feat(build): build.zig MVP: build and run functionaltests on linux

NEW BUILD SYSTEM!

This is a MVP implementation which supports building the "nvim" binary,
including cross-compilation for some targets.
As an example, you can build a aarch64-macos binary from
an x86-64-linux-gnu host, or vice versa

Add CI target for build.zig currently for functionaltests on linux
x86_64 only

Follow up items:

-  praxis for version and dependency bumping
-  windows 💀
-  full integration of libintl and gettext (or a desicion not to)
-  update help and API metadata files
-  installation into a $PREFIX
-  more tests and linters

src/nlua0.zig

@@ -0,0 +1,120 @@
+//! "nlua" is an abbreviation for nvim flavored lua, i e lua with the
+//! extended standard library functionality added by nvim such as json, mpack
+//! and libuv and a range of vim.* utility functions.
+//!
+//! nlua0 is an interpreter for the "bootstrap" lua code we need to run before
+//! nvim can be built, in order to run lua scripts which process and generate
+//! more .c code, which still need these extensions.
+const std = @import("std");
+const ziglua = @import("ziglua");
+const options = @import("options");
+
+const embedded_data = @import("embedded_data");
+
+// these are common dependencies used by many generators
+const hashy = @embedFile("gen/hashy.lua");
+const c_grammar = @embedFile("gen/c_grammar.lua");
+
+const Lua = ziglua.Lua;
+
+extern "c" fn luaopen_mpack(ptr: *anyopaque) c_int;
+extern "c" fn luaopen_lpeg(ptr: *anyopaque) c_int;
+extern "c" fn luaopen_bit(ptr: *anyopaque) c_int;
+
+fn init() !*Lua {
+    // Initialize the Lua vm
+    var lua = try Lua.init(std.heap.c_allocator);
+    lua.openLibs();
+
+    // this sets _G.vim by itself, so we don't need to
+    try lua.loadBuffer(embedded_data.shared_module, "shared.lua");
+    lua.call(.{ .results = 1 });
+
+    try lua.loadBuffer(embedded_data.inspect_module, "inspect.lua");
+    lua.call(.{ .results = 1 });
+    lua.setField(-2, "inspect");
+
+    try lua.loadBuffer(embedded_data.iter_module, "iter.lua");
+    lua.call(.{ .results = 1 });
+    lua.setField(-2, "iter");
+
+    _ = try lua.getGlobal("package");
+    _ = lua.getField(-1, "preload");
+    try lua.loadBuffer(hashy, "hashy.lua"); // [package, preload, hashy]
+    lua.setField(-2, "gen.hashy");
+    try lua.loadBuffer(c_grammar, "c_grammar.lua"); // [package, preload, c_grammar]
+    lua.setField(-2, "gen.c_grammar");
+    lua.pop(2);
+
+    const retval = luaopen_mpack(lua);
+    if (retval != 1) return error.LoadError;
+    _ = lua.getField(-1, "NIL"); // [vim, mpack, NIL]
+    lua.setField(-3, "NIL"); // vim.NIL = mpack.NIL (wow BOB wow)
+    lua.setField(-2, "mpack");
+
+    const retval2 = luaopen_lpeg(lua);
+    if (retval2 != 1) return error.LoadError;
+    lua.setField(-3, "lpeg");
+
+    lua.pop(2);
+
+    if (!options.use_luajit) {
+        lua.pop(luaopen_bit(lua));
+    }
+    return lua;
+}
+
+pub fn main() !void {
+    const argv = std.os.argv;
+
+    const lua = try init();
+    defer lua.deinit();
+
+    if (argv.len < 2) {
+        std.debug.print("USAGE: nlua0 script.lua args...\n\n", .{});
+        return;
+    }
+    lua.createTable(@intCast(argv.len - 2), 1);
+    for (0.., argv[1..]) |i, arg| {
+        _ = lua.pushString(std.mem.span(arg));
+        lua.rawSetIndex(-2, @intCast(i));
+    }
+    lua.setGlobal("arg");
+
+    _ = try lua.getGlobal("debug");
+    _ = lua.getField(-1, "traceback");
+    try lua.loadFile(std.mem.span(argv[1]));
+    lua.protectedCall(.{ .msg_handler = -2 }) catch |e| {
+        if (e == error.LuaRuntime) {
+            const msg = try lua.toString(-1);
+            std.debug.print("{s}\n", .{msg});
+        }
+        return e;
+    };
+}
+
+fn do_ret1(lua: *Lua, str: [:0]const u8) !void {
+    try lua.loadString(str);
+    try lua.protectedCall(.{ .results = 1 });
+}
+
+test "simple test" {
+    const lua = try init();
+    defer lua.deinit();
+
+    try do_ret1(lua, "return vim.isarray({2,3})");
+    try std.testing.expectEqual(true, lua.toBoolean(-1));
+    lua.pop(1);
+
+    try do_ret1(lua, "return vim.isarray({a=2,b=3})");
+    try std.testing.expectEqual(false, lua.toBoolean(-1));
+    lua.pop(1);
+
+    try do_ret1(lua, "return vim.inspect(vim.mpack.decode('\\146\\42\\69'))");
+    try std.testing.expectEqualStrings("{ 42, 69 }", try lua.toString(-1));
+    lua.pop(1);
+
+    try do_ret1(lua, "return require'bit'.band(7,12)");
+    try std.testing.expectEqualStrings("4", try lua.toString(-1));
+    lua.pop(1);
+}