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properly deny combining GCE and GCA #161525

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2 changes: 1 addition & 1 deletion compiler/rustc_ast_passes/src/feature_gate.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -741,7 +741,7 @@ fn warn_next_solver_and_gce(sess: &Session, features: &Features) {
}

fn check_features_requiring_new_solver(sess: &Session, features: &Features) {
if sess.opts.unstable_opts.next_solver.globally {
if sess.opts.unstable_opts.next_solver.globally && !features.generic_const_exprs() {

@fee1-dead fee1-dead Aug 26, 2026

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Are we sure this is the right way to do it? Shouldn't we really just emit an error when GCE and next_solver are both enabled instead of a warning? Downgrading next solver to coherence only appears the wrong approach.

What if we removed GCE as a feature?

return;
}

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3 changes: 1 addition & 2 deletions tests/ui/const-generics/generic_const_exprs/next-solver-gce-incompatible-issue-158428.rs
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@@ -1,16 +1,15 @@
//@ run-pass
//@ compile-flags: -Znext-solver=globally

#![feature(min_generic_const_args)]
#![feature(generic_const_args)]
//~^ ERROR:`generic_const_args` requires -Znext-solver=globally to be enabled

@fee1-dead fee1-dead Aug 26, 2026

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Suggested change
//~^ ERROR:`generic_const_args` requires -Znext-solver=globally to be enabled
//~^ ERROR: `generic_const_args` requires -Znext-solver=globally to be enabled

#![feature(generic_const_exprs)]
//~^ WARN: `feature(generic_const_exprs)` is not supported with the next-generation trait solver
//@ normalize-stderr: "(--> ).*/tests/ui/const-generics/generic_const_exprs" -> "$1$$DIR"

use std::mem::size_of;

union AsBytes<T> {
//~^ WARN: union `AsBytes` is never used
as_bytes: [u8; { size_of::<T>() }],
}

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12 changes: 6 additions & 6 deletions tests/ui/const-generics/generic_const_exprs/next-solver-gce-incompatible-issue-158428.stderr
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Expand Up @@ -9,13 +9,13 @@ LL | #![feature(generic_const_exprs)]
= note: the currently stable trait solver will be used for this crate
= note: see issues #160895 <https://github.com/rust-lang/rust/issues/160895> for more information

warning: union `AsBytes` is never used
--> $DIR/next-solver-gce-incompatible-issue-158428.rs:12:7
error: `generic_const_args` requires -Znext-solver=globally to be enabled
--> $DIR/next-solver-gce-incompatible-issue-158428.rs:4:12
|
LL | union AsBytes<T> {
| ^^^^^^^
LL | #![feature(generic_const_args)]
| ^^^^^^^^^^^^^^^^^^
|
= note: `#[warn(dead_code)]` (part of `#[warn(unused)]`) on by default
= help: enable all of these features

warning: 2 warnings emitted
error: aborting due to 1 previous error; 1 warning emitted

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