Don’t iterate over all lines when trying to report footnotes

It can be awfully long, and we only need to know if we have enough lines to please the
"widows" property.

Author: liZe

weasyprint/layout/block.py

@@ -301,7 +301,7 @@ def _out_of_flow_layout(context, box, index, child, new_children,
     return stop, resume_at, new_child, out_of_flow_resume_at
 
 
-def _break_line(context, box, line, new_children, next_lines, page_is_empty, index,
+def _break_line(context, box, line, new_children, needed, page_is_empty, index,
                 skip_stack, resume_at, absolute_boxes, fixed_boxes):
     """Break line where allowed by orphans and widows.
 
@@ -316,7 +316,6 @@ def _break_line(context, box, line, new_children, next_lines, page_is_empty, ind
         return True, False, resume_at
     # How many lines we need on the next page to satisfy widows
     # -1 for the current line.
-    needed = max(box.style['widows'] - 1 - next_lines, 0)
     if needed > over_orphans and not page_is_empty:
         # Total number of lines < orphans + widows
         remove_placeholders(context, line.children, absolute_boxes, fixed_boxes)
@@ -377,15 +376,21 @@ def _linebox_layout(context, box, index, child, new_children, page_is_empty,
             # If we couldn’t break the line before but can break now, first try to
             # report footnotes and see if we don’t overflow.
             could_break_before = can_break_now = True
-            next_lines = len(tuple(lines_iterator))
+            needed = box.style['widows'] - 1
+            for _ in lines_iterator:
+                needed -= 1
+                # Don’t iterate over all lines as it can be long.
+                if needed == -1:
+                    break
             if len(new_children) + 1 < box.style['orphans']:
                 can_break_now = False
-            elif next_lines < box.style['widows']:
+            elif needed >= 0:
                 can_break_now = False
             if len(new_children) < box.style['orphans']:
                 could_break_before = False
-            elif next_lines + 1 < box.style['widows']:
+            elif needed > 0:
                 could_break_before = False
+            needed = max(0, needed)
             report = not context.in_column and can_break_now and not could_break_before
             reported_footnotes = 0
             while report and context.current_page_footnotes:
@@ -397,9 +402,8 @@ def _linebox_layout(context, box, index, child, new_children, page_is_empty,
                     break
             else:
                 abort, stop, resume_at = _break_line(
-                    context, box, line, new_children, next_lines,
-                    page_is_empty, index, skip_stack, resume_at, absolute_boxes,
-                    fixed_boxes)
+                    context, box, line, new_children, needed, page_is_empty, index,
+                    skip_stack, resume_at, absolute_boxes, fixed_boxes)
 
             # Revert reported footnotes, as they’ve been reported starting from the last
             # one.
@@ -414,8 +418,7 @@ def _linebox_layout(context, box, index, child, new_children, page_is_empty,
         # "When an unforced page break occurs here, both the adjoining
         #  ‘margin-top’ and ‘margin-bottom’ are set to zero."
         # See issue #115.
-        elif page_is_empty and context.overflows_page(
-                bottom_space, new_position_y):
+        elif page_is_empty and context.overflows_page(bottom_space, new_position_y):
             # Remove the top border when a page is empty and the box is
             # too high to be drawn in one page
             new_position_y -= box.margin_top
@@ -433,8 +436,7 @@ def _linebox_layout(context, box, index, child, new_children, page_is_empty,
                 overflow = (
                     overflow or
                     context.reported_footnotes or
-                    context.overflows_page(
-                        bottom_space, new_position_y + offset_y))
+                    context.overflows_page(bottom_space, new_position_y + offset_y))
                 if overflow:
                     context.report_footnote(footnote)
                     # If we've put other content on this page, then we may want
@@ -443,11 +445,15 @@ def _linebox_layout(context, box, index, child, new_children, page_is_empty,
                     # even try.
                     if new_children or not page_is_empty:
                         if footnote.style['footnote_policy'] == 'line':
-                            next_lines = len(tuple(lines_iterator))
+                            if needed := box.style['widows'] - 1:
+                                for _ in lines_iterator:
+                                    needed -= 1
+                                    # Don’t iterate over all lines as it can be long.
+                                    if needed == 0:
+                                        break
                             abort, stop, resume_at = _break_line(
-                                context, box, line, new_children,
-                                next_lines, page_is_empty, index,
-                                skip_stack, resume_at, absolute_boxes,
+                                context, box, line, new_children, needed, page_is_empty,
+                                index, skip_stack, resume_at, absolute_boxes,
                                 fixed_boxes)
                             break_linebox = True
                             break