Sourcemap for child process is not generated.

When b.js is included by a.js as a file, a path, or a child process. A.js and b.js are built separately.
While Sourcemap for a.js is generated correctly. No sourcemap is generated for b.js.

input

// a.js
console.log('hello from a.js')

const path = require('path')

const bPath = path.resolve(__dirname, './b.js')

// do something with bPath ...

// b.js
console.log('hello from b.js')

npx ncc build ./a.js -o ./dist -s --no-source-map-register

output

• build/index.js

module.exports=(()=>{var e={536:(e,r,_)=>{console.log("hello from a.js");const t=_(622);const a=_.ab+"b.js"},622:e=>{"use strict";e.exports=require("path")}};var r={};function __nccwpck_require__(_){if(r[_]){return r[_].exports}var t=r[_]={exports:{}};var a=true;try{e[_](t,t.exports,__nccwpck_require__);a=false}finally{if(a)delete r[_]}return t.exports}__nccwpck_require__.ab=__dirname+"/";return __nccwpck_require__(536)})();
//# sourceMappingURL=index.js.map

• build/b.js

module.exports=(()=>{var e={463:()=>{console.log("hello from b.js")}};var r={};function __nccwpck_require__(_){if(r[_]){return r[_].exports}var a=r[_]={exports:{}};var o=true;try{e[_](a,a.exports,__nccwpck_require__);o=false}finally{if(o)delete r[_]}return a.exports}__nccwpck_require__.ab=__dirname+"/";return __nccwpck_require__(463)})();
//# sourceMappingURL=b.js.map

• build/index.js.map

{"version":3,"sources":["../webpack:/prj/a.js","../webpack:/prj/external \"path\"","../webpack:/prj/webpack/bootstrap","../webpack:/prj/webpack/runtime/compat","../webpack:/prj/webpack/startup"],"names":["console","log","bPath","__webpack_require__","ab","module","exports","require","__webpack_module_cache__","moduleId","threw","__webpack_modules__","__dirname"],"mappings":"0CAAAA,QAAAC,IAAA,kCAIA,MAAAC,EAAAC,EAAAC,GAAA,6BCJAC,EAAAC,QAAAC,QAAA,UCCA,IAAAC,EAAA,GAGA,SAAAL,oBAAAM,GAEA,GAAAD,EAAAC,GAAA,CACA,OAAAD,EAAAC,GAAAH,QAGA,IAAAD,EAAAG,EAAAC,GAAA,CAGAH,QAAA,IAIA,IAAAI,EAAA,KACA,IACAC,EAAAF,GAAAJ,EAAAA,EAAAC,QAAAH,qBACAO,EAAA,MACA,QACA,GAAAA,SAAAF,EAAAC,GAIA,OAAAJ,EAAAC,QCzBAH,oBAAAC,GAAAQ,UAAA,ICEA,OAAAT,oBAAA","file":"index.js","sourcesContent":[null,"module.exports = require(\"path\");;","// The module cache\nvar __webpack_module_cache__ = {};\n\n// The require function\nfunction __webpack_require__(moduleId) {\n\t// Check if module is in cache\n\tif(__webpack_module_cache__[moduleId]) {\n\t\treturn __webpack_module_cache__[moduleId].exports;\n\t}\n\t// Create a new module (and put it into the cache)\n\tvar module = __webpack_module_cache__[moduleId] = {\n\t\t// no module.id needed\n\t\t// no module.loaded needed\n\t\texports: {}\n\t};\n\n\t// Execute the module function\n\tvar threw = true;\n\ttry {\n\t\t__webpack_modules__[moduleId](module, module.exports, __webpack_require__);\n\t\tthrew = false;\n\t} finally {\n\t\tif(threw) delete __webpack_module_cache__[moduleId];\n\t}\n\n\t// Return the exports of the module\n\treturn module.exports;\n}\n\n","\n__webpack_require__.ab = __dirname + \"/\";","// module exports must be returned from runtime so entry inlining is disabled\n// startup\n// Load entry module and return exports\nreturn __webpack_require__(536);\n"]}

Lack of b.js.map. Got same result with -m or not.

version

• macos 11.2.1
• ncc 0.27.0
• node v14.12.0

Start by reproducing the issue with the provided a.js and b.js inputs and the npx ncc build command, then inspect the generated build directory and source-map handling. Done means the separately bundled child process produces b.js.map alongside b.js while index.js.map remains correct.