util.getCallSites() drops functionName when a source map has no name entry

[privatenumber]

Version

v24.15.0

Also reproduced on v23.6.0.

Platform

macOS 15.6 (Darwin 24.6.0), x86_64

Subsystem

util, source_map

What steps will reproduce the bug?

Create these two files in the same directory.

repro.js:

const{getCallSites}=require("node:util");function foo(){console.log(getCallSites(1,{sourceMap:!0})[0].functionName)}foo();
//# sourceMappingURL=repro.js.map

repro.js.map:

{
  "version": 3,
  "sources": ["original.js"],
  "sourcesContent": ["const { getCallSites } = require('node:util'); function foo() { console.log(getCallSites(1, { sourceMap: true })[0].functionName); } foo();"],
  "mappings": "AAAA,KAAM,CAAE,YAAa,EAAI,QAAQ,WAAW,EAAG,SAAS,KAAM,CAAE,QAAQ,IAAI,aAAa,EAAG,CAAE,UAAW,EAAK,CAAC,EAAE,CAAC,EAAE,YAAY,CAAG,CAAE,IAAI",
  "names": []
}

How often does it reproduce? Is there a required condition?

It reproduces every time on v23.6.0 and v24.15.0.

The source map must map the call-site location without providing a corresponding name entry. Source Map v3 permits an empty names array.

What is the expected behavior? Why is that the expected behavior?

The command should print:

foo

The generated V8 call site contains foo as its function name. Remapping its source location should preserve that name when the source map does not provide a replacement.

This is also consistent with Node.js's source-mapped stack trace formatter, which retains the generated function name when no mapped name exists.

What do you see instead?

The command prints an empty line because:

getCallSites(1, { sourceMap: true })[0].functionName === ''

Additional information

Running the same file without source-map remapping prints the expected name:

$ node repro.js
foo

reconstructCallSite() in lib/util.js currently assigns:

functionName: entry.name ?? ''

Consequently, an absent optional source-map name replaces the generated V8 function name with an empty string. It should instead fall back to the generated call site's functionName.