Add support for PNPM for installation commands

fixtures/package-helper/pnpm-yarn-npm/yarn.lock

@@ -0,0 +1,2 @@
+# THIS IS AN AUTOGENERATED FILE. DO NOT EDIT THIS FILE DIRECTLY.
+# yarn lockfile v1

lib/package-helper.js

@@ -32,8 +32,8 @@ ${missingPackagesRecommendation.message}
 }
 
 function getInstallCommand(packageConfigs) {
+    const hasPnpmLockfile = fs.existsSync('pnpm-lock.yaml');
     const hasYarnLockfile = fs.existsSync('yarn.lock');
-    const hasNpmLockfile = fs.existsSync('package-lock.json');
     const packageInstallStrings = packageConfigs.map((packageConfig) => {
         const firstPackage = packageConfig[0];
 
@@ -51,11 +51,15 @@ function getInstallCommand(packageConfigs) {
         return `${firstPackage.name}@${recommendedVersion}`;
     });
 
-    if (hasNpmLockfile && !hasYarnLockfile) {
-        return chalk.yellow(`npm install ${packageInstallStrings.join(' ')} --save-dev`);
+    if (hasPnpmLockfile) {
+        return chalk.yellow(`pnpm add ${packageInstallStrings.join(' ')} --save-dev`);
     }
 
-    return chalk.yellow(`yarn add ${packageInstallStrings.join(' ')} --dev`);
+    if (hasYarnLockfile) {
+        return chalk.yellow(`yarn add ${packageInstallStrings.join(' ')} --dev`);
+    }
+
+    return chalk.yellow(`npm install ${packageInstallStrings.join(' ')} --save-dev`);
 }
 
 function isPackageInstalled(packageConfig) {

test/package-helper.js

@@ -29,7 +29,7 @@ describe('package-helper', () => {
             const packageRecommendations = packageHelper.getMissingPackageRecommendations([
                 { name: 'foo' }, { name: 'webpack' }, { name: 'bar' }
             ]);
-            expect(packageRecommendations.installCommand).to.contain('yarn add foo bar');
+            expect(packageRecommendations.installCommand).to.contain('npm install foo bar');
             expect(stripAnsi(packageRecommendations.message)).to.contain('foo & bar');
         });
 
@@ -51,6 +51,15 @@ describe('package-helper', () => {
             expect(stripAnsi(packageRecommendations.message)).to.contain('foo & bar');
         });
 
+        it('missing packages with pnpm-lock.yaml only', () => {
+            process.chdir(path.join(__dirname, '../fixtures/package-helper/pnpm'));
+            const packageRecommendations = packageHelper.getMissingPackageRecommendations([
+                { name: 'foo' }, { name: 'webpack' }, { name: 'bar' }
+            ]);
+            expect(packageRecommendations.installCommand).to.contain('pnpm add foo bar');
+            expect(stripAnsi(packageRecommendations.message)).to.contain('foo & bar');
+        });
+
         it('missing packages with both package-lock.json and yarn.lock', () => {
             process.chdir(path.join(__dirname, '../fixtures/package-helper/yarn-npm'));
             const packageRecommendations = packageHelper.getMissingPackageRecommendations([
@@ -60,6 +69,15 @@ describe('package-helper', () => {
             expect(stripAnsi(packageRecommendations.message)).to.contain('foo & bar');
         });
 
+        it('missing packages with package-lock.json, yarn.lock and pnpm-lock.yaml', () => {
+            process.chdir(path.join(__dirname, '../fixtures/package-helper/pnpm-yarn-npm'));
+            const packageRecommendations = packageHelper.getMissingPackageRecommendations([
+                { name: 'foo' }, { name: 'webpack' }, { name: 'bar' }
+            ]);
+            expect(packageRecommendations.installCommand).to.contain('pnpm add foo bar');
+            expect(stripAnsi(packageRecommendations.message)).to.contain('foo & bar');
+        });
+
         it('missing packages with alternative packages', () => {
             process.chdir(path.join(__dirname, '../fixtures/package-helper/yarn'));
             const packageRecommendations = packageHelper.getMissingPackageRecommendations([