signature: use the suggested LSP signature when changed (#10655)

some LSPs does update the active signature and some not. To make both
worlds happy, make the active signature more intelligent.

1. SignatureHelp store now the suggested lsp_signature
2. if the lsp_signature changes then use it
3. otherwise use the last signature from the old popup
4. in case the old signature doesn't exist anymore, show the last signature

Signed-off-by: Ben Fekih, Hichem <hichem.f@live.de>

helix-term/src/handlers/signature_help.rs

@@ -238,19 +238,33 @@ pub fn show_signature_help(
         .collect();
 
     let old_popup = compositor.find_id::<Popup<SignatureHelp>>(SignatureHelp::ID);
-    let mut active_signature = old_popup
-        .as_ref()
-        .map(|popup| popup.contents().active_signature())
-        .unwrap_or_else(|| response.active_signature.unwrap_or_default() as usize);
+    let lsp_signature = response.active_signature.map(|s| s as usize);
 
-    if active_signature >= signatures.len() {
-        active_signature = signatures.len() - 1;
+    // take the new suggested lsp signature if changed
+    // otherwise take the old signature if possible
+    // otherwise the last one (in case there is less signatures than before)
+    let active_signature = old_popup
+        .as_ref()
+        .map(|popup| {
+            let old_lsp_sig = popup.contents().lsp_signature();
+            let old_sig = popup
+                .contents()
+                .active_signature()
+                .min(signatures.len() - 1);
+
+            if old_lsp_sig != lsp_signature {
+                lsp_signature.unwrap_or(old_sig)
+            } else {
+                old_sig
             }
+        })
+        .unwrap_or(lsp_signature.unwrap_or_default());
 
     let contents = SignatureHelp::new(
         language.to_string(),
         Arc::clone(&editor.syn_loader),
         active_signature,
+        lsp_signature,
         signatures,
     );
 

helix-term/src/ui/lsp.rs

@@ -27,6 +27,7 @@ pub struct SignatureHelp {
     language: String,
     config_loader: Arc<ArcSwap<syntax::Loader>>,
     active_signature: usize,
+    lsp_signature: Option<usize>,
     signatures: Vec<Signature>,
 }
 
@@ -37,12 +38,14 @@ impl SignatureHelp {
         language: String,
         config_loader: Arc<ArcSwap<syntax::Loader>>,
         active_signature: usize,
+        lsp_signature: Option<usize>,
         signatures: Vec<Signature>,
     ) -> Self {
         Self {
             language,
             config_loader,
             active_signature,
+            lsp_signature,
             signatures,
         }
     }
@@ -51,6 +54,10 @@ impl SignatureHelp {
         self.active_signature
     }
 
+    pub fn lsp_signature(&self) -> Option<usize> {
+        self.lsp_signature
+    }
+
     pub fn visible_popup(compositor: &mut Compositor) -> Option<&mut Popup<Self>> {
         compositor.find_id::<Popup<Self>>(Self::ID)
     }