Respect for indentation

package.json

@@ -26,6 +26,7 @@
     "chalk": "^1.1.3",
     "cli-cursor": "^2.1.0",
     "cli-spinners": "^1.0.0",
+    "detect-indent": "^5.0.0",
     "es6-error": "^4.0.2",
     "pify": "^3.0.0",
     "semver": "^5.3.0",

src/tasks/updatePackageJson.js

@@ -1,3 +1,4 @@
+import detectIndent from "detect-indent";
 import createUpdatedPackageJson from "./util/createUpdatedPackageJson";
 import Sequence from "./util/Sequence";
 
@@ -6,7 +7,8 @@ function lastChar(str) {
 }
 
 function stringify(newPackageJson, oldPackageJsonStr) {
-    let newPackageJsonStr = JSON.stringify(newPackageJson, null, "  ");
+    const indent = detectIndent(oldPackageJsonStr).indent || "  ";
+    let newPackageJsonStr = JSON.stringify(newPackageJson, null, indent);
     const lastCharFromOldPackageJson = lastChar(oldPackageJsonStr);
 
     // Preserve the new line character at the end if there was one

test/tasks/updatePackageJson.test.js

@@ -66,6 +66,25 @@ describe("updatePackageJson()", () => {
             )
         );
     });
+    it("should respect indentation", async () => {
+        const updtr = new FakeUpdtr();
+        const updateResults = [];
+        const fourSpacedPackageJson = outdatedRegular.replace(/ {2}/g, "    ");
+        const tabbedPackageJson = outdatedRegular.replace(/ {2}/g, "\t");
+
+        updtr.writeFile.resolves();
+
+        updtr.readFile.resolves(fourSpacedPackageJson);
+
+        await updatePackageJson(updtr, updateResults);
+
+        updtr.readFile.resolves(tabbedPackageJson);
+
+        await updatePackageJson(updtr, updateResults);
+
+        expect(updtr.writeFile.getCall(0).args[1]).toBe(fourSpacedPackageJson);
+        expect(updtr.writeFile.getCall(1).args[1]).toBe(tabbedPackageJson);
+    });
     it("should emit the expected events", async () => {
         const updtr = new FakeUpdtr();
         const updateResults = [module1ToLatestSuccess];