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/build_lua.zig

@@ -0,0 +1,138 @@
+const std = @import("std");
+const LazyPath = std.Build.LazyPath;
+
+pub fn build_nlua0(
+    b: *std.Build,
+    target: std.Build.ResolvedTarget,
+    optimize: std.builtin.OptimizeMode,
+    use_luajit: bool,
+    ziglua: *std.Build.Dependency,
+    lpeg: *std.Build.Dependency,
+) *std.Build.Step.Compile {
+    const options = b.addOptions();
+    options.addOption(bool, "use_luajit", use_luajit);
+
+    const nlua0_exe = b.addExecutable(.{
+        .name = "nlua0",
+        .root_source_file = b.path("src/nlua0.zig"),
+        .target = target,
+        .optimize = optimize,
+    });
+    const nlua0_mod = nlua0_exe.root_module;
+
+    const exe_unit_tests = b.addTest(.{
+        .root_source_file = b.path("src/nlua0.zig"),
+        .target = target,
+        .optimize = optimize,
+    });
+
+    const embedded_data = b.addModule("embedded_data", .{
+        .root_source_file = b.path("runtime/embedded_data.zig"),
+    });
+
+    for ([2]*std.Build.Module{ nlua0_mod, exe_unit_tests.root_module }) |mod| {
+        mod.addImport("ziglua", ziglua.module("lua_wrapper"));
+        mod.addImport("embedded_data", embedded_data);
+        // addImport already links by itself. but we need headers as well..
+        mod.linkLibrary(ziglua.artifact("lua"));
+
+        mod.addOptions("options", options);
+
+        mod.addIncludePath(b.path("src"));
+        mod.addIncludePath(b.path("src/includes_fixmelater"));
+        add_lua_modules(mod, lpeg, use_luajit, true);
+    }
+
+    // for debugging the nlua0 environment
+    // like this: `zig build nlua0 -- script.lua {args}`
+    const run_cmd = b.addRunArtifact(nlua0_exe);
+    if (b.args) |args| {
+        run_cmd.addArgs(args);
+    }
+    const run_step = b.step("nlua0", "Run nlua0 build tool");
+    run_step.dependOn(&run_cmd.step);
+
+    b.installArtifact(nlua0_exe); // DEBUG
+
+    const run_exe_unit_tests = b.addRunArtifact(exe_unit_tests);
+
+    const test_step = b.step("test_nlua0", "Run unit tests for nlua0");
+    test_step.dependOn(&run_exe_unit_tests.step);
+
+    return nlua0_exe;
+}
+
+pub fn add_lua_modules(mod: *std.Build.Module, lpeg: *std.Build.Dependency, use_luajit: bool, is_nlua0: bool) void {
+    const flags = [_][]const u8{
+        // Standard version used in Lua Makefile
+        "-std=gnu99",
+        if (is_nlua0) "-DNVIM_NLUA0" else "",
+    };
+
+    mod.addIncludePath(lpeg.path(""));
+    mod.addCSourceFiles(.{
+        .files = &.{
+            "src/mpack/lmpack.c",
+            "src/mpack/mpack_core.c",
+            "src/mpack/object.c",
+            "src/mpack/conv.c",
+            "src/mpack/rpc.c",
+        },
+        .flags = &flags,
+    });
+    mod.addCSourceFiles(.{
+        .root = .{ .dependency = .{ .dependency = lpeg, .sub_path = "" } },
+        .files = &.{
+            "lpcap.c",
+            "lpcode.c",
+            "lpcset.c",
+            "lpprint.c",
+            "lptree.c",
+            "lpvm.c",
+        },
+        .flags = &flags,
+    });
+
+    if (!use_luajit) {
+        mod.addCSourceFiles(.{
+            .files = &.{
+                "src/bit.c",
+            },
+            .flags = &flags,
+        });
+    }
+}
+
+pub fn build_libluv(
+    b: *std.Build,
+    target: std.Build.ResolvedTarget,
+    optimize: std.builtin.OptimizeMode,
+    lua: *std.Build.Step.Compile,
+    libuv: *std.Build.Step.Compile,
+) !*std.Build.Step.Compile {
+    const upstream = b.dependency("libluv", .{});
+    const compat53 = b.dependency("lua_compat53", .{});
+    const lib = b.addStaticLibrary(.{
+        .name = "luv",
+        .target = target,
+        .optimize = optimize,
+    });
+
+    lib.linkLibrary(lua);
+    lib.linkLibrary(libuv);
+
+    lib.addIncludePath(upstream.path("src"));
+    lib.addIncludePath(compat53.path("c-api"));
+
+    lib.installHeader(upstream.path("src/luv.h"), "luv/luv.h");
+
+    lib.addCSourceFiles(.{ .root = upstream.path("src/"), .files = &.{
+        "luv.c",
+    } });
+
+    lib.addCSourceFiles(.{ .root = compat53.path("c-api"), .files = &.{
+        "compat-5.3.c",
+    } });
+
+    return lib;
+}