Anvil

Anvil is a build-matrix tool for C/C++ projects. It compiles your code multiple times with different compilers, optimization levels, and compiler flags — all driven by simple JSON configuration files.

Perfect for:

• Benchmarking across compiler configurations (GCC, Clang, Zig, etc.)
• Testing code with different optimization levels and build flags
• CI/CD workflows that need multi-variant builds
• Exploring compiler behavior with systematically varied flags

Features

• Three build modes: Direct file compilation, folder recursion, or CMake projects
• Multi-compiler support: GCC, Clang, Zig, etc. (any compiler with a compatible CLI)
• Per-variant configuration: Each variant specifies compiler, C++ standard, optimization flags, and defines
• Parallel builds: Build multiple variants simultaneously for faster turnaround
• Config discovery: Looks for project config files named anvil_project.json or anvil.project.json, and variant files named anvil_variants.json or anvil.variants.json near the target or project directory
• Flexible output: Artifacts and metadata collected in a single directory

Installation

From source (editable)

git clone https://github.com/michezio/anvil.git
cd anvil
pip install -e .

Then use as:

python -m anvil --target myfile.cpp
# or
anvil --target myfile.cpp

From PyPI (future)

pip install anvil-matrix
anvil --target myfile.cpp

Quick Start

1. Compile a single file with default variants

python -m anvil --target src/myapp.cpp

Produces three binaries (O2, O3, Ofast):

.out/anvil_build/myapp/
  ├── myapp__o2_baseline
  ├── myapp__o3_baseline
  ├── myapp__ofast_fastmath
  └── build_summary.json

2. Compile all files in a folder

python -m anvil --target src/myproject/

3. Use custom variants

Create a variants file such as anvil_variants_quick.json (the repository examples use the same underscore-based naming):

[
  {
    "name": "gcc_o3",
    "compiler": "g++",
    "standard": "c++23",
    "cxx_flags": "-O3",
    "defines": []
  },
  {
    "name": "clang_o3",
    "compiler": "clang++",
    "standard": "c++23",
    "cxx_flags": "-O3",
    "defines": []
  }
]

Then point Anvil at it explicitly:

python -m anvil --target src/myapp.cpp --variants path/to/anvil_variants_quick.json

4. Control build behavior with config files

Create anvil_project.json next to your source. The sample project config in this repository uses the same nested cmake shape:

{
  "name": "myproject",
  "build_dir": "/build/anvil/myproject",
  "out_dir": ".out/anvil_build/myproject",
  "cmake": {
    "target": "my_target",
    "build_type": "Release",
    "args": []
  },
  "include_dirs": ["/opt/deps/include"],
  "link_flags": "-L/opt/deps/lib -lmydep",
  "jobs": 0,
  "parallel_variants": 4,
  "stop_on_error": false,
  "clean": false,
  "verbose": false
}

Then:

python -m anvil --target src/ --project path/to/anvil_project.json

Configuration

anvil_project.json

Field	Type	Default	Description
name	string	(inferred from parent directory)	Project name, used in output paths
build_dir	string	/build/anvil/<name>	CMake build directory (CMake mode)
out_dir	string	.out/anvil_build/<name>	Output directory for artifacts
cmake.target	string	""	CMake target name (required for CMake mode)
cmake.build_type	string	Release	CMake build type used in CMake mode
cmake.args	array	[]	Extra cmake configure arguments
env_setup	string	""	Script to source before building
include_dirs	array	[]	Extra -I paths (direct mode)
link_flags	string	""	Extra linker flags
jobs	int	0	Compile jobs per variant (0 = auto via nproc)
parallel_variants	int	1	Number of variants to build simultaneously
stop_on_error	bool	false	Abort on first variant failure
clean	bool	false	Clean build directories before building
verbose	bool	false	Print full compiler commands

Variants JSON

Anvil reads a top-level JSON array of variant objects. The file can be named anvil_variants.json or anvil.variants.json, or passed explicitly via --variants.

[
  {
    "name": "o3_baseline",
    "compiler": "g++",
    "standard": "c++23",
    "cxx_flags": "-O3",
    "defines": ["MY_DEFINE=1"]
  }
]

Field	Type	Default	Description
name	string	(required)	Variant identifier
compiler	string	g++	Compiler command (supports multi-word forms like zig c++)
standard	string	c++23	C++ standard flag (for example c++20 or c++23)
cxx_flags	string	""	Compiler flags (for example -O3 -march=native)
defines	array	[]	Preprocessor defines (for example ["NDEBUG", "MY_FLAG=1"])

Command Line

usage: anvil [-h] [--target TARGET] [--project PROJECT] [--variants VARIANTS]
             [--clean] [--stop-on-error] [--jobs JOBS] [--parallel PARALLEL]
             [--verbose] [--extra-args [EXTRA_ARGS ...]]

Build-matrix tool: compiles C/C++ targets with multiple variant configurations.

options:
  --target TARGET              Path to a .cpp file, folder, or CMake project root
  --project PROJECT            Path to an anvil_project.json or anvil.project.json file/folder
  --variants VARIANTS          Path to an anvil_variants.json or anvil.variants.json file/folder
  --clean                      Clean build directories before building
  --stop-on-error              Stop on first variant failure
  --jobs JOBS, -j JOBS         Compile jobs per variant (0 = nproc)
  --parallel PARALLEL, -p      Variants to build in parallel
  --verbose, -v                Print full compilation commands
  --extra-args [...]           Extra compiler/linker arguments (direct mode only)

Examples

See the examples/ directory for sample configurations.

Single-file benchmark

python -m anvil --target benchmark.cpp \
  --variants examples/anvil_variants_full.json \
  --parallel 4 --jobs 2

CMake project with custom environment

python -m anvil --target myproject \
  --project myproject/anvil_project.json \
  --variants myproject/anvil_variants_quick.json \
  --clean

Verbose output with stop-on-error

python -m anvil --target src/ --verbose --stop-on-error

Output

Artifacts are collected under out_dir (default: .out/anvil_build/<name>):

.out/anvil_build/myproject/
  ├── myproject__o2_gcc
  ├── myproject__o3_gcc
  ├── myproject__ofast_gcc
  ├── myproject__o2_gcc.json        # Metadata
  ├── myproject__o3_gcc.json
  ├── myproject__ofast_gcc.json
  └── build_summary.json            # Build stats

Each .json file contains:

• Variant name and configuration
• Compiler used
• Effective flags and defines
• Build directory
• Artifact path

License

MIT — see LICENSE

Contributing

Contributions welcome! Please open issues and PRs on GitHub.