Repository: oli-obk/cargo_metadata (rust)

Issue:
root_package returns None if no_deps is passed
Minimal Reproducible Example:

`src/main.rs`
```rust
use cargo_metadata::MetadataCommand;

fn main() {
    MetadataCommand::new()
        .exec()
        .unwrap()
        .root_package()
        .expect("root package exists");
    MetadataCommand::new()
        .no_deps()
        .exec()
        .unwrap()
        .root_package()
        .expect("root package exists w/ no_deps called");
}
```

`Cargo.toml`
```toml
[package]
name = "root_package_mre"
version = "0.1.0"
edition = "2021"

# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html

[dependencies]
cargo_metadata = "0.15.0"
```

The above crate panics at the second `expect` when run on itself. This is unexpected because there is a clear root crate and the choice to include/exclude dependencies doesn't seem like it should affect its detection.

The [documentation](https://docs.rs/cargo_metadata/0.15.0/cargo_metadata/struct.MetadataCommand.html#method.no_deps) for `MetadataCommand` states "Output information only about the root package", but this is incorrect in the presence of workspaces: I ran into this while loading metadata for [ripgrep](https://github.com/BurntSushi/ripgrep), which at this time has a root package and a workspace. This crate identifies all of the workspace's packages with `no_deps`, running counter to the documentation, though this is almost certainly the correct behavior.

This occurs because `no_deps` leaves `Metadata.resolve` as `None`, and root package detection assumes the resolver will identify the package. I have not yet looked at the raw output of `cargo metadata` and so do not know if there is an alternative way to find the root package.

If this behavior is can't/WONTFIX, a documentation update to `Metadata::root_package` noting this case would be useful.

Pull request description:
Add fallback to root_package when no_deps is set
This fixes #198. I added a fallback path for the case when the resolver is null which assumes the path of a root package, as well as a simple positive test case. I also clarified a few items in documentation to match the behavior which I implemented.

As far as I can tell, this is the correct behavior- `cargo metadata` [describes](https://doc.rust-lang.org/cargo/commands/cargo-metadata.html#output-options) `--no-deps` as returning the workspace members, not the root package. I doubt any packages rely on the current behavior, given it's somewhat unexpected, so this shouldn't be a breaking change.

Patch:
diff --git a/src/lib.rs b/src/lib.rs
index 4f7265c..4a9cb15 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -155,10 +155,22 @@ pub struct Metadata {
 }
 
 impl Metadata {
-    /// Get the root package of this metadata instance.
+    /// Get the workspace's root package of this metadata instance.
     pub fn root_package(&self) -> Option<&Package> {
-        let root = self.resolve.as_ref()?.root.as_ref()?;
-        self.packages.iter().find(|pkg| &pkg.id == root)
+        match &self.resolve {
+            Some(resolve) => {
+                // if dependencies are resolved, use Cargo's answer
+                let root = resolve.root.as_ref()?;
+                self.packages.iter().find(|pkg| &pkg.id == root)
+            }
+            None => {
+                // if dependencies aren't resolved, check for a root package manually
+                let root_manifest_path = self.workspace_root.join("Cargo.toml");
+                self.packages
+                    .iter()
+                    .find(|pkg| pkg.manifest_path == root_manifest_path)
+            }
+        }
     }
 
     /// Get the workspace packages.
@@ -533,7 +545,7 @@ pub struct MetadataCommand {
     manifest_path: Option<PathBuf>,
     /// Current directory of the `cargo metadata` process.
     current_dir: Option<PathBuf>,
-    /// Output information only about the root package and don't fetch dependencies.
+    /// Output information only about workspace members and don't fetch dependencies.
     no_deps: bool,
     /// Collections of `CargoOpt::SomeFeatures(..)`
     features: Vec<String>,
@@ -569,7 +581,7 @@ impl MetadataCommand {
         self.current_dir = Some(path.into());
         self
     }
-    /// Output information only about the root package and don't fetch dependencies.
+    /// Output information only about workspace members and don't fetch dependencies.
     pub fn no_deps(&mut self) -> &mut MetadataCommand {
         self.no_deps = true;
         self


Test patch:
diff --git a/tests/all/Cargo.toml b/tests/all/Cargo.toml
index b5e833b..9077aa4 100644
--- a/tests/all/Cargo.toml
+++ b/tests/all/Cargo.toml
@@ -1,3 +1,4 @@
+# Used in tests/test_samples.rs
 [package]
 name = "all"
 version = "0.1.0"
diff --git a/tests/basic_workspace/Cargo.toml b/tests/basic_workspace/Cargo.toml
new file mode 100644
index 0000000..d0a34ed
--- /dev/null
+++ b/tests/basic_workspace/Cargo.toml
@@ -0,0 +1,8 @@
+[package]
+name = "ex_bin"
+version = "0.1.0"
+
+[dependencies]
+ex_lib = { version = "0.1.0", path = "./ex_lib" }
+
+[workspace]
diff --git a/tests/basic_workspace/ex_lib/Cargo.toml b/tests/basic_workspace/ex_lib/Cargo.toml
new file mode 100644
index 0000000..811404c
--- /dev/null
+++ b/tests/basic_workspace/ex_lib/Cargo.toml
@@ -0,0 +1,7 @@
+[package]
+name = "ex_lib"
+version = "0.1.0"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]
diff --git a/tests/basic_workspace/ex_lib/src/lib.rs b/tests/basic_workspace/ex_lib/src/lib.rs
new file mode 100644
index 0000000..8b13789
--- /dev/null
+++ b/tests/basic_workspace/ex_lib/src/lib.rs
@@ -0,0 +1,1 @@
+
diff --git a/tests/basic_workspace/src/main.rs b/tests/basic_workspace/src/main.rs
new file mode 100644
index 0000000..f328e4d
--- /dev/null
+++ b/tests/basic_workspace/src/main.rs
@@ -0,0 +1,1 @@
+fn main() {}
diff --git a/tests/test_samples.rs b/tests/test_samples.rs
index a5c15b0..3c747c5 100644
--- a/tests/test_samples.rs
+++ b/tests/test_samples.rs
@@ -623,3 +623,25 @@ fn depkind_to_string() {
     assert_eq!(DependencyKind::Build.to_string(), "build");
     assert_eq!(DependencyKind::Unknown.to_string(), "Unknown");
 }
+
+#[test]
+fn basic_workspace_root_package_exists() {
+    // First try with dependencies
+    let meta = MetadataCommand::new()
+        .manifest_path("tests/basic_workspace/Cargo.toml")
+        .exec()
+        .unwrap();
+    assert_eq!(meta.root_package().unwrap().name, "ex_bin");
+    // Now with no_deps, it should still work exactly the same
+    let meta = MetadataCommand::new()
+        .manifest_path("tests/basic_workspace/Cargo.toml")
+        .no_deps()
+        .exec()
+        .unwrap();
+    assert_eq!(
+        meta.root_package()
+            .expect("workspace root still exists when no_deps used")
+            .name,
+        "ex_bin"
+    );
+}