Fix Path.buildParts

src/path.zig

@@ -70,12 +70,21 @@ pub const Path = struct {
     } {
         const len = @typeInfo(@TypeOf(parts)).Struct.fields.len;
         var result: [len]EntityPart = undefined;
-        inline for (&result, parts) |*res, part|
-            res.* = switch (@TypeOf(part)) {
-                []u8, []const u8 => |name| .{ .name = name },
-                u32, comptime_int => |id| .{ .id = id },
-                else => @compileError("Expected []u8, []const u8, u32 or comptime_int, got '" ++ @typeName(@TypeOf(part)) ++ "'"),
+        inline for (&result, parts) |*res, part| {
+            const msg = "Expected '[]const u8' or 'u32', got '" ++ @typeName(@TypeOf(part)) ++ "'";
+            res.* = switch (@typeInfo(@TypeOf(part))) {
+                .Pointer => |p| switch (p.size) {
+                    .One => switch (@typeInfo(p.child)) {
+                        .Array => |a| if (a.child == u8) .{ .name = part } else @compileError(msg),
+                        else => @compileError(msg),
+                    },
+                    .Slice => if (p.child == u8) .{ .name = part } else @compileError(msg),
+                    else => @compileError(msg),
+                },
+                .Int, .ComptimeInt => .{ .id = part },
+                else => @compileError(msg),
             };
+        }
         return result;
     }
 
@@ -130,12 +139,24 @@ pub const Path = struct {
         };
     }
 
+    /// Creates a `Path` for the specified `child` entity, optionally in
+    /// relation to the specified `parent` entity. If `parent` is not `null`,
+    /// the resulting path is relative. Otherwise it will be absolute.
+    ///
+    /// This function allocates an array for the parts that make up the entity's
+    /// path, however each part itself is owned by Flecs and could change or be
+    /// invalidated ay any time, such as when an entity is renamed or removed.
     pub fn fromEntity(comptime ctx: type, parent: ?Entity(ctx), child: Entity(ctx), alloc: Allocator) !Path {
-        if (parent) |p| std.debug.assert(p.raw != 0);
         std.debug.assert(child.raw != 0);
+        if (parent) |p| {
+            std.debug.assert(p.raw != 0);
+            std.debug.assert(p.raw != child.raw);
+        }
 
+        // TODO: Use a threadlocal field with reasonable size, then clone the result.
         const starting_capacity: usize = 12;
         var parts = try alloc.alloc(EntityPart, starting_capacity);
+        errdefer alloc.free(parts);
         var num_parts: usize = 0;
 
         // Traverse up the entity hierarchy starting from the specified child
@@ -148,7 +169,14 @@ pub const Path = struct {
             else
                 .{ .id = current.getEntityId() };
             num_parts += 1;
-            current = current.getParent() orelse break;
+
+            // Move to the parent entity, if any.
+            current = current.getParent() orelse
+                // If `parent` wasn't specified, we reached the root. Done.
+                // Otherwise, if the parent wasn't found, return an error.
+                if (parent == null) break else return error.ParentNotFound;
+
+            // If we reached the specified `parent`, we're done here!
             if (parent != null and current.raw == parent.?.raw) break;
         }