missing workspace_default_members should panic

src/lib.rs

@@ -151,10 +151,11 @@ pub struct Metadata {
     pub packages: Vec<Package>,
     /// A list of all workspace members
     pub workspace_members: Vec<PackageId>,
-    /// A list of all workspace members
+    /// The list of default workspace members
     ///
-    /// This is always `None` if running with a version of Cargo older than 1.71.
-    pub workspace_default_members: Option<Vec<PackageId>>,
+    /// This not available if running with a version of Cargo older than 1.71.
+    #[serde(skip_serializing_if = "workspace_default_members_is_missing")]
+    pub workspace_default_members: WorkspaceDefaultMembers,
     /// Dependencies graph
     pub resolve: Option<Resolve>,
     /// Workspace root
@@ -197,16 +198,14 @@ impl Metadata {
 
     /// Get the workspace default packages.
     ///
-    /// This will always return `None` if running with a version of Cargo older than 1.71.
-    pub fn workspace_default_packages(&self) -> Option<Vec<&Package>> {
-        self.workspace_default_members
-            .as_ref()
-            .map(|workspace_default_members| {
-                self.packages
-                    .iter()
-                    .filter(|&p| workspace_default_members.contains(&p.id))
-                    .collect()
-            })
+    /// # Panics
+    ///
+    /// This will panic if running with a version of Cargo older than 1.71.
+    pub fn workspace_default_packages(&self) -> Vec<&Package> {
+        self.packages
+            .iter()
+            .filter(|&p| self.workspace_default_members.contains(&p.id))
+            .collect()
     }
 }
 
@@ -221,6 +220,41 @@ impl<'a> std::ops::Index<&'a PackageId> for Metadata {
     }
 }
 
+#[derive(Clone, Debug, Deserialize, Serialize)]
+#[serde(transparent)]
+/// A list of default workspace members.
+///
+/// See [`Metadata::workspace_default_members`].
+///
+/// It is only available if running a version of Cargo of 1.71 or newer.
+///
+/// # Panics
+///
+/// Dereferencing when running an older version of Cargo will panic.
+pub struct WorkspaceDefaultMembers(Option<Vec<PackageId>>);
+
+impl core::ops::Deref for WorkspaceDefaultMembers {
+    type Target = [PackageId];
+
+    fn deref(&self) -> &Self::Target {
+        self.0
+            .as_ref()
+            .expect("WorkspaceDefaultMembers should only be dereferenced on Cargo versions >= 1.71")
+    }
+}
+
+/// Return true if a valid value for [`WorkspaceDefaultMembers`] is missing, and
+/// dereferencing it would panic.
+///
+/// Internal helper for `skip_serializing_if` and test code. Might be removed in
+/// the future.
+#[doc(hidden)]
+pub fn workspace_default_members_is_missing(
+    workspace_default_members: &WorkspaceDefaultMembers,
+) -> bool {
+    workspace_default_members.0.is_none()
+}
+
 #[derive(Clone, Serialize, Deserialize, Debug)]
 #[cfg_attr(feature = "builder", derive(Builder))]
 #[non_exhaustive]

tests/selftest.rs

@@ -135,9 +135,6 @@ fn metadata_deps() {
     let workspace_packages = metadata.workspace_packages();
     assert_eq!(workspace_packages.len(), 1);
     assert_eq!(&workspace_packages[0].id, this_id);
-    if let Some(default_packages) = metadata.workspace_default_packages() {
-        assert_eq!(default_packages, workspace_packages);
-    }
 
     let lib = this
         .targets
@@ -164,3 +161,20 @@ fn metadata_deps() {
     assert!(serde.req.matches(&Version::parse("1.99.99").unwrap()));
     assert!(!serde.req.matches(&Version::parse("2.0.0").unwrap()));
 }
+
+#[test]
+fn workspace_default_packages() {
+    use cargo_metadata::workspace_default_members_is_missing;
+
+    let metadata = MetadataCommand::new()
+        .manifest_path("Cargo.toml")
+        .exec()
+        .unwrap();
+    let workspace_packages = metadata.workspace_packages();
+    // this will only trigger on cargo versions that expose
+    // workspace_default_members (that is, cargo >= 1.71)
+    if !workspace_default_members_is_missing(&metadata.workspace_default_members) {
+        let default_packages = metadata.workspace_default_packages();
+        assert_eq!(default_packages, workspace_packages);
+    }
+}

tests/test_samples.rs

@@ -5,19 +5,19 @@ extern crate serde_json;
 
 use camino::Utf8PathBuf;
 use cargo_metadata::{
-    ArtifactDebuginfo, CargoOpt, DependencyKind, Edition, Message, Metadata, MetadataCommand,
+    workspace_default_members_is_missing, ArtifactDebuginfo, CargoOpt, DependencyKind, Edition,
+    Message, Metadata, MetadataCommand,
 };
 
-#[test]
-fn old_minimal() {
-    // Output from oldest supported version (1.24).
-    // This intentionally has as many null fields as possible.
-    // 1.8 is when metadata was introduced.
-    // Older versions not supported because the following are required:
-    // - `workspace_members` added in 1.13
-    // - `target_directory` added in 1.19
-    // - `workspace_root` added in 1.24
-    let json = r#"
+/// Output from oldest version ever supported (1.24).
+///
+/// This intentionally has as many null fields as possible.
+/// 1.8 is when metadata was introduced.
+/// Older versions not supported because the following are required:
+/// - `workspace_members` added in 1.13
+/// - `target_directory` added in 1.19
+/// - `workspace_root` added in 1.24
+const JSON_OLD_MINIMAL: &str = r#"
 {
   "packages": [
     {
@@ -65,7 +65,10 @@ fn old_minimal() {
   "workspace_root": "/foo"
 }
 "#;
-    let meta: Metadata = serde_json::from_str(json).unwrap();
+
+#[test]
+fn old_minimal() {
+    let meta: Metadata = serde_json::from_str(JSON_OLD_MINIMAL).unwrap();
     assert_eq!(meta.packages.len(), 1);
     let pkg = &meta.packages[0];
     assert_eq!(pkg.name, "foo");
@@ -121,6 +124,15 @@ fn old_minimal() {
     assert_eq!(meta.workspace_root, "/foo");
     assert_eq!(meta.workspace_metadata, serde_json::Value::Null);
     assert_eq!(meta.target_directory, "/foo/target");
+
+    assert!(workspace_default_members_is_missing(
+        &meta.workspace_default_members
+    ));
+    let serialized = serde_json::to_value(meta).unwrap();
+    assert!(!serialized
+        .as_object()
+        .unwrap()
+        .contains_key("workspace_default_members"));
 }
 
 macro_rules! sorted {
@@ -188,7 +200,7 @@ fn all_the_fields() {
         .unwrap();
     assert_eq!(meta.workspace_root.file_name().unwrap(), "all");
     assert_eq!(
-        serde_json::from_value::<WorkspaceMetadata>(meta.workspace_metadata).unwrap(),
+        serde_json::from_value::<WorkspaceMetadata>(meta.workspace_metadata.clone()).unwrap(),
         WorkspaceMetadata {
             testobject: TestObject {
                 myvalue: "abc".to_string()
@@ -198,9 +210,7 @@ fn all_the_fields() {
     assert_eq!(meta.workspace_members.len(), 1);
     assert!(meta.workspace_members[0].to_string().starts_with("all"));
     if ver >= semver::Version::parse("1.71.0").unwrap() {
-        assert_eq!(meta.workspace_default_members, Some(meta.workspace_members));
-    } else {
-        assert_eq!(meta.workspace_default_members, None);
+        assert_eq!(&*meta.workspace_default_members, &meta.workspace_members);
     }
 
     assert_eq!(meta.packages.len(), 9);
@@ -456,6 +466,18 @@ fn all_the_fields() {
         kind.target.as_ref().map(|x| x.to_string()),
         Some("cfg(windows)".to_string())
     );
+
+    let serialized = serde_json::to_value(meta).unwrap();
+    if ver >= semver::Version::parse("1.71.0").unwrap() {
+        assert!(serialized.as_object().unwrap()["workspace_default_members"]
+            .as_array()
+            .is_some());
+    } else {
+        assert!(!serialized
+            .as_object()
+            .unwrap()
+            .contains_key("workspace_default_members"));
+    }
 }
 
 #[test]
@@ -696,3 +718,10 @@ fn debuginfo_variants() {
         }
     }
 }
+
+#[test]
+#[should_panic = "WorkspaceDefaultMembers should only be dereferenced on Cargo versions >= 1.71"]
+fn missing_workspace_default_members() {
+    let meta: Metadata = serde_json::from_str(JSON_OLD_MINIMAL).unwrap();
+    let _ = &*meta.workspace_default_members;
+}