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fix(compile): Ignore unused deps if also transitive #16935

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Merged
arlosi merged 3 commits into from
Apr 23, 2026
+86 −40
Merged

fix(compile): Ignore unused deps if also transitive #16935

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36ae25a
test(lints): Make package selection test resilient against change
epage Apr 22, 2026
5442d49
refactor(compile): Track manifest deps in ExternState
epage Apr 16, 2026
944a540
fix(compile): Ignore unused deps if also transitive
epage Apr 22, 2026
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59 changes: 55 additions & 4 deletions src/cargo/core/compiler/unused_deps.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -98,7 +98,13 @@ impl UnusedDepState {
} else {
continue;
};
state.externs.insert(dep.extern_crate_name, manifest_deps);
state.externs.insert(
dep.extern_crate_name,
ExternState {
unit: dep.unit.clone(),
manifest_deps,
},
);
}
}

Expand Down Expand Up @@ -213,7 +219,7 @@ impl UnusedDepState {
continue;
}

for (ext, dependency) in &state.externs {
for (ext, extern_state) in &state.externs {
if state
.unused_externs
.values()
Expand All @@ -227,9 +233,17 @@ impl UnusedDepState {
);
continue;
}
if is_transitive_dep(&extern_state.unit, &state.unused_externs, build_runner) {
debug!(
"pkg {} v{} ({dep_kind:?}): ignoring unused extern `{ext}`, may be activating features",
pkg_id.name(),
pkg_id.version(),
);
continue;
}

// Implicitly added dependencies (in the same crate) aren't interesting
let dependency = if let Some(dependency) = dependency {
let dependency = if let Some(dependency) = &extern_state.manifest_deps {
dependency
} else {
continue;
Expand Down Expand Up @@ -318,7 +332,7 @@ impl UnusedDepState {
#[derive(Default)]
struct DependenciesState {
/// All declared dependencies
externs: IndexMap<InternedString, Option<Vec<Dependency>>>,
externs: IndexMap<InternedString, ExternState>,
/// Expected [`Self::unused_externs`] entries to know we've received them all
///
/// To avoid warning in cases where we didn't,
Expand All @@ -328,6 +342,12 @@ struct DependenciesState {
unused_externs: IndexMap<Unit, Vec<InternedString>>,
}

#[derive(Clone)]
struct ExternState {
unit: Unit,
manifest_deps: Option<Vec<Dependency>>,
}

fn dep_kind_of(unit: &Unit) -> DepKind {
match unit.target.kind() {
TargetKind::Lib(_) => match unit.mode {
Expand All @@ -352,3 +372,34 @@ fn unit_desc(unit: &Unit) -> String {
unit.mode,
)
}

#[instrument(skip_all)]
fn is_transitive_dep(
direct_dep_unit: &Unit,
unused_externs: &IndexMap<Unit, Vec<InternedString>>,
build_runner: &mut BuildRunner<'_, '_>,
) -> bool {
let mut queue = std::collections::VecDeque::new();
for root_unit in unused_externs.keys() {
for unit_dep in build_runner.unit_deps(root_unit) {
if root_unit.pkg.package_id() == unit_dep.unit.pkg.package_id() {
continue;
}
if unit_dep.unit == *direct_dep_unit {
continue;
}
queue.push_back(&unit_dep.unit);
}
}

while let Some(dep_unit) = queue.pop_front() {
for unit_dep in build_runner.unit_deps(dep_unit) {
if unit_dep.unit == *direct_dep_unit {
return true;
}
queue.push_back(&unit_dep.unit);
}
}

false
}
67 changes: 31 additions & 36 deletions tests/testsuite/lints/unused_dependencies.rs
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Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -968,7 +968,9 @@ fn package_selection() {
Package::new("used_bar", "0.1.0").publish();
Package::new("used_foo", "0.1.0").publish();
Package::new("used_external", "0.1.0").publish();
Package::new("unused", "0.1.0").publish();
Package::new("unused_bar", "0.1.0").publish();
Package::new("unused_foo", "0.1.0").publish();
Package::new("unused_external", "0.1.0").publish();
let p = project()
.file(
"Cargo.toml",
Expand All @@ -988,7 +990,7 @@ fn package_selection() {
edition = "2018"

[dependencies]
unused = "0.1.0"
unused_foo = "0.1.0"
used_foo = "0.1.0"
bar.path = "../bar"
external.path = "../external"
Expand All @@ -1013,7 +1015,7 @@ fn package_selection() {
edition = "2018"

[dependencies]
unused = "0.1.0"
unused_bar = "0.1.0"
used_bar = "0.1.0"

[lints.cargo]
Expand All @@ -1036,7 +1038,7 @@ fn package_selection() {
edition = "2018"

[dependencies]
unused = "0.1.0"
unused_external = "0.1.0"
used_external = "0.1.0"

[lints.cargo]
Expand All @@ -1056,30 +1058,33 @@ fn package_selection() {
.with_stderr_data(
str![[r#"
[UPDATING] `dummy-registry` index
[LOCKING] 7 packages to latest compatible versions
[DOWNLOADING] crates ...
[CHECKING] bar v0.1.0 ([ROOT]/foo/bar)
[FINISHED] `dev` profile [unoptimized + debuginfo] target(s) in [ELAPSED]s
[LOCKING] 5 packages to latest compatible versions
[DOWNLOADED] used_foo v0.1.0 (registry `dummy-registry`)
[DOWNLOADED] used_external v0.1.0 (registry `dummy-registry`)
[DOWNLOADED] unused_bar v0.1.0 (registry `dummy-registry`)
[DOWNLOADED] unused_external v0.1.0 (registry `dummy-registry`)
[DOWNLOADED] unused_foo v0.1.0 (registry `dummy-registry`)
[DOWNLOADED] used_bar v0.1.0 (registry `dummy-registry`)
[DOWNLOADED] unused v0.1.0 (registry `dummy-registry`)
[CHECKING] unused v0.1.0
[DOWNLOADED] used_external v0.1.0 (registry `dummy-registry`)
[DOWNLOADED] used_foo v0.1.0 (registry `dummy-registry`)
[CHECKING] used_bar v0.1.0
[CHECKING] unused_external v0.1.0
[CHECKING] used_external v0.1.0
[CHECKING] unused_bar v0.1.0
[CHECKING] used_foo v0.1.0
[CHECKING] unused_foo v0.1.0
[CHECKING] bar v0.1.0 ([ROOT]/foo/bar)
[CHECKING] external v0.1.0 ([ROOT]/foo/external)
[CHECKING] foo v0.1.0 ([ROOT]/foo/foo)
[WARNING] unused dependency
--> bar/Cargo.toml:9:13
|
9 | unused = "0.1.0"
| ^^^^^^^^^^^^^^^^
9 | unused_bar = "0.1.0"
| ^^^^^^^^^^^^^^^^^^^^
|
= [NOTE] `cargo::unused_dependencies` is set to `warn` in `[lints]`
[HELP] remove the dependency
|
9 - unused = "0.1.0"
9 - unused_bar = "0.1.0"
|
[WARNING] unused dependency
--> foo/Cargo.toml:11:13
Expand Down Expand Up @@ -1107,13 +1112,14 @@ fn package_selection() {
[WARNING] unused dependency
--> foo/Cargo.toml:9:13
|
9 | unused = "0.1.0"
| ^^^^^^^^^^^^^^^^
9 | unused_foo = "0.1.0"
| ^^^^^^^^^^^^^^^^^^^^
|
[HELP] remove the dependency
|
9 - unused = "0.1.0"
9 - unused_foo = "0.1.0"
|
[FINISHED] `dev` profile [unoptimized + debuginfo] target(s) in [ELAPSED]s

"#]]
.unordered(),
Expand All @@ -1124,7 +1130,6 @@ fn package_selection() {
.masquerade_as_nightly_cargo(&["cargo-lints"])
.with_stderr_data(
str![[r#"
[FINISHED] `dev` profile [unoptimized + debuginfo] target(s) in [ELAPSED]s
[WARNING] unused dependency
--> foo/Cargo.toml:11:13
|
Expand All @@ -1151,13 +1156,14 @@ fn package_selection() {
[WARNING] unused dependency
--> foo/Cargo.toml:9:13
|
9 | unused = "0.1.0"
| ^^^^^^^^^^^^^^^^
9 | unused_foo = "0.1.0"
| ^^^^^^^^^^^^^^^^^^^^
|
[HELP] remove the dependency
|
9 - unused = "0.1.0"
9 - unused_foo = "0.1.0"
|
[FINISHED] `dev` profile [unoptimized + debuginfo] target(s) in [ELAPSED]s

"#]]
.unordered(),
Expand All @@ -1168,18 +1174,18 @@ fn package_selection() {
.masquerade_as_nightly_cargo(&["cargo-lints"])
.with_stderr_data(
str![[r#"
[FINISHED] `dev` profile [unoptimized + debuginfo] target(s) in [ELAPSED]s
[WARNING] unused dependency
--> bar/Cargo.toml:9:13
|
9 | unused = "0.1.0"
| ^^^^^^^^^^^^^^^^
9 | unused_bar = "0.1.0"
| ^^^^^^^^^^^^^^^^^^^^
|
= [NOTE] `cargo::unused_dependencies` is set to `warn` in `[lints]`
[HELP] remove the dependency
|
9 - unused = "0.1.0"
9 - unused_bar = "0.1.0"
|
[FINISHED] `dev` profile [unoptimized + debuginfo] target(s) in [ELAPSED]s

"#]]
.unordered(),
Expand Down Expand Up @@ -1314,17 +1320,6 @@ pub fn fun() -> &'static str {
[CHECKING] transitive v0.1.1
[CHECKING] intermediate v0.1.0
[CHECKING] foo v0.1.0 ([ROOT]/foo)
[WARNING] unused dependency
--> Cargo.toml:10:13
|
10 | transitive = { version = "0.1.1", features = ["a"] }
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
|
= [NOTE] `cargo::unused_dependencies` is set to `warn` in `[lints]`
[HELP] remove the dependency
|
10 - transitive = { version = "0.1.1", features = ["a"] }
|
[FINISHED] `dev` profile [unoptimized + debuginfo] target(s) in [ELAPSED]s

"#]]
Expand Down