languagetool-org/languagetool · error · IllegalArgumentException

fromPos must be < toPos: fromPos: " + fromPos + ", toPos: "

Error message

fromPos must be < toPos: fromPos: " + fromPos + ", toPos: " + toPos

What it means

Constructor validation of the NERService.Span value class: a span with fromPos >= toPos is empty or reversed and cannot denote a text range. Generic argument guard — fires when callers pass swapped or bogus offsets, typically from misparsed NER output offsets.

Source

Thrown at languagetool-core/src/main/java/org/languagetool/tagging/ner/NERService.java:150

    return res;
  }

  private int getLastSlashFrom(String s, int startPos) {
    for (int i = startPos; i >= 0; i--) {
      char ch = s.charAt(i);
      if (ch == '/') {
        return i;
      }
    }
    return -1;
  }

  public static class Span {
    private final int fromPos;
    private final int toPos;
    public Span(int fromPos, int toPos) {
      if (fromPos >= toPos) {
        throw new IllegalArgumentException("fromPos must be < toPos: fromPos: " + fromPos + ", toPos: " + toPos);
      }
      this.fromPos = fromPos;
      this.toPos = toPos;
    }
    public int getStart() {
      return fromPos;
    }
    public int getEnd() {
      return toPos;
    }
    @Override
    public String toString() {
      return fromPos + "-" + toPos;
    }
  }
}

View on GitHub (pinned to 2e990059ce)

Solutions

1. Ensure NER output offsets are parsed correctly and ordered start-before-end
2. Swap the arguments if they were passed in reverse
3. Handle zero-length spans separately instead of constructing an invalid Span

When it happens

Trigger: Thrown at languagetool-core/src/main/java/org/languagetool/tagging/ner/NERService.java:150 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of languagetool-org/languagetool@2e990059ce (2026-09-06). Data as JSON: /api/errors/47dd96acff5dafde. Report an issue: GitHub.