From 0c3ae9a048484732181d6ac0bdbc15d86b4db60f Mon Sep 17 00:00:00 2001
From: Stephen Gutekanst <stephen@hexops.com>
Date: Wed, 20 Mar 2024 09:24:27 -0700
Subject: [PATCH] ecs: correctly update invalidated pointer post-allocation

Potentially fixes hexops/mach#1178

Signed-off-by: Stephen Gutekanst <stephen@hexops.com>
---
 src/ecs/entities.zig | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/src/ecs/entities.zig b/src/ecs/entities.zig
index 09b42d84..89defe40 100644
--- a/src/ecs/entities.zig
+++ b/src/ecs/entities.zig
@@ -315,6 +315,9 @@ pub fn Entities(comptime all_components: anytype) type {
 
                 const archetype_entry = try entities.archetypeOrPut(columns);
                 if (!archetype_entry.found_existing) {
+                    // Update prev_archetype pointer, as it would now be invalidated due to the allocation
+                    prev_archetype = &entities.archetypes.items[prev_archetype_idx];
+
                     archetype_entry.ptr.* = .{
                         .len = 0,
                         .capacity = 0,
@@ -412,6 +415,9 @@ pub fn Entities(comptime all_components: anytype) type {
 
                 const archetype_entry = try entities.archetypeOrPut(columns);
                 if (!archetype_entry.found_existing) {
+                    // Update prev_archetype pointer, as it would now be invalidated due to the allocation
+                    prev_archetype = &entities.archetypes.items[prev_archetype_idx];
+
                     archetype_entry.ptr.* = .{
                         .len = 0,
                         .capacity = 0,
@@ -492,6 +498,7 @@ pub fn Entities(comptime all_components: anytype) type {
 
             var archetype = entities.archetypeByID(entity);
             const ptr = entities.entities.get(entity).?;
+
             return archetype.get(ptr.row_index, name_id, Component);
         }
 
@@ -548,6 +555,9 @@ pub fn Entities(comptime all_components: anytype) type {
 
             const archetype_entry = try entities.archetypeOrPut(columns);
             if (!archetype_entry.found_existing) {
+                // Update prev_archetype pointer, as it would now be invalidated due to the allocation
+                prev_archetype = &entities.archetypes.items[prev_archetype_idx];
+
                 archetype_entry.ptr.* = .{
                     .len = 0,
                     .capacity = 0,