Detailed documentation here.

Nimterop is a Nim package that aims to make C/C++ interop seamless

Nim has one of the best FFI you can find - importing C/C++ is supported out of the box. All you need to provide is type and proc definitions for Nim to interop with C/C++ binaries. Generation of these wrappers is easy for simple libraries but quickly gets out of hand. c2nim greatly helps here by parsing and converting C/C++ into Nim but is limited due to the complex and constantly evolving C/C++ grammar. nimgen mainly focuses on automating the wrapping process and fills some holes but is again limited to c2nim's capabilities.

The goal of nimterop is to leverage the tree-sitter engine to parse C/C++ code and then convert relevant portions of the AST into Nim definitions. tree-sitter is a Github sponsored project that can parse a variety of languages into an AST which is then leveraged by the Atom editor for syntax highlighting and code folding. The advantages of this approach are multifold:

• Benefit from the tree-sitter community's investment into language parsing
• Wrap what is recognized in the AST rather than completely failing due to parsing errors

Most of the wrapping functionality is contained within the toast binary that is built when nimterop is installed and can be used standalone similar to how c2nim can be used today. In addition, nimterop also offers an API to pull in the generated Nim content directly into an application and other nimgen functionality that helps in automating the wrapping process. There is also support to statically or dynamically link to system installed libraries or downloading and building them with autoconf or cmake from a Git repo or source archive.

The nimterop wrapping functionality is still limited to C but is constantly expanding. C++ support will be added once most popular C libraries can be wrapped seamlessly. Meanwhile, c2nim can also be used in place of toast with the c2nImport() API call.

Nimterop has seen some adoption within the community and the simplicity and success of this approach justifies additional investment of time and effort. Regardless, the goal is to make interop seamless so nimterop will focus on wrapping headers and not the outright conversion of C/C++ implementation.

Also, given tree-sitter can parse a variety of other languages, there might also be value in investigating how to wrap Rust and Go libraries.

Installation

Nimterop can be installed via Nimble:

nimble install nimterop -y

or:

git clone http://github.com/nimterop/nimterop && cd nimterop
nimble develop -y
nimble build

This will download and install nimterop in the standard Nimble package location, typically ~/.nimble. Once installed, it can be imported into any Nim program. Note that the ~/.nimble/bin directory needs to be added to the PATH for nimterop to work.

Usage

Detailed documentation can be found here.

Check out the wiki for a list of all known wrappers that have been created using nimterop. Please do add your project once you are done so that others can benefit from your work.

Using the high-level getHeader API to perform all building and linking automatically:

import nimterop/[build, cimport]

static:
  cDebug()

getHeader(
  "header.h",
  giturl = "https://github.com/username/repo",
  dlurl = "https://website.org/download/repo-$1.tar.gz",
  outdir = "build",
  conFlags = "--disable-comp --enable-feature"
)

when not defined(headerStatic):
  cImport(headerPath, recurse = true, dynlib = "headerLPath")
else:
  cImport(headerPath, recurse = true)

This allows the user to control how the wrapper works - either pass -d:headerStd to search for header.h in the standard system path, -d:headerGit to clone the source from the specified git URL or -d:headerDL to get the source from download URL. Further, the -d:headerSetVer=X.Y.Z flag can be used to specify which version to use. It is used as the tag name for Git whereas for DL, it replaces $1 in the URL defined.

The -d:headerStatic attempts to statically link the library. If it is omitted, the library is dynamically linked instead.

lzma.nim is an example of a library using this high-level API.

The traditional approach is to manually compile in the code:

import nimterop/cimport

static:
  cDebug()
cDefine("HAS_ABC")
cDefine("HAS_ABC", "DEF")
cIncludeDir("clib/include")
cImport("clib.h")

cCompile("clib/src/*.c")

Check out template.nim as a starting point for wrapping a library using the traditional approach. The template can be copied and trimmed down and modified as required. templite.nim is a shorter version for more experienced users.

Refer to the tests directory for examples on how the library can be used.

The toast binary can also be used directly on the CLI:

> toast -h
Usage:
  main [optional-params] C/C++ source/header
Options:
  -h, --help                              print this cligen-erated help
  --help-syntax                           advanced: prepend,plurals,..
  -k, --check          bool      false    check generated wrapper with compiler
  -C=, --convention=   string    "cdecl"  calling convention for wrapped procs - default: cdecl
  -d, --debug          bool      false    enable debug output
  -D=, --defines=      strings   {}       definitions to pass to preprocessor
  -l=, --dynlib=       string    ""       import symbols from library in specified Nim string
  -f=, --feature=      Features  {}       flags to enable experimental features
  -H, --includeHeader  bool      false    add {.header.} pragma to wrapper
  -I=, --includeDirs=  strings   {}       include directory to pass to preprocessor
  -m=, --mode=         string    "cpp"    language parser: c or cpp
  --nim=               string    "nim"    use a particular Nim executable - default: $PATH/nim
  -c, --nocomments     bool      false    exclude top-level comments from output
  -o=, --output=       string    ""       file to output content - default: stdout
  -a, --past           bool      false    print AST output
  -g, --pgrammar       bool      false    print grammar
  --pluginSourcePath=  string    ""       nim file to build and load as a plugin
  -n, --pnim           bool      false    print Nim output
  -E=, --prefix=       strings   {}       strip prefix from identifiers
  -p, --preprocess     bool      false    run preprocessor on header
  -r, --recurse        bool      false    process #include files
  -s, --stub           bool      false    stub out undefined type references as objects
  -F=, --suffix=       strings   {}       strip suffix from identifiers
  -O=, --symOverride=  strings   {}       skip generating specified symbols

Implementation Details

In order to use the tree-sitter C library, it has to be compiled into a separate binary called toast (to AST) since the Nim VM doesn't yet support FFI. toast takes a C/C++ file and runs it through the tree-sitter API which returns an AST data structure. This can then be printed out to stdout in a Lisp S-Expression format or the relevant Nim wrapper output. This content can be saved to a .nim file and imported if so desired.

Alternatively, the cImport() macro allows easier creation of wrappers in code. It runs toast on the specified header file and injects the generated wrapper content into the application at compile time. A few other helper procs are provided to influence this process. Output is cached to save time on subsequent runs.

toast can also be used to run the header through the preprocessor which cleans up the code considerably. Along with the recursion capability which runs through all #include files, one large simpler header file can be created which can then be processed with toast or even c2nim if so desired. By default, the $CC environment variable is used. If not found, toast defaults to gcc.

The tree-sitter library is limited as well - it may fail on some advanced language constructs but is designed to handle them gracefully since it is expected to have bad code while actively typing in an editor. When an error is detected, tree-sitter includes an ERROR node at that location in the AST. At this time, cImport() will complain and continue if it encounters any errors. Depending on how severe the errors are, compilation may succeed or fail. Glaring issues will be communicated to the tree-sitter team but their goals may not always align with those of this project.

Credits

Nimterop depends on tree-sitter and all licensing terms of tree-sitter apply to the usage of this package. The tree-sitter functionality is pulled and wrapped using nimterop itself.

Feedback

Nimterop is a work in progress and any feedback or suggestions are welcome. It is hosted on GitHub with an MIT license so issues, forks and PRs are most appreciated.