test: warn about compiler not found, and gracefully report failure (PR #511)

jadx-core/src/test/java/jadx/tests/api/compiler/DynamicCompiler.java

@@ -4,6 +4,10 @@ import javax.tools.JavaCompiler;
 import javax.tools.JavaFileManager;
 import javax.tools.JavaFileObject;
 import javax.tools.ToolProvider;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
 import java.lang.reflect.Method;
 import java.util.ArrayList;
 import java.util.List;
@@ -14,6 +18,8 @@ import static javax.tools.JavaCompiler.CompilationTask;
 
 public class DynamicCompiler {
 
+	private static final Logger LOG = LoggerFactory.getLogger(DynamicCompiler.class);
+
 	private final ClassNode clsNode;
 
 	private JavaFileManager fileManager;
@@ -29,6 +35,10 @@ public class DynamicCompiler {
 		String code = clsNode.getCode().toString();
 
 		JavaCompiler compiler = ToolProvider.getSystemJavaCompiler();
+		if (compiler == null) {
+			LOG.error("Can not find compiler, please use JDK instead");
+			return false;
+		}
 		fileManager = new ClassFileManager(compiler.getStandardFileManager(null, null, null));
 
 		List<JavaFileObject> jFiles = new ArrayList<>(1);