xmake-style

Xmake Configuration Style & Conventions

xmake.lua is Lua, but idiomatic xmake code looks less like Lua and more like a declarative configuration. Following the conventions below keeps files readable, fast to parse, and consistent with the style used throughout xmake and xmake-repo.

1. The description / script split (the single most important rule)

xmake.lua has two domains and they have very different rules.

Description domain — keep it declarative

This is the top-level body of target(), option(), package(), task(), rule(), and their set_xxx/add_xxx calls.

target("app")
    set_kind("binary")
    add_files("src/*.cpp")
    add_defines("DEBUG")
    add_syslinks("pthread")

Rules for the description domain:

• Treat it as config, not code. Basic if is_plat(...) and for _, x in ipairs({...}) are fine; complex logic is not.
• It is parsed multiple times. Every set_/add_ call may run more than once as xmake re-enters the file at different configuration stages. Never print() here (you will see it twice), and never do expensive work (I/O, git, network, shell).
• Many APIs are forbidden or read-only here. os.getenv is read-only; most mutating os.* calls are blocked.
• If logic is not a trivial if or for, move it to the script domain.

Script domain — put complex logic here

Anything inside on_load, on_config, before_build, after_build, on_install, on_test, etc., is the script domain. It runs once per lifecycle hook and has the full xmake Lua environment.

target("app")
    set_kind("binary")
    add_files("src/*.cpp")
    on_load(function (target)
        if is_plat("linux", "macosx") then
            target:add("links", "pthread", "m", "dl")
        end
    end)
    after_build(function (target)
        import("core.project.config")
        os.cp(target:targetfile(), path.join(config.buildir(), "dist"))
    end)

Use on_load for dynamic per-target configuration that would be ugly as nested if blocks at description level.

Extract long scripts to separate files

Once a hook body exceeds ~15 lines, move it out:

target("app")
    on_load("modules.app.load")
    on_install("modules.app.install")

With files at modules/app/load.lua and modules/app/install.lua, each exporting a main function. Keeps the main xmake.lua scannable.

2. Indentation and layout

The conventions used throughout the xmake project itself:

-- 4 spaces, never tabs
add_rules("mode.debug", "mode.release")

-- blank line between top-level blocks
add_requires("fmt 10.x", "spdlog")

-- everything inside a target() is indented one level
target("mylib")
    set_kind("static")
    add_files("src/lib/*.cpp")
    add_includedirs("include", {public = true})
    add_packages("fmt")

target("app")
    set_kind("binary")
    add_files("src/app/*.cpp")
    add_deps("mylib")

• 4 spaces per level. No tabs. The xmake CONTRIBUTING guide makes this explicit.
• No explicit target_end() unless you have to. A new top-level call (target, option, package, rule, task) implicitly closes the previous one.
• Blank line between blocks. Makes visual scanning easier when a file has many targets.
• Related add_* calls stay grouped. Put add_files / add_headerfiles together; put add_includedirs / add_defines together; put add_packages / add_deps together.
• Comments use --. Use -- for single-line comments. Avoid --[[ ]] blocks unless you are commenting out several lines temporarily.

Parentheses are optional for single-arg string calls

Both of these are valid:

target("test")
    set_kind("binary")
    add_files("src/*.c")

target "test"
    set_kind "binary"
    add_files "src/*.c"

Pick one and stick with it per file. The xmake and xmake-repo codebases predominantly use parentheses — match that style unless you have a reason.

3. Naming conventions

• Target names: lowercase, - or _ for word separators. mylib, my-lib, my_lib. Match the produced binary name when it makes sense.
• Options: same — lowercase with _. Prefix with enable_ / with_ / has_ to signal intent (enable_foo, with_openssl, has_avx2).
• Rules: dotted namespaces for grouping (mycompany.codegen, mycompany.protobuf). Match how built-in rules are named (mode.debug, c++.unity_build, plugin.compile_commands.autoupdate).
• Custom toolchains: short, lowercase, no prefix. myclang, arm-muslgcc.
• Packages (in xmake-repo recipes): exactly the upstream name, lowercase, --separated. Match what add_requires users will type.

4. set_ vs add_: pick the right one

• set_xxx — replaces. Use for single-valued properties: set_kind, set_version, set_languages, set_optimize, set_symbols, set_default, set_toolchains.
• add_xxx — appends. Use for list-valued properties: add_files, add_includedirs, add_defines, add_links, add_deps, add_packages, add_cxflags.

If you call set_xxx twice for the same key, the second wins. If that is what you want, fine — but it is almost always a mistake.

-- ✗ wrong: second set_languages replaces the first
set_languages("c++17")
set_languages("c++20")

-- ✓ just set it once, at the level you want
set_languages("c++20")

5. Scope & visibility ({public = true})

Use {public = true} for anything a dependent target needs to see: public headers, public defines, public link libraries.

target("mylib")
    set_kind("static")
    add_files("src/*.cpp")
    add_includedirs("include", {public = true})    -- dependents get -Iinclude
    add_defines("MYLIB_STATIC", {public = true})   -- and this define

• Private by default is correct: a dependent target should not inherit your src/ include dir or your internal defines.
• {force = true} bypasses xmake's automatic flag-detection filter. Use sparingly and only when you know the flag is supported.

6. Conditionals: prefer is_plat / is_arch / is_mode

Idiomatic:

if is_plat("windows") then
    add_defines("WIN32_LEAN_AND_MEAN")
elseif is_plat("linux", "macosx") then
    add_syslinks("pthread")
end

if is_mode("debug") then
    add_defines("DEBUG")
    set_symbols("debug")
end

Avoid reaching into os.host() / os.arch() at description level for platform gating — that is the host, not the target. is_plat/is_arch reflect the configured target and are the right answer 99% of the time.

7. Options — declaration style

option("enable_foo")
    set_default(false)
    set_showmenu(true)
    set_description("Enable the foo subsystem")
    set_category("feature")         -- optional grouping in --menu
option_end()

Conventions:

• Always set_showmenu(true) if the option is meant for end users — otherwise it's invisible to xmake f --menu.
• Always set_description(...) — the description is what shows up in the configure menu.
• Use set_default(...) to pin a default; do not rely on nil.
• Use set_values(...) to constrain to an enum when applicable.
• For build-flag-style options, prefer has_config("name") over get_config("name") in the target body unless you need the actual value.

8. Packages — declaration style

In a project xmake.lua:

-- all add_requires at the top of the file
add_requires("fmt 10.x")
add_requires("spdlog", {configs = {header_only = false}})
add_requires("openssl", {system = false})

target("app")
    add_packages("fmt", "spdlog", "openssl")

• Declare add_requires near the top, before any target(). Keeps the dependency surface visible in one place.
• Pin major versions for anything you actually care about stability for ("fmt 10.x", "boost 1.84.x").
• Prefer add_packages(...) over manually setting add_links/add_includedirs — the package integration does the right thing automatically.

In a package recipe (packages/<a>/<name>/xmake.lua in xmake-repo):

package("mylib")
    set_homepage("https://example.com/mylib")
    set_description("A short one-line description")
    set_license("MIT")

    add_urls("https://github.com/example/mylib/archive/v$(version).tar.gz",
             "https://github.com/example/mylib.git")

    add_versions("1.2.3", "abcdef...sha256...")

    add_configs("shared", {description = "Build shared library", default = false, type = "boolean"})
    add_configs("with_ssl", {description = "Enable SSL support", default = true, type = "boolean"})

    add_deps("cmake")
    if is_plat("linux") then
        add_syslinks("pthread")
    end

    on_install(function (package)
        local configs = {"-DBUILD_TESTS=OFF"}
        table.insert(configs, "-DBUILD_SHARED_LIBS=" .. (package:config("shared") and "ON" or "OFF"))
        import("package.tools.cmake").install(package, configs)
    end)

    on_test(function (package)
        assert(package:has_cfuncs("mylib_init", {includes = "mylib.h"}))
    end)
package_end()

Recipe conventions:

• set_homepage / set_description / set_license in that order, at the top.
• Multiple add_urls for mirror fallback; the .git URL last.
• add_configs names lowercased with underscores: shared, with_ssl, header_only, enable_foo. Match what users already type in other recipes.
• add_versions kept in descending order (newest at top) in xmake-repo.
• on_install uses import("package.tools.cmake") (or autoconf, meson, make, msbuild, xmake) — almost always one of these. Don't hand-roll.
• on_test asserts a real symbol with has_cfuncs / has_cxxtypes / check_csnippets. Empty on_test is a red flag.

9. Don't reinvent common patterns

• Build modes → add_rules("mode.debug", "mode.release"). Don't hand-roll debug/release defines.
• compile_commands.json → add_rules("plugin.compile_commands.autoupdate", {outputdir = "."}).
• Unity builds → add_rules("c++.unity_build"), not hand-crafted aggregating files.
• Qt apps → add_rules("qt.widgetapp" / "qt.quickapp"), not manual uic/moc/rcc invocations.
• Generating a config header → add_configfiles("config.h.in") + set_configvar, not a before_build Lua shell script.

If the built-in exists, use it. It handles edge cases (cross-compilation, multiple platforms, caching) that your hand-rolled version will not.

10. Things to avoid

Anti-pattern	Why	Do this instead
print(...) at description level	Runs multiple times	Use cprint in on_load / on_config, or utils.vprint gated by -v
Complex for / nested if at description level	Parsed multiple times; harder to reason about	Move into on_load(function(target) ... end)
os.iorun / git calls at description level	Runs during every parse	Move into on_load or a task
add_cxflags("-std=c++20", {force = true})	Bypasses xmake's language handling	set_languages("c++20")
add_links("pthread") on cross-platform code	Not a library on Windows	add_syslinks("pthread")
set_languages called per-target when every target uses the same standard	Duplication	Call once at the top of xmake.lua
Using absolute paths	Not portable	Paths relative to xmake.lua; xmake resolves them
Re-exporting every header with add_includedirs	Pollutes dependents	{public = true} only on the public include dir
Empty on_test in a package recipe	Passes trivially	Use has_cfuncs / check_csnippets to actually exercise the library

11. Commit-message convention (contributor-facing)

From CONTRIBUTING.md of both xmake and xmake-repo:

• Commit messages in English.
• Use descriptive summaries: add ..., fix ..., improve ..., update ....
• New or changed public API should go through an issue/RFC first rather than straight into a PR.
• Indent edited code with 4 spaces, never tabs — same as the xmake.lua rule.

When to branch out

• The actual semantics of target / add_files / add_deps → xmake-targets
• The actual semantics of option / has_config → xmake-options
• The actual semantics of add_requires / add_packages → xmake-packages
• Recipe authoring workflow and testing → xmake-repo-testing
• Rule/toolchain semantics → xmake-rules / xmake-toolchains