Add 'comptime-topological-sort/' from commit 'a148d59decb1f874044b8b4b8baba793ce3ef354'

git-subtree-dir: comptime-topological-sort
git-subtree-mainline: 3b252de1ca
git-subtree-split: a148d59dec

comptime-topological-sort/main.zig

@@ -0,0 +1,52 @@
+const std = @import("std");
+
+const Render = struct {
+    const depends = .{};
+};
+
+const Window = struct {
+    const depends = .{Render};
+};
+
+const ImGui = struct {
+    const depends = .{ Render, Window };
+};
+
+const App = struct {
+    const depends = .{ImGui};
+};
+
+fn append(comptime T: type, comptime list: []const T, comptime val: T) []const T {
+    return list ++ [1]T{val};
+}
+
+fn contains(comptime T: type, comptime haystack: []const T, comptime needle: T) bool {
+    return std.mem.indexOfScalar(T, haystack, needle) != null;
+}
+
+pub fn dependencies(mod: type) []const type {
+    // todo add a "before" and "after" that impose ordering constraints but don't bring the items in as depednencies.
+
+    const Ctx = struct {
+        all: []const type = &.{},
+        mark: []const type = &.{},
+
+        fn visit(ctx: *@This(), x: type) void {
+            if (contains(type, ctx.all, x)) return;
+            if (contains(type, ctx.mark, x)) @compileError("cycle");
+            ctx.mark = append(type, ctx.mark, x);
+            for (x.depends) |dep| ctx.visit(dep);
+            ctx.all = append(type, ctx.all, x);
+        }
+    };
+
+    var ctx: Ctx = .{};
+    ctx.visit(mod);
+    return ctx.all;
+}
+
+pub fn main() !void {
+    inline for (dependencies(App)) |dep| {
+        std.debug.print("{s}\n", .{@typeName(dep)});
+    }
+}