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refactor(transformer): don't need to transform JSXExpression::EmptyExpression in JSX attributes #8817

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refactor(transformer): don't need to transform JSXExpression::EmptyExpression in JSX attributes #8817

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6 changes: 4 additions & 2 deletions crates/oxc_transformer/src/jsx/jsx_impl.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -872,8 +872,10 @@ impl<'a> JsxImpl<'a, '_> {
// SAFETY: `ast.copy` is unsound! We need to fix.
unsafe { ctx.ast.copy(e.to_expression()) }
}
JSXExpression::EmptyExpression(e) => {
ctx.ast.expression_boolean_literal(e.span, true)
JSXExpression::EmptyExpression(_) => {
// `<div attr={}></div>`
// ^^ Invalid empty expression here
unreachable!()
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@Boshen Boshen Feb 1, 2025

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We should not make this unreachable in situations where the semantic checker is not run or missed the check, do not emit anything instead.

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@Dunqing Dunqing Feb 1, 2025 •
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That makes sense. To achieve "do not emit anything" here we must return a None, which will cause more changes, I will do this later.

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@overlookmotel overlookmotel Feb 5, 2025

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From reading the JSX spec, it doesn't look like an EmptyExpression is ever valid in this position. If I've understood that right, could we make JSXExpressionContainer just contain an Expression, rather than a JSXExpression?

I assume the reason is recoverability. To achieve that, could we instead raise an error in the parser, and skip adding the JSXAttribute, so that parsing can continue?

It's going to cause a problem serializing to ESTree, because what does it serialize to? The "EmptyExpression" option doesn't exist.

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@Dunqing Dunqing Feb 10, 2025

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This is part of typescript-eslint, See https://ast.sxzz.dev/#eNpNzMEKwjAMgOFXGTlPvI+5o08gnnoJNUhH15SmFaX03Y1WZLfk+0kqeJhgxQeKTS5mGCEq5FekDgcS78LHrfp8Zh7wVNtiwlCbCfNRZdHKWqviYEC4JEsXfWFg0n3jW/E6jz2T3fBKSRyH3j1mkvzvCcP9e5lToZ+t8txJg/YGroc72A==.

I agree to throw an error in the parser as this is a pointless AST node.

}
},
None => ctx.ast.expression_boolean_literal(SPAN, true),
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