Properly set for_host for proc-macro tests.

src/cargo/core/compiler/unit_dependencies.rs

@@ -161,7 +161,13 @@ fn deps_of_roots(roots: &[Unit], mut state: &mut State<'_, '_>) -> CargoResult<(
         // without, once for `--test`). In particular, the lib included for
         // Doc tests and examples are `Build` mode here.
         let unit_for = if unit.mode.is_any_test() || state.global_mode.is_rustc_test() {
-            UnitFor::new_test(state.config)
+            if unit.target.proc_macro() {
+                // Special-case for proc-macros, which are forced to for-host
+                // since they need to link with the proc_macro crate.
+                UnitFor::new_host_test(state.config)
+            } else {
+                UnitFor::new_test(state.config)
+            }
         } else if unit.target.is_custom_build() {
             // This normally doesn't happen, except `clean` aggressively
             // generates all units.

src/cargo/core/profiles.rs

@@ -967,6 +967,16 @@ impl UnitFor {
         }
     }
 
+    /// This is a special case for unit tests of a proc-macro.
+    ///
+    /// Proc-macro unit tests are forced to be run on the host.
+    pub fn new_host_test(config: &Config) -> UnitFor {
+        let mut unit_for = UnitFor::new_test(config);
+        unit_for.host = true;
+        unit_for.host_features = true;
+        unit_for
+    }
+
     /// Returns a new copy based on `for_host` setting.
     ///
     /// When `for_host` is true, this clears `panic_abort_ok` in a sticky

tests/testsuite/features2.rs

@@ -1864,3 +1864,85 @@ warning: feat: enabled
         )
         .run();
 }
+
+#[cargo_test]
+fn test_proc_macro() {
+    // Running `cargo test` on a proc-macro, with a shared dependency that has
+    // different features.
+    //
+    // There was a bug where `shared` was built twice (once with feature "B"
+    // and once without), and both copies linked into the unit test. This
+    // would cause a type failure when used in an intermediate dependency
+    // (the-macro-support).
+    let p = project()
+        .file(
+            "Cargo.toml",
+            r#"
+                [package]
+                name = "runtime"
+                version = "0.1.0"
+                [dependencies]
+                the-macro = { path = "the-macro", features = ['a'] }
+                [build-dependencies]
+                shared = { path = "shared", features = ['b'] }
+            "#,
+        )
+        .file("src/lib.rs", "")
+        .file(
+            "the-macro/Cargo.toml",
+            r#"
+                [package]
+                name = "the-macro"
+                version = "0.1.0"
+                [lib]
+                proc-macro = true
+                test = false
+                [dependencies]
+                the-macro-support = { path = "../the-macro-support" }
+                shared = { path = "../shared" }
+                [dev-dependencies]
+                runtime = { path = ".." }
+                [features]
+                a = []
+            "#,
+        )
+        .file(
+            "the-macro/src/lib.rs",
+            "
+                fn _test() {
+                    the_macro_support::foo(shared::Foo);
+                }
+            ",
+        )
+        .file(
+            "the-macro-support/Cargo.toml",
+            r#"
+                [package]
+                name = "the-macro-support"
+                version = "0.1.0"
+                [dependencies]
+                shared = { path = "../shared" }
+            "#,
+        )
+        .file(
+            "the-macro-support/src/lib.rs",
+            "
+                pub fn foo(_: shared::Foo) {}
+            ",
+        )
+        .file(
+            "shared/Cargo.toml",
+            r#"
+                [package]
+                name = "shared"
+                version = "0.1.0"
+                [features]
+                b = []
+            "#,
+        )
+        .file("shared/src/lib.rs", "pub struct Foo;")
+        .build();
+    p.cargo("test -Zfeatures=all --manifest-path the-macro/Cargo.toml")
+        .masquerade_as_nightly_cargo()
+        .run();
+}