Fix panics in the grid algorithm (#691)

* Fix typo (max -> min) in grid track repetition resolution.

* Remove first/last optimisation that breaks with zero-sized track lists

* Grid: Fix crash when placing item with definite primary axis / indefinite secondary axis

src/compute/grid/explicit_grid.rs

@@ -106,7 +106,7 @@ pub(crate) fn compute_explicit_grid_size_in_axis(
  /// otherwise, flooring the max track sizing function by the min track sizing function if both are definite
  fn track_definite_value(sizing_function: &NonRepeatedTrackSizingFunction, parent_size: Option<f32>) -> f32 {
  let max_size = sizing_function.max.definite_value(parent_size);
- let min_size = sizing_function.max.definite_value(parent_size);
+ let min_size = sizing_function.min.definite_value(parent_size);
  max_size.map(|max| max.maybe_min(min_size)).or(min_size).unwrap()
  }
 

src/compute/grid/placement.rs

@@ -227,7 +227,6 @@ fn place_indefinitely_positioned_item(
  let primary_placement_style = placement.get(primary_axis);
  let secondary_placement_style = placement.get(primary_axis.other_axis());
 
- let primary_span = primary_placement_style.indefinite_span();
  let secondary_span = secondary_placement_style.indefinite_span();
  let has_definite_primary_axis_position = primary_placement_style.is_definite();
  let primary_axis_grid_start_line = cell_occupancy_matrix.track_counts(primary_axis).implicit_start_line();
@@ -256,7 +255,7 @@ fn place_indefinitely_positioned_item(
  // Item has fixed primary axis position: so we simply increment the secondary axis position
  // until we find a space that the item fits in
  loop {
- let primary_span = Line { start: primary_idx, end: primary_idx + primary_span };
+ let primary_span = Line { start: primary_idx, end: primary_idx + definite_primary_placement.span() };
  let secondary_span = Line { start: secondary_idx, end: secondary_idx + secondary_span };
 
  // If area is occupied, increment the index and try again
@@ -269,6 +268,8 @@ fn place_indefinitely_positioned_item(
  return (primary_span, secondary_span);
  }
  } else {
+ let primary_span = primary_placement_style.indefinite_span();
+
  // Item does not have any fixed axis, so we search along the primary axis until we hit the end of the already
  // existent tracks, and then we reset the primary axis back to zero and increment the secondary axis index.
  // We continue in this vein until we find a space that the item fits in.

src/compute/grid/track_sizing.rs

@@ -399,16 +399,7 @@ fn flush_planned_growth_limit_increases(tracks: &mut [GridTrack], set_infinitely
 /// Initialize each track’s base size and growth limit.
 #[inline(always)]
 fn initialize_track_sizes(axis_tracks: &mut [GridTrack], axis_inner_node_size: Option<f32>) {
- let last_track_idx = axis_tracks.len() - 1;
-
- // First and last grid lines are always zero-sized.
- axis_tracks[0].base_size = 0.0;
- axis_tracks[0].growth_limit = 0.0;
- axis_tracks[last_track_idx].base_size = 0.0;
- axis_tracks[last_track_idx].growth_limit = 0.0;
-
- let all_but_first_and_last = 1..last_track_idx;
- for track in axis_tracks[all_but_first_and_last].iter_mut() {
+ for track in axis_tracks.iter_mut() {
  // For each track, if the track’s min track sizing function is:
  // - A fixed sizing function
  // Resolve to an absolute length and use that size as the track’s initial base size.