Fix: page breaking on rows with rowspan.

[Ujifman]

1. I added restriction to break before row, if page_break_before: avoid specified for <tr>.
2. I added logic to define if current row has spanned from previous rows cells, so one restricts page breaking on rows connected with rowspan. Rowspanned TD element lost on page break #1388

[simonberger]

@Ujifman I tested this and got the following pdf from #1388
dompdf_2090.pdf
In comparsion the pdf from dompdf current develop branch.
dompdf_dev.pdf

The header is missed on the follwong pages. I guess this is known/intended to be able to render it. But it breaks later when having one more row on pdf page 4.

[simonberger]

@Ujifman To precise my testing and review of the code. Am I correct that your change delays the point a table with a spanned row breaks or should it completely fix the behavior?

[bsweeney]

I don't know that this change is sufficient enough for the designated issue. It does make an attempt to keep rows with a spanning cell together, but Dompdf will still split a rowspanned cell across pages when the row it's on has already been paged. And since the real issue is that the row-spanned cell is lost from the table layout after the page break this doesn't really provide much relief.

Let us know if you feel we're missing something.

[Ujifman]

@bsweeney, sorry I wasn't clear enough. I didn't solve the problem fully. In my case I have small rowspans in pdf, i.e. rowspan is never greater than page length, so I check if page break came to spanned row, and go up to the span beggining to make a split. So as @simonberger saw in test, if rowspan is bigger then page, cells are lost. The only general solution is to copy spanned cell on every page break. So my solution is not full, but I think, it will be useful for those projects, who has spanned cells less then page length.

[Ujifman]

I wasn't clear enough. I didn't solve the problem fully. In my case I have small rowspans in pdf, i.e. rowspan is never greater than page length, so I check if page break came to spanned row, and go up to the span beggining to make a split. So as @simonberger showed in test, if rowspan is bigger then page cells are still lost. The only general solution is to copy spanned cell on every page break. So my solution is not full, but I think, it will be useful for those projects, who has spanned cells less then page length.

[bsweeney]

Thanks for the clarification.

[simonberger]

I would prefer to fix the actual bug. There shouldn't be the need to avoid breaks on rowspans aside of the current obvious problem.
But I agree to your argument that this change can work around the issue in at least a lot of cases and vote to merge it if we won't fix it soon.
I yet failed to find the missing information in the splitted table causing the overwrite of the spanned column.

[sektonic]

1. I added restriction to break before row, if page_break_before: avoid specified for <tr>.
2. I added logic to define if current row has spanned from previous rows cells, so one restricts page breaking on rows connected with rowspan. Rowspanned TD element lost on page break #1388

Thank you sir

[bsweeney]

Let's push to the next release so we can better evaluate what to do with this. I don't want to implement something that we'll have to remember to roll back later even if it provides temporary relief.

[fillobotto]

Do you have any update about this problem?

[Mellthas]

Haven't looked into the second part, but the first change about page-break-before: avoid support for table rows would be nice to have independently of how the discussion is resolved. Can you put up a separate PR for just that change, @Ujifman, so it can be merged?