rust with cargo

This follows discussion on Homebrew#33322, where it has been hypothesized that
the best course of action may very well be to include cargo in the rust
formula. Reasons include:

- upstream packages releases with cargo
- cargo has no formal versioning rules, merely binding a particular
  cargo nightly to a given rust release
- cargo needs a non feature-gated rust to build
- cargo needs to fetch cargo to bootstrap itself (at the make stage)

The most practical way to get the cargo version bound to a rust release
is to download a binary rust release and run cargo -V, which shows the
SHA1 it was built from. This is what has been done for the beta.

Alternatively, building with --HEAD relaxes all version constrains and
builds both from their respective master HEADs.

Curl is a dependency of .travis.install.deps.sh while both curl and
python are a dependency of make (via src/etc/dl-snapshot.py) to download
a cargo snapshot. Each one makes respective use of a src/rustversion.txt
and a src/snapshots.txt file, combined with some very lighteight
processing, to find the required downloads.

Thus it is be possible to include fetched downloads as resources to
improve cacheability and reduce the dependency profile as long as one
maintains consistency between each build component.

Library/Formula/rust.rb

@@ -1,19 +1,45 @@
-require 'formula'
-
 class Rust < Formula
   homepage 'http://www.rust-lang.org/'
-  url 'https://static.rust-lang.org/dist/rustc-1.0.0-beta.3-src.tar.gz'
   version "1.0.0-beta.3"
-  sha256 'e751bc8a8ad236c8865697f866b2863e224af56b0194ddf9f3edd71f9ff6545f'
 
-  head 'https://github.com/rust-lang/rust.git'
+  stable do
+    url 'https://static.rust-lang.org/dist/rustc-1.0.0-beta.3-src.tar.gz'
+    sha256 'e751bc8a8ad236c8865697f866b2863e224af56b0194ddf9f3edd71f9ff6545f'
+
+    resource "cargo" do
+      url "https://github.com/rust-lang/cargo.git", :revision => "83a6d0ed8208d31a1f6dab5e5183ad9eb2d65eaf", :tag => "0.2.0"
+    end
+
+    # name includes date to satisfy cache
+    resource "cargo-nightly-2015-04-02" do
+      url "https://static-rust-lang-org.s3.amazonaws.com/cargo-dist/2015-04-02/cargo-nightly-x86_64-apple-darwin.tar.gz"
+      sha256 "18647dccb34acb6085a04b0ea1bfb9d150dc9c17f7829932ddf7e62d518df2fe"
+    end
+
+    # name includes date to satisfy cache
+    resource "rustc-nightly-2015-04-04" do
+      url "https://static-rust-lang-org.s3.amazonaws.com/dist/2015-04-04/rustc-nightly-x86_64-apple-darwin.tar.gz"
+      sha256 "87068b325802fee65a388d249b98a184aff7670140133de78560ef375bae70a5"
+    end
+  end
+
+  head do
+    url "https://github.com/rust-lang/rust.git"
+    resource "cargo" do
+      url "https://github.com/rust-lang/cargo.git"
+    end
+  end
 
   bottle do
     sha256 "60450a633c8c5f42e208b647699fd872e594fd5475f460b0367bbbf02063a466" => :yosemite
     sha256 "1c265ffd3c678acd05b6525c2de6730881b540d1b8419f2b496cf244b46d88c2" => :mavericks
     sha256 "2385a4baa211953a94bb93f5ce6f5ca5d5826f3e1d7c0d12310e78c5571f3c89" => :mountain_lion
   end
 
+  depends_on "openssl"
+  depends_on "cmake" => :build
+  depends_on "pkg-config" => :build
+
   def install
     args = ["--prefix=#{prefix}"]
     args << "--disable-rpath" if build.head?
@@ -22,6 +48,37 @@ def install
     system "./configure", *args
     system "make"
     system "make install"
+
+    resource("cargo").stage do
+      cargo_stage_path = pwd
+
+      if build.stable?
+        resource("rustc-nightly-2015-04-04").stage do
+          system "./install.sh", "--prefix=#{cargo_stage_path}/rustc"
+        end
+
+        resource("cargo-nightly-2015-04-02").stage do
+          system "./install.sh", "--prefix=#{cargo_stage_path}/target/snapshot/cargo"
+          # satisfy make target to skip download
+          touch "#{cargo_stage_path}/target/snapshot/cargo/bin/cargo"
+        end
+      end
+
+      args = ["--prefix=#{prefix}"]
+
+      if build.head?
+        args << "--local-rust-root=#{prefix}"
+      else
+        args << "--local-rust-root=#{cargo_stage_path}/rustc"
+      end
+
+      system "./configure", *args
+      system "make"
+      system "make", "install"
+    end
+
+    rm_rf prefix/"lib/rustlib/uninstall.sh"
+    rm_rf prefix/"lib/rustlib/install.log"
   end
 
   test do
@@ -33,5 +90,8 @@ def install
     EOS
     system "#{bin}/rustc", "hello.rs"
     assert_equal "Hello World!\n", `./hello`
+    system "#{bin}/cargo", "new", "hello_world", "--bin"
+    assert_equal "Hello, world!",
+                 (testpath/"hello_world").cd { `#{bin}/cargo run`.split("\n").last }
   end
 end