The NodeGit is Native Node bindings to Git，based on libgit2.

It's a great library, but not provides all APIs of libgit2.

I need to export the 3-Way-Merge algorithm from git_merge_file by myself.

• First of all, clone a depository from my forked project.

git clone git@github.com:myname/nodegit.git
cd nodegit
npm i

1. Edit the configuration file of Customize the generated code using.

generate/input/descriptor.json

{
  "types": {
    "merge": {
      "functions": {
        "git_merge_file": {
          // Remove `"ignore": true`, add config
          "args": {
            "out": {
              "isReturn": true, // As return value
              "shouldAlloc": true // Auto create
            },
            "opts": {
              "isOptional": true // Can be null
            }
          },
          "return": {
            "isErrorCode": true
          }
        }
      }
    },
    "merge_file_result": {
      "ignore": false // Can not be ignore
    }
  }
}

2. Generate detail configuration JSON

npm run generateJson

output at:

generate/output/idefs.json

search "cFunctionName": "git_merge_file",, have got args and returns configuration.

3. Build nodegit.node

npm run install

build/Release/nodegit.node

4. Define a new JS function Merge.file for convert args.

lib/merge.js

var _file = Merge.file;

/**
 * Merge two files as they exist in the in-memory data structures, using
 * the given common ancestor as the baseline. (git_merge_file)
 *
 * @param {MergeFileInput} ancestor The contents of the ancestor file
 * @param {MergeFileInput} ours The contents of the file in "our" side
 * @param {MergeFileInput} theirs The contents of the file in "theirs" side
 * @param {MergeFileOptions} [options] The merge file options or `NULL` for defaults
 */
Merge.file = function(ancestor, ours, theirs, options) {
  ancestor = normalizeOptions(ancestor, NodeGit.MergeFileInput);
  ours = normalizeOptions(ours, NodeGit.MergeFileInput);
  theirs = normalizeOptions(theirs, NodeGit.MergeFileInput);
  options = normalizeOptions(options || {}, NodeGit.MergeFileOptions);
  return _file.call(this, ancestor, ours, theirs, options);
};

5. Generate JS in dist/ with babel.

npm run prepublish

6. Create test.

Create three Markdown files.

printf "a" > test/base.md
printf "a\nb" > test/ours.md
printf "a\nc" > test/theirs.md

Create test JS file.

test/mergefile.js

var NodeGit = require('..');
var path = require('path');
var fse = require('fs-extra');

const dir = '/mnt/d/workspace/nodegit/test';

async function newMergeFileInput(filePath) {
  const stat = await fse.stat(filePath);
  const content = await fse.readFile(filePath, 'utf-8');

  // Wrong: It will case Crash while without normalizeOptions in 'lib/merge.js'
  // const input = {
  //   ptr: content,
  //   size: content.length,
  //   mode: stat.mode,
  //   path: filePath,
  // }

  // Correct: Must create object from NodeGit class.
  const input = new NodeGit.MergeFileInput();
  input.ptr = content;
  input.size = stat.size; // UTF8 size! (not content.length)
  input.mode = stat.mode;
  input.path = filePath;

  return input;
}

function getFilePath(fileName) {
  return path.join(dir, fileName);
}

async function test() {
  // 3 files.
  const base = await newMergeFileInput(getFilePath('base.md'));
  const ours = await newMergeFileInput(getFilePath('ours.md'));
  const theirs = await newMergeFileInput(getFilePath('theirs.md'));

  console.log({ base, ours, theirs });

  // Call merge file function.
  const res = await NodeGit.Merge.file(base, ours, theirs, {
    version: 0,
    ancestorLabel: 'BASE',
    ourLabel: 'OUR',
    theirLabel: 'THEIR',
    favor: 0,
    flags: 0,
    markerSize: 10,
  });

  // Must cut UTF8 Buff with len, or be wrong.
  const ptr = Buffer.from(res.ptr(), 'utf-8').slice(0, res.len()).toString();

  // Must call function to get field.
  console.log('res:', {
    automergeable: res.automergeable(),
    path: res.path(),
    mode: res.mode(),
    ptr,
    len: res.len(),
  });
}

test();

Run.

node test/mergefile.js

Output.

{
  base: MergeFileInput {
    mode: 33279,
    path: '/mnt/d/workspace/nodegit/test/base.md',
    size: 1,
    ptr: 'a',
    version: 1
  },
  ours: MergeFileInput {
    mode: 33279,
    path: '/mnt/d/workspace/nodegit/test/ours.md',
    size: 3,
    ptr: 'a\nb',
    version: 1
  },
  theirs: MergeFileInput {
    mode: 33279,
    path: '/mnt/d/workspace/nodegit/test/theirs.md',
    size: 3,
    ptr: 'a\nc',
    version: 1
  }
}
res: {
  automergeable: 0,
  path: null,
  mode: 33279,
  ptr: 'a\n<<<<<<<<<< OUR\nb\n==========\nc\n>>>>>>>>>> THEIR\n',
  len: 49
}

7. Publish

Change name and version in package.json for publish new version.

npm login
npm publish

Install it use yarn.

yarn add pj-nodegit@latest

IMPORTANT

If argument object don't create with NodeGit Class and without wrap normalizeOptions. The nodegit.node will be crash.

node: ../node_modules/nan/nan_object_wrap.h:32: static T* Nan::ObjectWrap::Unwrap(v8::Local<v8::Object>) [with T = GitMergeFileOptions]: Assertion `object->InternalFieldCount() > 0' failed.

Why?

It lacks embedder fields, by compare with object of correct function. The v8 object InternalFieldCount() only counts the embedder fields actually. What is it? I don't know, may be a special sign of v8 object. No mater how, create object with NodeGit Class will be correct. I found the solution according by function normalizeOptions in file lib/utils/normalize_options.js.

var NodeGit = require('../../');

function normalizeOptions(options, Ctor) {
  if (!options) {
    return null;
  }

  if (options instanceof Ctor) {
    return options;
  }

  var instance = new Ctor(); // here.

  Object.keys(options).forEach(function(key) {
    if (typeof options[key] !== 'undefined') {
      instance[key] = options[key];
    }
  });

  return instance;
}

NodeGit.Utils.normalizeOptions = normalizeOptions;