rust-1.94.0 fails to bootstrap with warning: hidden lifetime parameters in types are deprecated in serde_derive

[stefson]

hello everyone,

rust-1.94.0 stable fails to bootstrap for me with:

error: warnings are denied by `build.warnings` configuration
Traceback (most recent call last):
  File "/var/tmp/portage/dev-lang/rust-1.94.0/work/rustc-1.94.0-src/./x.py", line 53, in <module>
    bootstrap.main()
    ~~~~~~~~~~~~~~^^
  File "/var/tmp/portage/dev-lang/rust-1.94.0/work/rustc-1.94.0-src/src/bootstrap/bootstrap.py", line 1410, in main
    bootstrap(args)
    ~~~~~~~~~^^^^^^
  File "/var/tmp/portage/dev-lang/rust-1.94.0/work/rustc-1.94.0-src/src/bootstrap/bootstrap.py", line 1362, in bootstrap
    build.build_bootstrap()
    ~~~~~~~~~~~~~~~~~~~~~^^
  File "/var/tmp/portage/dev-lang/rust-1.94.0/work/rustc-1.94.0-src/src/bootstrap/bootstrap.py", line 1029, in build_bootstrap
    run(args, env=env, verbose=self.verbose, cwd=self.rust_root)
    ~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/var/tmp/portage/dev-lang/rust-1.94.0/work/rustc-1.94.0-src/src/bootstrap/bootstrap.py", line 237, in run
    raise RuntimeError(err)
RuntimeError: failed to run: /var/tmp/portage/dev-lang/rust-1.94.0/work/rust-stage0/bin/cargo build --jobs=default --manifest-path /var/tmp/portage/dev-lang/rust-1.94.0/work/rustc-1.94.0-src/src/bootstrap/Cargo.toml -Zroot-dir=/var/tmp/portage/dev-lang/rust-1.94.0/work/rustc-1.94.0-src --verbose --verbose -Zwarnings --locked --frozen

the warnings (1000+) are from serde_derive:

1211682-warning: hidden lifetime parameters in types are deprecated
1211763:   --> /var/tmp/portage/dev-lang/rust-1.94.0/work/rustc-1.94.0-src/vendor/serde_derive-1.0.215/src/internals/ast.rs:133:23
1211899-    |
1211918-133 |     let variants: Vec<Variant> = variants
--
1212539-
1212540-warning: hidden lifetime parameters in types are deprecated
1212621:   --> /var/tmp/portage/dev-lang/rust-1.94.0/work/rustc-1.94.0-src/vendor/serde_derive-1.0.215/src/internals/attr.rs:509:54
1212758-    |
1212777-509 |                 let _ = attr.parse_args_with(|input: ParseStream| {
--

this is my config.toml

[llvm]
download-ci-llvm = false
optimize = true
release-debuginfo = false
assertions = false
ninja = true
targets = "AArch64;X86;ARM;WebAssembly"
experimental-targets = ""
link-shared = true


enable-warnings = false
[llvm.build-config]
CMAKE_VERBOSE_MAKEFILE = "ON"
CMAKE_C_FLAGS_RELEASE = "-O2 -march=znver1 -pipe"
CMAKE_CXX_FLAGS_RELEASE = "-O2 -march=znver1 -pipe"
CMAKE_EXE_LINKER_FLAGS_RELEASE = "-Wl,-O1 -Wl,--as-needed -Wl,-z,pack-relative-relocs"
CMAKE_MODULE_LINKER_FLAGS_RELEASE = "-Wl,-O1 -Wl,--as-needed -Wl,-z,pack-relative-relocs"
CMAKE_SHARED_LINKER_FLAGS_RELEASE = "-Wl,-O1 -Wl,--as-needed -Wl,-z,pack-relative-relocs"
CMAKE_STATIC_LINKER_FLAGS_RELEASE = ""
[build]
build-stage = 2
test-stage = 2
build = "x86_64-unknown-linux-gnu"
host = ["x86_64-unknown-linux-gnu"]
target = ["x86_64-unknown-linux-gnu","wasm32-unknown-unknown"]
cargo = "/var/tmp/portage/dev-lang/rust-1.94.0/work/rust-stage0/bin/cargo"
rustc = "/var/tmp/portage/dev-lang/rust-1.94.0/work/rust-stage0/bin/rustc"
rustfmt = "/var/tmp/portage/dev-lang/rust-1.94.0/work/rust-stage0/bin/rustfmt"
docs = false
compiler-docs = false
submodules = false
python = "python3.13"
locked-deps = true
vendor = true
extended = true
tools = ["cargo","rustdoc","rustfmt"]
verbose = 2
sanitizers = false
profiler = true
cargo-native-static = false
description = "gentoo"
[install]
prefix = "/usr/lib/rust/1.94.0"
sysconfdir = "etc"
docdir = "share/doc/rust"
bindir = "bin"
libdir = "lib"
mandir = "share/man"
[rust]
# https://github.com/rust-lang/rust/issues/54872
codegen-units-std = 1
optimize = true
debug = false
debug-assertions = false
debug-assertions-std = false
debuginfo-level = 0
debuginfo-level-rustc = 0
debuginfo-level-std = 0
debuginfo-level-tools = 0
debuginfo-level-tests = 0
backtrace = true
incremental = false
default-linker = "x86_64-pc-linux-gnu-gcc"
channel = "stable"
rpath = false
verbose-tests = true
optimize-tests = true
codegen-tests = true
dist-src = false
remap-debuginfo = true
lld = false
# only deny warnings if doc+wasm are NOT requested, documenting stage0 wasm std fails without it
# https://github.com/rust-lang/rust/issues/74976
# https://github.com/rust-lang/rust/issues/76526
deny-warnings = true
backtrace-on-ice = true
jemalloc = false
# See https://github.com/rust-lang/rust/issues/121124
lto = "off"
[dist]
src-tarball = false
compression-formats = ["xz"]
compression-profile = "balanced"
[target.x86_64-unknown-linux-gnu]
ar = "x86_64-pc-linux-gnu-ar"
cc = "x86_64-pc-linux-gnu-gcc"
cxx = "x86_64-pc-linux-gnu-g++"
linker = "x86_64-pc-linux-gnu-gcc"
ranlib = "x86_64-pc-linux-gnu-ranlib"
llvm-libunwind = "no"
llvm-config = "/usr/lib/llvm/21/bin/llvm-config"
[target.wasm32-unknown-unknown]
linker = "lld"
# wasm target does not have profiler_builtins https://bugs.gentoo.org/848483
profiler = false

I'm on x86_64 gentoo

the rust version I'm using to build is 1.93.1:

rustc 1.93.1 (01f6ddf75 2026-02-11) (gentoo)
binary: rustc
commit-hash: 01f6ddf7588f42ae2d7eb0a2f21d44e8e96674cf
commit-date: 2026-02-11
host: x86_64-unknown-linux-gnu
release: 1.93.1
LLVM version: 21.1.8

you can find the complete log here: build.log.gz

[bjorn3]

It should work if you use rust.deny-warnings = false. That will still give the warnings, but that is because cargo doesn't suppress warnings of dependencies when dependencies are vendored.

[ehuss]

because cargo doesn't suppress warnings of dependencies when dependencies are vendored.

This isn't the entire story. Normally vendored dependencies are capped to allow.

The problem here seems that the user is running ./x build -vvv (three verbose), which looks to be incompatible with deny-warnings.

This seems to be introduced by #148332, cc @Kobzol.

Previously, --cap-lints=warn would take precedence over -Dwarnings. However, cargo's CARGO_BUILD_WARNINGS=deny does not honor --cap-lints.

This is exacerbated by the use of -Wrust_2018_idioms.

cc @epage, about the interaction of CARGO_BUILD_WARNINGS=deny and --verbose --verbose.