A template for a ninja configuration file.

configure.py

import os
import sys
import fnmatch


__doc__ = """Build configurator.

Usage:
    configure.py [options] [-D var[=val]]...

Options:
  --native           Enable native optimizations.
  -d, --debug        Compile with debug.
  -D var=val         Define variable.
  -o file            Output ninja file [default: build.ninja].
  -h, --help         Show this screen.
"""


def build_files(n, args):
    exe_ext = ".exe" if os.name == "nt" else ""
    obj_ext = ".o"

    # # Precompiled header.
    # n.build("src/precompile.h.gch", "cxx", "src/precompile.h",
    #         variables={"xtype": "-x c++-header"})
    # precompiled_header = "src/precompile.h.gch"

    objects = []
    for root, dirnames, filenames in os.walk("src"):
        for filename in fnmatch.filter(filenames, "*.cpp"):
            src = os.path.join(root, filename)
            obj = os.path.join("obj", os.path.splitext(src)[0] + obj_ext)
            n.build(obj, "cxx", src)
            # n.build(obj, "cxx", src, precompiled_header)
            objects.append(obj)

    n.build("main" + exe_ext, "cxxlink", objects)
    n.default("main" + exe_ext)


def build_rules(n, args):
    n.variable("cc", "gcc")
    n.variable("cxx", "g++")

    if args["--debug"]:
        n.variable("dbgflags", "-ggdb")
        debug_flag = ""
    else:
        n.variable("dbgflags", "")
        debug_flag = " -DNDEBUG"

    native_flag = " -march=native" if args["--native"] else ""
    n.variable("optflags", "-O2" + native_flag + debug_flag)

    defines = [" -D" + d for d in args["-D"]]

    cflags = "-std=c99 -Wall -pedantic -fwrapv"
    cxxflags = "-std=c++11 -Wall -pedantic -fwrapv"
    n.variable("cflags", cflags + "".join(defines))
    n.variable("clinkflags", "")
    n.variable("cxxflags", cxxflags + "".join(defines))
    n.variable("cxxlinkflags", "")

    n.rule("cc",
           "$cc $xtype -MMD -MF $out.d $optflags $dbgflags $cflags -c $in -o $out",
           depfile="$out.d")

    n.rule("cxx",
           "$cxx $xtype -MMD -MF $out.d $optflags $dbgflags $cxxflags -c $in -o $out",
           depfile="$out.d")

    n.rule("clink", "$cc $optflags $dbgflags $in $clinkflags -o $out")
    n.rule("cxxlink", "$cxx $optflags $dbgflags $in $cxxlinkflags -o $out")


# Everything below this line is dependency boilerplate.


try:
    from docopt import docopt
    import ninja_syntax
except ImportError:
    msg = """You are missing one or more dependencies, install using:

    {} -m pip install --user docopt ninja-syntax

If you are using an old version of Python, and don't have pip,
download https://bootstrap.pypa.io/get-pip.py and run it."""

    print(msg.format(os.path.basename(sys.executable)))
    sys.exit(1)


args = docopt(__doc__)

# Check if we're likely running for the first time.
first_time = not os.path.isfile(args["-o"])

# Write ninja build file.
with open(args["-o"], "w") as ninja_file:
    n = ninja_syntax.Writer(ninja_file)
    build_rules(n, args)
    build_files(n, args)

# Check if we have ninja in path.
path = os.environ.get("PATH", os.defpath).split(os.pathsep)
if sys.platform == "win32":
    path.insert(0, os.curdir)
    pathext = os.environ.get("PATHEXT", "").split(os.pathsep)
    files = ["ninja" + ext for ext in pathext]
else:
    files = ["ninja"]


def is_exe(path):
    return os.path.exists(path) and os.access(path, os.F_OK | os.X_OK) and not os.path.isdir(path)

has_ninja = any(is_exe(os.path.join(d, f)) for d in path for f in files)

if first_time and not has_ninja:
    msg = """It appears you're running configure.py for the first time, but do not have
ninja in your path. On Windows we recommend simply downloading the binary:

    https://github.com/ninja-build/ninja/releases/download/v1.6.0/ninja-win.zip

Extract anywhere in your path, or even inside this directory.

On linux it's easiest to compile from source:

    wget https://github.com/ninja-build/ninja/archive/v1.6.0.tar.gz
    tar xf v1.6.0.tar.gz && rm v1.6.0.tar.gz && cd ninja-1.6.0
    {} configure.py --bootstrap
    sudo cp ninja /usr/local/bin

This should only take half a minute or so."""
    print(msg.format(os.path.basename(sys.executable)))

Loving the file man!

Question though: You go out of your way to define all the c (as opposed to cxx) compiler rules, but you never use them. Our project is pure c, so we have been commenting out all the cxx lines and replacing them with c rules, but would there be a better way?

EDIT: We used your file to create our own system without (nearly any) loss of generality. If you would like, we could post it.