{module,ecs}: Mach ECS becomes the Mach' module system

This moves the bulk of the ECS code into `src/module`. It also makes
types like `mach.ecs.EntityID` accessible at the top-level `mach.EntityID`
instead.

The motivation of this change is to make the Mach module system a
first-class property of Mach.

Signed-off-by: Stephen Gutekanst <stephen@hexops.com>

src/engine.zig

@@ -2,8 +2,6 @@ const std = @import("std");
 const mach = @import("main.zig");
 const core = mach.core;
 const gpu = mach.core.gpu;
-const ecs = mach.ecs;
-const module = @import("module.zig");
 
 var gpa = std.heap.GeneralPurposeAllocator(.{}){};
 const allocator = gpa.allocator();

src/gfx/Sprite.zig

@@ -2,7 +2,6 @@ const std = @import("std");
 const mach = @import("../main.zig");
 const core = mach.core;
 const gpu = mach.core.gpu;
-const ecs = mach.ecs;
 const Engine = mach.Engine;
 
 const math = mach.math;

src/gfx/Text.zig

@@ -2,7 +2,6 @@ const std = @import("std");
 const mach = @import("../main.zig");
 const core = mach.core;
 const gpu = mach.gpu;
-const ecs = mach.ecs;
 const Engine = mach.Engine;
 const gfx = mach.gfx;
 
@@ -49,7 +48,7 @@ pub const components = .{
     \\ Expected to match the length of the style component.
     },
 
-    .style = .{ .type = []const mach.ecs.EntityID, .description = 
+    .style = .{ .type = []const mach.EntityID, .description = 
     \\ The style to apply to each segment of text.
     \\
     \\ Expected to match the length of the text component.

src/main.zig

@@ -8,7 +8,6 @@ pub const gpu = if (build_options.want_core) core.gpu else struct {};
 pub const sysjs = if (build_options.want_core) @import("mach-sysjs") else struct {};
 
 // Mach standard library
-pub const ecs = @import("ecs/main.zig");
 // gamemode requires libc on linux
 pub const gamemode = if (builtin.os.tag != .linux or builtin.link_libc) @import("gamemode.zig");
 pub const gfx = if (build_options.want_mach) @import("gfx/main.zig") else struct {};
@@ -21,17 +20,19 @@ pub const sysgpu = if (build_options.want_sysgpu) @import("sysgpu/main.zig") els
 // Engine exports
 pub const App = @import("engine.zig").App;
 pub const Engine = @import("engine.zig").Engine;
-pub const ModSet = @import("module.zig").ModSet;
 
-// TODO: perhaps this could be a comptime var rather than @import("root")?
+// Module system
+pub const ModSet = @import("module/main.zig").ModSet;
 pub const modules = blk: {
     if (!@hasDecl(@import("root"), "modules")) {
         @compileError("expected `pub const modules = .{};` in root file");
     }
     break :blk @import("root").modules;
 };
-pub const Modules = @import("module.zig").Modules(modules);
+pub const Modules = @import("module/main.zig").Modules(modules);
 pub const Mod = ModSet(modules).Mod;
+pub const EntityID = @import("module/main.zig").EntityID;
+pub const Archetype = @import("module/main.zig").Archetype;
 
 test {
     const std = @import("std");
@@ -44,8 +45,7 @@ test {
     _ = gfx;
     _ = math;
     _ = testing;
-    std.testing.refAllDeclsRecursive(@import("module.zig"));
-    std.testing.refAllDeclsRecursive(ecs);
+    std.testing.refAllDeclsRecursive(@import("module/main.zig"));
     std.testing.refAllDeclsRecursive(gamemode);
     std.testing.refAllDeclsRecursive(math);
 }

src/module/entities.zig

@@ -6,7 +6,7 @@ const assert = std.debug.assert;
 const query_mod = @import("query.zig");
 const Archetype = @import("Archetype.zig");
 const StringTable = @import("StringTable.zig");
-const ComponentTypesByName = @import("../module.zig").ComponentTypesByName;
+const ComponentTypesByName = @import("module.zig").ComponentTypesByName;
 
 /// An entity ID uniquely identifies an entity globally within an Entities set.
 pub const EntityID = u64;

src/module/main.zig

@@ -1,16 +1,3 @@
-//! mach/ecs is an Entity component system implementation.
-//!
-//! ## Design principles:
-//!
-//! * Initially a 100% clean-room implementation, working from first-principles. Later informed by
-//!   research into how other ECS work, with advice from e.g. Bevy and Flecs authors at different
-//!   points (thank you!)
-//! * Solve the problems ECS solves, in a way that is natural to Zig and leverages Zig comptime.
-//! * Fast. Optimal for CPU caches, multi-threaded, leverage comptime as much as is reasonable.
-//! * Simple. Small API footprint, should be natural and fun - not like you're writing boilerplate.
-//! * Enable other libraries to provide tracing, editors, visualizers, profilers, etc.
-//!
-
 const std = @import("std");
 const mach = @import("../main.zig");
 const testing = std.testing;
@@ -18,15 +5,8 @@ const testing = std.testing;
 pub const EntityID = @import("entities.zig").EntityID;
 pub const Entities = @import("entities.zig").Entities;
 pub const Archetype = @import("Archetype.zig");
-
-pub const Modules = @import("../module.zig").Modules;
-
-// TODO:
-// * Iteration
-// * Querying
-// * Multi threading
-// * Multiple entities having one value
-// * Sparse storage?
+pub const ModSet = @import("module.zig").ModSet;
+pub const Modules = @import("module.zig").Modules;
 
 test {
     std.testing.refAllDeclsRecursive(@This());
@@ -36,7 +16,7 @@ test {
     std.testing.refAllDeclsRecursive(@import("StringTable.zig"));
 }
 
-test "example" {
+test "entities DB" {
     const allocator = testing.allocator;
 
     const root = struct {

src/module/module.zig

@@ -61,11 +61,11 @@
 
 const builtin = @import("builtin");
 const std = @import("std");
-const testing = @import("testing.zig");
+const testing = @import("../testing.zig");
 
-const Entities = @import("ecs/entities.zig").Entities;
-const EntityID = @import("ecs/entities.zig").EntityID;
-const is_debug = @import("ecs/Archetype.zig").is_debug;
+const Entities = @import("entities.zig").Entities;
+const EntityID = @import("entities.zig").EntityID;
+const is_debug = @import("Archetype.zig").is_debug;
 
 /// Verifies that M matches the basic layout of a Mach module
 fn ModuleInterface(comptime M: type) type {

src/module/query.zig

@@ -1,6 +1,6 @@
 const std = @import("std");
 const testing = std.testing;
-const ComponentTypesByName = @import("../module.zig").ComponentTypesByName;
+const ComponentTypesByName = @import("module.zig").ComponentTypesByName;
 
 pub const QueryTag = enum {
     any,