Source map adds null.<anonymous> to stack trace

[privatenumber]

Description

When providing a file with a source map (via native source maps), the stack trace includes null.<anonymous> in the location of the error.

Since there are actually no transformation happening (source map and source file are 1:1), I'm suspicious that this is a bug in Node.js.

My goal is to load the source map to show a stack trace identical to the one without a source map.

Error with source map

I use a loader to apply a transformation and create a source map. In this case, I don't actually make any changes, and I generate a 1:1 source map.

Strangely, it displays null.<anonymous> in the first row of the stack.

(Note: the :1:1 location is a little inaccurate but it's because I provide a low-resolution map. It maps accurately when I use a high-resolution map.)

Error
    at null.<anonymous> (/Users/osame/Desktop/test-node-source-map/index.mjs:1:1)
    at ModuleJob.run (node:internal/modules/esm/module_job:197:25)
    at async Promise.all (index 0)
    at async ESMLoader.import (node:internal/modules/esm/loader:337:24)
    at async loadESM (node:internal/process/esm_loader:88:5)
    at async handleMainPromise (node:internal/modules/run_main:61:12)

Expected error

When there is no loader/source maps provided, the error displays correctly:

Error
    at file:///Users/osame/Desktop/test-node-source-map/index.mjs:1:7
    at ModuleJob.run (node:internal/modules/esm/module_job:197:25)
    at async Promise.all (index 0)
    at async ESMLoader.import (node:internal/modules/esm/loader:337:24)
    at async loadESM (node:internal/process/esm_loader:88:5)
    at async handleMainPromise (node:internal/modules/run_main:61:12)

Reproduction

1. Create a file mapped.mjs with the following contents:

throw new Error();

//# sourceMappingURL=data:application/json;base64,eyJ2ZXJzaW9uIjozLCJmaWxlIjpudWxsLCJzb3VyY2VzIjpbImZpbGU6Ly8vVXNlcnMvb3NhbWUvRGVza3RvcC90ZXN0LW5vZGUtc291cmNlLW1hcC9pbmRleC5tanMiXSwic291cmNlc0NvbnRlbnQiOlsidGhyb3cgbmV3IEVycm9yKCk7XG4iXSwibmFtZXMiOltdLCJtYXBwaW5ncyI6IkFBQUE7In0=

(The source map is Base64 inlined—details below.)

2. Run:

node --enable-source-maps ./mapped.mjs

Details

Code

index.mjs

throw new Error();

Generated source map

{
	"code": "throw new Error();\n",
	"map": {
		"version": 3,
		"file": null,
		"sources": [
			"file:///Users/osame/Desktop/test-node-source-map/index.mjs"
		],
		"sourcesContent": [
			"throw new Error();\n"
		],
		"names": [],
		"mappings": "AAAA;"
	}
}

The source map is a 1:1 mapping as demonstrated via source map visualization.