fix: deduplicate dependencies by artifact target

Signed-off-by: Roman Volosatovs <rvolosatovs@riseup.net>

src/cargo/core/compiler/standard_lib.rs

@@ -214,6 +214,7 @@ pub fn generate_std_roots(
                 /*is_std*/ true,
                 /*dep_hash*/ 0,
                 IsArtifact::No,
+                None,
             ));
         }
     }

src/cargo/core/compiler/unit.rs

@@ -1,6 +1,8 @@
-use crate::core::compiler::{unit_dependencies::IsArtifact, CompileKind, CompileMode, CrateType};
+use crate::core::compiler::unit_dependencies::IsArtifact;
+use crate::core::compiler::{CompileKind, CompileMode, CompileTarget, CrateType};
 use crate::core::manifest::{Target, TargetKind};
-use crate::core::{profiles::Profile, Package};
+use crate::core::profiles::Profile;
+use crate::core::Package;
 use crate::util::hex::short_hash;
 use crate::util::interning::InternedString;
 use crate::util::Config;
@@ -72,6 +74,11 @@ pub struct UnitInner {
     /// This value initially starts as 0, and then is filled in via a
     /// second-pass after all the unit dependencies have been computed.
     pub dep_hash: u64,
+
+    /// This is used for target-dependent feature resolution and is copied from
+    /// [`FeaturesFor::ArtifactDep`](crate::core::resolver::features::FeaturesFor::ArtifactDep), if the enum
+    /// matches the variant.
+    pub artifact_target_for_features: Option<CompileTarget>,
 }
 
 impl UnitInner {
@@ -139,6 +146,10 @@ impl fmt::Debug for Unit {
             .field("mode", &self.mode)
             .field("features", &self.features)
             .field("artifact", &self.artifact.is_true())
+            .field(
+                "artifact_target_for_features",
+                &self.artifact_target_for_features,
+            )
             .field("is_std", &self.is_std)
             .field("dep_hash", &self.dep_hash)
             .finish()
@@ -184,6 +195,7 @@ impl UnitInterner {
         is_std: bool,
         dep_hash: u64,
         artifact: IsArtifact,
+        artifact_target_for_features: Option<CompileTarget>,
     ) -> Unit {
         let target = match (is_std, target.kind()) {
             // This is a horrible hack to support build-std. `libstd` declares
@@ -216,6 +228,7 @@ impl UnitInterner {
             is_std,
             dep_hash,
             artifact,
+            artifact_target_for_features,
         });
         Unit { inner }
     }

src/cargo/core/compiler/unit_dependencies.rs

@@ -885,6 +885,10 @@ fn new_unit_dep_with_profile(
         .resolve()
         .is_public_dep(parent.pkg.package_id(), pkg.package_id());
     let features_for = unit_for.map_to_features_for(artifact);
+    let artifact_target = match features_for {
+        FeaturesFor::ArtifactDep(target) => Some(target),
+        _ => None,
+    };
     let features = state.activated_features(pkg.package_id(), features_for);
     let unit = state.interner.intern(
         pkg,
@@ -896,6 +900,7 @@ fn new_unit_dep_with_profile(
         state.is_std,
         /*dep_hash*/ 0,
         artifact.map_or(IsArtifact::No, |_| IsArtifact::Yes),
+        artifact_target,
     );
     Ok(UnitDep {
         unit,

src/cargo/ops/cargo_compile/mod.rs

@@ -424,20 +424,24 @@ pub fn create_bcx<'a, 'cfg>(
         remove_duplicate_doc(build_config, &units, &mut unit_graph);
     }
 
-    if build_config
+    let host_kind_requested = build_config
         .requested_kinds
         .iter()
-        .any(CompileKind::is_host)
+        .any(CompileKind::is_host);
+    if host_kind_requested
+        || unit_graph
+            .iter()
+            .any(|(unit, _)| unit.artifact_target_for_features.is_some())
     {
         // Rebuild the unit graph, replacing the explicit host targets with
-        // CompileKind::Host, merging any dependencies shared with build
-        // dependencies.
+        // CompileKind::Host, removing `artifact_target_for_features` and merging any dependencies
+        // shared with build and artifact dependencies.
         let new_graph = rebuild_unit_graph_shared(
             interner,
             unit_graph,
             &units,
             &scrape_units,
-            explicit_host_kind,
+            host_kind_requested.then_some(explicit_host_kind),
         );
         // This would be nicer with destructuring assignment.
         units = new_graph.0;
@@ -549,29 +553,31 @@ pub fn create_bcx<'a, 'cfg>(
 /// This is used to rebuild the unit graph, sharing host dependencies if possible.
 ///
 /// This will translate any unit's `CompileKind::Target(host)` to
-/// `CompileKind::Host` if the kind is equal to `to_host`. This also handles
-/// generating the unit `dep_hash`, and merging shared units if possible.
+/// `CompileKind::Host` if `to_host` is not `None` and the kind is equal to `to_host`.
+/// This also handles generating the unit `dep_hash`, and merging shared units if possible.
 ///
 /// This is necessary because if normal dependencies used `CompileKind::Host`,
 /// there would be no way to distinguish those units from build-dependency
-/// units. This can cause a problem if a shared normal/build dependency needs
+/// units or artifact dependency units.
+/// This can cause a problem if a shared normal/build/artifact dependency needs
 /// to link to another dependency whose features differ based on whether or
-/// not it is a normal or build dependency. If both units used
+/// not it is a normal, build or artifact dependency. If all units used
 /// `CompileKind::Host`, then they would end up being identical, causing a
 /// collision in the `UnitGraph`, and Cargo would end up randomly choosing one
 /// value or the other.
 ///
-/// The solution is to keep normal and build dependencies separate when
+/// The solution is to keep normal, build and artifact dependencies separate when
 /// building the unit graph, and then run this second pass which will try to
 /// combine shared dependencies safely. By adding a hash of the dependencies
 /// to the `Unit`, this allows the `CompileKind` to be changed back to `Host`
-/// without fear of an unwanted collision.
+/// and `artifact_target_for_features` to be removed without fear of an unwanted
+/// collision for build or artifact dependencies.
 fn rebuild_unit_graph_shared(
     interner: &UnitInterner,
     unit_graph: UnitGraph,
     roots: &[Unit],
     scrape_units: &[Unit],
-    to_host: CompileKind,
+    to_host: Option<CompileKind>,
 ) -> (Vec<Unit>, Vec<Unit>, UnitGraph) {
     let mut result = UnitGraph::new();
     // Map of the old unit to the new unit, used to avoid recursing into units
@@ -604,7 +610,7 @@ fn traverse_and_share(
     new_graph: &mut UnitGraph,
     unit_graph: &UnitGraph,
     unit: &Unit,
-    to_host: CompileKind,
+    to_host: Option<CompileKind>,
 ) -> Unit {
     if let Some(new_unit) = memo.get(unit) {
         // Already computed, no need to recompute.
@@ -624,10 +630,9 @@ fn traverse_and_share(
         })
         .collect();
     let new_dep_hash = dep_hash.finish();
-    let new_kind = if unit.kind == to_host {
-        CompileKind::Host
-    } else {
-        unit.kind
+    let new_kind = match to_host {
+        Some(to_host) if to_host == unit.kind => CompileKind::Host,
+        _ => unit.kind,
     };
     let new_unit = interner.intern(
         &unit.pkg,
@@ -639,6 +644,9 @@ fn traverse_and_share(
         unit.is_std,
         new_dep_hash,
         unit.artifact,
+        // Since `dep_hash` is now filled in, there's no need to specify the artifact target
+        // for target-dependent feature resolution
+        None,
     );
     assert!(memo.insert(unit.clone(), new_unit.clone()).is_none());
     new_graph.entry(new_unit.clone()).or_insert(new_deps);
@@ -797,6 +805,7 @@ fn override_rustc_crate_types(
             unit.is_std,
             unit.dep_hash,
             unit.artifact,
+            unit.artifact_target_for_features,
         )
     };
     units[0] = match unit.target.kind() {

src/cargo/ops/cargo_compile/unit_generator.rs

@@ -171,6 +171,7 @@ impl<'a> UnitGenerator<'a, '_> {
                     /*is_std*/ false,
                     /*dep_hash*/ 0,
                     IsArtifact::No,
+                    None,
                 )
             })
             .collect()