Improve backend error handling

lib/rust/parser/generate-java/java/org/enso/syntax2/Parser.java

@@ -75,10 +75,10 @@ private static boolean searchFromDirToTop(Throwable chain, File root, String...
     return false;
   }
 
-  private long state;
+  private long stateUnlessClosed;
 
   private Parser(long stateIn) {
-    state = stateIn;
+    stateUnlessClosed = stateIn;
   }
 
   private static native long allocState();
@@ -115,14 +115,24 @@ public long isIdentOrOperator(CharSequence input) {
     return isIdentOrOperator(inputBuf);
   }
 
+  private long getState() {
+    if (stateUnlessClosed != 0) {
+      return stateUnlessClosed;
+    } else {
+      throw new IllegalStateException("Parser used after close()");
+    }
+  }
+
   public ByteBuffer parseInputLazy(CharSequence input) {
+    var state = getState();
     byte[] inputBytes = input.toString().getBytes(StandardCharsets.UTF_8);
     ByteBuffer inputBuf = ByteBuffer.allocateDirect(inputBytes.length);
     inputBuf.put(inputBytes);
     return parseTreeLazy(state, inputBuf);
   }
 
   public Tree parse(CharSequence input) {
+    var state = getState();
     byte[] inputBytes = input.toString().getBytes(StandardCharsets.UTF_8);
     ByteBuffer inputBuf = ByteBuffer.allocateDirect(inputBytes.length);
     inputBuf.put(inputBytes);
@@ -140,7 +150,7 @@ public static String getWarningMessage(Warning warning) {
 
   @Override
   public void close() {
-    freeState(state);
-    state = 0;
+    freeState(stateUnlessClosed);
+    stateUnlessClosed = 0;
   }
 }

std-bits/base/src/main/java/org/enso/base/polyglot/EnsoMeta.java

@@ -18,7 +18,7 @@ public static Value getType(String moduleName, String typeName) {
       var ex =
           new NullPointerException(
               "Cannot get type for " + moduleName + " type: " + typeName + " at " + module);
-      ex.initCause(ex);
+      ex.initCause(e);
       throw ex;
     }
   }