curly: multi-or-nest option reports an error for a single-statment block with a semicolon on the next line

[cherryblossom000]

Tell us about your environment

• ESLint Version: 6.5.1
• Node Version: 12.11.0
• npm Version: 6.11.3

What parser (default, Babel-ESLint, etc.) are you using? default

Please show your full configuration:

Configuration

{
  "rules": {
    "curly": [2, "multi-or-nest"]
  }
}

What did you do? Please include the actual source code causing the issue, as well as the command that you used to run ESLint.

I used the following code in file.js:

if (true) console.log('some statement')
;(function () {})()

The issue occurs whenever the statement in the if block (or any block) has the semicolon on the following line.

Then I linted it:

eslint file.js

What did you expect to happen?
No error would occur as there is only 1 statement in the if block.

What actually happened? Please include the actual, raw output from ESLint.
I got the following error:

file.js
  1:1  error  Expected { after 'if' condition  curly

✖ 1 problem (1 error, 0 warnings)
  1 error and 0 warnings potentially fixable with the `--fix` option.

When fixing it with eslint --fix file.js, it gets changed to

if (true) {console.log('some statement')
;}(function () {})()

which conflicts with the "semi": [2, "never"] rule as that would change it to:

if (true) {console.log('some statement')
}(function () {})()

which would cause curly to report Unnecessary { after 'if' condition.

Are you willing to submit a pull request to fix this bug?
Yes.

[cherryblossom000]

I think the issue is here:

eslint/lib/rules/curly.js

Lines 99 to 104 in c47fa0d

	function isOneLiner(node) {
	const first = sourceCode.getFirstToken(node),
	last = sourceCode.getLastToken(node);
	return first.loc.start.line === last.loc.end.line;
	}

last would be the semicolon, which is on a different line to the first token in

console.log('some statement')
;

[kaicataldo]

Verified using our demo. Nice find! Definitely seems like we should use the previous token for this check in this case.

[cherryblossom000]

I fixed it in #12378.