From a8b123fe177d8cd7f5a610a0a50c16c9f64069bd Mon Sep 17 00:00:00 2001
From: Gokul Soumya
Date: Fri, 22 Jul 2022 21:53:08 +0530
Subject: Fix byte index error in signature help highlighting

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]: https://github.com/helix-editor/helix/pull/1755#discussion_r906715371
[2]: https://github.com/rust-lang/rust-analyzer/pull/12272
---
 helix-term/src/commands/lsp.rs | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

(limited to 'helix-term')

diff --git a/helix-term/src/commands/lsp.rs b/helix-term/src/commands/lsp.rs
index 1785a50c..38507e4d 100644
--- a/helix-term/src/commands/lsp.rs
+++ b/helix-term/src/commands/lsp.rs
@@ -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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