Add internal option to only use the main mirror

We use that in some places to avoid mirror issues and things being
out of sync, like msys2-installer and msys2-autobuild.

Move into the action so we can maintain it in one place.

Use an env var instead of an action input, so it's more hidden,
and doesn't confuse users.

Please don't use this as a normal action user, as it adds strain
to our main mirror.

Fixes #571

Author: lazka

.github/workflows/Test.yml

@@ -699,3 +699,47 @@ jobs:
       run: |
         uname -a
         openssl help
+
+
+  main-mirror:
+    name: 🔒 main-mirror-only
+    needs: [cache]
+    runs-on: windows-latest
+    steps:
+    - name: 🧰 Checkout
+      uses: actions/checkout@v6
+      with:
+        persist-credentials: false
+    - name: 📥 Download artifact
+      uses: actions/download-artifact@v7
+      with:
+        name: action
+    - name: 🚧 run action
+      uses: ./
+      with:
+        update: true
+        install: git
+      env:
+        __SETUP_MSYS2_USE_MAIN_MIRROR_ONLY: 'true'
+    - shell: msys2 {0}
+      run: |
+        # Verify pacman-conf.exe output doesn't contain mirror.msys2.org
+        echo "Checking pacman-conf.exe output:"
+        pacman-conf.exe
+        if pacman-conf.exe | grep -q 'mirror\.msys2\.org'; then
+          echo "ERROR: pacman-conf.exe output contains mirror.msys2.org"
+          exit 1
+        fi
+        echo "✓ No mirror.msys2.org found in pacman-conf.exe output"
+
+        # Verify mirrorlist files only contain repo.msys2.org
+        echo "Checking mirrorlist.mingw:"
+        cat /etc/pacman.d/mirrorlist.mingw
+        grep -q 'repo.msys2.org/mingw' /etc/pacman.d/mirrorlist.mingw
+        [ $(wc -l < /etc/pacman.d/mirrorlist.mingw) -eq 1 ] || exit 1
+        echo "Checking mirrorlist.msys:"
+        cat /etc/pacman.d/mirrorlist.msys
+        grep -q 'repo.msys2.org/msys' /etc/pacman.d/mirrorlist.msys
+        [ $(wc -l < /etc/pacman.d/mirrorlist.msys) -eq 1 ] || exit 1
+
+        git --version

main.js

@@ -44,6 +44,8 @@ class Input {
         this.location;
         /** @type {boolean} */
         this.cache;
+        /** @type {boolean} */
+        this.usemainmirroronly;
     }
 }
 
@@ -61,6 +63,14 @@ function parseInput() {
   let p_location = core.getInput('location');
   let p_cache = core.getBooleanInput('cache');
 
+  // Configures pacman to use only repo.msys2.org instead of the mirrorlist.
+  // See: https://github.com/msys2/setup-msys2/issues/571
+  let p_use_main_mirror_only = false;
+  const envValue = process.env['__SETUP_MSYS2_USE_MAIN_MIRROR_ONLY'];
+  if (envValue === 'true' || envValue === '1') {
+    p_use_main_mirror_only = true;
+  }
+
   const msystem_allowed = ['MSYS', 'MINGW32', 'MINGW64', 'UCRT64', 'CLANG64', 'CLANGARM64'];
   if (!msystem_allowed.includes(p_msystem.toUpperCase())) {
     throw new Error(`'msystem' needs to be one of ${ msystem_allowed.join(', ') }, got ${p_msystem}`);
@@ -85,6 +95,7 @@ function parseInput() {
   input.platformcheckseverity = p_platformcheckseverity;
   input.location = (p_location == "RUNNER_TEMP") ? process.env['RUNNER_TEMP'] : p_location;
   input.cache = p_cache;
+  input.usemainmirroronly = p_use_main_mirror_only;
 
   return input;
 }
@@ -136,6 +147,18 @@ async function disableKeyRefresh(msysRootDir) {
   await fs.promises.writeFile(postFile, newContent, 'utf8');
 }
 
+/**
+ * @param {string} msysRootDir
+ * @returns {Promise<void>}
+ */
+async function configureMainMirror(msysRootDir) {
+  const mirrorlistMingw = path.join(msysRootDir, 'etc', 'pacman.d', 'mirrorlist.mingw');
+  const mirrorlistMsys = path.join(msysRootDir, 'etc', 'pacman.d', 'mirrorlist.msys');
+
+  await fs.promises.writeFile(mirrorlistMingw, 'Server = https://repo.msys2.org/mingw/$repo/\n', 'utf8');
+  await fs.promises.writeFile(mirrorlistMsys, 'Server = https://repo.msys2.org/msys/$arch/\n', 'utf8');
+}
+
 /**
  * @param {string[]} paths
  * @param {string} restoreKey
@@ -200,7 +223,7 @@ class PackageCache {
     // We want a cache key that is ideally always the same for the same kind of job.
     // So that mingw32 and ming64 jobs, and jobs with different install packages have different caches.
     let shasum = crypto.createHash('sha1');
-    shasum.update([CACHE_FLUSH_COUNTER, input.release, input.update, input.pathtype, input.msystem, input.install].toString() + INSTALLER_CHECKSUM);
+    shasum.update([CACHE_FLUSH_COUNTER, input.release, input.update, input.pathtype, input.msystem, input.install, input.usemainmirroronly].toString() + INSTALLER_CHECKSUM);
     this.jobCacheKey = this.fallbackCacheKey + '-conf:' + shasum.digest('hex').slice(0, 8);
 
     this.restoreKey = undefined;
@@ -390,6 +413,12 @@ async function run() {
       core.endGroup();
     }
 
+    if (input.usemainmirroronly) {
+      core.startGroup('Configuring main mirror...');
+      await configureMainMirror(msysRootDir);
+      core.endGroup();
+    }
+
     core.startGroup('Disable CheckSpace...');
     // Reduce time required to install packages by disabling pacman's disk space checking
     await runMsys(['sed', '-i', 's/^CheckSpace/#CheckSpace/g', '/etc/pacman.conf']);