Terser: Cached variables can lead to incorrect toplevel trasnpilation

[ma2ciek]

Bug report or Feature request?

Bug

Version (complete output of terser -V)

3.10.11

Complete CLI command or minify() options used

// Terser options
{
    toplevel: true,
    mangle: true,
    nameCache: {
        vars: {
            props: {
                $add: 'foo'
            }
        },
        props: {
            props: {}
        }
    }
}

terser input

// a.js
import { add as someAdd } from './b';

console.log( someAdd( 1, 2 ) );

// b.js
export function add( x, y ) {
    return x + y;
}

terser output or error

export function foo(n,r){return n+r}
import{add as o}from"./b";console.log(o(1,2));

Expected result

The original exported add function should stay as it is. Eventually, its name should be transformed along with all its occurrences in imports.

[ma2ciek]

I've created a repository with this bug reproducible: https://github.com/ma2ciek/terser-bug.

[kzc]

Thanks for the detailed bug report.

Initially I thought that the nameCache was contrived and couldn't be created through normal minification, but that's not the case:

$ rm -f cache.json

$ echo 'function add(){Math.random();} add(); add();' | terser --toplevel -mc --name-cache cache.json
function n(){Math.random()}n(),n();

$ cat cache.json && echo
{"vars":{"props":{"$add":"n"}}}

$ echo 'export function add(x, y){ return x + y; }' | terser --toplevel -mc --name-cache cache.json
export function n(n,r){return n+r}

I have a fix for this.

[kzc]

Other bug variations:

$ cat cache.json && echo
{"vars":{"props":{"$add":"n"}}}

$ echo 'export class add{}' | terser --toplevel -mc --name-cache cache.json
export class n{}

$ echo 'export var add = 1;' | terser -mc --name-cache cache.json
export var n=1;

$ echo 'export let add = 1;' | terser -mc --name-cache cache.json
export let n=1;

$ echo 'export const add = 1;' | terser -mc --name-cache cache.json
export const n=1;

$ echo 'export let sub = 0, add = 1;' | terser --module -mc --name-cache cache.json
export let sub=0,n=1;

$ echo 'export let {x: add} = obj;' | terser --module -mc --name-cache cache.json
export let{x:n}=obj;

Any other failing scenarios?

[kzc]

Okay, I have a more general fix that should handle all export declaration scenarios.

[kzc]

@ma2ciek Please try #166 and report your findings.

[ma2ciek]

Thanks for the quick fix! It works perfectly on that branch for our needs. I've tested it on our codebase and no error has occured after the minification.