[beta] Fix clean -p with a build dependency.

src/cargo/ops/cargo_clean.rs

@@ -112,6 +112,12 @@ pub fn clean(ws: &Workspace<'_>, opts: &CleanOptions<'_>) -> CargoResult<()> {
         for target in pkg.targets() {
             for kind in [CompileKind::Host, build_config.requested_kind].iter() {
                 for mode in CompileMode::all_modes() {
+                    if target.is_custom_build() && (mode.is_any_test() || !kind.is_host()) {
+                        // Workaround where the UnitFor code will panic
+                        // because it is not expecting strange combinations
+                        // like "testing a build script".
+                        continue;
+                    }
                     for unit_for in UnitFor::all_values() {
                         let profile = if mode.is_run_custom_build() {
                             bcx.profiles

tests/testsuite/clean.rs

@@ -319,3 +319,41 @@ fn clean_remove_rlib_rmeta() {
     assert!(!p.target_debug_dir().join("libfoo.rlib").exists());
     assert!(!rmeta.exists());
 }
+
+#[cargo_test]
+fn clean_with_build_dep() {
+    // Test for panic when there was a build dep with `-p`.
+    Package::new("bar", "0.1.0").publish();
+    let p = project()
+        .file(
+            "Cargo.toml",
+            r#"
+            [package]
+            name = "foo"
+            version = "0.1.0"
+
+            [build-dependencies]
+            bar = "0.1"
+            "#,
+        )
+        .file("src/lib.rs", "")
+        .file("build.rs", "fn main() {}")
+        .build();
+
+    p.cargo("build").run();
+    // Two build directories, one for the executable, one for the run output.
+    assert_eq!(p.glob(p.target_debug_dir().join("build/foo-*")).count(), 2);
+    // Produces both an rlib and rmeta.
+    assert_eq!(
+        p.glob(p.target_debug_dir().join("deps/libfoo-*.*")).count(),
+        2
+    );
+    p.cargo("clean -p foo").run();
+    // `clean -p` doesn't clean the output directory, it should.
+    // Will be fixed via https://github.com/rust-lang/cargo/pull/8210
+    assert_eq!(p.glob(p.target_debug_dir().join("build/foo-*")).count(), 1);
+    assert_eq!(
+        p.glob(p.target_debug_dir().join("deps/libfoo-*.*")).count(),
+        0
+    );
+}