ci: add showcase version check workflow

A Go script and workflow are added to check that the showcase commit in librarian.yaml is in sync with the gapic-showcase.version property in java-showcase/gapic-showcase/pom.xml.

Fixes googleapis/librarian#6200

Author: sofisl

.github/scripts/verify_showcase_version.go

@@ -0,0 +1,69 @@
+// Copyright 2026 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package main
+
+import (
+	"flag"
+	"fmt"
+	"os"
+	"os/exec"
+	"strings"
+)
+
+func main() {
+	showcaseVersion := flag.String("version", "", "The showcase version from pom.xml (e.g. 0.39.0)")
+	showcaseCommit := flag.String("commit", "", "The showcase commit from librarian.yaml (e.g. 328bec...)")
+	flag.Parse()
+
+	if *showcaseVersion == "" || *showcaseCommit == "" {
+		fmt.Fprintf(os.Stderr, "Error: Both -version and -commit flags must be provided\n")
+		os.Exit(1)
+	}
+
+	tagName := "v" + *showcaseVersion
+	remoteURL := "https://github.com/googleapis/gapic-showcase.git"
+
+	fmt.Printf("Showcase version: %s\n", *showcaseVersion)
+	fmt.Printf("Showcase commit: %s\n", *showcaseCommit)
+
+	// Query the remote gapic-showcase repository for the commit hash of the tag v{version}.
+	gitCommand := exec.Command("git", "ls-remote", remoteURL, "refs/tags/"+tagName)
+	outputBytes, err := gitCommand.Output()
+	if err != nil {
+		fmt.Fprintf(os.Stderr, "Error running git ls-remote: %v\n", err)
+		os.Exit(1)
+	}
+
+	outputLine := strings.TrimSpace(string(outputBytes))
+	if outputLine == "" {
+		fmt.Fprintf(os.Stderr, "Error: Tag %s not found on remote %s\n", tagName, remoteURL)
+		os.Exit(1)
+	}
+
+	outputFields := strings.Fields(outputLine)
+	if len(outputFields) < 2 {
+		fmt.Fprintf(os.Stderr, "Error parsing git ls-remote output: %q\n", outputLine)
+		os.Exit(1)
+	}
+	expectedCommit := strings.TrimSpace(outputFields[0])
+	fmt.Printf("Expected commit for tag %s: %s\n", tagName, expectedCommit)
+
+	if *showcaseCommit != expectedCommit {
+		fmt.Fprintf(os.Stderr, "Mismatch: librarian.yaml has commit %q, but tag %q is at commit %q\n", *showcaseCommit, tagName, expectedCommit)
+		os.Exit(1)
+	}
+
+	fmt.Println("Showcase version and commit are in sync!")
+}

.github/workflows/showcase_version_check.yaml

@@ -0,0 +1,69 @@
+# Copyright 2026 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     https://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+name: Showcase Version Check
+
+on:
+  schedule:
+    - cron: '30 3 * * *' # Run daily at 3:30 AM UTC
+  workflow_dispatch: # Allow manual trigger
+  pull_request:
+    paths:
+      - 'librarian.yaml'
+      - 'java-showcase/gapic-showcase/pom.xml'
+      - '.github/workflows/showcase_version_check.yaml'
+      - '.github/scripts/verify_showcase_version.go'
+
+jobs:
+  check-version:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Extract showcase version from pom.xml
+        id: extract_version
+        shell: bash
+        run: |
+          version=$(mvn help:evaluate -f java-showcase/gapic-showcase/pom.xml -Dexpression=gapic-showcase.version -q -DforceStdout 2>/dev/null || true)
+          if [ -z "$version" ]; then
+            echo "Warning: Maven evaluation failed. Falling back to XML parsing of pom.xml..."
+            version=$(grep -oE '<gapic-showcase\.version>[0-9]+\.[0-9]+\.[0-9]+</gapic-showcase\.version>' java-showcase/gapic-showcase/pom.xml | sed -E 's/<[^>]+>//g')
+          fi
+          if [ -z "$version" ]; then
+            echo "Error: Could not find gapic-showcase.version in pom.xml"
+            exit 1
+          fi
+          echo "version=$version" >> "$GITHUB_OUTPUT"
+
+      - name: Extract showcase commit from librarian.yaml
+        id: extract_commit
+        shell: bash
+        run: |
+          commit=$(grep -A 1 "showcase:" librarian.yaml | grep "commit:" | awk '{print $2}')
+          if [ -z "$commit" ]; then
+            echo "Error: Could not find showcase commit in librarian.yaml"
+            exit 1
+          fi
+          echo "commit=$commit" >> "$GITHUB_OUTPUT"
+
+      - name: Set up Go
+        uses: actions/setup-go@v5
+        with:
+          go-version: '1.24'
+
+      - name: Verify showcase version and commit match
+        run: |
+          go run .github/scripts/verify_showcase_version.go \
+            -version "${{ steps.extract_version.outputs.version }}" \
+            -commit "${{ steps.extract_commit.outputs.commit }}"