repl: refine handling of illegal tokens

[Trott]

Checklist

• a test and/or benchmark is included
• tests and code linting passes
• the commit message follows commit guidelines

Affected core subsystem(s)

Description of change

Illegal tokens are only recoverable in string literals, RegExp literals,
and block comments. If not in one of these constructs, immediately
return an error rather than giving the user false hope by giving them a
chance to try to recover.

Fixes: #3611

[Trott]

Before:

$ node
> a = 3.5e
... wha?
... ;
... Argh!
... 

After:

$ node
> a = 3.5e
SyntaxError: Unexpected token ILLEGAL
    at Object.exports.createScript (vm.js:24:10)
    at REPLServer.defaultEval (repl.js:236:25)
    at bound (domain.js:280:14)
    at REPLServer.runBound [as eval] (domain.js:293:12)
    at REPLServer.<anonymous> (repl.js:441:10)
    at emitOne (events.js:101:20)
    at REPLServer.emit (events.js:188:7)
    at REPLServer.Interface._onLine (readline.js:223:10)
    at REPLServer.Interface._line (readline.js:565:8)
    at REPLServer.Interface._ttyWrite (readline.js:842:14)
> 

[Trott]

But this still works, as expected:

Before:

$ node
> 'come\
... on\
... fhqwhgads'
'comeonfhqwhgads'
>

After:

$ ./node
> 'come\
... on\
... fhqwhgads'
'comeonfhqwhgads'
>

(No change between the two.)

[bnoordhuis]

LGTM although checking for ILLEGAL could break when we upgrade V8.

[Fishrock123]

@bnoordhuis Seems fine, the test will catch it.

[Fishrock123]

parser rather than lp?

[Fishrock123]

CI: https://ci.nodejs.org/job/node-test-pull-request/2901/

[Trott]

Is it possible to generate Unexpected token: ILLEGAL while in a block comment? Maybe I don't need to check for that? (And if I do need to check for it, there ought to be a test...)

EDIT: Yes, it is very very possible. /* foo on a line by itself will do it.

[Trott]

Nits addressed, re-running CI: https://ci.nodejs.org/job/node-test-pull-request/2919/

[Trott]

Only CI failure was a single build failure on a Raspberry Pi. Trying again because YOU CAN'T BE TOO CAREFUL!!!11!!! or something like that.

CI: https://ci.nodejs.org/job/node-test-pull-request/2920/

[Trott]

Landed in de0aa23

[MylesBorins]

@Trott lts?

[Trott]

@thealphanerd If it lands cleanly, yes.

[MylesBorins]

this one does not land cleanly