Add JAR integration test for JDK compatibility (#704)

* Add Enable-Native-Access manifest attribute for JDK 24+

Add the Enable-Native-Access: ALL-UNNAMED attribute to the JAR manifest
to suppress native access warnings on JDK 24+ without requiring users
to add the --enable-native-access=ALL-UNNAMED command-line flag.

This manifest attribute allows the library to declare its need for
native access, which helps suppress the warnings introduced by JEP 472
when snappy-java loads native libraries via JNI.

Benefits:
- Users no longer need to add JVM flags for basic usage
- Warnings are suppressed automatically when the JAR is on the classpath
- Backwards compatible with all JDK versions (attribute is ignored on JDK < 24)

Related to #689

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

* Add integration test for JAR manifest and native access

Add a comprehensive integration test that verifies snappy-java works
in a separate JVM process. This test:

1. Builds the JAR with sbt
2. Compiles a simple test program that uses snappy-java
3. Runs the test in a fresh JVM WITHOUT --enable-native-access flag
4. Verifies the compression/decompression works correctly
5. Checks for JEP 472 warnings on JDK 24+

The test can be run two ways:
- Via JUnit: testOnly org.xerial.snappy.JarManifestIntegrationTest
- Via script: ./script/test-jar-integration.sh

Findings: The Enable-Native-Access manifest attribute is present but
does NOT suppress warnings when the JAR is used as a library on the
classpath. The attribute only works for executable JARs (java -jar).
Users still need to add --enable-native-access=ALL-UNNAMED for now.

Related to #689

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

* Clean up and finalize integration test

Changes:
- Remove Enable-Native-Access manifest attribute (doesn't work for library JARs)
- Remove unused JUnit integration test (using shell script instead)
- Add JAR integration test to CI workflow for all JDK versions

The integration test now runs in CI after regular tests, verifying that
the built JAR works correctly in a separate JVM process on each tested
JDK version (8, 11, 17, 21, 25).

Related to #689

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

* Remove unnecessary manifest check from integration test

The manifest check is no longer needed since we decided not to
include the Enable-Native-Access attribute.

Related to #689

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

---------

Co-authored-by: Claude <noreply@anthropic.com>

Author: xerial

.github/workflows/test.yml

@@ -63,3 +63,5 @@ jobs:
             export _JAVA_OPTIONS="--enable-native-access=ALL-UNNAMED"
           fi
           ./sbt test
+      - name: JAR Integration Test
+        run: ./script/test-jar-integration.sh

script/test-jar-integration.sh

@@ -0,0 +1,61 @@
+#!/bin/bash
+set -e
+
+echo "=========================================="
+echo "Snappy-Java Integration Test"
+echo "=========================================="
+
+# Detect Java version
+JAVA_VERSION=$(java -version 2>&1 | head -1 | cut -d'"' -f2 | sed 's/^1\.//' | cut -d'.' -f1)
+echo "Java version: $JAVA_VERSION"
+
+# Build the JAR
+echo ""
+echo "Building JAR..."
+./sbt package
+
+# Find the JAR
+JAR_FILE=$(ls -t target/snappy-java-*.jar | grep -v sources | grep -v javadoc | head -1)
+if [ -z "$JAR_FILE" ]; then
+    echo "ERROR: Could not find snappy-java JAR"
+    exit 1
+fi
+echo "Using JAR: $JAR_FILE"
+
+# Create temp directory
+TEMP_DIR=$(mktemp -d)
+echo ""
+echo "Using temp directory: $TEMP_DIR"
+
+# Copy test source
+cp src/test/resources/integration/SnappyIntegrationTest.java "$TEMP_DIR/"
+
+# Compile test
+echo ""
+echo "Compiling test program..."
+javac -cp "$JAR_FILE" -d "$TEMP_DIR" "$TEMP_DIR/SnappyIntegrationTest.java"
+
+# Run test WITHOUT --enable-native-access flag
+echo ""
+echo "=========================================="
+echo "Running test (WITHOUT --enable-native-access flag)..."
+echo "=========================================="
+
+cd "$TEMP_DIR"
+java -cp ".:$OLDPWD/$JAR_FILE" SnappyIntegrationTest 2>&1
+EXIT_CODE=$?
+cd - > /dev/null
+
+echo ""
+echo "=========================================="
+if [ $EXIT_CODE -eq 0 ]; then
+    echo "✓ Test PASSED (exit code: $EXIT_CODE)"
+else
+    echo "✗ Test FAILED (exit code: $EXIT_CODE)"
+fi
+echo "=========================================="
+
+# Cleanup
+rm -rf "$TEMP_DIR"
+
+exit $EXIT_CODE

src/test/resources/integration/SnappyIntegrationTest.java

@@ -0,0 +1,32 @@
+import org.xerial.snappy.Snappy;
+
+/**
+ * Simple integration test to verify snappy-java works in a separate JVM.
+ * This is compiled and run as a standalone program to test the JAR manifest
+ * and native library loading on different JDK versions.
+ */
+public class SnappyIntegrationTest {
+    public static void main(String[] args) throws Exception {
+        String input = "Hello snappy-java! Snappy-java is a JNI-based wrapper of "
+            + "Snappy, a fast compresser/decompresser.";
+
+        // Test compression
+        byte[] compressed = Snappy.compress(input.getBytes("UTF-8"));
+        System.out.println("Compressed " + input.length() + " bytes to " + compressed.length + " bytes");
+
+        // Test decompression
+        byte[] uncompressed = Snappy.uncompress(compressed);
+        String result = new String(uncompressed, "UTF-8");
+
+        // Verify result matches input
+        if (!result.equals(input)) {
+            System.err.println("ERROR: Decompressed data does not match input!");
+            System.err.println("Expected: " + input);
+            System.err.println("Got: " + result);
+            System.exit(1);
+        }
+
+        System.out.println("SUCCESS: " + result);
+        System.exit(0);
+    }
+}