Fix attribute strings spec to match implementations

[strager]

According to my understanding of the JSX specification, the following
code should define one attribute whose name is attr and whose value is
hello/*"*/world:

function MyComponent() {
  return <div attr="hello/*"*/world" />;
}

However, I found no implementation which parses the code this way. All
implementations treat /* as part of the JSXSingleStringCharacters
rule rather than the beginning of a block comment.

Disallow parsing Comment and WhiteSpace rules between elements of
JSXSingleStringCharacters, etc. This makes the specification match
implementations.

Implementations tested, all of which agree with the modified grammar:

• @babel/parser version 7.15.3
• Flow version 0.144.0
• TypeScript version 4.0.3
• acorn version 8.3.0
• espree version 6.2.1

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[wooorm]

The text contains:

Whitespace and Comments

JSX uses the same punctuators and braces as ECMAScript. WhiteSpace, LineTerminators and Comments are generally allowed between any punctuators.

There are several other cases where the text is theoretically ambiguous (e.g., comments or whitespace inside inside identifiers?).

But to me I don’t see any reason to assume that comments or whitespace would be allowed in a group of characters?

---

It seems a bit too over the top to add that big bold capitalized “NO WHITESPACE OR COMMENT” everywhere?

[nicolo-ribaudo]

If we want to make the spec "correct" as an extension to the ECMAScript spec, the solution is to use JSXDoubleStringCharacters :
: instead of JSXDoubleStringCharacters :
 (two :s), to make it part of the "lexical grammar" which disallows comments/spaces: https://tc39.es/ecma262/#sec-lexical-and-regexp-grammars

[strager]

There are several other cases where the text is theoretically ambiguous (e.g., comments or whitespace inside inside identifiers?).

JSXIdentifier excludes whitespace and comments explicitly.

It seems a bit too over the top to add that big bold capitalized “NO WHITESPACE OR COMMENT” everywhere?

I was following the lead of JSXIdentifier.

If we want to make the spec "correct" as an extension to the ECMAScript spec, the solution is to use JSXDoubleStringCharacters :
: instead of JSXDoubleStringCharacters :
 (two :s), to make it part of the "lexical grammar" which disallows comments/spaces: https://tc39.es/ecma262/#sec-lexical-and-regexp-grammars

This sounds like a great solution!

[wooorm]

@strager Sorry, you are right that JSXIdentifier does! JSXText doesn’t.