Print all matches instead of erring

src/main.rs

@@ -5,7 +5,7 @@ use cargo::core::package::PackageSet;
 use cargo::core::registry::PackageRegistry;
 use cargo::core::resolver::Method;
 use cargo::core::shell::Shell;
-use cargo::core::{Package, PackageId, Resolve, Workspace};
+use cargo::core::{Package, PackageId, PackageIdSpec, Resolve, Workspace};
 use cargo::ops;
 use cargo::util::{self, important_paths, CargoResult, Cfg, Rustc};
 use cargo::{CliResult, Config};
@@ -209,9 +209,9 @@ fn real_main(args: Args, config: &mut Config) -> CliResult {
     let ids = packages.package_ids().collect::<Vec<_>>();
     let packages = registry.get(&ids)?;
 
-    let root = match args.package {
-        Some(ref pkg) => resolve.query(pkg)?,
-        None => package.package_id(),
+    let roots = match args.package {
+        Some(ref pkg) => query_all(&resolve, pkg)?,
+        None => vec![package.package_id()],
     };
 
     let rustc = config.load_global_rustc(Some(&workspace))?;
@@ -252,14 +252,20 @@ fn real_main(args: Args, config: &mut Config) -> CliResult {
         Prefix::Indent
     };
 
-    if args.duplicates {
-        let dups = find_duplicates(&graph);
-        for dup in &dups {
-            print_tree(dup, &graph, &format, direction, symbols, prefix, args.all)?;
+    let packages = if args.duplicates {
+        find_duplicates(&graph)
+    } else {
+        roots
+    };
+
+    if packages.len() != 1 {
+        for package in &packages {
+            print_tree(package, &graph, &format, direction, symbols, prefix, args.all)?;
             println!();
         }
     } else {
-        print_tree(&root, &graph, &format, direction, symbols, prefix, args.all)?;
+        let package = &packages[0];
+        print_tree(package, &graph, &format, direction, symbols, prefix, args.all)?;
     }
 
     Ok(())
@@ -346,6 +352,17 @@ fn resolve<'a, 'cfg>(
     Ok((packages, resolve))
 }
 
+fn query_all(resolve: &Resolve, spec: &str) -> CargoResult<Vec<PackageId>> {
+    let spec = PackageIdSpec::parse(spec)?;
+    let mut result = vec![];
+    for package in resolve.iter() {
+        if spec.matches(package) {
+            result.push(package);
+        }
+    }
+    Ok(result)
+}
+
 struct Node<'a> {
     id: PackageId,
     metadata: &'a ManifestMetadata,