Allow keywords in named import/export syntax #107
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Progress toward AssemblyScript#98 See the imports and exports grammar from the spec: https://www.ecma-international.org/ecma-262/8.0/index.html#sec-imports https://www.ecma-international.org/ecma-262/8.0/index.html#sec-exports In particular, ImportSpecifier and ExportSpecifier use IdentifierName to identify the import/export name rather than the more restrictive ImportedBinding (or just Identifier). That means any keyword is allowed. There are (at least) three contexts to think about in JS identifier parsing: * In most contexts, identifiers like variable names can be any name except a reserved word. * Some keywords, like "as", are normally not keywords but have special keyword-like meaning in specific situations. Acorn and Babel call these "contextual keywords", and `tokenIsAlsoIdentifier` and `preferIdentifier` in AssemblyScript appear to handle that case. * In some contexts, like object keys and named imports/exports, any name is allowed, even keywords. This change adds that third case in order to handle imports/exports. I added a `forceIdentifier` flag that tells the tokenizer that any identifier name should be treated as a plain identifier, then used it in the import and export cases.
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Now that there are effectively three modes, what do you think of adding an enum that indicates how to handle identifiers? Something like enum IdentifierHandling {
DEFAULT,
PREFER,
ALWAYS
} |
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Sure, sounds reasonable to me. (It wouldn't surprise me if it got more complicated than that in more obscure cases, but the three modes seems fine for now.) |
src/tokenizer.ts
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| /** | ||
| * Skip any name token, whether or not it is a keyword. | ||
| */ | ||
| skipIdentifierName(): bool { |
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Could this become an IdentifierHandling option on skip(), maybe? :)
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Make sense, yeah this copied function is a bit ugly. I guess it felt a bit weird given the special case in skip.
How about this: I get rid of the special case in skip and specify it using an optional param like you suggested. Then, to make the common case the most natural to write, I'll make skipIdentifier as a shorthand for skip(Token.IDENTIFIER, IdentifierHandling.PREFER) and keep skipIdentifierName as a shorthand for skip(Token.IDENTIFIER, IdentifierHandling.ALWAYS). Let me know what you think.
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Great, thank you! :) |
Progress toward #98
See the imports and exports grammar from the spec:
https://www.ecma-international.org/ecma-262/8.0/index.html#sec-imports
https://www.ecma-international.org/ecma-262/8.0/index.html#sec-exports
In particular, ImportSpecifier and ExportSpecifier use IdentifierName to
identify the import/export name rather than the more restrictive ImportedBinding
(or just Identifier). That means any keyword is allowed.
There are (at least) three contexts to think about in JS identifier parsing:
reserved word.
keyword-like meaning in specific situations. Acorn and Babel call these
"contextual keywords", and
tokenIsAlsoIdentifierandpreferIdentifierinAssemblyScript appear to handle that case.
allowed, even keywords.
This change adds that third case in order to handle imports/exports. I added a
forceIdentifierflag that tells the tokenizer that any identifier name shouldbe treated as a plain identifier, then used it in the import and export cases.