Saxon

The code currently does

throw new XPathException("Incorrect syntax for Java regular expression", e);

so we have the Java exception as a nested exception.

In XPathException.getMessage() we expand the message with the message from the underlying cause exception, so getMessage() returns

 Incorrect syntax for Java regular expression: Dangling meta character '*' near index 0
**
^

(3 lines)

The StandardErrorReporter calls getExpandedMessage() which calls formatNestedMessages(). Because the Java exception is a RuntimeException this unfortunately adds a stack trace to the message, which we really don't want in this case.

In fact, we end up with three copies of the nested message being output, as well as the stack trace.

In the light of this, it seems best to avoid including the nested exception as a cause, and only include its message, so we're left with

throw new XPathException("Incorrect syntax for Java regular expression: " + e.getMessage());

which produces the output:

Error on line 1 column 9 of file:/Users/mike/GitHub/saxon2020-saxon11/src/test/xmark/:
   Incorrect syntax for Java regular expression: Dangling meta character '*' near index 0
**
^

(4 lines)

I think we should also add the error code FORX0001.

I was looking at this in the context of an invalid regex in fn:matches(). The xsl:analyze-string case is a little different.

With the supplied example, and with my changes applied, we're getting

Error in xsl:analyze-string/@regex on line 4 column 65 of test.xsl:
  XTDE1140  Error in regular expression: Incorrect syntax for Java regular expression:
  Unclosed group near index 7
 ((\.+)
Errors were reported during JIT compilation of template rule with match="/"

The phrase "Error in regular expression" seems redundant here, but I think I'll live with it, because the ";j" case is a bit unusual. But I will change the word "Java" to "native" so it works on both Java and C#.