Fix copy/paste of empty lines

[silverwind]

Fixes: #19331
Regressed by: #18270

Needed to do another string replacement in the Chroma output HTML to get copy/paste work again. The previous replacement conditions are probably obsolete, but as I'm not 100% sure, I opted to keep them.

Specifically, the Chroma HTML change mentioned in #18270 (comment) broke our previous newline replacement for such empty lines.

Also included are a few changes to make the test more pleasant to work with.

[wxiaoguang]

The dedent.Dedent could be replaced by a regex like ^\s*(.*?)\s*$ => $1 , then the dependency can be removed.

func main() {
	m := regexp.MustCompile(`(?m:^\s*(.*?)\s*$)`)   // use multi-line mode to trim spaces
	s := "  a  \n\tb c  \n"
	t := m.ReplaceAllString(s, "$1")
	fmt.Printf("origin:\n%s\n--------\ntrimed:\n%s\n(len=%d)\n", s, t, len(t))
}

origin:
  a  
        b c  

--------
trimed:
a
b c
(len=5)

[silverwind]

The dedent.Dedent could be replaced by a regex like ^\s*(.?)\s$ => $1 , then the dependency can be removed.

Might be an option, yeah. One thing I don't like about the dependency is that it does not handle leading/trailing newlines, I mentioned it in lithammer/dedent#14.

[silverwind]

The dedent.Dedent could be replaced by a regex like ^\s*(.*?)\s*$ => $1 , then the dependency can be removed.

func main() {
	m := regexp.MustCompile(`(?m:^\s*(.*?)\s*$)`)   // use multi-line mode to trim spaces
	s := "  a  \n\tb c  \n"
	t := m.ReplaceAllString(s, "$1")
	fmt.Printf("origin:\n%s\n--------\ntrimed:\n%s\n(len=%d)\n", s, t, len(t))
}

origin:
  a  
        b c  

--------
trimed:
a
b c
(len=5)

Actually, this is not a true dedent because b should not indent to 0 but only be dedented by 2 places. I think it's not possible with a regex alone to achieve a proper detent so I think the module is fine to keep, but I'll add a wrapper function that also performs strings.TrimSpace on the result because that's what I would expect from a proper dedent.

[wxiaoguang]

Oh yup, I was thinking that the spaces should have been wrapped inside tags, so all spaces around the line could be trimmed. If it's not the case, then regex won't work.

[silverwind]

Refactored to util.Dedent that also does the trimming. I think it will be useful in the future, especially for test code.

[silverwind]

ready to merge from my side.

[wxiaoguang]

I think this could be in 1.17 (keep it open for one or two days for more suggestions)

[silverwind]

I'd even backport it to 1.16. I copy a lot of code from UI and it's a big issue for me.