[rust gem] Make cargo test work by default

Manifest.txt

@@ -221,6 +221,7 @@ bundler/lib/bundler/templates/newgem/bin/setup.tt
 bundler/lib/bundler/templates/newgem/circleci/config.yml.tt
 bundler/lib/bundler/templates/newgem/exe/newgem.tt
 bundler/lib/bundler/templates/newgem/ext/newgem/Cargo.toml.tt
+bundler/lib/bundler/templates/newgem/ext/newgem/build.rs.tt
 bundler/lib/bundler/templates/newgem/ext/newgem/extconf-c.rb.tt
 bundler/lib/bundler/templates/newgem/ext/newgem/extconf-rust.rb.tt
 bundler/lib/bundler/templates/newgem/ext/newgem/newgem.c.tt

bundler/lib/bundler/cli/gem.rb

@@ -205,6 +205,7 @@ def run
         templates.merge!(
           "Cargo.toml.tt" => "Cargo.toml",
           "ext/newgem/Cargo.toml.tt" => "ext/#{name}/Cargo.toml",
+          "ext/newgem/build.rs.tt" => "ext/#{name}/build.rs",
           "ext/newgem/extconf-rust.rb.tt" => "ext/#{name}/extconf.rb",
           "ext/newgem/src/lib.rs.tt" => "ext/#{name}/src/lib.rs",
         )

bundler/lib/bundler/templates/newgem/ext/newgem/Cargo.toml.tt

@@ -12,4 +12,11 @@ publish = false
 crate-type = ["cdylib"]
 
 [dependencies]
-magnus = { version = "0.6.2" }
+magnus = { version = "0.6.3" }
+rb-sys = { version = "0.9", features = ["stable-api-compiled-fallback"] }
+
+[build-dependencies]
+rb-sys-env = "0.1.2"
+
+[dev-dependencies]
+rb-sys-test-helpers = { version = "0.2.0" }

bundler/lib/bundler/templates/newgem/ext/newgem/build.rs.tt

@@ -0,0 +1,5 @@
+pub fn main() -> Result<(), Box<dyn std::error::Error>> {
+    let _rb_env = rb_sys_env::activate()?;
+
+    Ok(())
+}

bundler/lib/bundler/templates/newgem/ext/newgem/src/lib.rs.tt

@@ -10,3 +10,14 @@ fn init(ruby: &Ruby) -> Result<(), Error> {
     module.define_singleton_method("hello", function!(hello, 1))?;
     Ok(())
 }
+
+#[cfg(test)]
+mod tests {
+    use rb_sys_test_helpers::ruby_test;
+
+    #[ruby_test]
+    fn test_hello() {
+        use magnus::RString;
+        assert_eq!(12, RString::new("rust ❤️ ruby").length())
+    }
+}

bundler/spec/commands/newgem_spec.rb

@@ -1454,6 +1454,7 @@ def create_temporary_dir(dir)
         expect(bundled_app("#{gem_name}/ext/#{gem_name}/Cargo.toml")).to exist
         expect(bundled_app("#{gem_name}/ext/#{gem_name}/extconf.rb")).to exist
         expect(bundled_app("#{gem_name}/ext/#{gem_name}/src/lib.rs")).to exist
+        expect(bundled_app("#{gem_name}/ext/#{gem_name}/build.rs")).to exist
       end
 
       it "includes rake-compiler, rb_sys gems and required_rubygems_version constraint" do
@@ -1482,6 +1483,28 @@ def create_temporary_dir(dir)
 
         expect(bundled_app("#{gem_name}/Rakefile").read).to eq(rakefile)
       end
+
+      it "configures the crate such that `cargo test` works", :ruby_repo, :mri_only do
+        env = setup_rust_env
+        gem_path = bundled_app(gem_name)
+        result = sys_exec("cargo test", env: env, dir: gem_path)
+
+        expect(result).to include("1 passed")
+      end
+
+      def setup_rust_env
+        skip "rust toolchain of mingw is broken" if RUBY_PLATFORM.match?("mingw")
+
+        env = {
+          "CARGO_HOME" => ENV.fetch("CARGO_HOME", File.join(ENV["HOME"], ".cargo")),
+          "RUSTUP_HOME" => ENV.fetch("RUSTUP_HOME", File.join(ENV["HOME"], ".rustup")),
+          "RUSTUP_TOOLCHAIN" => ENV.fetch("RUSTUP_TOOLCHAIN", "stable"),
+        }
+
+        system(env, "cargo", "-V", out: IO::NULL, err: [:child, :out])
+        skip "cargo not present" unless $?.success?
+        env
+      end
     end
   end
 

bundler/spec/support/filters.rb

@@ -33,6 +33,7 @@ def inspect
   config.filter_run_excluding jruby_only: RUBY_ENGINE != "jruby"
   config.filter_run_excluding truffleruby_only: RUBY_ENGINE != "truffleruby"
   config.filter_run_excluding man: Gem.win_platform?
+  config.filter_run_excluding mri_only: RUBY_ENGINE != "ruby"
 
   config.filter_run_when_matching :focus unless ENV["CI"]
 end