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Fix byte index error in signature help highlighting
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The language server sends a char offset range within the
signature help label text to highlight as the current parameter,
but helix uses byte offset ranges for rendering highlights. This
was brought up in the [review of the original signature help PR][1],
but the ranges were being highlighted correctly, and there were no
out of bound or indexing panics. Turns out rust-analyzer was
[incorrectly sending byte offsets] instead of char offsets and this
made it seem like all was well and good with offsets in helix during
initial testing.

[1]: #1755 (comment)
[2]: rust-lang/rust-analyzer#12272
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sudormrfbin authored and archseer committed Jul 29, 2022
1 parent 14eca31 commit a8b123f
Showing 1 changed file with 6 additions and 1 deletion.
7 changes: 6 additions & 1 deletion helix-term/src/commands/lsp.rs
Original file line number Diff line number Diff line change
Expand Up @@ -904,7 +904,12 @@ pub fn signature_help_impl(cx: &mut Context, invoked: SignatureHelpInvoked) {
Some((start, start + string.len()))
}
lsp::ParameterLabel::LabelOffsets([start, end]) => {
Some((*start as usize, *end as usize))
// LS sends offsets based on utf-16 based string representation
// but highlighting in helix is done using byte offset.
use helix_core::str_utils::char_to_byte_idx;
let from = char_to_byte_idx(&signature.label, *start as usize);
let to = char_to_byte_idx(&signature.label, *end as usize);
Some((from, to))
}
}
};
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