Fix: prefer-template autofix produces syntax error with octal escapes

[mdjermanovic]

What is the purpose of this pull request? (put an "X" next to item)

[X] Bug fix

Tell us about your environment

• ESLint Version: 6.1.0
• Node Version: 10.16.0
• npm Version: 6.9.0

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

default

Please show your full configuration:

Configuration

module.exports = {
  parserOptions: {
    ecmaVersion: 2015,
  },
};

What did you do? Please include the actual source code causing the issue.

/*eslint prefer-template: "error"*/

"\0 \1" + foo

/*eslint prefer-template: "error"*/

"\08" + foo

What did you expect to happen?

Not a syntax error in autofix.

What actually happened? Please include the actual, raw output from ESLint.

/*eslint prefer-template: "error"*/

`\0 \1${  foo}`

Parsing error: Octal literal in template string

/*eslint prefer-template: "error"*/

`\08${  foo}`

Parsing error: Octal literal in template string

What changes did you make? (Give an overview)

Made a new regex in astUtils, which fixes two bugs:

• Octal escapes after a valid \0 were missed (e.g. "\0 \1"). This bug was probably inherited from no-octal-escape (fixed there in Update: fix no-octal-escape false negatives after \0 #12079)
• Whether or not "\08" and "\09" are octal escapes (Report '\08' and '\09' in no-octal-escape #12080) these two de facto produce parsing errors in template literals.

Is there anything you'd like reviewers to focus on?

• Regex and its performance.

I'll also fix the quotes rule in another PR when this gets merged.

[platinumazure]

LGTM, but would like another set of eyes on this before merging. Thanks!

[platinumazure]

Reproduction:

• Original code (example 1), showing fix
• Fixed code (example 1), shows parse error
• Original code (example 2)
• Fixed code (example 2), shows parse error

Marking as accepted.

[kaicataldo]

LGTM. I actually didn't know about this restriction and had to go do some reading. Thanks for contributing and for the learning opportunity!