Only apply default-members when building root manifest

Author: Nemo157

src/cargo/core/workspace.rs

@@ -452,11 +452,15 @@ impl<'cfg> Workspace<'cfg> {
                 WorkspaceConfig::Root(ref root_config) => {
                     members_paths = root_config
                         .members_paths(root_config.members.as_ref().unwrap_or(&vec![]))?;
-                    default_members_paths = if let Some(ref default) = root_config.default_members {
-                        Some(root_config.members_paths(default)?)
+                    default_members_paths = if root_manifest_path == self.current_manifest {
+                        if let Some(ref default) = root_config.default_members {
+                            Some(root_config.members_paths(default)?)
+                        } else {
+                            None
+                        }
                     } else {
                         None
-                    }
+                    };
                 }
                 _ => failure::bail!(
                     "root of a workspace inferred but wasn't a root: {}",

src/doc/man/options-packages.adoc

@@ -1,9 +1,13 @@
 By default, when no package selection options are given, the packages selected
-depend on the current working directory. In the root of a virtual workspace,
-all workspace members are selected (`--all` is implied). Otherwise, only the
-package in the current directory will be selected. The default packages may be
-overridden with the `workspace.default-members` key in the root `Cargo.toml`
-manifest.
+depend on the selected manifest file (based on the current working directory if
+`--manifest-path` is not given). If the manifest is the root of a workspace then
+the workspaces default members are selected, otherwise only the package defined
+by the manifest will be selected.
+
+The default members of a workspace can be set explicitly with the
+`workspace.default-members` key in the root manifest. If this is not set, a
+virtual workspace will include all workspace members (equivalent to passing
+`--all`), and a non-virtual workspace will include only the root crate itself.
 
 *-p* _SPEC_...::
 *--package* _SPEC_...::

tests/testsuite/workspaces.rs

@@ -82,6 +82,44 @@ fn simple_explicit_default_members() {
     assert!(!p.bin("foo").is_file());
 }
 
+#[cargo_test]
+fn non_virtual_default_members_build_other_member() {
+    let p = project()
+        .file(
+            "Cargo.toml",
+            r#"
+            [project]
+            name = "foo"
+            version = "0.1.0"
+            authors = []
+
+            [workspace]
+            members = [".", "bar", "baz"]
+            default-members = ["baz"]
+        "#,
+        )
+        .file("src/main.rs", "fn main() {}")
+        .file("bar/Cargo.toml", &basic_manifest("bar", "0.1.0"))
+        .file("bar/src/lib.rs", "pub fn bar() {}")
+        .file("baz/Cargo.toml", &basic_manifest("baz", "0.1.0"))
+        .file("baz/src/lib.rs", "pub fn baz() {}")
+        .build();
+
+    p.cargo("build")
+        .with_stderr(
+            "[..] Compiling baz v0.1.0 ([..])\n\
+             [..] Finished dev [unoptimized + debuginfo] target(s) in [..]\n",
+        )
+        .run();
+
+    p.cargo("build --manifest-path bar/Cargo.toml")
+        .with_stderr(
+            "[..] Compiling bar v0.1.0 ([..])\n\
+             [..] Finished dev [unoptimized + debuginfo] target(s) in [..]\n",
+        )
+        .run();
+}
+
 #[cargo_test]
 fn inferred_root() {
     let p = project()
@@ -848,6 +886,31 @@ but is not a member.
         .run();
 }
 
+#[cargo_test]
+fn virtual_default_members_build_other_member() {
+    let p = project()
+        .file(
+            "Cargo.toml",
+            r#"
+            [workspace]
+            members = ["bar", "baz"]
+            default-members = ["baz"]
+        "#,
+        )
+        .file("bar/Cargo.toml", &basic_manifest("bar", "0.1.0"))
+        .file("bar/src/lib.rs", "pub fn bar() {}")
+        .file("baz/Cargo.toml", &basic_manifest("baz", "0.1.0"))
+        .file("baz/src/lib.rs", "pub fn baz() {}")
+        .build();
+
+    p.cargo("build --manifest-path bar/Cargo.toml")
+        .with_stderr(
+            "[..] Compiling bar v0.1.0 ([..])\n\
+             [..] Finished dev [unoptimized + debuginfo] target(s) in [..]\n",
+        )
+        .run();
+}
+
 #[cargo_test]
 fn virtual_build_no_members() {
     let p = project().file(