Merged in lettertwo/merge-driver (pull request #64)

Add custom merge driver

Approved-by: Brian Do

.gitattributes

@@ -5,3 +5,5 @@
 *.png binary
 *.wasm binary
 *.woff2 binary
+package.json merge=atlassian-package-json
+test/**/package.json !merge

.husky/post-checkout

@@ -0,0 +1,6 @@
+#!/bin/sh
+. "$(dirname "$0")/_/husky.sh"
+
+# ATLASSIAN: Configure a custom merge driver to make merges from upstream easier
+git config merge.atlassian-package-json.name "Merge driver for @atlassian/parcel package.json files"
+git config merge.atlassian-package-json.driver "./scripts/atlassian-merge-package-json.js %A %O %B %P"

scripts/atlassian-merge-package-json.js

@@ -0,0 +1,142 @@
+#!/usr/bin/env node
+
+/* eslint-disable no-console */
+
+// Custom git merge driver for @atlassian/parcel package.json files
+
+let fs = require('fs');
+let spawnSync = require('child_process').spawnSync;
+
+function merge(ours, base, theirs) {
+  return spawnSync(
+    'git',
+    [
+      'merge-file',
+      '-p',
+      '-L',
+      'current',
+      '-L',
+      'base',
+      '-L',
+      'incoming',
+      ours,
+      base,
+      theirs,
+    ],
+    {stdio: [0, 'pipe', 2]},
+  );
+}
+
+function loadPackageJson(filepath) {
+  return JSON.parse(fs.readFileSync(filepath, 'utf-8'));
+}
+
+function writePackageJson(filepath, data) {
+  return fs.writeFileSync(filepath, JSON.stringify(data, null, 2));
+}
+
+function has(obj, key) {
+  if (obj == null) return false;
+  return Object.prototype.hasOwnProperty.call(obj, key);
+}
+
+function copyValue(path, ours, base, theirs) {
+  let name = path;
+  if (Array.isArray(path)) {
+    for (let i = 0; i < path.length - 1; i++) {
+      ours = ours?.[path[i]];
+      base = base?.[path[i]];
+      theirs = theirs?.[path[i]];
+    }
+    name = path[path.length - 1];
+  }
+  if (has(ours, name) && has(base, name) && has(theirs, name)) {
+    base[name] = ours[name];
+    theirs[name] = ours[name];
+    return true;
+  }
+  return false;
+}
+
+let cfg = {
+  // @parcel packages that are versioned separately from parcel
+  // (e.g., not in the monorepo) should be explicitly excluded.
+  '@parcel/css': false,
+  '@parcel/source-map': false,
+  '@parcel/watcher': false,
+
+  // Packages that should be patched but don't match @parcel/*
+  fuzzer: true,
+  parcel: true,
+};
+
+function shouldPatch(name) {
+  return name && (cfg[name] ?? name.startsWith('@parcel/'));
+}
+
+function patchVersions(ours, base, theirs) {
+  let patched = copyValue('version', ours, base, theirs);
+  patched = copyValue(['engines', 'parcel'], ours, base, theirs) || patched;
+  for (let type of [
+    'dependencies',
+    'devDependencies',
+    'peerDependencies',
+    'parcelDependencies',
+  ]) {
+    if (has(ours, type)) {
+      for (let name of Object.keys(ours[type])) {
+        if (shouldPatch(name)) {
+          patched = copyValue([type, name], ours, base, theirs) || patched;
+        }
+      }
+    }
+  }
+  return patched;
+}
+
+if (require.main === module) {
+  let args = process.argv.slice(2);
+  if (args.length < 4) {
+    console.log(
+      `To use this merge driver, do the following:
+
+       git config merge.atlassian-package-json.name "Merge driver for @atlassian/parcel package.json files"
+       git config merge.atlassian-package-json.driver "./scripts/atlassian-merge-package-json.js %A %O %B %P"
+     `,
+    );
+    process.exit(1);
+  }
+
+  let [ours, base, theirs, src] = args;
+
+  // Try a merge first. Maybe it will be fine?
+  let {stdout, status} = merge(ours, base, theirs);
+
+  // Non-zero status means the merge failed.
+  if (status) {
+    try {
+      let ourJson = loadPackageJson(ours);
+      if (shouldPatch(ourJson.name)) {
+        let baseJson = loadPackageJson(base);
+        let theirJson = loadPackageJson(theirs);
+        if (patchVersions(ourJson, baseJson, theirJson)) {
+          console.error(`Patching Parcel versions in ${src}`);
+          writePackageJson(base, baseJson);
+          writePackageJson(theirs, theirJson);
+          // Try to merge again after patching version numbers.
+          ({stdout, status} = merge(ours, base, theirs));
+        }
+      }
+    } catch (e) {
+      console.error(e);
+    }
+  }
+
+  // from `man gitattributes`:
+  // > The merge driver is expected to leave the result of the merge
+  // > in the file named with %A by overwriting it, and exit
+  // > with zero status if it managed to merge them cleanly,
+  // > or non-zero if there were conflicts.
+  fs.writeFileSync(ours, stdout);
+  process.exit(status);
+}