Replace well-defined variable with undefined in for statement

Context

I use Vue.js, and when I replace process.env.NODE_ENV with 'production', and minify my bundle with babel-preset-minify the resulting code is broken in this function actuallySetSelected, and more precisely the i < l expression in the for statement is replaced with i < undefined.

Steps to reproduce

I use:

• @babel/core v7.0.0-beta.51;
• babel-preset-minify v0.4.3.

With this config for babel-preset-minify:

{
  evaluate: true,
  simplify: true,
  mergeVars: true,

  removeUndefined: false,
  deadcode: false,
  booleans: false,
  builtIns: false,
  consecutiveAdds: false,
  flipComparisons: false,
  guards: false,
  infinity: false,
  mangle: false,
  memberExpressions: false,
  numericLiterals: false,
  propertyLiterals: false,
  regexpConstructors: false,
  replace: false,
  simplifyComparisons: false,
  typeConstructors: false,
  undefinedToVoid: false
}

I’ve simplified the test case:

Input

function test () {
  if (false) return
  var i
  for (var l=1; i < l; i++) {}
}

Expected output

function test(){if(true)for(var i,l=1;i<l;i++);}

Actual output

function test(){if(true)for(var i,l=1;i<undefined;i++);}

It seems I’ve managed to reduce it to an interaction between those three plugins:

• babel-plugin-minify-simplify
• babel-plugin-transform-merge-sibling-variables
• babel-plugin-minify-constant-folding

You can pull this repo to test it for yourself.

[kevinv11n]

@trevor-bliss and I just ran into the same issue.

[tex0l]

I noticed version 0.5.0 just got out, I updated the test case here: https://github.com/tex0l/bug-report-babel

@boopathi : the bug still exists in the latest version.