Using esbuild minifier breaks code

[surgicaI]

We are using 1.8.38 version of gojs library and the library(which is valid javascript code) breaks after minification with esbuild.

Here is repo that can be used to reproduce the issue. Instructions to build and run code can be found in the README file in the repo.
https://github.com/surgicaI/esbuild-gojs-minify-bug

In the above repo, rollup is used to generate javascript bundle from source code and rollup config can be found here. Gojs library is used to create diagrams and notice that when the generated javascript bundle is minified using minify module from esbuild, the code breaks and no diagram is rendered in the app.

Please look into the issue

[hyrious]

This could be caused by minify-syntax. You can turn it off by adding options to the rollup plugin:

minify({
  minify: false,
  minifyWhitespace: true,
  minifyIdentifiers: true,
})

However it is hard to tell what's wrong in the minified code, keepNames does not work too. Searching the source code to see if it uses eval or Function() also does not give me any clue. We have to investigate it more deeply to see if it relies on a function's toString().

Update: I've tried some older versions of esbuild (from 0.10.1, since the rollup plugin specified that version range) and there's no luck.

Update2: I've noticed gojs' latest version 2.2.5 (current 1.8.38), just tried upgrade that package and now it all works. The oldest working version most close to 1.8.38 is 2.0.2.

[evanw]

Thanks for the report. I've traced it down to this optimization:

esbuild/internal/js_parser/js_parser.go

Lines 9219 to 9221 in 2244c09

	if len(s.Stmts) == 1 && !statementCaresAboutScope(s.Stmts[0]) {
	// Unwrap blocks containing a single statement
	stmt = s.Stmts[0]

The issue is with if statements of the following form:

if (a)
  b: {
    if (c) {
      break b
    }
  }
else if (d)
  e()

That code is incorrectly minified into this:

if (a)
  b:
    if (c)
      break b;
else
  d && e();

The problem is that the AST printer doesn't add braces to avoid the inner if merging with the outer else when the inner if is the child of a label. I will change esbuild to print the AST this way instead:

if (a) {
  b:
    if (c)
      break b;
} else
  d && e();