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

2 files changed, 108 insertions, 24 deletions

diff --git a/helix-term/src/commands/lsp.rs b/helix-term/src/commands/lsp.rs
index a91e3792..1785a50c 100644
--- a/helix-term/src/commands/lsp.rs
+++ b/helix-term/src/commands/lsp.rs
@@ -6,18 +6,19 @@ use helix_lsp::{
 };
 use tui::text::{Span, Spans};
 
-use super::{align_view, push_jump, Align, Context, Editor};
+use super::{align_view, push_jump, Align, Context, Editor, Open};
 
 use helix_core::{path, Selection};
 use helix_view::{editor::Action, theme::Style};
 
 use crate::{
     compositor::{self, Compositor},
-    ui::{self, overlay::overlayed, FileLocation, FilePicker, Popup, PromptEvent},
+    ui::{
+        self, lsp::SignatureHelp, overlay::overlayed, FileLocation, FilePicker, Popup, PromptEvent,
+    },
 };
 
-use std::collections::BTreeMap;
-use std::{borrow::Cow, path::PathBuf};
+use std::{borrow::Cow, collections::BTreeMap, path::PathBuf, sync::Arc};
 
 /// Gets the language server that is attached to a document, and
 /// if it's not active displays a status message. Using this macro
@@ -805,31 +806,116 @@ pub fn goto_reference(cx: &mut Context) {
     );
 }
 
+#[derive(PartialEq)]
+pub enum SignatureHelpInvoked {
+    Manual,
+    Automatic,
+}
+
 pub fn signature_help(cx: &mut Context) {
+    signature_help_impl(cx, SignatureHelpInvoked::Manual)
+}
+
+pub fn signature_help_impl(cx: &mut Context, invoked: SignatureHelpInvoked) {
     let (view, doc) = current!(cx.editor);
-    let language_server = language_server!(cx.editor, doc);
+    let was_manually_invoked = invoked == SignatureHelpInvoked::Manual;
+
+    let language_server = match doc.language_server() {
+        Some(language_server) => language_server,
+        None => {
+            // Do not show the message if signature help was invoked
+            // automatically on backspace, trigger characters, etc.
+            if was_manually_invoked {
+                cx.editor
+                    .set_status("Language server not active for current buffer");
+            }
+            return;
+        }
+    };
     let offset_encoding = language_server.offset_encoding();
 
     let pos = doc.position(view.id, offset_encoding);
 
-    let future = language_server.text_document_signature_help(doc.identifier(), pos, None);
+    let future = match language_server.text_document_signature_help(doc.identifier(), pos, None) {
+        Some(f) => f,
+        None => return,
+    };
 
     cx.callback(
         future,
-        move |_editor, _compositor, response: Option<lsp::SignatureHelp>| {
-            if let Some(signature_help) = response {
-                log::info!("{:?}", signature_help);
-                // signatures
-                // active_signature
-                // active_parameter
-                // render as:
-
-                // signature
-                // ----------
-                // doc
-
-                // with active param highlighted
+        move |editor, compositor, response: Option<lsp::SignatureHelp>| {
+            let config = &editor.config();
+
+            if !(config.lsp.auto_signature_help
+                || SignatureHelp::visible_popup(compositor).is_some()
+                || was_manually_invoked)
+            {
+                return;
             }
+
+            let response = match response {
+                // According to the spec the response should be None if there
+                // are no signatures, but some servers don't follow this.
+                Some(s) if !s.signatures.is_empty() => s,
+                _ => {
+                    compositor.remove(SignatureHelp::ID);
+                    return;
+                }
+            };
+            let doc = doc!(editor);
+            let language = doc
+                .language()
+                .and_then(|scope| scope.strip_prefix("source."))
+                .unwrap_or("");
+
+            let signature = match response
+                .signatures
+                .get(response.active_signature.unwrap_or(0) as usize)
+            {
+                Some(s) => s,
+                None => return,
+            };
+            let mut contents = SignatureHelp::new(
+                signature.label.clone(),
+                language.to_string(),
+                Arc::clone(&editor.syn_loader),
+            );
+
+            let signature_doc = if config.lsp.display_signature_help_docs {
+                signature.documentation.as_ref().map(|doc| match doc {
+                    lsp::Documentation::String(s) => s.clone(),
+                    lsp::Documentation::MarkupContent(markup) => markup.value.clone(),
+                })
+            } else {
+                None
+            };
+
+            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, start + string.len()))
+                    }
+                    lsp::ParameterLabel::LabelOffsets([start, end]) => {
+                        Some((*start as usize, *end as usize))
+                    }
+                }
+            };
+            contents.set_active_param_range(active_param_range());
+
+            let old_popup = compositor.find_id::<Popup<SignatureHelp>>(SignatureHelp::ID);
+            let popup = Popup::new(SignatureHelp::ID, contents)
+                .position(old_popup.and_then(|p| p.get_position()))
+                .position_bias(Open::Above)
+                .ignore_escape_key(true);
+            compositor.replace_or_push(SignatureHelp::ID, popup);
         },
     );
 }
diff --git a/helix-term/src/commands/typed.rs b/helix-term/src/commands/typed.rs
index 4e1ac0da..fb03af44 100644
--- a/helix-term/src/commands/typed.rs
+++ b/helix-term/src/commands/typed.rs
@@ -1501,11 +1501,9 @@ fn run_shell_command(
                         format!("```sh\n{}\n```", output),
                         editor.syn_loader.clone(),
                     );
-                    let mut popup = Popup::new("shell", contents);
-                    popup.set_position(Some(helix_core::Position::new(
-                        editor.cursor().0.unwrap_or_default().row,
-                        2,
-                    )));
+                    let popup = Popup::new("shell", contents).position(Some(
+                        helix_core::Position::new(editor.cursor().0.unwrap_or_default().row, 2),
+                    ));
                     compositor.replace_or_push("shell", popup);
                 });
             Ok(call)