Add CI check to ensure examples are documented in README (#19371)

…#19294)

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- part of ##19294.

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---------

Co-authored-by: Sergey Zhukov <[email protected]>

Author: cj-zhukov

.github/workflows/rust.yml

@@ -709,6 +709,23 @@ jobs:
           ./dev/update_function_docs.sh
           git diff --exit-code
 
+  examples-docs-check:
+    name: check example README is up-to-date
+    needs: linux-build-lib
+    runs-on: ubuntu-latest
+    container:
+      image: amd64/rust
+
+    steps:
+      - uses: actions/checkout@8e8c483db84b4bee98b60c0593521ed34d9990e8 # v6.0.1
+        with:
+          submodules: true
+          fetch-depth: 1
+
+      - name: Run examples docs check script
+        run: |
+          bash ci/scripts/check_examples_docs.sh
+
   # Verify MSRV for the crates which are directly used by other projects:
   # - datafusion
   # - datafusion-substrait

ci/scripts/check_examples_docs.sh

@@ -0,0 +1,64 @@
+#!/usr/bin/env bash
+#
+# Licensed to the Apache Software Foundation (ASF) under one
+# or more contributor license agreements.  See the NOTICE file
+# distributed with this work for additional information
+# regarding copyright ownership.  The ASF licenses this file
+# to you 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.
+
+set -euo pipefail
+
+EXAMPLES_DIR="datafusion-examples/examples"
+README="datafusion-examples/README.md"
+
+# ffi examples are skipped because they were not part of the recent example
+# consolidation work and do not follow the new grouping and execution pattern.
+# They are not documented in the README using the new structure, so including
+# them here would cause false CI failures.
+SKIP_LIST=("ffi")
+
+missing=0
+
+skip() {
+    local value="$1"
+    for item in "${SKIP_LIST[@]}"; do
+        if [[ "$item" == "$value" ]]; then
+            return 0
+        fi
+    done
+    return 1
+}
+
+# collect folder names
+folders=$(find "$EXAMPLES_DIR" -mindepth 1 -maxdepth 1 -type d -exec basename {} \;)
+
+# collect group names from README headers
+groups=$(grep "^### Group:" "$README" | sed -E 's/^### Group: `([^`]+)`.*/\1/')
+
+for folder in $folders; do
+    if skip "$folder"; then
+        echo "Skipped group: $folder"
+        continue
+    fi
+
+    if ! echo "$groups" | grep -qx "$folder"; then
+        echo "Missing README entry for example group: $folder"
+        missing=1
+    fi
+done
+
+if [[ $missing -eq 1 ]]; then
+    echo "README is out of sync with examples"
+    exit 1
+fi