[C Data] Format.asString emits locale dependent digits in format strings

c/src/main/java/org/apache/arrow/c/Format.java の issue で示されている String.format 呼び出しから始め、次に ar-EG ロケールで提供された再現手順を実行します。Format.asString が FixedSizeList、FixedSizeBinary、Decimal パラメーターに対して ASCII digits を出力し、既存の Java import 動作との互換性が維持されれば完了です。

Describe the bug, including details regarding any error messages, version, and platform.

Format.asString builds the parameterised format strings with String.format("+w:%d", ...) and no explicit Locale. java.util.Formatter localises the digits of %d with Locale.getDefault(Locale.Category.FORMAT), so on a JVM whose default locale uses digits outside ASCII (ar-EG, fa-IR, bn-BD, mr-IN, 98 of the 1069 locales available on JDK 21) a FixedSizeList(8) is exported as +w:٨ instead of +w:8. The same applies to FixedSizeBinary and Decimal.

https://github.com/apache/arrow-java/blob/b410fb26d01c7cefc4c6e3443a53562164001371/c/src/main/java/org/apache/arrow/c/Format.java#L66
https://github.com/apache/arrow-java/blob/b410fb26d01c7cefc4c6e3443a53562164001371/c/src/main/java/org/apache/arrow/c/Format.java#L68-L69
https://github.com/apache/arrow-java/blob/b410fb26d01c7cefc4c6e3443a53562164001371/c/src/main/java/org/apache/arrow/c/Format.java#L96
https://github.com/apache/arrow-java/blob/b410fb26d01c7cefc4c6e3443a53562164001371/c/src/main/java/org/apache/arrow/c/Format.java#L91

Other implementations parse the parameter as an ASCII integer and reject the string. arrow-rs fails at https://github.com/apache/arrow-rs/blob/58.0.0/arrow-schema/src/ffi.rs#L494-L503 with C Data interface error: The FixedSizeList type requires an integer parameter representing number of elements per list. The Java importer reads the parameter with Integer.parseInt (https://github.com/apache/arrow-java/blob/v19.0.0/c/src/main/java/org/apache/arrow/c/Format.java#L352-L354), which accepts Unicode digits, so a Java to Java round trip does not expose the problem.

Reproduction (arrow-java 19.0.0 and 18.1.0, Temurin 21.0.6, run with --add-opens=java.base/java.nio=ALL-UNNAMED):

import java.nio.charset.StandardCharsets;
import java.util.HexFormat;
import java.util.List;
import java.util.Locale;
import org.apache.arrow.c.ArrowSchema;
import org.apache.arrow.c.Data;
import org.apache.arrow.c.NativeUtil;
import org.apache.arrow.memory.BufferAllocator;
import org.apache.arrow.memory.RootAllocator;
import org.apache.arrow.vector.types.FloatingPointPrecision;
import org.apache.arrow.vector.types.pojo.ArrowType;
import org.apache.arrow.vector.types.pojo.Field;
import org.apache.arrow.vector.types.pojo.FieldType;

public class FormatLocale {
  public static void main(String[] args) {
    Locale.setDefault(Locale.forLanguageTag("ar-EG"));
    Field item = new Field("item",
        FieldType.nullable(new ArrowType.FloatingPoint(FloatingPointPrecision.SINGLE)), null);
    Field vec = new Field("vec", FieldType.nullable(new ArrowType.FixedSizeList(8)), List.of(item));
    try (BufferAllocator allocator = new RootAllocator()) {
      ArrowSchema schema = ArrowSchema.allocateNew(allocator);
      Data.exportField(allocator, vec, null, schema);
      String format = NativeUtil.toJavaString(schema.snapshot().format);
      System.out.println(format + "  "
          + HexFormat.ofDelimiter(" ").formatHex(format.getBytes(StandardCharsets.UTF_8)));
      System.out.println("Java import: " + Data.importField(allocator, schema, null).getType());
    }
  }
}

+w:٨  2b 77 3a d9 a8
Java import: FixedSizeList(8)

With Locale.US the first line is +w:8 2b 77 3a 38.