Refactor the compiler detection module

ext/libv8/compiler.rb

@@ -19,24 +19,39 @@ module Libv8
     end
 
     def available_compilers(*compiler_names)
-      compiler_names.map { |name| find name }.reject(&:nil?)
+      available = compiler_names.select { |compiler_name| available? compiler_name }
+      available.map { |compiler_name| type_of(compiler_name).new compiler_name }
     end
 
-    def find(name)
-      return nil if name.empty?
-      path, _, status = Open3.capture3 "which #{name}"
-      path.chomp!
-      determine_type(path).new(path) if status.success?
-    end
-
-    def determine_type(compiler_path)
-      compiler_version = Open3.capture3("#{compiler_path} -v")[0..1].join
-
-      case compiler_version
+    def type_of(compiler_name)
+      case version_string_of(compiler_name)
       when /\bclang\b/i then Clang
       when /^gcc/i      then GCC
       else                   GenericCompiler
       end
     end
+
+    def version_string_of(compiler_name)
+      command_result = execute_command "#{compiler_name} -v 2>&1"
+
+      unless command_result.status.success?
+        raise "Could not get version string of compiler #{compiler_name}"
+      end
+
+      command_result.output
+    end
+
+    def available?(command)
+      execute_command("which #{command} 2>&1").status.success?
+    end
+
+    def execute_command(command)
+      output = `#{command}`
+      status = $?
+      ExecutionResult.new output, status
+    end
+
+    class ExecutionResult < Struct.new(:output, :status)
+    end
   end
 end

spec/compiler_spec.rb

@@ -0,0 +1,64 @@
+$:.unshift File.expand_path '../../ext/libv8', __FILE__
+
+require 'spec_helper'
+require 'compiler'
+
+RSpec.configure do |c|
+  c.include CompilerHelpers
+end
+
+module Libv8
+  describe Compiler do
+    describe '::type_of' do
+      it 'returns a GCC class for GCC 4.9.0' do
+        stub_as_available 'c++', :gcc, '4.9.0'
+        Compiler.available_compilers('c++').first.should be_a Compiler::GCC
+      end
+
+      it 'returns a Clang class for Clang 3.4.1' do
+        stub_as_available 'c++', :clang, '3.4.1'
+        Compiler.available_compilers('c++').first.should be_a Compiler::Clang
+      end
+    end
+
+    describe '::available_compilers' do
+      it 'returns instances of the available compilers' do
+        stub_as_available 'c++', :clang, '3.4.1'
+        stub_as_unavailable 'g++'
+        stub_as_available 'clang++', :clang, '3.4.1'
+
+        available_compilers = Compiler.available_compilers 'c++', 'g++', 'clang++'
+        available_compilers.map(&:class).should have(2).items
+        available_compilers.all? { |compiler| compiler.should be_a Compiler::Clang }
+      end
+    end
+
+    describe '::version_string_of' do
+      context 'when calling the compiler command succedes' do
+        it 'returns the version string of the compiler' do
+          stub_as_available 'c++', :clang, '3.4.1'
+          Compiler.version_string_of('c++').should eq version_output_of(:clang, '3.4.1')
+        end
+      end
+
+      context 'when calling the compiler command fails' do
+        it 'raises an exception' do
+          stub_as_unavailable 'c++'
+          expect { Compiler.version_string_of('c++') }.to raise_exception
+        end
+      end
+    end
+
+    describe '::available?' do
+      it 'returns true when the command is available' do
+        stub_as_available 'c++', :clang, '3.4.1'
+        Compiler::available?('c++').should be_true
+      end
+
+      it 'returns false when the command cannot be found ' do
+        stub_as_unavailable 'c++'
+        Compiler::available?('c++').should be_false
+      end
+    end
+  end
+end

spec/spec_helper.rb

@@ -2,3 +2,41 @@ $:.unshift File.expand_path '../../lib', __FILE__
 require 'rspec'
 require 'rspec-spies'
 require 'libv8'
+
+module CompilerHelpers
+  VERSION_OUTPUTS = {
+    :gcc => {
+      "4.9.0" => %Q{Using built-in specs.\nCOLLECT_GCC=c++\nCOLLECT_LTO_WRAPPER=/usr/lib/gcc/x86_64-unknown-linux-gnu/4.9.0/lto-wrapper\nTarget: x86_64-unknown-linux-gnu\nConfigured with: /build/gcc-multilib/src/gcc-4.9-20140604/configure --prefix=/usr --libdir=/usr/lib --libexecdir=/usr/lib --mandir=/usr/share/man --infodir=/usr/share/info --with-bugurl=https://bugs.archlinux.org/ --enable-languages=c,c++,ada,fortran,go,lto,objc,obj-c++ --enable-shared --enable-threads=posix --with-system-zlib --enable-__cxa_atexit --disable-libunwind-exceptions --enable-clocale=gnu --disable-libstdcxx-pch --disable-libssp --enable-gnu-unique-object --enable-linker-build-id --enable-cloog-backend=isl --disable-cloog-version-check --enable-lto --enable-plugin --enable-install-libiberty --with-linker-hash-style=gnu --enable-multilib --disable-werror --enable-checking=release\nThread model: posix\ngcc version 4.9.0 20140604 (prerelease) (GCC)\n}
+    },
+    :clang => {
+      "3.4.1" => %Q{clang version 3.4.1 (tags/RELEASE_34/dot1-final)\nTarget: x86_64-unknown-linux-gnu\nThread model: posix\nFound candidate GCC installation: /usr/bin/../lib/gcc/x86_64-unknown-linux-gnu/4.9.0\nFound candidate GCC installation: /usr/bin/../lib64/gcc/x86_64-unknown-linux-gnu/4.9.0\nFound candidate GCC installation: /usr/lib/gcc/x86_64-unknown-linux-gnu/4.9.0\nFound candidate GCC installation: /usr/lib64/gcc/x86_64-unknown-linux-gnu/4.9.0\nSelected GCC installation: /usr/bin/../lib64/gcc/x86_64-unknown-linux-gnu/4.9.0\n}
+    }
+  }
+
+  def version_output_of(name, version)
+    VERSION_OUTPUTS[name][version]
+  end
+
+  def success_status
+    double success?: true
+  end
+
+  def failure_status
+    double success?: false
+  end
+
+  def stub_shell_command(command, output, status)
+    allow(Libv8::Compiler).to receive(:execute_command).with(command) do
+      double output: output, status: status
+    end
+  end
+
+  def stub_as_available(command, name, version)
+    stub_shell_command "which #{command} 2>&1", '', success_status
+    stub_shell_command "#{command} -v 2>&1", version_output_of(name, version), success_status
+  end
+
+  def stub_as_unavailable(command)
+    stub_shell_command "which #{command} 2>&1", '', failure_status
+  end
+end