]::sys::backtrace::__rust_begin_short_backtrace::<rustc_interface[e9bf703edc77c76f]::util::run_in_thread_with_globals<rustc_interface[e9bf703edc77c76f]::util::run_in_thread_pool_with_globals<rustc_interface[e9bf703edc77c76f]::interface::run_compiler<(), rustdoc[efd1ab9c578d77eb]::main_args::{closure#2}>::{closure#1}, ()>::{closure#0}, ()>::{closure#0}::{closure#0}, ()>
  21:     0x55da86cc7b6d - <std[a2c4e7691074cc7]::thread::lifecycle::spawn_unchecked<rustc_interface[e9bf703edc77c76f]::util::run_in_thread_with_globals<rustc_interface[e9bf703edc77c76f]::util::run_in_thread_pool_with_globals<rustc_interface[e9bf703edc77c76f]::interface::run_compiler<(), rustdoc[efd1ab9c578d77eb]::main_args::{closure#2}>::{closure#1}, ()>::{closure#0}, ()>::{closure#0}::{closure#0}, ()>::{closure#1} as core[fe3f0cb4d355ec52]::ops::function::FnOnce<()>>::call_once::{shim:vtable#0}
  22:     0x7f8148b8136c - <std[a2c4e7691074cc7]::sys::thread::unix::Thread>::new::thread_start
  23:     0x7f814209caa4 - start_thread
                               at ./nptl/pthread_create.c:447:8
  24:     0x7f8142129c6c - clone3
                               at ./misc/../sysdeps/unix/sysv/linux/x86_64/clone3.S:78:0
  25:                0x0 - <unknown>


rustc version: 1.98.0-nightly (e7815e522 2026-06-04)
platform: x86_64-unknown-linux-gnu

query stack during panic:
end of query stack

[fmease]

Right, that's a separate issue; that's #156487 (to be fixed by #149019).

[fmease]

I'm closing this issue as works as intended (user error: RUSTFLAGS used instead of RUSTDOCFLAGS) plus duplicate of #156487.

[nazar-pc]

How do I specify it for Miri? Neither RUSTFLAGS nor MIRIFLAGS seem to work. Or should I file that as a separate issue under Miri repository?

[fmease]

That seems surprising, how does your invocation look like, roughly?

I've just tried MIRIFLAGS=-Znext-solver cargo miri run on a crate containing

#![feature(generic_const_args, min_generic_const_args)]
fn main() {}

and that seemed to work. Maybe miri doesn't properly propagate -Znext-solver to some of its "internal subsystems" that only get exercised on more complex inputs? If so, you should indeed report it over at https://github.com/rust-lang/miri.