Tweak rubygems input behavior

When a fixed version is passed, it should be the minimum RubyGems
version for the whole matrix, i.e., RubyGems should not be dowgraded
past the default version of the oldest Ruby in the matrix.

Author: deivid-rodriguez

.github/workflows/test.yml

@@ -123,16 +123,27 @@ jobs:
         rubygems: latest
     - run: ruby -e "exit(Gem.rubygems_version > Gem::Version.new('3.0.3'))"
 
-  testFixedRubygemsVersion:
-    name: "Test rubygems input set to a fixed version upgrades RubyGems to that versoin"
+  testFixedRubygemsVersionUpgrades:
+    name: "Test rubygems input set to a fixed version upgrades RubyGems to that version if the default is older"
     runs-on: ubuntu-latest
     steps:
     - uses: actions/checkout@v2
     - uses: ./
       with:
         ruby-version: 2.6
-        rubygems: 3.3.5
-    - run: gem --version | grep -F "3.3.5"
+        rubygems: 3.2.3
+    - run: gem --version | grep -F "3.2.3"
+
+  testFixedRubygemsVersionNoop:
+    name: "Test rubygems input set to a fixed version noops if the default is newer"
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@v2
+    - uses: ./
+      with:
+        ruby-version: 3.1
+        rubygems: 3.2.3
+    - run: gem --version | grep -F "3.3.3"
 
   testExactBundlerVersion:
     name: "Test with an exact Bundler version"

action.yml

@@ -14,7 +14,7 @@ inputs:
       The version of RubyGems to use. Either 'default', 'latest', or a version number (e.g., 3.3.5).
       For 'default', no action is taken and the version of RubyGems that comes with Ruby by default is used.
       For 'latest', `gem update --system` is run to update to the latest RubyGems version.
-      Similarly, if a version number is given, `gem update --system <version>` is run to update to that version of RubyGems.
+      Similarly, if a version number is given, `gem update --system <version>` is run to update to that version of RubyGems, as long as that version is newer than the one provided by default.
       Defaults to 'default'.
   bundler:
     description: |

dist/index.js

@@ -26,7 +26,8 @@
     "@actions/core": "^1.4.0",
     "@actions/exec": "^1.1.0",
     "@actions/io": "^1.1.1",
-    "@actions/tool-cache": "^1.7.1"
+    "@actions/tool-cache": "^1.7.1",
+    "semver": "^6.1.0"
   },
   "devDependencies": {
     "@vercel/ncc": "^0.31.1"

package.json

@@ -1,11 +1,30 @@
 const path = require('path')
 const exec = require('@actions/exec')
+const semver = require('semver')
 
 export async function rubygemsUpdate(rubygemsVersionInput, rubyPrefix) {
   const gem = path.join(rubyPrefix, 'bin', 'gem')
-  const rubygemsVersion = (rubygemsVersionInput === 'latest') ? [] : [rubygemsVersionInput]
 
-  await exec.exec(gem, ['update', '--system', ...rubygemsVersion])
+  let gemVersion = ''
+
+  await exec.exec(gem, ['--version'], {
+    listeners: {
+      stdout: (data) => (gemVersion += data.toString()),
+    }
+  });
+
+  gemVersion = semver.coerce(gemVersion.trim())
+  console.log(`Default RubyGems version is ${gemVersion}`)
+
+  if (rubygemsVersionInput === 'latest') {
+    console.log('Updating RubyGems to latest version')
+    await exec.exec(gem, ['update', '--system'])
+  } else if (semver.gt(rubygemsVersionInput, gemVersion)) {
+    console.log(`Updating RubyGems to ${rubygemsVersionInput}`)
+    await exec.exec(gem, ['update', '--system', rubygemsVersionInput])
+  } else {
+    console.log(`Skipping RubyGems update because the given version (${rubygemsVersionInput}) is not newer than the default version (${gemVersion})`)
+  }
 
   return true
 }