[Bug]: duplicate modules in dev build with persistent cache

[escaton]

System Info

  System:
    OS: macOS 15.7.2
    CPU: (14) arm64 Apple M4 Pro
    Memory: 2.47 GB / 24.00 GB
    Shell: 5.9 - /bin/zsh
  Binaries:
    Node: 24.12.0 - /Users/escaton/.nvm/versions/node/v24.12.0/bin/node
    npm: 11.6.2 - /Users/escaton/.nvm/versions/node/v24.12.0/bin/npm
    bun: 1.3.6 - /opt/homebrew/bin/bun
  Browsers:
    Chrome: 144.0.7559.97
    Firefox: 147.0.1
    Safari: 26.1
  npmPackages:
    @rsbuild/core: 1.7.2 => 1.7.2 
    @rsbuild/plugin-type-check: 1.3.3 => 1.3.3 
    @rsbuild/plugin-vue: 1.2.3 => 1.2.3 

Details

I'm using rsbuild, and my cache config looks like this (rsbuild inspect)

cache: {
  type: 'persistent',
  version: 'web-development',
  storage: {
    type: 'filesystem',
    directory: '/Users/escaton/Projects/playgama/portal-frontend-vue/node_modules/.cache/rspack'
  },
  buildDependencies: [
    '/Users/escaton/Projects/playgama/portal-frontend-vue/package.json',
    '/Users/escaton/Projects/playgama/portal-frontend-vue/tsconfig.json',
    '/Users/escaton/Projects/playgama/portal-frontend-vue/rsbuild.config.ts',
    '/Users/escaton/Projects/playgama/portal-frontend-vue/.browserslistrc',
    '/Users/escaton/Projects/playgama/portal-frontend-vue/.env'
  ]
},

which is a default set by rsbuild.

Sometimes when I switch branches, or change anything in rsbuild.config, and run rsbuild dev I got an invalid build of my app. It crashes like there are duplicates of modules that were supposed to be singletons. Indeed when I inspected built index.js I see multiple duplicates of some modules like

"./src/i18n/i18n.ts?abb2": (function (__unused_rspack_module, __webpack_exports__, __webpack_require__) {
...
},
"./src/i18n/i18n.ts?a942": (function (__unused_rspack_module, __webpack_exports__, __webpack_require__) {
...
},

After I remove the cache rm ./node_modules/.cache/rspack
the content becomes

"./src/i18n/i18n.ts": (function (__unused_rspack_module, __webpack_exports__, __webpack_require__) {
...
},

I did't recognize any pattern of why certain modules got duplicated and some not, and don't know how to dig deeper. For now I just remove cache and move on, but that is annoying.

I understand it is pretty vague bug report, but I have no idea how to make a small repro.
Can you at least tell me how is it even possible to have multiple copies of same module with those ?XXXX queries, so I can try to investigate further.

Reproduce link

No response

Reproduce Steps

[github-actions]

Hello @escaton, sorry we can't investigate the problem further without reproduction demo, please provide a repro demo by forking rspack-repro, or provide a minimal GitHub repository by yourself. Issues labeled by need reproduction will be closed if no activities in 14 days.

[escaton]

@jerrykingxyz I cannot make repro, but that doesn't mean that the problem does not exist. I'm asking for a guidance to investigate it. One clue that I found is that sometimes same module is declared twice in the built js file with strange suffixes "module.ts?1234": function {...} Can you tell me in what cases rspack can do that, so I can maybe better understand the root cause?

[jerrykingxyz]

@escaton This issue is usually caused by two different modules having the same lib_ident(eg. ./src/i18n/i18n.ts). In your scenario, I think it's possible that the persistent cache reverted to the previous module, but changes in loader configurations caused rspack to generate a similar module with a different identifier. When repro this problem, you can output stats.modules and compare the module.identifier of these two similar modules.

[github-actions]

Since the issue was labeled with awaiting more feedback, but no response in 14 days. This issue will be closed. Feel free to comment and reopen it if you have any further questions.