Add method for parsing namespaced names

This adds the new `Purl::builder_with_combined_name` function that
allows parsing package names that include the namespace in their name.

The parsing is done according to its package type, which is why this
function is only implemented for `Purl` rather than `GenericPurl<T>`.

purl/src/lib.rs

@@ -321,6 +321,41 @@ impl<T> GenericPurl<T> {
     }
 }
 
+impl Purl {
+    /// Create a new [`PurlBuilder`] with a combined name and namespace.
+    pub fn builder_with_combined_name<S>(
+        package_type: PackageType,
+        namespaced_name: S,
+    ) -> PurlBuilder
+    where
+        S: Into<SmallString>,
+    {
+        // Split apart namespace and name based on ecosystem.
+        let namespaced_name = namespaced_name.into();
+        let (namespace, name) = match package_type {
+            PackageType::Cargo | PackageType::Gem | PackageType::NuGet | PackageType::PyPI => {
+                (None, namespaced_name)
+            },
+            PackageType::Golang | PackageType::Npm => match namespaced_name.rsplit_once('/') {
+                Some((namespace, name)) => (Some(namespace), name.into()),
+                None => (None, namespaced_name),
+            },
+            PackageType::Maven => match namespaced_name.split_once(':') {
+                Some((namespace, name)) => (Some(namespace), name.into()),
+                None => (None, namespaced_name),
+            },
+        };
+
+        // Create the PURL builder.
+        let mut builder = GenericPurlBuilder::new(package_type, name);
+        if let Some(namespace) = namespace {
+            builder = builder.with_namespace(namespace);
+        }
+
+        builder
+    }
+}
+
 /// Check whether a package type string is valid according to the rules of the
 /// PURL spec.
 #[must_use]
@@ -554,4 +589,18 @@ mod tests {
         let purl = GenericPurl::new(Cow::Borrowed("type"), "name").unwrap();
         assert_eq!(None, purl.subpath());
     }
+
+    #[test]
+    fn namespaced_name() {
+        let purl =
+            Purl::builder_with_combined_name(PackageType::Npm, "@angular/cli").build().unwrap();
+        assert_eq!(purl.namespace(), Some("@angular"));
+        assert_eq!(purl.name(), "cli");
+
+        let purl = Purl::builder_with_combined_name(PackageType::Maven, "org.maven.plugins:pom")
+            .build()
+            .unwrap();
+        assert_eq!(purl.namespace(), Some("org.maven.plugins"));
+        assert_eq!(purl.name(), "pom");
+    }
 }