Fixing infinite loop when calling .multi_cell() without enough horizontal space - close #389

CHANGELOG.md

@@ -17,6 +17,8 @@ in order to get warned about deprecated features used in your code.
 This can also be enabled programmatically with `warnings.simplefilter('default', DeprecationWarning)`.
 
 ## [2.5.3] - not released yet
+### Fixed
+- infinite loop when calling `.multi_cell()` without enough horizontal space - _cf._ [#389](https://github.com/PyFPDF/fpdf2/issues/389)
 
 ## [2.5.2] - 2022-04-13
 ### Added

fpdf/fpdf.py

@@ -2854,11 +2854,15 @@ def multi_cell(
             self.add_page = lambda *args, **kwargs: None
             self._perform_page_break_if_need_be = lambda *args, **kwargs: None
 
+        if h is None:
+            h = self.font_size
         # If width is 0, set width to available width between margins
         if w == 0:
             w = self.w - self.r_margin - self.x
-        if h is None:
-            h = self.font_size
+        if w <= 2 * self.c_margin:
+            raise FPDFException(
+                "Not enough horizontal space to render cell. Consider introducing a line break."
+            )
         maximum_allowed_emwidth = (w - 2 * self.c_margin) * 1000 / self.font_size
 
         # Calculate text length

test/text/test_multi_cell.py

@@ -2,7 +2,7 @@
 
 import pytest
 
-from fpdf import FPDF, XPos, YPos
+from fpdf import FPDF, FPDFException, XPos, YPos
 from test.conftest import assert_pdf_equal, LOREM_IPSUM
 
 
@@ -305,3 +305,12 @@ def test_multi_cell_font_leakage(tmp_path):  # Issue #359
     pdf.set_font("Roboto", "", 12)
     pdf.multi_cell(0, txt="abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ")
     assert_pdf_equal(pdf, HERE / "multi_cell_font_leakage.pdf", tmp_path)
+
+
+def test_multi_cell_with_zero_horizontal_space():  # issue #389
+    pdf = FPDF()
+    pdf.add_page()
+    pdf.set_font("Helvetica", "", 10)
+    pdf.multi_cell(w=0, h=5, txt="test")
+    with pytest.raises(FPDFException):
+        pdf.multi_cell(w=0, h=5, txt="test")