panic: Expected scope, found scope while parsing

[dloebl]

While updating to esbuild v0.25.0, we noticed that some inputs cause esbuild to panic. I've tried my best to minify the input JS, but it's still a rather large reproducer.

Input:
min_js.zip

Steps:

$ esbuild min.js

✘ [ERROR] panic: Expected scope (7, 186) in min.js, found scope (7, 165) (while parsing "min.js")

  debug.Stack (runtime/debug/stack.go:26)
  helpers.PrettyPrintedStack (internal/helpers/stack.go:9)
  bundler.parseFile.func1 (internal/bundler/bundler.go:254)
  panic (runtime/panic.go:785)
  js_parser.Parse.func1 (internal/js_parser/js_parser.go:17334)
  panic (runtime/panic.go:785)
  js_parser.(*parser).pushScopeForVisitPass (internal/js_parser/js_parser.go:8421)
  js_parser.(*parser).visitFn (internal/js_parser/js_parser.go:16735)
  js_parser.(*parser).visitExprInOut (internal/js_parser/js_parser.go:15432)
  js_parser.(*parser).visitExpr (internal/js_parser/js_parser.go:12819)
[..]

1 error

Version: 0.25.0

[evanw]

Huh, that's some crazy code. Here's the code for ease of access:

(function(){[(function(){})]|function(){for([(function(){})];;)e}(((/)/))=function(){for([({})];;)[]}((function(){((([(f)])))}))=function(){switch(((L))){case(u):([(function(){})]);case(function(){}):((("")))}(function(){})}()[(f)])[(f)]&function(){for(;([(f)])[(f)];)[(i)]}(function(){return{n(){for(;[(0)];){((([])))}}}[(c)](function(){try{[];if(t){}}catch{}}) try{}catch{}if(([({})])){(([]))}try{for([(f)];;){}}catch{}}[({})]);try{}catch{}for(;;([(i)]=function(){([(f)]=t)}));})

I'm guessing this is related to some unintentional scope manipulation in the new switch optimizations.

Edit: Here's a minimal reproduction:

switch (0) {
  case 1: x = function() {}
  case function() {}: break
}

Perhaps related to function expressions inside case statements, which isn't something I've ever seen real code do.

[goliafrs]

After updating to Vite version 6.2.0, which includes an upgrade to esbuild version 0.25.0, I encountered the following error during the build process:

[plugin:vite:esbuild] Transform failed with 1 error:
error: panic: Expected scope (7, 1596) in /var/client-side/src/plugins/router.ts, found scope (0, 908) (while parsing "/var/client-side/src/plugins/router.ts")

Environment:
Build Tool: Vite 6.2.0
Package Manager: pnpm
Dependencies:

• vite: ^6.2.0
• vue: ^3.5.13
• vue-router: ^4.5.0
• @vitejs/plugin-vue: ^5.2.1
• @vitejs/plugin-vue-jsx: ^4.1.1
• typescript: 5.7.3

The error appears to be related to a switch-case statement within the router.ts file. Here's the relevant portion of the code:

router.beforeEach(async (to, from, next) => {
  // ... other code

  switch (true) {
    case to.matched.some(({ meta }) => meta.layout === 'authorized'):
      // ... handling
      break;
    // ... other cases
    default:
      next();
  }

  // ... other code
});

I've been using similar code for several years, and such constructs are common in my codebase.

For those seeking a quick temporary solution to this issue, downgrading Vite to version 6.1.x may help, as it uses an earlier version of esbuild.

pnpm add --save-dev vite@6.1.1

[Leonya]

Had the same issue in my codebase, worked around it by extracting case conditions to const.

[pumano]

looks like 0.25.1 not fix problem got panic while parsing some ugly case code:

 switch (true) {
    case some1 && some1.includes(another):
    case some2 && some2.includes(another2):
      // ... handling
      break;
    // ... other cases
    default:
      next();
  }

maybe some ugly cases from here can help to find problem?

[evanw]

I'm not able to reproduce a panic with that code: link

If you have a bug report for esbuild, then please provide a way to reproduce the bug.