Normative: add hashbang comments #2816
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ljharb
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normative change
This was referenced Jul 7, 2022
bakkot
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Jul 20, 2022
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syg
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Aug 10, 2022
| <h1>ECMAScript Language: Lexical Grammar</h1> | ||
| <p>The source text of an ECMAScript |Script| or |Module| is first converted into a sequence of input elements, which are tokens, line terminators, comments, or white space. The source text is scanned from left to right, repeatedly taking the longest possible sequence of code points as the next input element.</p> | ||
| <p>There are several situations where the identification of lexical input elements is sensitive to the syntactic grammar context that is consuming the input elements. This requires multiple goal symbols for the lexical grammar. The |InputElementRegExpOrTemplateTail| goal is used in syntactic grammar contexts where a |RegularExpressionLiteral|, a |TemplateMiddle|, or a |TemplateTail| is permitted. The |InputElementRegExp| goal symbol is used in all syntactic grammar contexts where a |RegularExpressionLiteral| is permitted but neither a |TemplateMiddle|, nor a |TemplateTail| is permitted. The |InputElementTemplateTail| goal is used in all syntactic grammar contexts where a |TemplateMiddle| or a |TemplateTail| is permitted but a |RegularExpressionLiteral| is not permitted. In all other contexts, |InputElementDiv| is used as the lexical goal symbol.</p> | ||
| <p>There are several situations where the identification of lexical input elements is sensitive to the syntactic grammar context that is consuming the input elements. This requires multiple goal symbols for the lexical grammar. The |InputElementHashbangOrRegExp| goal is used at the start of a |Script| or |Module|. The |InputElementRegExpOrTemplateTail| goal is used in syntactic grammar contexts where a |RegularExpressionLiteral|, a |TemplateMiddle|, or a |TemplateTail| is permitted. The |InputElementRegExp| goal symbol is used in all syntactic grammar contexts where a |RegularExpressionLiteral| is permitted but neither a |TemplateMiddle|, nor a |TemplateTail| is permitted. The |InputElementTemplateTail| goal is used in all syntactic grammar contexts where a |TemplateMiddle| or a |TemplateTail| is permitted but a |RegularExpressionLiteral| is not permitted. In all other contexts, |InputElementDiv| is used as the lexical goal symbol.</p> |
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So I guess this sentence is the actual normative requirement to accept hashbangs at the start of programs. No real concerns, but I am a little surprised that we do this via prose.
michaelficarra
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Aug 15, 2022
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See https://tc39.es/proposal-hashbang/out.html / https://github.com/tc39/proposal-hashbang