error: can't find crate for `compiler_builtins`

[Wyvern]

After update to latest nightly rustc 9eb4a2652 2025-08-18, cargo 71eb84f21 2025-08-17, -Zbuild-std generate failed message error[: can't find crate for compiler_builtins``.

Not sure it's a cargo or rustc change.

[bjorn3]

What exactly are you building and what cargo invocation did you use?

[Wyvern]

@bjorn3 -Zbuild-std=std,proc_macro,panic_abort -Zbuild-std-features=panic_immediate_abort,optimize_for_size

[bjorn3]

Does -Zbuild-std=core,alloc,std,proc_macro,panic_abort -Zbuild-std-features=panic_immediate_abort,optimize_for_size work? Also can you post the full error message?

[Vollbrecht]

We also see it our builds running with cargo clippy --no-deps --target riscv32imc-esp-espidf -Zbuild-std=std,panic_abort -Zbuild-std-features=panic_immediate_abort -- -Dwarnings.

Interestingly the CI runs pass against a pretty similar target with no errors. E.g against the riscv32imac-esp-espidf it is working.

Changing the the buildflags to something like
cargo +nightly clippy --features nightly,experimental --no-deps --target riscv32imc-esp-espidf -Zbuild-std=core,alloc,std,proc_macro,panic_abort -Zbuild-std-features=panic_immediate_abort,optimize_for_size -- -Dwarnings also would not work. Its resulting in the same exact error.

Here is the raw output

 cargo +nightly clippy --features nightly,experimental --no-deps --target riscv32imc-esp-espidf -Zbuild-std=core,alloc,std,proc_macro,panic_abort -Zbuild-std-features=panic_immediate_abort,optimize_for_size -- -Dwarnings
   Compiling compiler_builtins v0.1.160 (/home/fred/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/compiler-builtins/compiler-builtins)
   Compiling core v0.0.0 (/home/fred/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/core)
   Compiling libc v0.2.174
   Compiling std v0.0.0 (/home/fred/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/std)
   Compiling proc-macro2 v1.0.86
   Compiling unicode-ident v1.0.12
   Compiling memchr v2.7.4
   Compiling cfg-if v1.0.0
   Compiling libc v0.2.158
   Compiling serde v1.0.209
   Compiling bitflags v2.6.0
   Compiling crossbeam-utils v0.8.20
   Compiling regex-syntax v0.8.4
   Compiling glob v0.3.1
   Compiling cfg_aliases v0.2.1
   Compiling nix v0.29.0
   Compiling syn v1.0.109
   Compiling rustix v0.38.35
   Compiling rustversion v1.0.17
   Compiling log v0.4.22
   Compiling clang-sys v1.8.1
   Compiling prettyplease v0.2.22
   Compiling aho-corasick v1.1.3
   Compiling crossbeam-epoch v0.9.18
   Compiling bstr v1.10.0
   Compiling minimal-lexical v0.2.1
   Compiling serde_json v1.0.127
   Compiling linux-raw-sys v0.4.14
   Compiling shlex v1.3.0
   Compiling quote v1.0.37
   Compiling thiserror v1.0.63
   Compiling either v1.13.0
   Compiling same-file v1.0.6
   Compiling crossbeam-deque v0.8.5
   Compiling syn v2.0.77
   Compiling walkdir v2.5.0
   Compiling nom v7.1.3
   Compiling cvt v0.1.2
   Compiling libloading v0.8.5
   Compiling once_cell v1.19.0
   Compiling ryu v1.0.18
   Compiling bindgen v0.71.1
   Compiling itoa v1.0.11
   Compiling anyhow v1.0.86
   Compiling heck v0.4.1
   Compiling itertools v0.12.1
   Compiling regex-automata v0.4.7
   Compiling cc v1.1.15
   Compiling fs_at v0.2.1
   Compiling cexpr v0.6.0
   Compiling rustc-hash v2.1.0
   Compiling normpath v1.3.0
   Compiling home v0.5.9
   Compiling fastrand v2.1.1
   Compiling bitflags v1.3.2
   Compiling which v4.4.2
   Compiling tempfile v3.12.0
   Compiling remove_dir_all v0.8.3
   Compiling cmake v0.1.53
   Compiling filetime v0.2.25
   Compiling semver v1.0.23
   Compiling camino v1.1.9
   Compiling fnv v1.0.7
   Compiling ident_case v1.0.1
   Compiling autocfg v1.3.0
   Compiling globset v0.4.14
   Compiling regex v1.10.6
   Compiling darling_core v0.20.10
   Compiling embedded-io-async v0.6.1
   Compiling heapless v0.8.0
   Compiling iana-time-zone v0.1.60
   Compiling ignore v0.4.22
   Compiling num-traits v0.2.19
   Compiling globwalk v0.8.1
   Compiling unicode-xid v0.2.5
   Compiling const_format_proc_macros v0.2.32
   Compiling strum_macros v0.24.3
   Compiling chrono v0.4.38
   Compiling embassy-sync v0.6.2
   Compiling version_check v0.9.5
   Compiling embedded-hal-async v1.0.0
   Compiling uncased v0.9.10
   Compiling serde_derive v1.0.209
   Compiling thiserror-impl v1.0.63
   Compiling num_enum_derive v0.7.3
   Compiling strum v0.24.1
   Compiling build-time v0.1.3
   Compiling darling_macro v0.20.10
   Compiling darling v0.20.10
   Compiling enumset_derive v0.10.0
   Compiling cargo-platform v0.1.8
   Compiling envy v0.4.2
   Compiling rustc-std-workspace-core v1.99.0 (/home/fred/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/rustc-std-workspace-core)
   Compiling alloc v0.0.0 (/home/fred/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/alloc)
   Compiling cfg-if v1.0.1
   Compiling rustc-demangle v0.1.26
   Compiling panic_abort v0.0.0 (/home/fred/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/panic_abort)
   Compiling embuild v0.33.0
   Compiling unwind v0.0.0 (/home/fred/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/unwind)
   Compiling cargo_metadata v0.18.1
   Compiling esp-idf-sys v0.36.1 (https://github.com/esp-rs/esp-idf-sys#2749423f)
   Compiling esp-idf-hal v0.45.2 (https://github.com/esp-rs/esp-idf-hal#b25201ce)
   Compiling esp-idf-svc v0.51.0 (/home/fred/rust/esp-idf-svc)
   Compiling rustc-std-workspace-alloc v1.99.0 (/home/fred/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/rustc-std-workspace-alloc)
   Compiling std_detect v0.1.5 (/home/fred/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/std_detect)
   Compiling panic_unwind v0.0.0 (/home/fred/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/panic_unwind)
   Compiling hashbrown v0.15.5
error[E0463]: can't find crate for `compiler_builtins`

For more information about this error, try `rustc --explain E0463`.
error: could not compile `std_detect` (lib) due to 1 previous error
warning: build failed, waiting for other jobs to finish...

``

[bjorn3]

I think the issue is that std_detect directly refers to libcore rather than through rustc-std-workspace-core, causing it to not pull in compiler_builtins when std_detect_file_io is not enabled. As workaround -Zbuild-std-features=panic_immediate_abort,optimize_for_size,std_detect_file_io may work.

[Wyvern]

@bjorn3 yeah, tried add -Zbuild-std-features=...,std_detect_file_io as a workaround works.

[ehuss]

cc @joshtriplett I believe this regressed from #145489. Can you take a look?

[joshtriplett]

Looked into this. Some potentially relevant details:

• library: Migrate from cfg_if to cfg_select #145489 removed the dependency from std_detect to cfg-if.
• cfg-if depends on rustc-std-workspace-core, which depends on compiler-builtins.
• I think this would be solved by having std_detect add a direct dependency on rustc-std-workspace-core, so that it pulls in compiler-builtins itself.

I think that means replacing the current dependency on:

core = { path = "../core" }

with this instead:

core = { path = "../rustc-std-workspace-core", package = "rustc-std-workspace-core" }