multi_cell table is broken

[mcerveny]

New features breaks table rendering with multi_cell().
multi_cell() is not rendered if txt="". It breaks table design (cell() is ok).

test.pdf

import fpdf

pdf = fpdf.FPDF(orientation='portrait', unit='mm', format='A4')
pdf.add_page()
pdf.set_font('helvetica',size=10)
for i in range(1,5):
  pdf.multi_cell(20, ln=3, txt=str(i))
pdf.ln(10)
for i in range(1,5):
  pdf.multi_cell(20, ln=3, txt=str(i) if i>2 else "")
pdf.ln(10)
for i in range(1,5):
  pdf.cell(20, txt=str(i))
pdf.ln(10)
for i in range(1,5):
  pdf.cell(20, txt=str(i) if i>2 else "")
pdf.output('test.pdf')

[Lucas-C]

Hi @mcerveny

Thanks for reporting this.
The behaviour of multi_cell() with empty text input was never tested before.

Here is a unit test we should add, based on your code @mcerveny:

def test_multi_cell_with_empty_contents(tmp_path):  # issue 349
    pdf = fpdf.FPDF()
    pdf.add_page()
    pdf.set_font('helvetica', size=10)
    for i in range(1,5):
        pdf.multi_cell(20, ln=3, txt=str(i))
    pdf.ln(10)
    for i in range(1,5):
        pdf.multi_cell(20, ln=3, txt=str(i) if i>2 else "")
    assert_pdf_equal(pdf, HERE / "multi_cell_with_empty_contents.pdf", tmp_path)

Ping @gmischler: what do you think would be the best approach here, to keep the same behaviour as before?
In the new code, _render_styled_cell_text() is responsible for incrementing FPDF.x but is never called by multi_cell() in that case, because text_lines is empty.

[gmischler]

Ping @gmischler: what do you think would be the best approach here, to keep the same behaviour as before? In the new code, _render_styled_cell_text() is responsible for incrementing FPDF.x but is never called by multi_cell() in that case, because text_lines is empty.

The simplest solution might be to check if text_lines is None right before the while loop, and invoke _render_styled_cell_text() with a dummy line, so it can do its positioning magic.

[Lucas-C]

Fixed!