From 8e4f56d1477b33a9c1eb66a68f8dd8534d446c88 Mon Sep 17 00:00:00 2001
From: Squibid <me@zacharyscheiman.com>
Date: Wed, 22 Oct 2025 22:40:19 -0400
Subject: [PATCH] add a basic filesystem library and use it for path concat

---
 runtime/share/mezzaluna/init.lua |  6 ++---
 src/lua/fs.zig                   | 43 ++++++++++++++++++++++++++++++++
 src/lua/lua.zig                  |  6 +++++
 3 files changed, 52 insertions(+), 3 deletions(-)

diff --git a/runtime/share/mezzaluna/init.lua b/runtime/share/mezzaluna/init.lua
index 9976a90..cfef496 100644
--- a/runtime/share/mezzaluna/init.lua
+++ b/runtime/share/mezzaluna/init.lua
@@ -4,8 +4,8 @@ if not env_conf then
   if not env_conf then
     error("Couldn't determine potential config directory is $HOME set?")
   end
-  env_conf = env_conf.."/.config/"
+  env_conf = mez.fs.joinpath(env_conf, ".config")
 end
 
-mez.path.config = env_conf.."/mez/init.lua"
-package.path = package.path..";"..env_conf.."/mez/lua/?.lua"
+mez.path.config = mez.fs.joinpath(env_conf, "mez", "init.lua")
+package.path = package.path..";"..mez.fs.joinpath(env_conf, "mez", "lua", "?.lua")
diff --git a/src/lua/fs.zig b/src/lua/fs.zig
index e69de29..3e5ea2c 100644
--- a/src/lua/fs.zig
+++ b/src/lua/fs.zig
@@ -0,0 +1,43 @@
+const Fs = @This();
+
+const std = @import("std");
+const zlua = @import("zlua");
+
+const Lua = @import("lua.zig");
+
+const gpa = std.heap.c_allocator;
+
+pub fn joinpath(L: *zlua.Lua) i32 {
+  const nargs: i32 = L.getTop();
+  if (nargs < 2) {
+    L.raiseErrorStr("Expected at least two paths to join", .{});
+    return 0;
+  }
+
+  var paths = std.ArrayList([:0]const u8).initCapacity(gpa, @intCast(nargs)) catch {
+    return 0;
+  };
+  defer paths.deinit(gpa);
+
+  var i: u8 = 1;
+  while (i <= nargs) : (i += 1) {
+    if (!L.isString(i)) {
+      L.raiseErrorStr("Expected string at argument %d", .{i});
+      return 0;
+    }
+
+    const partial_path = L.toString(i) catch unreachable;
+    paths.append(gpa, partial_path) catch {
+      // TODO: tell lua?
+      return 0;
+    };
+  }
+
+  const final_path: []const u8 = std.fs.path.join(gpa, paths.items) catch {
+    // TODO: tell lua?
+    return 0;
+  };
+  _ = L.pushString(final_path);
+
+  return 1;
+}
diff --git a/src/lua/lua.zig b/src/lua/lua.zig
index ae5c23b..7a3e6cd 100644
--- a/src/lua/lua.zig
+++ b/src/lua/lua.zig
@@ -5,6 +5,7 @@ const config = @import("config");
 const zlua = @import("zlua");
 
 const Bridge = @import("bridge.zig");
+const Fs = @import("fs.zig");
 
 const gpa = std.heap.c_allocator;
 
@@ -51,6 +52,11 @@ pub fn init(self: *Lua) !void {
       self.state.newTable();
       defer _ = self.state.setField(-2, "path");
     }
+    {
+      const funcs = zlua.fnRegsFromType(Fs);
+      self.state.newLib(funcs);
+      self.state.setField(-2, "fs");
+    }
   }
 
   loadRuntimeDir(self) catch |err| {