signature: use the suggested LSP signature when changed

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 <[email protected]>

helix-term/src/handlers/signature_help.rs

@@ -238,19 +238,32 @@ 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();
+
+            if old_lsp_sig != lsp_signature {
+                lsp_signature.unwrap_or(old_sig)
+            } else if old_sig < signatures.len() {
+                old_sig
+            } else {
+                signatures.len() - 1
+            }
+        })
+        .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)
     }