FIX Retry running nvm install

action.yml

@@ -227,18 +227,23 @@ runs:
         fi
         # this loads nvm into the current terminal
         [[ -s "$NVM_DIR/nvm.sh" ]] && \. "$NVM_DIR/nvm.sh" --no-use
+        # this loads nvm_install_retry, which retries `nvm install` on network failures
+        \. ${{ github.action_path }}/nvm-install-retry.sh
         ADMIN_NPM_VERSION=
         if [[ -d vendor/silverstripe/admin ]]; then
           cd vendor/silverstripe/admin
-          nvm install
+          nvm_install_retry
           nvm use
           ADMIN_NPM_VERSION=$(npm -v)
           npm install --ignore-scripts -g yarn
           yarn install --ignore-scripts --network-concurrency 1
           cd ../../..
         fi
-        nvm install
-        nvm use
+        # `nvm use` is enough if this module uses the same node version as admin
+        if ! nvm use; then
+          nvm_install_retry
+          nvm use
+        fi
         if [[ $(npm -v) != $ADMIN_NPM_VERSION ]]; then
           npm install --ignore-scripts -g yarn;
         fi
@@ -344,9 +349,11 @@ runs:
         export NVM_DIR="$HOME/.nvm"
         # this loads nvm into the current terminal
         [[ -s "$NVM_DIR/nvm.sh" ]] && \. "$NVM_DIR/nvm.sh"
+        # this loads nvm_install_retry, which retries `nvm install` on network failures
+        \. ${{ github.action_path }}/nvm-install-retry.sh
         # Swap to correct version and make sure yarn is installed
         NPM_VERSION=$(cat vendor/silverstripe/documentation-lint/.nvmrc)
-        nvm install $NPM_VERSION && nvm use $NPM_VERSION
+        nvm_install_retry $NPM_VERSION && nvm use $NPM_VERSION
         npm install --ignore-scripts --global yarn
         # Run the linting script
         vendor/bin/doclint

nvm-install-retry.sh

@@ -0,0 +1,29 @@
+#!/usr/bin/env bash
+
+# Wrapper for `nvm install` that retries on failure.
+#
+# nvm resolves loose versions such as "18" by downloading https://nodejs.org/dist/index.tab.
+# That download is made with curl in silent mode, so a network blip or a 429 from nodejs.org
+# produces an empty version list and nvm exits 3 with a misleading
+# "Version '18' not found - try `nvm ls-remote`" message rather than a download error.
+#
+# Source this file after loading nvm.sh, then call `nvm_install_retry` in place of `nvm install`.
+# Any arguments are passed through to `nvm install`.
+nvm_install_retry() {
+    local attempt
+    local attempts=3
+    for ((attempt = 1; attempt <= attempts; attempt++)); do
+        if nvm install "$@"; then
+            return 0
+        fi
+        echo "nvm install ${*} failed (attempt ${attempt} of ${attempts})"
+        if [[ $attempt -lt $attempts ]]; then
+            # Show what the remote version list actually did, to distinguish a genuinely
+            # missing version from a failed download, then back off before retrying
+            nvm ls-remote --no-colors > /dev/null || echo "nvm ls-remote also failed"
+            sleep $((attempt * 10))
+        fi
+    done
+    echo "Could not install the node version requested by .nvmrc"
+    return 1
+}