Crafter Build

A C++26 modules build system. Project descriptions are written in C++ with no JSON, no Lua, no embedded DSL. You write a project.cpp that constructs a Configuration and returns it; Crafter Build compiles, loads, and executes it.

Install

crafter-build ships as a Flatpak that carries its own clang, lld, libc++ and WASI sysroot, so every machine builds with the same compiler:

flatpak remote-add --if-not-exists catcrafts https://flatpak.catcrafts.net/catcrafts.flatpakrepo
flatpak install catcrafts net.catcrafts.CrafterBuild
alias crafter-build='flatpak run net.catcrafts.CrafterBuild'

Pre-release builds of master are the beta branch (flatpak install catcrafts net.catcrafts.CrafterBuild//beta), and every release also attaches a single-file bundle on the Forgejo releases page (flatpak install --user crafter-build-<version>.flatpak). The sandbox sees the whole host filesystem, so projects can live anywhere. Binaries built for the host link the bundled libc++.so.1 through an rpath into the Flatpak: they run inside it (-r, the test runner), and are not meant to be copied out onto the host.

Building from source (Linux)

The development loop is native. It needs clang, cmake, git, lld and libc++ with its std module source:

./build.sh                                # produces bin/crafter-build
./bin/crafter-build                       # rebuild via project.cpp

The compiler is resolved once per run: CRAFTER_BUILD_LLVM_DIR if set, else a clang++ installed beside crafter-build (<prefix>/bin), else PATH. crafter-build --version prints the version and the compiler in use; crafter-build --help lists the other overrides (CRAFTER_BUILD_LIBCXX_DIR, CRAFTER_BUILD_LIBCLANG, CRAFTER_BUILD_WASI_SYSROOT, CRAFTER_MINGW_DIR). A Configuration targets the host triple unless cfg.target says otherwise.

The bootstrap targets the toolchain's own triple (clang++ -print-target-triple); override with CRAFTER_BUILD_TARGET=. The Flatpak is built from packaging/flatpak/net.catcrafts.CrafterBuild.yaml, which runs this same bootstrap, the self-host build and the test suite inside the sandbox against the bundled toolchain (CRAFTER_BUILD_LLVM_DIR=/app).

Writing a project.cpp

Crafter Build loads a project.cpp from the current directory. The file exports one function that returns a populated Configuration:

import std;
import Crafter.Build;
namespace fs = std::filesystem;
using namespace Crafter;

extern "C" Configuration CrafterBuildProject(std::span<const std::string_view> args) {
    Configuration cfg;
    cfg.path = "./";
    cfg.name = "myapp";
    cfg.outputName = "myapp";
    cfg.type = ConfigurationType::Executable;

    std::array<fs::path, 1> ifaces = { "interfaces/Hello" };
    std::array<fs::path, 2> impls  = { "implementations/Hello", "implementations/main" };
    cfg.GetInterfacesAndImplementations(ifaces, impls);

    return cfg;
}

Run crafter-build in that directory; outputs land at bin/myapp-<target>-<march>/myapp and intermediates at build/myapp-<target>-<march>/. Add -r to run the produced executable straight after a successful build.

Dependencies

Three kinds, all fetched/built incrementally:

Cross-project Crafter sub-projects — point cfg.dependencies at another Configuration*. Cross-project module imports (import OtherProject;) are tracked per-import: only the modules that actually import a changed dep rebuild.

External git+cmake deps — for things like glslang. Declare in cfg.externalDependencies:

ExternalDependency& glslang = cfg.externalDependencies.emplace_back();
glslang.name = "glslang";
glslang.source.url = "https://github.com/KhronosGroup/glslang.git";
glslang.source.branch = "main";
glslang.builder = ExternalBuilder::CMake;
glslang.options = { "-DENABLE_OPT=OFF" };
glslang.includeDirs = { "" };
glslang.libs = { "SPIRV", "glslang", "OSDependent" };

Clones live at ~/.cache/crafter.build/external/<name>-<hash>/, keyed by (url, branch, commit, options) so different projects sharing the same dep with the same spec reuse the clone and cmake build, while projects with diverging specs each get their own cache entry. The clone is resilient to partial-clone recovery and CMake reconfigure is triggered automatically on options changes.

Header-only git deps — same as cmake deps but builder = ExternalBuilder::None. Just clones and propagates -I flags.

Sibling crafter-build projects — GitProject / LocalProject load another project's project.cpp in-process and return a Configuration* for cfg.dependencies:

Configuration* math = GitProject({
    .source = { .url = "https://forgejo.catcrafts.net/Catcrafts/Crafter.Math.git" },  // .branch or .commit to pin
    .args = depArgs,                                                                   // forwarded to its CrafterBuildProject
});
Configuration* sibling = LocalProject({ .projectFile = "../Crafter.Math/project.cpp", .args = depArgs });
cfg.dependencies = { math };

Clones share the external cache and identical specs share one Configuration. An unpinned source is git pulled on every invocation; set .commit for reproducible, offline-after-first-fetch builds.

A project loaded this way runs its CrafterBuildProject as a dependency, and IsTopLevelProject() is false while it does (true in the project crafter-build was pointed at, and outside any project file). Wire test-only dependencies behind it: a library whose test links crafter-build itself would otherwise load crafter-build's project.cpp from inside crafter-build and recurse.

Dependencies of project.cpp itself

project.cpp can import modules from another crafter-build project. The file has to compile before it can say anything, so the dependency is a directive next to the import it enables:

import std;
import Crafter.Build;
#pragma crafter dependency "https://forgejo.catcrafts.net/Catcrafts/Crafter.LintRules.git"
import Crafter.LintRules;

#pragma crafter dependency "<source>" [branch "<name>" | commit "<sha>"] [project "<file>"]

Install layout

Inside the Flatpak:

/app/bin/crafter-build                   # the executable
/app/bin/clang++ lld llvm-ar wasmtime    # the bundled toolchain the executable resolves first
/app/lib/libcrafter-build.a              # static archive for downstream consumers
/app/share/crafter-build/*.cppm          # module sources (rebuilt on the user's machine on first run)
/app/share/wasi-sysroot/                 # WASI sysroot for wasm32 targets
~/.var/app/net.catcrafts.CrafterBuild/cache/crafter.build/<target>-<march>-<clang>-<hash>/
                                         # std.pcm + Crafter.Build*.pcm, built locally per toolchain

A source build uses the same shape under the checkout (bin/, lib/, share/crafter-build/) with the system compiler and ~/.cache/crafter.build/.

Tests

Tests live under tests/<Name>/. The simplest case is a single C++ file:

tests/Smoke/main.cpp        # int main() — exit 0 = pass, nonzero = fail, 77 = skipped

Run them all:

crafter-build test

Test conventions:

• Exit codes: 0 = ✅ pass, nonzero = ❌ fail, 77 = ⏭ skipped (autoconf convention; use it for runtime opt-outs like "tool not on PATH").
• Each test runs in its own subprocess — a segfault doesn't take the runner down.
• Default timeout is 60 s per test; runs in parallel up to hardware_concurrency().
• Stdout+stderr is captured and printed atomically on completion. Failed/crashed/timed-out tests also write to build/test-logs/<name>.log.
• A broken fixture project.cpp is reported as a single failed test, not a fatal error — other tests still run.

CLI:

crafter-build test                                              # run all
crafter-build test 'Unit*'                                      # glob-filter test names
crafter-build test --list                                       # enumerate without running
crafter-build test --target=x86_64-w64-mingw32                  # only tests for this target
crafter-build test --target=x86_64-w64-mingw32 --runner=cmd:wine
crafter-build test --jobs=1                                     # serial mode
crafter-build test --timeout=5                                  # override per-test timeout

Outcomes: ✅ pass, ❌ fail, 💥 crash (with signal name), ⏱ timeout, ⏭ skipped. The runner exits 0 only if every non-skipped test passed.

--target= filters the run to tests whose cfg.target matches; default is the host triple. Per-target tests parse --target=... from their own args span and build for it; tests with hardcoded targets (e.g. host-only meta-tests) are filtered out under non-matching --target=.

Cross-target test runners

Test::runner runs the test binary somewhere other than this machine. Four factories:

TestRunner::Local()                                  // run on this machine (default)
TestRunner::Cmd("wine")                              // local exec via prefix command

Cmd(cmd) is a generic <cmd> <bin> <args> prefix runner — covers wine, qemu-user, valgrind, gdbserver, anything with that shape. Probes via which <cmd>.

For elaborate setups (rsync, ssh ControlMaster, env vars on the spawn, QEMU_LD_PREFIX for sysroots), construct TestRunner directly — copy/exec/cleanup/probe are public string fields with {bundle}, {remote_bundle}, {bin}, {bin_name}, {args} placeholders.

For cross-arch builds, set cfg.sysroot on the Configuration to point at a sysroot for the target. BuildStdPcm and the compile/link commands both consume it: --sysroot=<path> is passed to clang, and <sysroot>/usr/share/libc++/v1/std.cppm is precompiled instead of the host's. The cheapest aarch64 sysroot is an extracted Arch Linux ARM rootfs plus libc++ + libc++abi + gcc installed into it via pacman --root <rootfs> --config <alarm-pacman.conf> --dbpath <rootfs>/var/lib/pacman -Sy … (point pacman at ALARM's mirrors via explicit config to avoid pulling host-arch packages).

For --target=x86_64-w64-mingw32 (Windows from Linux), the pipeline cross-compiles as long as mingw-w64 is installed. Pair it with --runner=cmd:wine to run the result. Only the MinGW ABI is supported; there is no MSVC target and no Windows host. -fuse-ld=lld is auto-injected on every link, and -lstdc++exp is auto-linked for the mingw target so user projects don't need to declare those flags.

Configuring runners

Two layers, CLI wins over env, both override the per-test default of Local():

Env var (persistent, per shell or in CI):

export CRAFTER_BUILD_RUNNER_x86_64_w64_mingw32=cmd:wine
export CRAFTER_BUILD_RUNNER_aarch64_linux_gnu=cmd:qemu-aarch64
crafter-build test --target=x86_64-w64-mingw32           # uses cmd:wine

The variable name is CRAFTER_BUILD_RUNNER_<NORMALIZED_TARGET> (target triple with - and . replaced by _).

CLI (per invocation, scoped to --target=):

crafter-build test --target=x86_64-w64-mingw32 --runner=cmd:wine

Spec grammar:

local
cmd:<command>                  # cmd:wine, cmd:qemu-aarch64, cmd:valgrind, ...

Each runner carries a probe command (e.g. which wine); if it fails, every test using that runner is reported as ⏭ skipped and the rest of the suite continues. Skipped tests count toward the summary but don't fail the suite (AllPassed() returns true on skip-only runs).

Linking the parent project's library

A test fixture can depend on the project's own library so it can import and exercise its API:

// tests/UnitFoo/project.cpp
extern "C" Configuration CrafterBuildProject(std::span<const std::string_view>) {
    Configuration cfg;
    cfg.path = "tests/UnitFoo/";
    cfg.name = "UnitFoo";
    cfg.outputName = "UnitFoo";
    cfg.type = ConfigurationType::Executable;
    cfg.dependencies = { ParentLib("MyLib") };       // <-- the magic line

    std::array<fs::path, 0> ifaces = {};
    std::array<fs::path, 1> impls = { "main" };
    cfg.GetInterfacesAndImplementations(ifaces, impls);
    return cfg;
}

ParentLib(name) walks the parent project's dependency graph (and the parent itself) to find a Configuration* by Configuration::name. The build links it into the test exe, so import MyLib; resolves naturally. See examples/tests/ for the complete worked example.

Linting & formatting

Lint rules are C++ in project.cpp with no .lintrc, no YAML, and no built-in rules. A rule is a named callback that runs once per source file; register it on the Configuration before returning:

cfg.AddLintRule("no-tabs", [](Crafter::LintContext& ctx) {
    if (ctx.Extension() != ".cpp" && ctx.Extension() != ".cppm") return;
    for (std::size_t n = 1; n <= ctx.lines.size(); ++n) {
        if (ctx.Line(n).contains('\t')) ctx.Report(n, "tab character (use spaces)");
    }
});

A rule that calls ctx.SetContent(newContent) is a transform which is defined once, it powers both verbs: lint reports where the transform would change the file (dry, never writes), and format applies it to disk:

cfg.AddLintRule("final-newline", [](Crafter::LintContext& ctx) {
    if (!ctx.content.empty() && !ctx.content.ends_with('\n')) {
        ctx.SetContent(ctx.content + '\n');
    }
});

crafter-build lint            # full dry gate: Report() findings + would-reformat, exit 1 on any
crafter-build lint 'spdx*'    # rule-name glob filter
crafter-build lint --list     # enumerate rules without running them
crafter-build format          # apply transforms, rewrite changed files in place (exit 0)
crafter-build format --check  # CI gate: list files that would change, exit 1 if any

Lint findings print compiler-style — file:line: warning: message [rule] — so editors and CI pick them up. format rewrites files in place (gofmt convention) and only touches files whose bytes actually change; report-only findings are lint's business and don't affect format's exit code. A project with no rules registered exits 1 with a message showing how to add one.

LintContext gives each rule:

Member	Meaning
file	absolute path of the file under lint
content	the whole file
lines	pre-split line views (report 1-based via Line(n))
Extension()	file extension, e.g. ".cppm"
CommentStripped()	content with comments and string/char literal bodies blanked to spaces — newlines kept, so line numbers stay valid (raw strings not recognized yet)
Report(line, msg)	record a finding (line == 0 for whole-file)
SetContent(str)	replace the file's content — makes the rule a transform; lines re-splits, CommentStripped() re-derives. Build the new string, call once at the end; don't assign content directly

Suppression is comment-based :

// lint-disable-next-line no-char-pointer      — one rule, the following line
// lint-disable-next-line naming, wrap-join    — several rules (space- or comma-separated)
// lint-disable-next-line                      — all rules, the following line
// lint-disable-file fixed-width-types         — one rule, whole file (any position)
// lint-disable-file                           — all rules, whole file

Examples

examples/ contains progressively larger self-contained projects:

Example	Shows
hello-world	Smallest possible project: project.cpp + main.cpp
with-module	Adding a C++ module interface
library	Library + executable, linked via cfg.dependencies
tests	tests linking the parent library

Each builds standalone: cd examples/<name> && crafter-build.

License

This project is licensed under the GNU Lesser General Public License, version 3 only (LGPL-3.0-only). See LICENSE for the license text. The LGPL supplements the GNU General Public License version 3, a copy of which is included as LICENSE.GPL.

The example code under examples/ is licensed under the MIT license (see examples/LICENSE), so it can be freely copied into your own projects.

The lib/ directory contains vendored third-party code (nlohmann/json, glslang's DirStackFileIncluder) that remains under its own permissive licenses; see the headers of those files.

Copyright

Copyright (C) 2026 Catcrafts® catcrafts.net