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Enable -Zembed-metadata=no by default on nightly Cargo #17267

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Enable -Zembed-metadata=no by default on nightly Cargo #17267

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6 changes: 4 additions & 2 deletions src/compiler/build_context/target_info.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -574,9 +574,10 @@ impl TargetInfo {
target_kind: &TargetKind,
target_triple: &str,
gctx: &GlobalContext,
rustc: &Rustc,
) -> CargoResult<(Vec<FileType>, Vec<CrateType>)> {
match mode {
CompileMode::Build => self.calc_rustc_outputs(target_kind, target_triple, gctx),
CompileMode::Build => self.calc_rustc_outputs(target_kind, target_triple, gctx, rustc),
CompileMode::Test => {
match self.file_types(&CrateType::Bin, FileFlavor::Normal, target_triple)? {
Some(fts) => Ok((fts, Vec::new())),
Expand All @@ -598,6 +599,7 @@ impl TargetInfo {
target_kind: &TargetKind,
target_triple: &str,
gctx: &GlobalContext,
rustc: &Rustc,
) -> CargoResult<(Vec<FileType>, Vec<CrateType>)> {
let mut unsupported = Vec::new();
let mut result = Vec::new();
Expand All @@ -619,7 +621,7 @@ impl TargetInfo {
}
}
if !result.is_empty() {
if !gctx.should_embed_metadata()
if !gctx.should_embed_metadata(rustc)
&& crate_types
.iter()
.any(|ct| ct.benefits_from_no_embed_metadata())
Expand Down
3 changes: 2 additions & 1 deletion src/compiler/build_runner/compilation_files.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -421,6 +421,7 @@ impl<'a, 'gctx: 'a> CompilationFiles<'a, 'gctx> {
&TargetKind::Bin,
bcx.target_data.short_name(&kind),
bcx.gctx,
bcx.rustc(),
)
.expect("target must support `bin`");

Expand Down Expand Up @@ -664,7 +665,7 @@ impl<'a, 'gctx: 'a> CompilationFiles<'a, 'gctx> {
let info = bcx.target_data.info(unit.kind);
let triple = bcx.target_data.short_name(&unit.kind);
let (file_types, unsupported) =
info.rustc_outputs(unit.mode, unit.target.kind(), triple, bcx.gctx)?;
info.rustc_outputs(unit.mode, unit.target.kind(), triple, bcx.gctx, bcx.rustc())?;
if file_types.is_empty() {
if !unsupported.is_empty() {
let unsupported_strs: Vec<_> = unsupported.iter().map(|ct| ct.as_str()).collect();
Expand Down
2 changes: 1 addition & 1 deletion src/compiler/fingerprint/mod.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -1676,7 +1676,7 @@ fn calculate_normal(
build_runner
.bcx
.gctx
.should_embed_metadata()
.should_embed_metadata(build_runner.bcx.rustc())
.not()
.hash(&mut config);

Expand Down
11 changes: 9 additions & 2 deletions src/compiler/mod.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -1320,7 +1320,11 @@ fn build_base_args(

if unit.mode.is_check() {
cmd.arg("--emit=dep-info,metadata");
} else if !build_runner.bcx.gctx.should_embed_metadata() {
} else if !build_runner
.bcx
.gctx
.should_embed_metadata(build_runner.bcx.rustc())
{
// Nightly rustc supports the -Zembed-metadata=no flag, which tells it to avoid including
// full metadata in rlib/dylib artifacts, to save space on disk. In this case, metadata
// will only be stored in .rmeta files.
Expand Down Expand Up @@ -1814,7 +1818,10 @@ pub fn extern_args(
let mut result = Vec::new();
let deps = build_runner.unit_deps(unit);

let no_embed_metadata = !build_runner.bcx.gctx.should_embed_metadata();
let no_embed_metadata = !build_runner
.bcx
.gctx
.should_embed_metadata(build_runner.bcx.rustc());
let public_dependency_enabled = is_public_dependency_enabled(build_runner, unit);

// Closure to add one dependency to `result`.
Expand Down
15 changes: 13 additions & 2 deletions src/context/mod.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -1269,8 +1269,19 @@ impl GlobalContext {
self.extra_verbose
}

pub fn should_embed_metadata(&self) -> bool {
self.cli_unstable().embed_metadata.unwrap_or(true)
pub fn should_embed_metadata(&self, rustc: &Rustc) -> bool {
match self.cli_unstable().embed_metadata {
Some(v) => v,
None => {
let cargo_nightly = matches!(
crate::version().release_channel.as_deref(),
Some("nightly" | "dev")
);
// Enable -Zembed-metadata=no by default if both cargo and rustc are nightly
let is_nightly = cargo_nightly && rustc.is_nightly;
!is_nightly
Comment on lines +1280 to +1282

@epage epage Jul 27, 2026 •
edited by rustbot
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We should mirror the check done in #17258 (and maybe need to document this)

View changes since the review

@Kobzol Kobzol Jul 27, 2026

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My PR currently allows using the new default on stable via RUSTC_BOOTSTRAP. I can disable that, if you want.

But I think that the new build dir layout and this flag differs in how the nightly detection should work. The new build dir layout is purely a Cargo thing; regardless of which layout is used, it will woth with both stable and nightly rustc, the compiler doesn't really care. While the -Zembed-metadata flag requires the nightly compiler right now.

So my check only sets it by default when both Cargo and rustc are nightly. It could also just take a look at rustc, and not at Cargo, in theory.

@epage epage Jul 27, 2026

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Like with #17258, this should not change the default with the presence of RUSTC_BOOTSTRAP. That is my main care about.

The rest is more styling (being consistent, being less invasive, etc).

Are there situations where a nightly Cargo is used with stable Rust that we care about? I've not checked what local; builds of Cargo consider itself (which I do run regularly).

@Kobzol Kobzol Jul 27, 2026

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I could use the exact same approach as in #17258, and just enable -Zembed-metadata=no in nightly Cargo. But I cannot know the rustc version at the time the CLI options are created. So then I'd have to always check the rustc version even if the embed-metadata flag was set explicitly. So =no would essentially have to act as =no-if-nightly-rustc. Which is also valid, but it seems weird if you pass -Zembed-metadata=no explicitly and then the flag doesn't get used if the rustc isn't nightly.

Or I could use a fourth variant, EmbedMetadata::NoIfNightlyRustc, and use that on nightly be default. Though #17266 actually removes the enum and just turns it into Option<bool> to make it easier to load from the config.

Are there situations where a nightly Cargo is used with stable Rust that we care about? I've not checked what local; builds of Cargo consider itself (which I do run regularly).

I don't know about others, but when doing perf. benchmarks or various experiments with Cargo, I do often override RUSTC and use different cargo/rustc channels, it usually works fine. Local builds of Cargo should be dev, so the same as nightly.

}
}
}

pub fn network_allowed(&self) -> bool {
Expand Down
22 changes: 16 additions & 6 deletions src/ops/cargo_clean.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -298,9 +298,14 @@ fn clean_specs(
] {
for (compile_kind, layout) in &layouts {
let triple = target_data.short_name(compile_kind);
let (file_types, _unsupported) = target_data
.info(*compile_kind)
.rustc_outputs(mode, target.kind(), triple, clean_ctx.gctx)?;
let (file_types, _unsupported) =
target_data.info(*compile_kind).rustc_outputs(
mode,
target.kind(),
triple,
clean_ctx.gctx,
&target_data.rustc,
)?;
let artifact_dir = layout
.artifact_dir()
.expect("artifact-dir was not locked during clean");
Expand Down Expand Up @@ -375,9 +380,14 @@ fn clean_specs(
] {
for (compile_kind, layout) in &layouts {
let triple = target_data.short_name(compile_kind);
let (file_types, _unsupported) = target_data
.info(*compile_kind)
.rustc_outputs(mode, target.kind(), triple, clean_ctx.gctx)?;
let (file_types, _unsupported) =
target_data.info(*compile_kind).rustc_outputs(
mode,
target.kind(),
triple,
clean_ctx.gctx,
&target_data.rustc,
)?;
let artifact_dir = layout
.artifact_dir()
.expect("artifact-dir was not locked during clean");
Expand Down
7 changes: 6 additions & 1 deletion src/util/rustc.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -12,7 +12,7 @@ use tracing::{debug, info, warn};

use crate::compiler::apply_env_config;
use crate::util::interning::InternedString;
use crate::util::{CargoResult, GlobalContext, StableHasher};
use crate::util::{CargoResult, GlobalContext, StableHasher, VersionExt};

/// Information on the `rustc` executable
#[derive(Debug)]
Expand All @@ -32,6 +32,8 @@ pub struct Rustc {
pub host: InternedString,
/// The rustc full commit hash, this comes from `verbose_version`.
pub commit_hash: Option<String>,
/// Is the rustc on a nightly or a dev channel?
pub is_nightly: bool,
cache: Mutex<Cache>,
}

Expand Down Expand Up @@ -88,6 +90,8 @@ impl Rustc {
verbose_version
)
})?;
let is_nightly =
version.is_prerelease() && matches!(version.pre.as_str(), "dev" | "nightly");
let commit_hash = extract("commit-hash: ").ok().map(|hash| {
// Possible commit-hash values from rustc are SHA hex string and "unknown". See:
// * https://github.com/rust-lang/rust/blob/531cb83fc/src/bootstrap/src/utils/channel.rs#L73
Expand All @@ -114,6 +118,7 @@ impl Rustc {
version,
host,
commit_hash,
is_nightly,
cache: Mutex::new(cache),
})
}
Expand Down
4 changes: 1 addition & 3 deletions tests/testsuite/build.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -6539,7 +6539,7 @@ fn embed_metadata_no_invalidate() {
)
.build();

p.cargo("build -Z embed-metadata=no")
p.cargo("build -Z embed-metadata=yes")
.masquerade_as_nightly_cargo(&["-Z embed-metadata"])
.with_stderr_data(str![[r#"
[LOCKING] 1 package to highest compatible version
Expand All @@ -6552,8 +6552,6 @@ fn embed_metadata_no_invalidate() {
p.cargo("build")
.masquerade_as_nightly_cargo(&["-Z embed-metadata"])
.with_stderr_data(str![[r#"
[COMPILING] bar v0.5.0 ([ROOT]/foo/bar)
[COMPILING] foo v0.5.0 ([ROOT]/foo)
[FINISHED] `dev` profile [unoptimized + debuginfo] target(s) in [ELAPSED]s

"#]])
Expand Down
2 changes: 2 additions & 0 deletions tests/testsuite/build_script_env.rs
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Expand Up @@ -142,6 +142,7 @@ fn rustc_bootstrap() {
// NOTE: uses RUSTC_BOOTSTRAP so it will be propagated to rustc
// (this matters when tests are being run with a beta or stable cargo)
.env("RUSTC_BOOTSTRAP", "1")
.arg("-Zembed-metadata=yes")
.with_stderr_data(str![[r#"
[COMPILING] has-dashes v0.0.1 ([ROOT]/foo)
[WARNING] has-dashes@0.0.1: cannot set `RUSTC_BOOTSTRAP=1` from build script of `has-dashes v0.0.1 ([ROOT]/foo)`.
Expand Down Expand Up @@ -187,6 +188,7 @@ fn rustc_bootstrap() {
// NOTE: uses RUSTC_BOOTSTRAP so it will be propagated to rustc
// (this matters when tests are being run with a beta or stable cargo)
.env("RUSTC_BOOTSTRAP", "1")
.arg("-Zembed-metadata=yes")
.with_stderr_data(str![[r#"
[COMPILING] foo v0.0.1 ([ROOT]/foo)
[WARNING] foo@0.0.1: cannot set `RUSTC_BOOTSTRAP=1` from build script of `foo v0.0.1 ([ROOT]/foo)`.
Expand Down