fix(playground): multi-byte character issue #647
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From the deploy preview, the link in biomejs/biome#3250 (comment) no longer crashes: https://deploy-preview-647--biomejs.netlify.app/playground/?code=PABkAGkAdgAgAGQAYQBuAGcAZQByAG8AdQBzAGwAeQBTAGUAdABJAG4AbgBlAHIASAB0AG0AbAA9AHsAewAgAF8AXwBoAHQAbQBsADoAIAAnACYgJwAgAH0AfQAgAC8A |
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Summary
In Rust we use UTF-8 byte offsets for
TextSize, which will be used inTextRangeand ultimately be passed to the JavaScript side as the numbers indiagnostic.location.span. However, in JavaScript, we use UTF-16 code unit offsets to access the characters.So when a character is represented by multiple bytes in UTF-8 encoding and is placed before or is part of the code that triggers a diagnostic, the playground will wrongly interpret its byte offset as a code unit offset, thus causing an out of bounds indexing error when it tries to highlight the range or make a selection of the code that triggers the diagnostic.
To fix this problem, we need to convert the UTF-8 byte offset into a code unit offset that can be used directly by JavaScript
Stringmethods likeslice. I took the solution here and adapted it to fit our use case.This conversion will inevitably introduce an
O(n)overhead because the byte length of an UTF-8 encoded character is variable and we have to scan from the beginning to calculate the byte offset of a certain character in the middle. However, I think it's acceptable, because the code in the playground is usually not very long, and for it performance is also not our first consideration. The benefit is that we no longer have to worry about playground crashes triggered by non-English characters, especailly for users that use a second IME.Closes biomejs/biome#1385
Closes biomejs/biome#3250