no-extra-semi exception or new option

[Mouvedia]

http://eslint.org/docs/rules/no-extra-semi

• ESLint 2.9.0
• being able to safely concatenate several JS files into one and use no-extra-semi at the same time

If the first character of the file—excluding the eventual preceding whitespace—is ; it should be ignored.
cf http://stackoverflow.com/q/1873983/248058

[platinumazure]

I could support a new option for this, where if semicolon is the first token (not counting comments or whitespace) then this rule would not report that violation. Leading semicolon is a common defense against ASI problems when concatenating scripts.

Maybe something like "allow-bof": true or "except-bof": true?

Haven't had a chance to make sure this is still an issue on latest, but I hope I would remember PRs being merged for something like this in the last couple of minor releases.

[platinumazure]

Oh, and I am happy to implement if this issue is accepted, unless @Mouvedia should prefer to have the opportunity.

[Mouvedia]

@platinumazure Ill let you have it.

Not sure about the name though.

[platinumazure]

Certainly open to other options, but we have used eof and bof to mean end
of file and beginning of file elsewhere in this repository.
On May 28, 2016 8:46 PM, "Marc G." notifications@github.com wrote:

@platinumazure https://github.com/platinumazure Ill let you have it.

Concerning the name. I am gonna have to google "bof" to know what it is so
it's probably not good.

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[Mouvedia]

I am all for consistency. 👍 for BOF then.

[platinumazure]

@eslint/eslint-team Thoughts on this? Leading semicolons at the beginning of a file are somewhat commonplace and I think this is a worthwhile enhancement. I am happy to implement, as well, so I think we just need a champion and three 👍's.

[michaelficarra]

👎 for a number of reasons

• you should never naively concatenate your files together
• a semicolon at the beginning is not even effective in allowing you to safely naively concatenate files
• adding this option will implicitly endorse this anti-pattern

[platinumazure]

@michaelficarra I'm not sure that "it's an anti-pattern" really counts since ESLint is not supposed to be opinionated. I would love to see an example of why a semicolon is not always effective here.

[Mouvedia]

a semicolon at the beginning is not even effective in allowing you to safely naively concatenate files

@michaelficarra interesting; do you have a source that supports that claim?

[michaelficarra]

@Mouvedia You shouldn't rely on appeal to authority. Instead, I will describe for you a pair of programs that cause it to fail. If the left program ends in a single-line comment (// ...), the leading semicolon in the right program will be contained within the comment. To avoid this, you would need to join on a LineTerminator-semicolon sequence. As a second example, if either program has a directive (but not both), the right program's behaviour may be changed.