Add lsp signature help (#1755)

* Add lsp signature help

* Do not move signature help popup on multiple triggers

* Highlight current parameter in signature help

* Auto close signature help

* Position signature help above to not block completion

* Update signature help on backspace/insert mode delete

* Add lsp.auto-signature-help config option

* Add serde default annotation for LspConfig

* Show LSP inactive message only if signature help is invoked manually

* Do not assume valid signature help response from LSP

Malformed LSP responses are common, and these should not crash the
editor.

* Check signature help capability before sending request

* Reuse Open enum for PositionBias in popup

* Close signature popup and exit insert mode on escape

* Add config to control signature help docs display

* Use new Margin api in signature help

* Invoke signature help on changing to insert mode

1 files changed, 17 insertions, 2 deletions

diff --git a/helix-view/src/editor.rs b/helix-view/src/editor.rs
index babb5c43..0178d399 100644
--- a/helix-view/src/editor.rs
+++ b/helix-view/src/editor.rs
@@ -167,10 +167,25 @@ pub struct Config {
     pub color_modes: bool,
 }
 
-#[derive(Debug, Default, Clone, PartialEq, Serialize, Deserialize)]
-#[serde(rename_all = "kebab-case", deny_unknown_fields)]
+#[derive(Debug, Clone, PartialEq, Serialize, Deserialize)]
+#[serde(default, rename_all = "kebab-case", deny_unknown_fields)]
 pub struct LspConfig {
+    /// Display LSP progress messages below statusline
     pub display_messages: bool,
+    /// Enable automatic pop up of signature help (parameter hints)
+    pub auto_signature_help: bool,
+    /// Display docs under signature help popup
+    pub display_signature_help_docs: bool,
+}
+
+impl Default for LspConfig {
+    fn default() -> Self {
+        Self {
+            display_messages: false,
+            auto_signature_help: true,
+            display_signature_help_docs: true,
+        }
+    }
 }
 
 #[derive(Debug, Clone, PartialEq, Serialize, Deserialize)]