assertion failure when Paragraph constructed with empty segment list

[hwaite]

org.fxmisc.richtext.model.Paragraph(PS,List<StyledText<S>>) fails when assertions are enabled and second argument is empty. Is assertion truly necessary? If so, perhaps invariant should be verified even when assertions not enabled (e.g. "if (segments.isEmpty()) throw new IllegalArgumentException();").

Stack trace:

org.fxmisc.richtext.model.Paragraph.(Paragraph.java:42)
org.fxmisc.richtext.model.Paragraph.restyle(Paragraph.java:218)
org.fxmisc.richtext.model.SimpleEditableStyledDocument.lambda$setStyleSpans$7(SimpleEditableStyledDocument.java:147)
org.fxmisc.richtext.model.SimpleEditableStyledDocument$$Lambda$1131.137893627.apply(Unknown Source:-1)
org.fxmisc.richtext.model.ReadOnlyStyledDocument.lambda$null$7(ReadOnlyStyledDocument.java:288)
org.fxmisc.richtext.model.ReadOnlyStyledDocument$$Lambda$1093.523297059.apply(Unknown Source:-1)
org.reactfx.util.Tuple2.map(Tuple2.java:31)
org.fxmisc.richtext.model.ReadOnlyStyledDocument.lambda$replace$8(ReadOnlyStyledDocument.java:287)
org.fxmisc.richtext.model.ReadOnlyStyledDocument$$Lambda$1091.1289685895.apply(Unknown Source:-1)
org.reactfx.util.Tuple2.map(Tuple2.java:31)
org.fxmisc.richtext.model.ReadOnlyStyledDocument.replace(ReadOnlyStyledDocument.java:286)
org.fxmisc.richtext.model.ReadOnlyStyledDocument.replace(ReadOnlyStyledDocument.java:276)
org.fxmisc.richtext.model.SimpleEditableStyledDocument.setStyleSpans(SimpleEditableStyledDocument.java:141)
org.fxmisc.richtext.model.StyledTextAreaModel.setStyleSpans(StyledTextAreaModel.java:566)
org.fxmisc.richtext.StyledTextArea.setStyleSpans(StyledTextArea.java:995)

[TomasMikula]

Thanks for reporting! You are right, it should be an IllegalArgumentException. Probably the assertion is there from times when the constructor was not public.

[TomasMikula]

Do you want to open a pull request?

[hwaite]

Sure, I could fix this by throwing exception but am not 100% sure that doing so would fully address problem.

If you look at stack trace, you'll see that I'm not directly calling constructor. I make a seemingly reasonable call to setStyleSpans(int,StyleSpans) with a non-empty StyleSpans object. I probably need to investigate what's wrong with arguments to this call. Perhaps I'm adding empty span via StyleSpansBuilder? Should that be prohibited? Whatever the case, it's probable that error condition could be detected before Paragraph ctor is invoked.

[TomasMikula]

Or you can provide a simple self-contained example and I will investigate when I come back from vacation.

[hwaite]

Possibly caused by applying style to a line break?

public class Bug345 extends Application {
    public void start(Stage pStage) {
        pStage.setOnCloseRequest(pEvt -> Platform.exit());

        final String txt = String.join("\n", "x", "", "y");

        final CodeArea c = new CodeArea(txt);

        final VBox root = new VBox();
        root.getChildren().add(c);

        pStage.setScene(new Scene(root, 300, 250));
        pStage.show();

        final StyleSpansBuilder<Collection<String>> ssb = new StyleSpansBuilder<>();


        ssb.add(Collections.singleton("x"), 1);

        // uncomment line to prevent error
//      ssb.add(Collections.emptySet(), 1);

        ssb.add(Collections.emptySet(), 1);
        ssb.add(Collections.singleton("y"), 1);
        final StyleSpans<Collection<String>> spans = ssb.create();

        System.out.println("text len: " + txt.length());
        System.out.println("span len: " + spans.length());

        c.setStyleSpans(0, spans);
    }

    public static void main(String[] pArgs) {launch(pArgs);}
}

[JordanMartinez]

@hwaite I ran the demo you listed above and was not able to reproduce the issue.

My Environment:

Linux Mint 18.1

java version "1.8.0_121"
Java(TM) SE Runtime Environment (build 1.8.0_121-b13)
Java HotSpot(TM) 64-Bit Server VM (build 25.121-b13, mixed mode)

[hwaite]

@JordanMartinez, you're running with assertions enabled?

[JordanMartinez]

@hwaite Nope! I learned Groovy first, which has assertions enabled by default, not Java. So, that would explain why I didn't even know you had to enable them.

I can reproduce the issue now.

[JordanMartinez]

If I update Paragraph's restyle method to return itself when middleSegs is empty, this fixes the problem. However, is this error caused by a bug in this method? Or a bug elsewhere?

public Paragraph<PS, SEG, S> restyle(int from, StyleSpans<? extends S> styleSpans) {
    int len = styleSpans.length();
    if(styleSpans.equals(getStyleSpans(from, from + len))) {
        return this;
    }

    Paragraph<PS, SEG, S> left = trim(from);
    Paragraph<PS, SEG, S> right = subSequence(from + len);

    Paragraph<PS, SEG, S> middle = subSequence(from, from + len);
    List<SEG> middleSegs = new ArrayList<>(styleSpans.getSpanCount());
    int offset = 0;
    for(StyleSpan<? extends S> span: styleSpans) {
        int end = offset + span.getLength();
        Paragraph<PS, SEG, S> text = middle.subSequence(offset, end);
        middleSegs.addAll(text.restyle(span.getStyle()).segments);
        offset = end;
    }
//// ---------------------------------
    if (middleSegs.isEmpty()) {
        return this;
    } else {
//// ---------------------------------
        Paragraph<PS, SEG, S> newMiddle = new Paragraph<>(paragraphStyle, segmentOps, middleSegs);

        return left.concat(newMiddle).concat(right);
    }
}