Uglifyjs: Do not optimize unused variables within the scope of eval()

[uiteoi]

Bug report, ES5, Uglify version 3.0.3
This is working properly in version 2.x.

JavaScript input
test.js:

!function(){
  var a;
  eval( 'a=1' );
  console.log( a );
}()

The uglifyjs CLI command executed or minify() options used.

uglifyjs test.js -c

JavaScript output

!function(){var a;eval("a=1"),console.log(void 0)}();

It appears that uglify thinks that variable a is not used, leading to an optimization that replaces it with void 0.

Workaround
Using compress option unused set to false:

uglifyjs test.js -c unused=false

Generates correct code:

!function(){var a;eval("a=1"),console.log(a)}();

I did not find which option to use with the API to workaround the problem. I have tried:

 var output = ugly.minify( sources, { compress: { unused: false  } } );

Suggested fix
Always set unused option within the scope of eval.

[kzc]

This is working properly in version 2.x.

2.8.23 has the same bug as 3.0.3.

[uiteoi]

I did test with version 2.8.22, and it was working properly.

[kzc]

$ node_modules/uglify-js/bin/uglifyjs -V
uglify-js 2.8.22

$ node_modules/uglify-js/bin/uglifyjs test.js -c
!function(){var a;eval("a=1"),console.log(void 0)}();

$ node_modules/uglify-js/bin/uglifyjs test.js -c | node
undefined

$ node test.js
1

[uiteoi]

To be more specific, I did not have the problem in version 2.8.22, using the low-level API. I noticed the problem while migrating to version 3.0.3 where I am now using minify().

[alexlamsl]

@uiteoi @kzc thanks for the report and detailed investigation - fix is on the way.