Minify breaks eval which refers const

[sapphi-red]

Input:

console.log((function (){ const v = 0; return eval('v') })()) // 0

Output:

console.log(function(){return eval("v")}()); // Error: v is not defined

repl

---

Input

console.log((() => { const v = 0; return eval('v') })());  // 0

Output

console.log((()=>eval("v"))()); // Error: v is not defined

repl

---

const v = 0 was dropped here.

esbuild/internal/js_parser/js_parser.go

Lines 9312 to 9317 in 698898f

	// Only keep this declaration if it's top-level or exported (which
	// could be in a nested TypeScript namespace), otherwise erase it
	if p.currentScope.Parent == nil || s.IsExport {
	s.Decls[end] = d
	end++
	}

I found this while working on #2360.

version: esbuild 0.14.48

[hyrious]

Did you mean esbuild should take care of eval? I mean this can be really hard with eval(whatever_expression), which has been stated in the doc.

[evanw]

Using eval is supposed to poison all enclosing scopes to disable tree shaking. So this behavior should be disabled in this case. It’s an oversight that this code isn’t checking to see if it’s in an eval scope before removing the variable.

[sapphi-red]

Sorry that I forgot to write the expected behavior.
What I expected is to disable this minify transform for this case like other minify transforms.