artifact deps should works when target field specified coexists with optional = true

src/cargo/core/compiler/unit_dependencies.rs

@@ -1103,7 +1103,7 @@ impl<'a, 'cfg> State<'a, 'cfg> {
                         // If this is an optional dependency, and the new feature resolver
                         // did not enable it, don't include it.
                         if dep.is_optional() {
-                            let features_for = unit_for.map_to_features_for(dep.artifact());
+                            let features_for = unit_for.map_to_features_for(None);
                             if !self.is_dep_activated(pkg_id, features_for, dep.name_in_toml()) {
                                 return false;
                             }

src/cargo/core/resolver/features.rs

@@ -853,12 +853,14 @@ impl<'a, 'cfg> FeatureResolver<'a, 'cfg> {
                                     ArtifactTarget::BuildDependencyAssumeTarget => self
                                         .requested_targets
                                         .iter()
-                                        .filter_map(|kind| match kind {
-                                            CompileKind::Host => None,
-                                            CompileKind::Target(target) => {
-                                                Some(FeaturesFor::ArtifactDep(*target))
+                                        .map(|kind| match kind {
+                                            CompileKind::Host => {
+                                                let host_triple = self.target_data.rustc.host;
+                                                CompileTarget::new(&host_triple).unwrap()
                                             }
+                                            CompileKind::Target(target) => *target,
                                         })
+                                        .map(FeaturesFor::ArtifactDep)
                                         .collect(),
                                 }),
                             )

tests/testsuite/artifact_dep.rs

@@ -2342,3 +2342,108 @@ fn calc_bin_artifact_fingerprint() {
         )
         .run();
 }
+
+#[cargo_test]
+fn with_target_and_optional() {
+    // See rust-lang/cargo#10526
+    if cross_compile::disabled() {
+        return;
+    }
+    let target = cross_compile::alternate();
+    let p = project()
+        .file(
+            "Cargo.toml",
+            &r#"
+                [package]
+                name = "foo"
+                version = "0.0.1"
+                edition = "2021"
+                [dependencies]
+                d1 = { path = "d1", artifact = "bin", optional = true, target = "$TARGET" }
+            "#
+            .replace("$TARGET", target),
+        )
+        .file(
+            "src/main.rs",
+            r#"
+                fn main() {
+                    let _b = include_bytes!(env!("CARGO_BIN_FILE_D1"));
+                }
+            "#,
+        )
+        .file(
+            "d1/Cargo.toml",
+            r#"
+                [package]
+                name = "d1"
+                version = "0.0.1"
+                edition = "2021"
+            "#,
+        )
+        .file("d1/src/main.rs", "fn main() {}")
+        .build();
+
+    p.cargo("check -Z bindeps -F d1 -v")
+        .masquerade_as_nightly_cargo(&["bindeps"])
+        .with_stderr(
+            "\
+[COMPILING] d1 v0.0.1 [..]
+[RUNNING] `rustc --crate-name d1 [..]--crate-type bin[..]
+[CHECKING] foo v0.0.1 [..]
+[RUNNING] `rustc --crate-name foo [..]--cfg[..]d1[..]
+[FINISHED] dev [..]
+",
+        )
+        .run();
+}
+
+#[cargo_test]
+fn with_assumed_host_target_and_optional_build_dep() {
+    let p = project()
+        .file(
+            "Cargo.toml",
+            r#"
+                [package]
+                name = "foo"
+                version = "0.0.1"
+                edition = "2021"
+                [build-dependencies]
+                d1 = { path = "d1", artifact = "bin", optional = true, target = "target" }
+            "#,
+        )
+        .file("src/main.rs", "fn main() {}")
+        .file(
+            "build.rs",
+            r#"
+                fn main() {
+                    std::env::var("CARGO_BIN_FILE_D1").unwrap();
+                }
+            "#,
+        )
+        .file(
+            "d1/Cargo.toml",
+            r#"
+                [package]
+                name = "d1"
+                version = "0.0.1"
+                edition = "2021"
+            "#,
+        )
+        .file("d1/src/main.rs", "fn main() {}")
+        .build();
+
+    p.cargo("check -Z bindeps -F d1 -v")
+        .masquerade_as_nightly_cargo(&["bindeps"])
+        .with_stderr_unordered(
+            "\
+[COMPILING] foo v0.0.1 ([CWD])
+[COMPILING] d1 v0.0.1 ([CWD]/d1)
+[RUNNING] `rustc --crate-name build_script_build [..]--crate-type bin[..]
+[RUNNING] `rustc --crate-name d1 [..]--crate-type bin[..]
+[RUNNING] `[CWD]/target/debug/build/foo-[..]/build-script-build`
+[RUNNING] `rustc --crate-name foo [..]--cfg[..]d1[..]
+[FINISHED] dev [..]
+",
+        )
+        .run();
+}