Retry CI bundler installs on rubygems.org blips

.github/workflows/ci.yml

@@ -1610,7 +1610,7 @@ jobs:
         shell: bash
         env:
           BUNDLER_TEST_VERSION: ${{ matrix.bundler }}
-        run: gem install bundler -v "$BUNDLER_TEST_VERSION" --no-document
+        run: scripts/gem-install-retry.sh bundler -v "$BUNDLER_TEST_VERSION" --no-document
 
       # Installing a bundler does not make `bundle` run it: with no lockfile
       # to read, RubyGems' binstub activates the HIGHEST installed bundler,
@@ -2847,11 +2847,21 @@ jobs:
         uses: ruby/setup-ruby@319994f95fa847cf3fb3cd3dbe89f6dcde9f178f # v1.295.0
         with:
           ruby-version: '3.2.10'
-          # The gem hosted rewrite pins into the Gemfile.lock CHECKSUMS
-          # section, which `bundle lock --add-checksums` only emits on >= 2.6.
-          bundler: '2.6'
+          # Bundler comes from the next step, which retries rubygems.org
+          # blips; setup-ruby's own install is a single bare `gem install`.
+          bundler: 'none'
           bundler-cache: false
 
+      - name: Install Bundler
+        if: steps.gate.outputs.run == 'true'
+        # The gem hosted rewrite pins into the Gemfile.lock CHECKSUMS
+        # section, which `bundle lock --add-checksums` only emits on >= 2.6.
+        # `~> 2.6.0` is what setup-ruby's `bundler: '2.6'` installed; as the
+        # highest installed bundler it is the one `bundle` runs.
+        run: |
+          scripts/gem-install-retry.sh bundler -v '~> 2.6.0' --no-document
+          bundle --version
+
       - name: Setup Go
         if: steps.gate.outputs.run == 'true'
         uses: actions/setup-go@4a3601121dd01d1626a1e23e37211e3254c1c06c # v6.4.0

scripts/gem-install-retry.sh

@@ -0,0 +1,31 @@
+#!/usr/bin/env bash
+# `gem install` that survives a rubygems.org connection blip.
+#
+#   scripts/gem-install-retry.sh <gem install args...>
+#
+# RubyGems has no retry of its own: one failed TCP connect to rubygems.org
+# ("SocketError: Failed to open TCP connection to rubygems.org:443") aborts
+# the install at once. ruby/setup-ruby's `bundler:` input runs exactly such
+# a bare `gem install bundler`, and one blip there evicted a merge-queue
+# entry in hosted-e2e, so the CI bundler installs go through here: up to 4
+# attempts with a growing pause. The args are passed through unchanged, so
+# a pinned `-v X.Y.Z` stays pinned.
+set -euo pipefail
+
+if [ "$#" -eq 0 ]; then
+  echo "usage: $0 <gem install args...>" >&2
+  exit 2
+fi
+
+attempts=4
+for attempt in $(seq 1 "$attempts"); do
+  if gem install "$@"; then
+    exit 0
+  fi
+  if [ "$attempt" = "$attempts" ]; then
+    echo "::error::gem install $* failed on all $attempts attempts"
+    exit 1
+  fi
+  echo "::warning::gem install $* attempt $attempt failed; retrying"
+  sleep $((attempt * 10))
+done