cargo-completion: import from homebrew/completions.

Formula/cargo-completion.rb

@@ -0,0 +1,23 @@
+class CargoCompletion < Formula
+  desc "Bash and Zsh completion for Cargo"
+  homepage "https://github.com/rust-lang/cargo"
+  url "https://github.com/rust-lang/cargo/archive/0.15.0.tar.gz"
+  version "20161222.0.15.0"
+  sha256 "6ebe9e0de255d5bd912528bef0f57db7746e162c6d9875a89c6c8b2b40a21d64"
+
+  head "https://github.com/rust-lang/cargo.git"
+
+  bottle :unneeded
+
+  def install
+    bash_completion.install "src/etc/cargo.bashcomp.sh" => "cargo"
+    zsh_completion.install "src/etc/_cargo"
+  end
+
+  test do
+    # we need to define a dummy 'cargo' command to force the script to define
+    # the completion function
+    assert_match "-F _cargo",
+      shell_output("cargo() { true;} && source #{bash_completion}/cargo && complete -p cargo")
+  end
+end