From b7631ffc6568818416ebfdd68403caa77bf63ac6 Mon Sep 17 00:00:00 2001
From: Adam Hines <ahines57@gmail.com>
Date: Thu, 17 Feb 2022 08:50:57 -0700
Subject: [PATCH] Make source maps plain objects for use with `t.valueToNode`
 (#14283)
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Co-authored-by: Adam J. Hines <ahines@factset.com>
Co-authored-by: Nicolò Ribaudo <nicolo.ribaudo@gmail.com>
---
 .../src/transformation/file/merge-map.ts      |  8 +++++-
 packages/babel-core/test/merge-map.js         | 27 +++++++++++++++++++
 2 files changed, 34 insertions(+), 1 deletion(-)
 create mode 100644 packages/babel-core/test/merge-map.js

diff --git a/packages/babel-core/src/transformation/file/merge-map.ts b/packages/babel-core/src/transformation/file/merge-map.ts
index fb12d6f2d839..2deefa638a8f 100644
--- a/packages/babel-core/src/transformation/file/merge-map.ts
+++ b/packages/babel-core/src/transformation/file/merge-map.ts
@@ -38,7 +38,13 @@ export default function mergeSourceMap(
   if (typeof inputMap.sourceRoot === "string") {
     result.sourceRoot = inputMap.sourceRoot;
   }
-  return result;
+
+  // remapping returns a SourceMap class type, but this breaks code downstream in
+  // @babel/traverse and @babel/types that relies on data being plain objects.
+  // When it encounters the sourcemap type it outputs a "don't know how to turn
+  // this value into a node" error. As a result, we are converting the merged
+  // sourcemap to a plain js object.
+  return { ...result };
 }
 
 function rootless(map: SourceMap): SourceMap {
diff --git a/packages/babel-core/test/merge-map.js b/packages/babel-core/test/merge-map.js
new file mode 100644
index 000000000000..bc13bb35a99a
--- /dev/null
+++ b/packages/babel-core/test/merge-map.js
@@ -0,0 +1,27 @@
+import _mergeSourceMap from "../lib/transformation/file/merge-map.js";
+const mergeSourceMap = _mergeSourceMap.default;
+
+describe("merge-map", () => {
+  it("returns a plain js object", () => {
+    const inputMap = {
+      file: "file.js",
+      mappings: [],
+      names: [],
+      sources: ["file.ts"],
+      version: 3,
+    };
+
+    const outputMap = {
+      file: "file.transpiled.js",
+      mappings: [],
+      names: [],
+      sources: ["file.js"],
+      version: 3,
+    };
+
+    const map = mergeSourceMap(inputMap, outputMap, "file.transpiled.js");
+    expect(typeof map).toBe("object");
+    expect(Object.prototype.toString.call(map)).toBe("[object Object]");
+    expect(Object.getPrototypeOf(map)).toBe(Object.prototype);
+  });
+});