net/url: `QueryEscape` escapes its own escape characters

[UndeadBaneGitHub]

What version of Go are you using (go version)?

$ go version
go1.19.2

But really, affects 1.18 and other versions too

Does this issue reproduce with the latest release?

Yes

What operating system and processor architecture are you using (go env)?

It's universal anywhere, since it's a bug in logic implementation of internal shouldEscape method

What did you do?

Playground link: https://go.dev/play/p/WXXx4EiSy_E

What did you expect to see?

Already escaped string should not be escaped again (example behavior: Javascript encodeURIComponent method and similar)

What did you see instead?

It gets escaped as many times as the method is called.

[seankhliao]

The + sign carries semantic meaning within url query escaping, in general it won't be possible to know if it has been escaped before.

Closing as working as intended.

[UndeadBaneGitHub]

@seankhliao It also escapes % sign as shown in the playground, it is not working as intended.

[ianlancetaylor]

The JavaScript encodeURIComponent function also escapes a % character in its input string, encoding it as %25.

We aren't going to make any changes here.