Issue applying babel-plugin-transform-remove-undefined in babel7-beta.40

[diervo]

Input Code

(function () {
  function test() {
    let a;
  }
}());

Actual Output

TypeError: Cannot read property 'isPure' of null
    at Object.checkPath (/Users/dval/Sites/minify/node_modules/@babel/traverse/lib/path/lib/virtual-types.js:120:23)
    at NodePath.(anonymous function) [as isPure] (/Users/dval/Sites/minify/node_modules/@babel/traverse/lib/path/index.js:205:24)
    at isPureAndUndefined (/Users/dval/Sites/minify/packages/babel-plugin-transform-remove-undefined/lib/index.js:28:13)
    at PluginPass.VariableDeclaration (/Users/dval/Sites/minify/packages/babel-plugin-transform-remove-undefined/lib/index.js:180:21)

Expected Output

(function(){})();

Details

I trace it down to the following code in babel-plugin-transform-remove-undefined :

When visiting VariableDeclaration node, and accessing the path for its property init, that path should have a scope pointing to the parent function declaration. Instead scope is null.

Not sure if is a bug in babel.

[diervo]

Some more digging: it seems that the issue on remove-undefined is a side-effect from when also enabling babel-plugin-minify-constant-folding.

A trivial workaround is to add a guard for !rval.scope || !rval.isPure() in as the first par of the expression insideisPureAndUndefined() function, but you guys will probably know better?

FYI, for more accurate testing I updated all dependencies to babel40
#804

[diervo]

Also I believe the constant-folding is why the CI is failing. Its all related with scope property being undefined.

[boopathi]

I kinda drilled it down to simplify. So, maybe both the transforms are.

In some places of babel-minify, we avoid the babel's re-queueing (path.replaceWith) deliberately and mutate the node directly. Maybe these transforms in simplify and constant folding does this.

Also, interestingly, the mangle's re-queueing had to be turned off for babel-minify to work with babel-7 - c0c712d#diff-18ba673c600d34ebd7daef11f67829f9R438

[boopathi]

This is merged to master. Thanks for the fix @diervo .