Ignore workspace.default-members when running cargo install on ro…

…ot package of a non-virtual workspace

src/cargo/core/workspace.rs

@@ -552,6 +552,23 @@ impl<'cfg> Workspace<'cfg> {
         })
     }
 
+    /// Reset "default build" behavior for non-virtual workspaces, so that a build in
+    /// the workspace root would build the root package, not the packages specified
+    /// in `workspace.default-members`.
+    pub fn ignore_default_members(&mut self) -> &mut Workspace<'cfg> {
+        // If we're building a virtual workspace, then there is no root package to build
+        if self.is_virtual() {
+            return self;
+        }
+        // If we're not building the root package, then the default members do not matter
+        if self.current_manifest != self.root_manifest() {
+            return self;
+        }
+
+        self.default_members = vec![self.current_manifest.clone()];
+        self
+    }
+
     /// Returns true if the package is a member of the workspace.
     pub fn is_member(&self, pkg: &Package) -> bool {
         self.member_ids.contains(&pkg.package_id())

src/cargo/ops/cargo_install.rs

@@ -734,6 +734,11 @@ fn make_ws_rustc_target<'cfg>(
     ws.set_ignore_lock(config.lock_update_allowed());
     ws.set_require_optional_deps(false);
 
+    // `cargo install` effectively does `cargo build` in `pkg`. But when this is the root
+    // of a non-virtual workspace, that would accidentally build `workspace.default-members`
+    // instead of `pkg` (possibly not even including `pkg` at all!)
+    ws.ignore_default_members();
+
     let rustc = config.load_global_rustc(Some(&ws))?;
     let target = match &opts.build_config.single_requested_kind()? {
         CompileKind::Host => rustc.host.as_str().to_owned(),

tests/testsuite/install.rs

@@ -1294,6 +1294,46 @@ fn use_path_workspace() {
     assert_eq!(lock, lock2, "different lockfiles");
 }
 
+#[cargo_test]
+fn path_install_workspace_root_despite_default_members() {
+    let p = project()
+        .file(
+            "Cargo.toml",
+            r#"
+                [package]
+                name = "ws-root"
+                version = "0.1.0"
+                authors = []
+
+                [workspace]
+                members = ["ws-member"]
+                default-members = ["ws-member"]
+            "#,
+        )
+        .file("src/main.rs", "fn main() {}")
+        .file(
+            "ws-member/Cargo.toml",
+            r#"
+                [package]
+                name = "ws-member"
+                version = "0.1.0"
+                authors = []
+            "#,
+        )
+        .file("ws-member/src/main.rs", "fn main() {}")
+        .build();
+
+    p.cargo("install --path")
+        .arg(p.root())
+        .arg("ws-root")
+        .with_stderr_contains(
+            "[INSTALLED] package `ws-root v0.1.0 ([..])` (executable `ws-root[EXE]`)",
+        )
+        // Particularly avoid "Installed package `ws-root v0.1.0 ([..]])` (executable `ws-member`)":
+        .with_stderr_does_not_contain("ws-member")
+        .run();
+}
+
 #[cargo_test]
 fn dev_dependencies_no_check() {
     Package::new("foo", "1.0.0").publish();