JS: Use JSX syntax in first attempt when extension is .jsx #18658
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erik-krogh
approved these changes
Feb 4, 2025
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Fixes a rare JSX parse error, reported in #18651.
We parse JavaScript files in two attempts: the first attempt only allows standard syntax and the second attempt includes various extensions, such as JSX and Flow.
This is because some syntax extensions can result in parse errors, even though the file is valid standard JS. For example, when the JSX parser sees a
<token it has to guess whether this is a part of a JSX tag or a less-than operator. This guesswork is imperfect and if it guesses wrong, a valid file may be rejected.The syntax error occurred in a case where the file was valid JSX but the Flow syntax extension caused a parsing error due to an incorrect guess about Flow syntax.
This PR changes parsing of
.jsxfiles so that JSX syntax is enabled in the first attempt, where Flow syntax can not interfere. Note that Flow files use the.jsextension and do permit JSX syntax, so we cannot outright disable JSX parsing for non-.jsxfiles.