2 files changed, 43 insertions, 6 deletions

diff --git a/crates/ra_lsp_server/src/main_loop/handlers.rs b/crates/ra_lsp_server/src/main_loop/handlers.rs
index ab8be15e9..5acb39b60 100644
--- a/crates/ra_lsp_server/src/main_loop/handlers.rs
+++ b/crates/ra_lsp_server/src/main_loop/handlers.rs
@@ -13,7 +13,7 @@ use ra_syntax::{
     text_utils::contains_offset_nonstrict
 };
 
-use ::{
+use crate::{
     req::{self, Decoration}, Result,
     conv::{Conv, ConvWith, TryConvWith, MapConvWith, to_location},
     server_world::ServerWorld,
@@ -411,6 +411,42 @@ pub fn handle_folding_range(
     Ok(res)
 }
 
+pub fn handle_signature_help(
+    world: ServerWorld,
+    params: req::TextDocumentPositionParams,
+    token: JobToken,
+) -> Result<Option<req::SignatureHelp>> {
+    use languageserver_types::{ParameterInformation, SignatureInformation};
+
+    let file_id = params.text_document.try_conv_with(&world)?;
+    let line_index = world.analysis().file_line_index(file_id);
+    let offset = params.position.conv_with(&line_index);
+
+    if let Some((descriptor, active_param)) = world.analysis().resolve_callable(file_id, offset, &token) {
+        let parameters : Vec<ParameterInformation> =
+            descriptor.params.iter().map(|param|
+                ParameterInformation {
+                    label: param.clone(),
+                    documentation: None
+                }
+            ).collect();
+
+        let sig_info = SignatureInformation {
+            label: descriptor.label,
+            documentation: None,
+            parameters: Some(parameters)
+        };
+
+        Ok(Some(req::SignatureHelp {
+            signatures: vec![sig_info],
+            active_signature: Some(0),
+            active_parameter: active_param.map(|a| a as u64)
+        }))
+    } else {
+        Ok(None)
+    }
+}
+
 pub fn handle_code_action(
     world: ServerWorld,
     params: req::CodeActionParams,
@@ -442,7 +478,7 @@ pub fn handle_code_action(
 }
 
 pub fn publish_diagnostics(
-    world: ServerWorld,
+    world: &ServerWorld,
     file_id: FileId,
 ) -> Result<req::PublishDiagnosticsParams> {
     let uri = world.file_id_to_uri(file_id)?;
@@ -461,7 +497,7 @@ pub fn publish_diagnostics(
 }
 
 pub fn publish_decorations(
-    world: ServerWorld,
+    world: &ServerWorld,
     file_id: FileId,
 ) -> Result<req::PublishDecorationsParams> {
     let uri = world.file_id_to_uri(file_id)?;
diff --git a/crates/ra_lsp_server/src/main_loop/mod.rs b/crates/ra_lsp_server/src/main_loop/mod.rs
index 402615e42..cf2477cb5 100644
--- a/crates/ra_lsp_server/src/main_loop/mod.rs
+++ b/crates/ra_lsp_server/src/main_loop/mod.rs
@@ -16,7 +16,7 @@ use gen_lsp_server::{
 };
 use rustc_hash::FxHashMap;
 
-use {
+use crate::{
     req,
     Result,
     vfs::{self, FileEvent},
@@ -255,6 +255,7 @@ fn on_request(
         .on::<req::Completion>(handlers::handle_completion)?
         .on::<req::CodeActionRequest>(handlers::handle_code_action)?
         .on::<req::FoldingRangeRequest>(handlers::handle_folding_range)?
+        .on::<req::SignatureHelpRequest>(handlers::handle_signature_help)?
         .finish();
     match req {
         Ok((id, handle)) => {
@@ -390,7 +391,7 @@ fn update_file_notifications_on_threadpool(
 ) {
     pool.spawn(move || {
         for file_id in subscriptions {
-            match handlers::publish_diagnostics(world.clone(), file_id) {
+            match handlers::publish_diagnostics(&world, file_id) {
                 Err(e) => {
                     error!("failed to compute diagnostics: {:?}", e)
                 }
@@ -399,7 +400,7 @@ fn update_file_notifications_on_threadpool(
                     sender.send(Task::Notify(not));
                 }
             }
-            match handlers::publish_decorations(world.clone(), file_id) {
+            match handlers::publish_decorations(&world, file_id) {
                 Err(e) => {
                     error!("failed to compute decorations: {:?}", e)
                 }