Skip ALP in encoding equivalence test

ALP encoding is not yet part of the parquet-format Thrift specification,
so it cannot be converted to org.apache.parquet.format.Encoding. Skip it
in the testEnumEquivalence test and add a clear error message in the
converter for when ALP conversion is attempted.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: julienledem

parquet-hadoop/src/main/java/org/apache/parquet/format/converter/ParquetMetadataConverter.java

@@ -748,6 +748,11 @@ public org.apache.parquet.column.Encoding getEncoding(Encoding encoding) {
   }
 
   public Encoding getEncoding(org.apache.parquet.column.Encoding encoding) {
+    // ALP encoding is not yet part of the parquet-format specification
+    if (encoding == org.apache.parquet.column.Encoding.ALP) {
+      throw new IllegalArgumentException(
+          "ALP encoding is not yet supported in the parquet-format specification");
+    }
     return Encoding.valueOf(encoding.name());
   }
 

parquet-hadoop/src/test/java/org/apache/parquet/format/converter/TestParquetMetadataConverter.java

@@ -471,6 +471,10 @@ public void testLogicalToConvertedTypeConversion() {
   public void testEnumEquivalence() {
     ParquetMetadataConverter parquetMetadataConverter = new ParquetMetadataConverter();
     for (org.apache.parquet.column.Encoding encoding : org.apache.parquet.column.Encoding.values()) {
+      // Skip ALP encoding as it's not yet in the parquet-format specification
+      if (encoding == org.apache.parquet.column.Encoding.ALP) {
+        continue;
+      }
       assertEquals(
           encoding, parquetMetadataConverter.getEncoding(parquetMetadataConverter.getEncoding(encoding)));
     }