From db2232ffa9ade4d1bbcc4958e9ecf32d37923f40 Mon Sep 17 00:00:00 2001
From: Gokul Soumya <gokulps15@gmail.com>
Date: Wed, 2 Mar 2022 23:08:15 +0530
Subject: [PATCH] Highlight current parameter in signature help

---
 helix-term/src/commands/lsp.rs | 33 ++++++++++++++++++++++++++-------
 helix-term/src/ui/lsp.rs       | 10 ++++++++++
 2 files changed, 36 insertions(+), 7 deletions(-)

diff --git a/helix-term/src/commands/lsp.rs b/helix-term/src/commands/lsp.rs
index d700ae0017dd3..bf2dadb9b6f35 100644
--- a/helix-term/src/commands/lsp.rs
+++ b/helix-term/src/commands/lsp.rs
@@ -589,6 +589,7 @@ pub fn signature_help(cx: &mut Context) {
                 .language()
                 .and_then(|scope| scope.strip_prefix("source."))
                 .unwrap_or("");
+
             // If there are no signatures, response will be None, therefore
             // at least one signature exists.
             let signature = &response.signatures[response.active_signature.unwrap_or(0) as usize];
@@ -597,13 +598,31 @@ pub fn signature_help(cx: &mut Context) {
                 language.to_string(),
                 Arc::clone(&editor.syn_loader),
             );
-            if let Some(ref signature_doc) = signature.documentation {
-                let doc_text = match signature_doc {
-                    lsp::Documentation::String(s) => &s,
-                    lsp::Documentation::MarkupContent(markup) => &markup.value,
-                };
-                contents.set_signature_doc(doc_text.clone());
-            }
+
+            let signature_doc = signature.documentation.as_ref().map(|doc| match doc {
+                lsp::Documentation::String(s) => s.clone(),
+                lsp::Documentation::MarkupContent(markup) => markup.value.clone(),
+            });
+            contents.set_signature_doc(signature_doc);
+
+            let active_param_range = || -> Option<(usize, usize)> {
+                let param_idx = signature
+                    .active_parameter
+                    .or(response.active_parameter)
+                    .unwrap_or(0) as usize;
+                let param = signature.parameters.as_ref()?.get(param_idx)?;
+                match &param.label {
+                    lsp::ParameterLabel::Simple(string) => {
+                        let start = signature.label.find(string.as_str())?;
+                        Some((start, string.len()))
+                    }
+                    lsp::ParameterLabel::LabelOffsets([start, end]) => {
+                        Some((*start as usize, *end as usize))
+                    }
+                }
+            };
+            contents.set_active_param_range(active_param_range());
+
             let mut popup = Popup::new("signature-help", contents);
             let old_popup = compositor.find_id::<Popup<SignatureHelp>>("signature-help");
             popup.set_position(old_popup.and_then(|p| p.position().copied()));
diff --git a/helix-term/src/ui/lsp.rs b/helix-term/src/ui/lsp.rs
index 10c8a5b0e8cdd..9b248822d8941 100644
--- a/helix-term/src/ui/lsp.rs
+++ b/helix-term/src/ui/lsp.rs
@@ -46,12 +46,21 @@ impl Component for SignatureHelp {
             horizontal: 1,
         };
 
+        let active_param_span = self.active_param_range.map(|(start, end)| {
+            vec![(
+                cx.editor.theme.find_scope_index("ui.selection").unwrap(),
+                start..end,
+            )]
+        });
+
         let sig_text = crate::ui::markdown::highlighted_code_block(
             self.signature.clone(),
             &self.language,
             Some(&cx.editor.theme),
             Arc::clone(&self.config_loader),
+            active_param_span,
         );
+
         let (_, sig_text_height) = crate::ui::text::required_size(&sig_text, area.width);
         let sig_text_area = area.clip_top(1).with_height(sig_text_height);
         let sig_text_para = Paragraph::new(sig_text).wrap(Wrap { trim: false });
@@ -95,6 +104,7 @@ impl Component for SignatureHelp {
             &self.language,
             None,
             Arc::clone(&self.config_loader),
+            None,
         );
         let (sig_width, sig_height) =
             crate::ui::text::required_size(&signature_text, max_text_width);