fix: output.format should be esm instead of es

[JounQin]

This PR contains:

• bugfix
• feature
• refactor
• documentation
• other

Are tests included?

• yes (bugfixes and features will not be merged without tests)
• no, seems no need

Breaking Changes?

• yes (breaking changes will not be merged unless absolutely necessary)
• no

List any relevant issue numbers:

Description

[codecov]

Codecov Report

Merging #3220 into master will not change coverage.
The diff coverage is 100%.

@@           Coverage Diff           @@
##           master    #3220   +/-   ##
=======================================
  Coverage   90.64%   90.64%           
=======================================
  Files         167      167           
  Lines        5911     5911           
  Branches     1793     1793           
=======================================
  Hits         5358     5358           
  Misses        336      336           
  Partials      217      217

Impacted Files	Coverage Δ
src/rollup/index.ts	93.93% <100%> (ø)	⬆️

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[lukastaegert]

It is impossible to write a test because nothing was broken. If you disagree, prove it by adding a test that fails without the change. The reason is that internally for compatibility with plugins, esm is mapped to es. This will change with the 2.0 release. Please do not guess how the code works, test it. The requirement of tests in the issue template is there for a reason.

[JounQin]

@lukastaegert It breaks my codes like following which was working for a long time:

-      rollup(opts).then(bundle => bundle.write(opts as OutputOptions)),
+      rollup(opts).then(bundle => bundle.write(opts.output as OutputOptions)),

I'm wondering why it was not even mentioned in CHANGLOG.

[lukastaegert]

Something breaks your code, but it is not fixed by your change, and if you had tested it, you would have known. And I would have known what you were actually trying to achieve. I will push a fix for #3222, which I accidentally broke. To my defence, this was an undocumented and untested feature from before my time.

[JounQin]

I would say that it did work by adding esm instead of replacing es to esm on my testing.

And the internal esm -> es mapping and the error message is very confusing for someone new to the source code like me.

Whatever, glad to hear that we're going to have a fix for it.