feat(debug): log manifest deps changes

relates #27

lib/updateDeps.js

@@ -1,6 +1,9 @@
 const { writeFileSync } = require("fs");
-const recognizeFormat = require("./recognizeFormat");
 const semver = require("semver");
+const { isObject, isEqual, transform } = require("lodash");
+const recognizeFormat = require("./recognizeFormat");
+const getManifest = require("./getManifest");
+const debug = require("debug")("msr:updateDeps");
 
 /**
  * Resolve next package version.
@@ -176,10 +179,54 @@ const updateManifestDeps = (pkg) => {
 			throw Error(`Cannot release because dependency ${d.name} has not been released`);
 	});
 
+	if (!auditManifestChanges(manifest, path)) {
+		return;
+	}
+
 	// Write package.json back out.
 	writeFileSync(path, JSON.stringify(manifest, null, indent) + trailingWhitespace);
 };
 
+// https://gist.github.com/Yimiprod/7ee176597fef230d1451
+const difference = (object, base) =>
+	transform(object, (result, value, key) => {
+		if (!isEqual(value, base[key])) {
+			result[key] =
+				isObject(value) && isObject(base[key]) ? difference(value, base[key]) : `${base[key]} → ${value}`;
+		}
+	});
+
+/**
+ * Clarify what exactly was changed in manifest file.
+ * @param {object} actualManifest manifest object
+ * @param {string} path manifest path
+ * @returns {boolean} has changed or not
+ * @internal
+ */
+const auditManifestChanges = (actualManifest, path) => {
+	const oldManifest = getManifest(path);
+	const depScopes = ["dependencies", "devDependencies", "peerDependencies", "optionalDependencies"];
+	const changes = depScopes.reduce((res, scope) => {
+		const diff = difference(actualManifest[scope], oldManifest[scope]);
+
+		if (Object.keys(diff).length) {
+			res[scope] = diff;
+		}
+
+		return res;
+	}, {});
+
+	debug(actualManifest.name, path);
+
+	if (Object.keys(changes).length) {
+		debug(changes);
+		return true;
+	}
+
+	debug("no deps changes");
+	return false;
+};
+
 module.exports = {
 	getNextVersion,
 	getNextPreVersion,