Lift Template Literal Restriction on Backslashes

Overview

Everyone loves L^AT_EX so ESNext will likely allow tagged template strings to contain backslashes on any sequence - even ones that look like they might contain an invalid Unicode escapes.

In other words, something like

let x = tag `\u{wat}`;

is now valid, whereas previously it would be considered an error.

Reference: https://tc39.github.io/proposal-template-literal-revision/

As of this writing, the linked proposal is at Stage 3.

Notes

This restriction lift doesn't apply to untagged template strings. For example:

// All of these are still invalid.
let bad = `bad escape sequence: \unicode`;
let bracingOurselves = `\u{shouldntDoThis}`;
let theWorst = `\xtremely bad`;

Because there is no appropriate representation for a "cooked" string that contains one of these escapes, the returned value at a position on the top-level array will be undefined, but the raw representation will be available. For example:
```
function tag(strs) {
  console.log(strs[0] === undefined);
  console.log(strs.raw[0] === "\\unicode and \\u{55}");
}
```

// Prints 'true' twice.
tag\unicode and \u{55}

Proposed Emit

Input:

let x = tag `\u{hello} ${ 100 } \xtraordinary ${ 200 } wonderful ${ 300 } \uworld`;

Output:

var x = (
    _a = [undefined, undefined, " wonderful ", undefined],
    _a.raw = ["\\u{hello} ", " \\xtraordinary ", " wonderful ", " \\uworld"],
    tag(_a, 100, 200, 300)
);

This was bumped to stage 4 in 2017-03. It is slated for inclusion in ES2018

https://github.com/tc39/proposals/blob/master/finished-proposals.md

Interested in this😉

Wenlu Wang (@Kingwl)

Wenlu Wang (@Kingwl) In implementing it, or using it? 😃

related #5291
should we re-implement EscapeSequence in the scanner ?

should we re-implement EscapeSequence in the scanner ?

I don't know why that'd be necessary, I think you just need to potentially thread through some extra context when you're scanning these things (which is what the ECMAScript spec does in the grammar now). But I might've missed something, so feel free to send the PR and we can iterate on it!

By the way, template emit now uses a helper, so the proposed emit is a little different.

Should the new grammar be always used or what options are needed?
more than 90 baseline changed

Jake Ginnivan (@JakeGinnivan)

Jake Ginnivan (@JakeGinnivan)

We have just hit this issue upgrading from 2.4.1 to 2.6.1.

glamorous.h3({
'&::after': {
content: "\\00BB"
}
})
Before it output chevrons, after the upgrade it output x000BB.

seems could fixed in this change

how could i know that template is tagged in,scanner？ i have no idea😓

I think you'll have to actually add a rescan method on the scanner (e.g. rescanTaggedTemplateHead or something).

ahhh, reScan is work, but the error which first time scan are preserved,
how could i remove those incorrect error

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Lift Template Literal Restriction on Backslashes #12700

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Lift Template Literal Restriction on Backslashes #12700

Description

Overview

Notes

Proposed Emit

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clavecoder commented on May 22, 2017

Kingwl commented on Apr 28, 2018

DanielRosenwasser commented on Apr 28, 2018

Kingwl commented on Apr 28, 2018

DanielRosenwasser commented on Apr 28, 2018

DanielRosenwasser commented on Apr 28, 2018

Kingwl commented on Apr 29, 2018

Kingwl commented on Apr 29, 2018

Kingwl commented on Apr 30, 2018

DanielRosenwasser commented on Apr 30, 2018

Kingwl commented on May 1, 2018

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