feat: add version operation to managers

README.md

@@ -117,6 +117,16 @@ Unless otherwise noted for a particular method, each method:
   of what underlying package manager is being used; if an option is not
   supported by the manager, it will be ignored
 
+### Get the version of the package manager
+
+```ruby
+package_json.manager.version
+```
+
+This is suitable for checking that the package manager is actually available
+before performing other operations. Unlike other non-bang methods, this will
+error if the underlying command exits with a non-zero code.
+
 ### Installing dependencies
 
 ```ruby

lib/package_json/managers/base.rb

@@ -8,6 +8,19 @@ def initialize(package_json, manager_cmd:)
         @manager_cmd = manager_cmd
       end
 
+      def version
+        require "open3"
+
+        command = "#{@manager_cmd} --version"
+        stdout, stderr, status = Open3.capture3(command)
+
+        unless status.success?
+          raise PackageJson::Error, "#{command} failed with exit code #{status.exitstatus}: #{stderr}"
+        end
+
+        stdout.chomp
+      end
+
       # Installs the dependencies specified in the `package.json` file
       def install(
         frozen: false,

sig/package_json/managers/base.rbs

@@ -3,6 +3,8 @@ class PackageJson
     class Base
       def initialize: (PackageJson package_json, manager_cmd: String) -> self
 
+      def version: () -> String
+
       def install: (
           ?frozen: bool,
           ?ignore_scripts: bool,

sig/package_json/managers/npm_like.rbs

@@ -3,6 +3,8 @@ class PackageJson
     class NpmLike
       def initialize: (PackageJson package_json, ?manager_cmd: String) -> self
 
+      def version: () -> String
+
       def install: (
           ?frozen: bool,
           ?ignore_scripts: bool,

sig/package_json/managers/pnpm_like.rbs

@@ -3,6 +3,8 @@ class PackageJson
     class PnpmLike < Base
       def initialize: (PackageJson package_json, ?manager_cmd: String) -> self
 
+      def version: () -> String
+
       def install: (
           ?frozen: bool,
           ?ignore_scripts: bool,

sig/package_json/managers/yarn_classic_like.rbs

@@ -3,6 +3,8 @@ class PackageJson
     class YarnClassicLike
       def initialize: (PackageJson package_json, ?manager_cmd: String) -> self
 
+      def version: () -> String
+
       def install: (
           ?frozen: bool,
           ?ignore_scripts: bool,

spec/package_json/managers/base_spec.rb

@@ -3,7 +3,48 @@
 require "spec_helper"
 
 RSpec.describe PackageJson::Managers::Base do
-  subject(:base) { described_class.new(instance_double(PackageJson), manager_cmd: "") }
+  subject(:base) { described_class.new(instance_double(PackageJson), manager_cmd: "base") }
+
+  describe "#version" do
+    require "open3"
+
+    Struct.new("Status", :exit_code) do
+      def success?
+        exit_code.zero?
+      end
+
+      def exitstatus
+        exit_code
+      end
+    end
+
+    before do
+      allow(Open3).to receive(:capture3).and_return(["1.2.3\n", "", Struct::Status.new(0)])
+    end
+
+    it "calls the package manager with --version" do
+      base.version
+
+      expect(Open3).to have_received(:capture3).with("base --version")
+    end
+
+    it "returns the output without a trailing newline" do
+      expect(base.version).to eq("1.2.3")
+    end
+
+    context "when the package manager errors" do
+      before do
+        allow(Open3).to receive(:capture3).and_return(["", "oh noes!", Struct::Status.new(1)])
+      end
+
+      it "raises an error" do
+        expect { base.version }.to raise_error(
+          PackageJson::Error,
+          "base --version failed with exit code 1: oh noes!"
+        )
+      end
+    end
+  end
 
   describe "#install" do
     it "does not have an implementation" do

spec/package_json/managers/npm_like_spec.rb

@@ -12,6 +12,12 @@
 
   before { allow_kernel_to_receive_system }
 
+  describe "#version" do
+    it "returns the version" do
+      expect(manager.version).to start_with("9.")
+    end
+  end
+
   describe "#install" do
     it "runs and returns true" do
       with_package_json_file do

spec/package_json/managers/pnpm_like_spec.rb

@@ -12,6 +12,12 @@
 
   before { allow_kernel_to_receive_system }
 
+  describe "#version" do
+    it "returns the version" do
+      expect(manager.version).to start_with("8.")
+    end
+  end
+
   describe "#install" do
     it "runs and returns true" do
       with_package_json_file do

spec/package_json/managers/yarn_classic_like_spec.rb

@@ -12,6 +12,12 @@
 
   before { allow_kernel_to_receive_system }
 
+  describe "#version" do
+    it "returns the version" do
+      expect(manager.version).to start_with("1.22")
+    end
+  end
+
   describe "#install" do
     it "runs and returns true" do
       with_package_json_file do