language-ninja is a Haskell library for parsing, pretty-printing, and
compiling the Ninja build language.
language-ninja was written as a part of Awake Security's efforts in creating
incremental build infrastructure for the Nix package manager, and in particular
for Haskell packages. This library is the basis for a tool, ninja2nix, that,
given a Ninja file, will output a JSON file containing information that a Nix
function can use to compute a derivation representing an incremental build
using one derivation per build edge in the parsed Ninja build graph.
In conjunction with an as-of-yet unwritten tool, cabal2ninja, that will
generate a Ninja file based on information from cabal and ghc -M, we will
have incremental builds for any Haskell package that uses a default Setup.hs
file.
Using Ninja as an intermediate representation has advantages here, since it
means that ninja2nix could be useful for building other projects that use
a build system that can output Ninja, like the Linux kernel (with kninja),
Chromium, any CMake project, any Bazel project, or some Make-based projects
(with kati).
Originally, language-ninja used the Ninja lexer/parser from Neil Mitchell's
shake project. However, we now use a megaparsec-based lexer and a highly
modified version of the old parser. There is still work to be done on improving
the diagnostic data and pretty-printability of the AST from this parser.
In my view, it is very important that a parser output an AST that can be
pretty-printed exactly to same sequence of bytes that were in the parsed file,
as this makes tests and diagnostics much easier to write.
Currently there is a rudimentary pretty-printer in Language.Ninja.Pretty.
It simply outputs text such that if that text is parsed and the parsed data
is pretty-printed again, the resulting text will be identical to the original
text (this is tested on a variety of Ninja files in the test suite).
The Ninja type from Language.Ninja.IR.Ninja contains precisely the data
that must be acted on dynamically in a Ninja. In converting from the parsed
AST to the intermediate representation using Language.Ninja.Compile.compile,
you are eliminating all statically-dischargeable language features in Ninja,
like variables. It also "monomorphizes" Ninja rules, since rule-level $out
references are a kind of parametric polymorphism. This IR is thus far more
suitable for processing than the original parsed AST.
The staging branch is used for active development; i.e.: force pushes may
happen on staging but will not happen on master.
To build this, I recommend installing the Nix package manager and running
nix-build release.nix -A language-ninja.