René's URL Explorer Experiment

{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"util.getCallSites() drops functionName when a source map has no name entry","articleBody":"### Version\n\nv24.15.0\n\nAlso reproduced on v23.6.0.\n\n### Platform\n\n```text\nmacOS 15.6 (Darwin 24.6.0), x86_64\n```\n\n### Subsystem\n\nutil, source_map\n\n### What steps will reproduce the bug?\n\nCreate these two files in the same directory.\n\n`repro.js`:\n\n```js\nconst{getCallSites}=require(\"node:util\");function foo(){console.log(getCallSites(1,{sourceMap:!0})[0].functionName)}foo();\n//# sourceMappingURL=repro.js.map\n```\n\n`repro.js.map`:\n\n```json\n{\n  \"version\": 3,\n  \"sources\": [\"original.js\"],\n  \"sourcesContent\": [\"const { getCallSites } = require('node:util'); function foo() { console.log(getCallSites(1, { sourceMap: true })[0].functionName); } foo();\"],\n  \"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\",\n  \"names\": []\n}\n```\n\n### How often does it reproduce? Is there a required condition?\n\nIt reproduces every time on v23.6.0 and v24.15.0.\n\nThe source map must map the call-site location without providing a corresponding name entry. Source Map v3 permits an empty `names` array.\n\n### What is the expected behavior? Why is that the expected behavior?\n\nThe command should print:\n\n```text\nfoo\n```\n\nThe 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.\n\nThis is also consistent with Node.js's source-mapped stack trace formatter, which retains the generated function name when no mapped name exists.\n\n### What do you see instead?\n\nThe command prints an empty line because:\n\n```js\ngetCallSites(1, { sourceMap: true })[0].functionName === ''\n```\n\n### Additional information\n\nRunning the same file without source-map remapping prints the expected name:\n\n```console\n$ node repro.js\nfoo\n```\n\n`reconstructCallSite()` in `lib/util.js` currently assigns:\n\n```js\nfunctionName: entry.name ?? ''\n```\n\nConsequently, 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`.\n","author":{"url":"https://github.com/privatenumber","@type":"Person","name":"privatenumber"},"datePublished":"2026-08-07T14:16:17Z","url":"https://github.com/nodejs/node/issues/65104"}