oracle/graal · error · IllegalArgumentException

got illegal fromIndex value: %d. fromIndex must be >= region

Error message

got illegal fromIndex value: %d. fromIndex must be >= regionFrom (%d) and <= regionTo (%d)

What it means

In RegexExecNode's 5-argument form, the search start index fromIndex must lie inside the declared region: regionFrom <= fromIndex <= regionTo. An out-of-region fromIndex throws IllegalArgumentException.

Source

Thrown at regex/src/com.oracle.truffle.regex/src/com/oracle/truffle/regex/RegexExecNode.java:93

        }
        final int toIndex;
        final int regionFrom;
        final int regionTo;
        if (args.length == 5) {
            long toIndexLong = toLongNode.execute(args[2]);
            long regionFromLong = toLongNode.execute(args[3]);
            long regionToLong = toLongNode.execute(args[4]);
            if (regionFromLong < 0 || regionFromLong > length) {
                CompilerDirectives.transferToInterpreterAndInvalidate();
                throw new IllegalArgumentException(String.format("got illegal regionFrom value: %d. regionFrom must be >= 0 and <= input length (%d)", regionFromLong, length));
            }
            if (regionToLong < regionFromLong || regionToLong > length) {
                CompilerDirectives.transferToInterpreterAndInvalidate();
                throw new IllegalArgumentException(String.format("got illegal regionTo value: %d. regionTo must be >= regionFrom (%d) and <= input length (%d)", regionToLong, regionFromLong, length));
            }
            if (fromIndex < regionFromLong || fromIndex > regionToLong) {
                CompilerDirectives.transferToInterpreterAndInvalidate();
                throw new IllegalArgumentException(
                                String.format("got illegal fromIndex value: %d. fromIndex must be >= regionFrom (%d) and <= regionTo (%d)", fromIndex, regionFromLong, regionToLong));
            }
            if (toIndexLong < fromIndex || toIndexLong > regionToLong) {
                CompilerDirectives.transferToInterpreterAndInvalidate();
                throw new IllegalArgumentException(String.format("got illegal toIndex value: %d. toIndex must be >= fromIndex (%d) and <= regionTo (%d)", toIndexLong, fromIndex, regionToLong));
            }
            if (toIndexLong != regionToLong) {
                CompilerDirectives.transferToInterpreterAndInvalidate();
                throw new UnsupportedOperationException(String.format("got non-equal toIndex (%d) and regionTo (%d), support for this is not implemented yet", toIndexLong, regionToLong));
            }
            toIndex = (int) toIndexLong;
            regionFrom = (int) regionFromLong;
            regionTo = (int) regionToLong;
        } else {
            assert args.length == 2;
            toIndex = length;
            regionFrom = 0;
            regionTo = length;

View on GitHub (pinned to a66e9ccd1d)

Solutions

1. Clamp fromIndex into the region: fromIndex = Math.max(regionFrom, Math.min(fromIndex, regionTo)).
2. Reset lastIndex/nextSearchIndex to regionFrom whenever a region is applied.
3. Double-check whether your API contract treats fromIndex as absolute or region-relative and convert accordingly.

Example fix

// before
exec(input, lastIndex, regionTo, regionFrom, regionTo); // lastIndex may be < regionFrom

// after
lastIndex = Math.max(regionFrom, Math.min(lastIndex, regionTo));
exec(input, lastIndex, regionTo, regionFrom, regionTo);

static boolean validFromIndex(long fromIndex, long regionFrom, long regionTo) {
    return fromIndex >= regionFrom && fromIndex <= regionTo;
}

When it happens

Trigger: Calling 5-arg exec with fromIndex < regionFrom or fromIndex > regionTo, e.g. fromIndex=0 with regionFrom=5, or fromIndex=input.length() while regionTo is smaller.

Common situations: Reusing a lastIndex from an unbounded search together with a narrowed region (e.g. emulating Matcher.region().find(lastIndex)); adapters that pass the string offset as fromIndex while the engine expects a region-relative start.

Related errors

• got illegal regionFrom value: %d. regionFrom must be >= 0 an
• got illegal regionTo value: %d. regionTo must be >= regionFr
• got illegal toIndex value: %d. toIndex must be >= fromIndex
• got non-equal toIndex (%d) and regionTo (%d), support for th
• got illegal fromIndex value: %d. fromIndex must be >= 0 and

AI-assisted analysis of oracle/graal@a66e9ccd1d (2026-08-14). Data as JSON: /api/errors/4801e71a77fc9d20. Report an issue: GitHub.