[BUG] Fatal logic error when modify function argument by function define statement.

[tinymins]

Bug report or Feature request?
Bug report.

Version (complete output of terser -V or specific git commit)
terser 4.0.0

Complete CLI command or minify() options used

terser --compress -- test.js

terser input

// test.js
var printTest = function (ret) {
    function ret() {
        console.log('Value after override');
    }
    return ret;
}('Value before override');

printTest();

terser output or error

var printTest=function(ret){return"Value before override"}();printTest();

Expected result

var printTest=function(ret){function ret(){console.log("Value after override")}return ret}();printTest();

or

var printTest=function(ret){return function ret(){console.log("Value after override")}}();printTest();

or

var printTest=function(){console.log("Value after override")};printTest();

Link
https://github.com/tinymins/terser/blob/issue-369/test/compress/issue-369.js
https://github.com/tinymins/terser/blob/issue-369/lib/compress/index.js#L1394

[fabiosantoscode]

Thank you very much for your report and the test!

Does this occur even if you specify different variable names for the argument ret and the function ret? If so this is high priority.

[tinymins]

@fabiosantoscode Yes, in my test file the argument name is a. https://github.com/tinymins/terser/blob/issue-369/test/compress/issue-369.js

[tinymins]

I'm not sure if I got a misunderstanding.

The bug is, if you assign the argument by define function statement, unused and collapse_vars config will cause compress error. The compressor think the define statement is an unused code block, and will remove it.

[fabiosantoscode]

Got it. This is low priority as I don't see too many people creating functions that are the same name as variables which already exist.

[tinymins]

Yep, I also think nobody will code like this.
But I triggered this bug by using a 3rd-party dev tools. I have to disable 'collapse_vars' config for using this tool. https://eruda.liriliri.io/
I don't know why they write this kind of code: https://github.com/liriliri/eruda/blob/8027c2435ca78f91927121e18faa78292b27e0bf/src/lib/util.js#L1272 , maybe it was created by webpack module?

[TrySound]

@fabiosantoscode lodash is one of the most popular libraries. Similar problem with collapse_vars.
#333