Toolchain upgrade to nightly-2025-11-21 failed

[github-actions]

Updating Rust toolchain from nightly-2025-11-20 to nightly-2025-11-21 requires source changes.
The failed automated run can be found here.
Please review the changes at https://github.com/rust-lang/rust from rust-lang/rust@07bdbae up to rust-lang/rust@53732d5. The log for this commit range is:
rust-lang/rust@53732d5e07 Auto merge of #149109 - scottmcm:align-always-alignment, r=tgross35
rust-lang/rust@7281a3bc4b Auto merge of #149132 - matthiaskrgr:rollup-8khp9s2, r=matthiaskrgr
rust-lang/rust@8613f0e7ef Rollup merge of #149108 - daltenty:daltenty/add-maintainer, r=Noratrieb
rust-lang/rust@aecee50487 Rollup merge of #149095 - tshepang:rdg-sync, r=tshepang
rust-lang/rust@37dc26c816 Rollup merge of #149071 - ferrocene:pvdrz/remote-test-client-timeout-tests, r=jieyouxu
rust-lang/rust@5172159dfd Rollup merge of #149056 - fneddy:fix_s390_test_padding_overwrite, r=RalfJung
rust-lang/rust@7198d31e4b Rollup merge of #149041 - folkertdev:sparc64-mips64-ignore-unsized, r=bjorn3
rust-lang/rust@34b3c9dd4d Rollup merge of #148261 - aDotInTheVoid:no-sync-for-smir, r=celinval
rust-lang/rust@422b83aeee Rollup merge of #147173 - androm3da:bcain/hexagon_qurt, r=davidtwco,tgross35
rust-lang/rust@cd4ce66e50 Rollup merge of #147035 - joboet:extract_if_debug, r=tgross35
rust-lang/rust@2eeec770fe Rollup merge of #146925 - DiuDiu777:va-doc-fix, r=tgross35
rust-lang/rust@2c0f4860cc Auto merge of #149118 - folkertdev:stdarch-sync-2025-11-19, r=tgross35
rust-lang/rust@683dd08db5 Auto merge of #89917 - davidtwco:issue-60705-stabilize-rust-symbol-mangling-scheme, r=wesleywiser
rust-lang/rust@d2f887349f Auto merge of #149073 - weihanglo:update-cargo, r=weihanglo
rust-lang/rust@30f4a2ae16 See if this is the time we can remove layout::size_align
rust-lang/rust@a74d572b74 [AIX][ppc64le-linux-gnu] Add Amy Kwan to target maintainers

[celinval]

@tautschnig, this seems to be related to the KaniFunction lookup. The problem here is that we used the Query structure to lazyly initialize the lookup, and reuse it across Kani code so it could be easily shared around. Kani only invokes that in the context of initialized rustc_public.

Note that we have even added a check to ensure the stored FnDefs are still valid here:

kani/kani-compiler/src/kani_queries/mod.rs

Lines 53 to 57 in 56a4268

	if let Some(kani_functions) = self.kani_functions.get() {
	// Sanity check the values stored to ensure the cache is being within the rustc_public
	// context used to populate the cache.
	validate_kani_functions(kani_functions);
	kani_functions

In practice that worked fine because we didn't misuse the map despite the rust compiler APIs we invoke require Query to implement Send.

With the change introduced here: rust-lang/rust@34b3c9dd4d, Query can no longer hold FnDef, which isn't Send.

See full error logs here:

error[E0277]: `*const ()` cannot be sent between threads safely
    --> kani-compiler/src/kani_compiler.rs:101:29
     |
 101 |         run_compiler(&args, self);
     |                             ^^^^ `*const ()` cannot be sent between threads safely
     |
     = help: within `(KaniFunction, rustc_public::ty::FnDef)`, the trait `Send` is not implemented for `*const ()`
note: required because it appears within the type `std::marker::PhantomData<*const ()>`
    --> /home/runner/.rustup/toolchains/nightly-2025-11-21-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/core/src/marker.rs:819:12
     |
 819 | pub struct PhantomData<T: PointeeSized>;
     |            ^^^^^^^^^^^
note: required because it appears within the type `rustc_public::ThreadLocalIndex`
    --> /home/runner/.rustup/toolchains/nightly-2025-11-21-x86_64-unknown-linux-gnu/lib/rustlib/rustc-src/rust/compiler/rustc_public/src/lib.rs:308:19
     |
 308 | pub(crate) struct ThreadLocalIndex {
     |                   ^^^^^^^^^^^^^^^^
note: required because it appears within the type `rustc_public::DefId`
    --> /home/runner/.rustup/toolchains/nightly-2025-11-21-x86_64-unknown-linux-gnu/lib/rustlib/rustc-src/rust/compiler/rustc_public/src/crate_def.rs:9:12
     |
   9 | pub struct DefId(pub(crate) usize, ThreadLocalIndex);
     |            ^^^^^
note: required because it appears within the type `rustc_public::ty::FnDef`
    --> /home/runner/.rustup/toolchains/nightly-2025-11-21-x86_64-unknown-linux-gnu/lib/rustlib/rustc-src/rust/compiler/rustc_public/src/ty.rs:688:9
     |
 688 |     pub FnDef;
     |         ^^^^^
     = note: required because it appears within the type `(KaniFunction, rustc_public::ty::FnDef)`
     = note: required for `hashbrown::raw::RawTable<(KaniFunction, rustc_public::ty::FnDef)>` to implement `Send`
note: required because it appears within the type `hashbrown::map::HashMap<KaniFunction, rustc_public::ty::FnDef, RandomState>`
    --> /rust/deps/hashbrown-0.15.5/src/map.rs:185:11
note: required because it appears within the type `HashMap<KaniFunction, rustc_public::ty::FnDef>`
    --> /home/runner/.rustup/toolchains/nightly-2025-11-21-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/std/src/collections/hash/map.rs:246:12
     |
 246 | pub struct HashMap<K, V, S = RandomState> {
     |            ^^^^^^^
note: required because it appears within the type `std::option::Option<HashMap<KaniFunction, rustc_public::ty::FnDef>>`
    --> /home/runner/.rustup/toolchains/nightly-2025-11-21-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/core/src/option.rs:600:10
     |
 600 | pub enum Option<T> {
     |          ^^^^^^
note: required because it appears within the type `std::cell::UnsafeCell<std::option::Option<HashMap<KaniFunction, rustc_public::ty::FnDef>>>`
    --> /home/runner/.rustup/toolchains/nightly-2025-11-21-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/core/src/cell.rs:2289:12
     |
2289 | pub struct UnsafeCell<T: ?Sized> {
     |            ^^^^^^^^^^
note: required because it appears within the type `OnceCell<HashMap<KaniFunction, rustc_public::ty::FnDef>>`
    --> /home/runner/.rustup/toolchains/nightly-2025-11-21-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/core/src/cell/once.rs:35:12
     |
  35 | pub struct OnceCell<T> {
     |            ^^^^^^^^
note: required because it appears within the type `QueryDb`
    --> kani-compiler/src/kani_queries/mod.rs:18:12
     |
  18 | pub struct QueryDb {
     |            ^^^^^^^
     = note: required for `std::sync::Mutex<QueryDb>` to implement `std::marker::Sync`
     = note: 1 redundant requirement hidden
     = note: required for `Arc<std::sync::Mutex<QueryDb>>` to implement `Send`
note: required because it appears within the type `KaniCompiler`
    --> kani-compiler/src/kani_compiler.rs:82:8
     |
  82 | struct KaniCompiler {
     |        ^^^^^^^^^^^^
     = note: required for the cast from `&mut KaniCompiler` to `&mut dyn Callbacks + Send`

error[E0277]: `*const ()` cannot be sent between threads safely
    --> kani-compiler/src/kani_compiler.rs:110:44
     |
 110 |           config.make_codegen_backend = Some(Box::new({
     |  ____________________________________________^
 111 | |             let queries = self.queries.clone();
 112 | |             move |_cfg| backend(queries)
 113 | |         }));
     | |__________^ `*const ()` cannot be sent between threads safely
     |
     = help: within `(KaniFunction, rustc_public::ty::FnDef)`, the trait `Send` is not implemented for `*const ()`
note: required because it appears within the type `std::marker::PhantomData<*const ()>`
    --> /home/runner/.rustup/toolchains/nightly-2025-11-21-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/core/src/marker.rs:819:12
     |
 819 | pub struct PhantomData<T: PointeeSized>;
     |            ^^^^^^^^^^^
note: required because it appears within the type `rustc_public::ThreadLocalIndex`
    --> /home/runner/.rustup/toolchains/nightly-2025-11-21-x86_64-unknown-linux-gnu/lib/rustlib/rustc-src/rust/compiler/rustc_public/src/lib.rs:308:19
     |
 308 | pub(crate) struct ThreadLocalIndex {
     |                   ^^^^^^^^^^^^^^^^
note: required because it appears within the type `rustc_public::DefId`
    --> /home/runner/.rustup/toolchains/nightly-2025-11-21-x86_64-unknown-linux-gnu/lib/rustlib/rustc-src/rust/compiler/rustc_public/src/crate_def.rs:9:12
     |
   9 | pub struct DefId(pub(crate) usize, ThreadLocalIndex);
     |            ^^^^^
note: required because it appears within the type `rustc_public::ty::FnDef`
    --> /home/runner/.rustup/toolchains/nightly-2025-11-21-x86_64-unknown-linux-gnu/lib/rustlib/rustc-src/rust/compiler/rustc_public/src/ty.rs:688:9
     |
 688 |     pub FnDef;
     |         ^^^^^
     = note: required because it appears within the type `(KaniFunction, rustc_public::ty::FnDef)`
     = note: required for `hashbrown::raw::RawTable<(KaniFunction, rustc_public::ty::FnDef)>` to implement `Send`
note: required because it appears within the type `hashbrown::map::HashMap<KaniFunction, rustc_public::ty::FnDef, RandomState>`
    --> /rust/deps/hashbrown-0.15.5/src/map.rs:185:11
note: required because it appears within the type `HashMap<KaniFunction, rustc_public::ty::FnDef>`
    --> /home/runner/.rustup/toolchains/nightly-2025-11-21-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/std/src/collections/hash/map.rs:246:12
     |
 246 | pub struct HashMap<K, V, S = RandomState> {
     |            ^^^^^^^
note: required because it appears within the type `std::option::Option<HashMap<KaniFunction, rustc_public::ty::FnDef>>`
    --> /home/runner/.rustup/toolchains/nightly-2025-11-21-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/core/src/option.rs:600:10
     |
 600 | pub enum Option<T> {
     |          ^^^^^^
note: required because it appears within the type `std::cell::UnsafeCell<std::option::Option<HashMap<KaniFunction, rustc_public::ty::FnDef>>>`
    --> /home/runner/.rustup/toolchains/nightly-2025-11-21-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/core/src/cell.rs:2289:12
     |
2289 | pub struct UnsafeCell<T: ?Sized> {
     |            ^^^^^^^^^^
note: required because it appears within the type `OnceCell<HashMap<KaniFunction, rustc_public::ty::FnDef>>`
    --> /home/runner/.rustup/toolchains/nightly-2025-11-21-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/core/src/cell/once.rs:35:12
     |
  35 | pub struct OnceCell<T> {
     |            ^^^^^^^^
note: required because it appears within the type `QueryDb`
    --> kani-compiler/src/kani_queries/mod.rs:18:12
     |
  18 | pub struct QueryDb {
     |            ^^^^^^^
     = note: required for `std::sync::Mutex<QueryDb>` to implement `std::marker::Sync`
     = note: 1 redundant requirement hidden
     = note: required for `Arc<std::sync::Mutex<QueryDb>>` to implement `Send`
note: required because it's used within this closure
    --> kani-compiler/src/kani_compiler.rs:112:13
     |
 112 |             move |_cfg| backend(queries)
     |             ^^^^^^^^^^^
     = note: required for the cast from `std::boxed::Box<{closure@kani-compiler/src/kani_compiler.rs:112:13: 112:24}>` to `Box<dyn FnOnce(&Options) -> Box<dyn CodegenBackend> + Send>`
     = note: the full name for the type has been written to '/home/runner/work/kani/kani/target/debug/deps/kani_compiler-8bb6bd4e5d5ef62b.long-type-14192919698064175694.txt'
     = note: consider using `--verbose` to print the full type name to the console

For more information about this error, try `rustc --explain E0277`.
error: could not compile `kani-compiler` (bin "kani-compiler") due to 2 previous errors
warning: build failed, waiting for other jobs to finish...
Error: Failed to build binaries.

[celinval]

Here are a few possible solutions:

1. Don't cache the map and generate at every call. Need to measure the performance impact.
2. Cache it somewhere else. You could use a thread local to keep the cache on a per-thread base.