[bugfix] fn:transform - clean up error handling

When the cause chain for an error contains an XPathException in native eXist, or the Saxon type for an XPathException, work harder to get the correct error code out of that cause, and reflect it in the XPathException ultimately thrown out of FnTransform.

This has an effect on the error thrown by XQTS test transform-68, which becomes consistent with the proposed test suite fix here w3c/qt3tests#44

Author: alanpaxton

exist-core/src/main/java/org/exist/xquery/functions/fn/FnTransform.java

@@ -178,15 +178,8 @@ private XsltExecutable compileExecutable(final Options options) throws XPathExce
             FnTransform.ERROR_LISTENER.clear();
             return xsltCompiler.compile(options.xsltSource._2); // .compilePackage //TODO(AR) need to implement support for xslt-packages
         } catch (final SaxonApiException e) {
-            //Generated by us, possibly in URI resolution, above - throw it directly
-            throwOriginalXPathException(e, ErrorCodes.FOXT0003);
-            final Optional<TransformerException> compilerException = FnTransform.ERROR_LISTENER.getWorst();
-            if (compilerException.isPresent()) {
-                throwOriginalXPathException(compilerException.get(), ErrorCodes.FOXT0003);
-                throw new XPathException(this, ErrorCodes.FOXT0003, compilerException.get());
-            }
-            //Wrap any other error
-            throw new XPathException(this, ErrorCodes.FOXT0003, e.getMessage());
+            final Optional<Exception> compilerException = FnTransform.ERROR_LISTENER.getWorst().map(e1 -> e1);
+            throw originalXPathException(compilerException.orElse(e), ErrorCodes.FOXT0003);
         }
     }
 
@@ -199,11 +192,11 @@ private XsltExecutable compileExecutable(final Options options) throws XPathExce
      * @param defaultErrorCode use this code and its description to fill in blanks in what we finally throw
      * @throws XPathException the eventual eXist exception we may throw
      */
-    private void throwOriginalXPathException(final Throwable e, final ErrorCodes.ErrorCode defaultErrorCode) throws XPathException {
+    private XPathException originalXPathException(final Throwable e, final ErrorCodes.ErrorCode defaultErrorCode) {
         Throwable cause = e;
         while (cause != null) {
             if (cause instanceof XPathException) {
-                throw (XPathException) cause;
+                return (XPathException) cause;
             }
             cause = cause.getCause();
         }
@@ -215,14 +208,16 @@ private void throwOriginalXPathException(final Throwable e, final ErrorCodes.Err
                 final StructuredQName from = xPathException.getErrorCodeQName();
                 if (from != null) {
                     final QName errorCodeQName = new QName(from.getLocalPart(), from.getURI(), from.getPrefix());
-                    final ErrorCodes.ErrorCode errorCode = new ErrorCodes.ErrorCode(errorCodeQName, defaultErrorCode.getDescription());
-                    throw new XPathException(errorCode, cause.getMessage());
+                    final ErrorCodes.ErrorCode errorCode = new ErrorCodes.ErrorCode(errorCodeQName, cause.getMessage());
+                    return new XPathException(errorCode, cause.getMessage());
                 } else {
-                    throw new XPathException(this, defaultErrorCode, cause.getMessage());
+                    return new XPathException(this, defaultErrorCode, cause.getMessage());
                 }
             }
             cause = cause.getCause();
         }
+
+        return new XPathException(this, defaultErrorCode, e.getMessage());
     }
 
     /**
@@ -339,16 +334,8 @@ public Sequence eval(final Sequence[] args, final Sequence contextSequence) thro
                         options, sourceNode, delivery, xslt30Transformer, resultDocuments);
                 return invocation.invoke();
 
-            } catch (final SaxonApiException e) {
-                if (e.getErrorCode() != null) {
-                    final QName errorQn = QName.fromJavaQName(e.getErrorCode().getStructuredQName().toJaxpQName());
-                    throw new XPathException(this, new ErrorCodes.ErrorCode(errorQn, e.getMessage()), e.getMessage());
-                } else {
-                    throwOriginalXPathException(e, ErrorCodes.FOXT0003);
-                    throw new XPathException(this, ErrorCodes.FOXT0003, e.getMessage());
-                }
-            } catch (final UncheckedXPathException e) {
-                throw new XPathException(this, ErrorCodes.FOXT0003, e.getMessage());
+            } catch (final SaxonApiException | UncheckedXPathException e) {
+                throw originalXPathException(e, ErrorCodes.FOXT0003);
             }
 
         } else {