allow primitive type signatures on fields

The grammar for generic signatures in the JVMS is pretty clear that
a signature for a field is a reference type signature. However,
there are class files in the wild that contain a primitive type
signature for a field. This commit makes that acceptable in Jandex,
even though it technically isn't valid bytecode.

core/src/main/java/org/jboss/jandex/GenericSignatureParser.java

@@ -286,7 +286,14 @@ Type parseFieldSignature(String signature) {
         this.typeParameters = this.elementTypeParameters;
         this.pos = 0;
 
-        return parseReferenceType();
+        // the grammar in the JVMS says:
+        //
+        // FieldSignature:
+        //   ReferenceTypeSignature
+        //
+        // however, there are class files in the wild that contain
+        // a primitive type signature as a field signature
+        return parseJavaType();
     }
 
     MethodSignature parseMethodSignature(String signature) {

core/src/test/java/org/jboss/jandex/test/FieldWithPrimitiveTypeSignatureTest.java

@@ -0,0 +1,65 @@
+package org.jboss.jandex.test;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertNotNull;
+
+import java.io.IOException;
+
+import org.jboss.jandex.ClassInfo;
+import org.jboss.jandex.FieldInfo;
+import org.jboss.jandex.Index;
+import org.jboss.jandex.PrimitiveType;
+import org.junit.jupiter.api.Test;
+
+import net.bytebuddy.ByteBuddy;
+import net.bytebuddy.asm.AsmVisitorWrapper;
+import net.bytebuddy.description.field.FieldDescription;
+import net.bytebuddy.description.field.FieldList;
+import net.bytebuddy.description.method.MethodList;
+import net.bytebuddy.description.type.TypeDescription;
+import net.bytebuddy.implementation.Implementation;
+import net.bytebuddy.jar.asm.ClassVisitor;
+import net.bytebuddy.jar.asm.FieldVisitor;
+import net.bytebuddy.pool.TypePool;
+import net.bytebuddy.utility.OpenedClassReader;
+
+public class FieldWithPrimitiveTypeSignatureTest {
+    private static final String TEST_CLASS = "org.jboss.jandex.test.TestClass";
+
+    // the Oracle JDBC driver in version 23.3.0.23.09 contains a class with a field
+    // whose generic signature encodes a primitive type, which is invalid per JVMS
+
+    @Test
+    public void test() throws IOException {
+        byte[] bytecode = new ByteBuddy()
+                .subclass(Object.class)
+                .name(TEST_CLASS)
+                .defineField("foo", boolean.class)
+                .visit(new AsmVisitorWrapper.AbstractBase() {
+                    @Override
+                    public ClassVisitor wrap(TypeDescription instrumentedType, ClassVisitor classVisitor,
+                            Implementation.Context implementationContext, TypePool typePool,
+                            FieldList<FieldDescription.InDefinedShape> fields, MethodList<?> methods,
+                            int writerFlags, int readerFlags) {
+                        return new ClassVisitor(OpenedClassReader.ASM_API, classVisitor) {
+                            @Override
+                            public FieldVisitor visitField(int access, String name, String descriptor, String signature,
+                                    Object value) {
+                                if ("foo".equals(name)) {
+                                    signature = "Z"; // boolean
+                                }
+                                return super.visitField(access, name, descriptor, signature, value);
+                            }
+                        };
+                    }
+                })
+                .make()
+                .getBytes();
+        ClassInfo clazz = Index.singleClass(bytecode);
+
+        assertEquals(1, clazz.fields().size());
+        FieldInfo field = clazz.field("foo");
+        assertNotNull(field);
+        assertEquals(PrimitiveType.BOOLEAN, field.type());
+    }
+}