4 files changed, 42 insertions, 1 deletions

diff --git a/crates/ra_lsp_server/src/caps.rs b/crates/ra_lsp_server/src/caps.rs
index 3c628f29c..5598ec75f 100644
--- a/crates/ra_lsp_server/src/caps.rs
+++ b/crates/ra_lsp_server/src/caps.rs
@@ -7,6 +7,7 @@ use languageserver_types::{
     TextDocumentSyncKind,
     ExecuteCommandOptions,
     CompletionOptions,
+    SignatureHelpOptions,
     DocumentOnTypeFormattingOptions,
 };
 
@@ -26,7 +27,9 @@ pub fn server_capabilities() -> ServerCapabilities {
             resolve_provider: None,
             trigger_characters: None,
         }),
-        signature_help_provider: None,
+        signature_help_provider: Some(SignatureHelpOptions {
+            trigger_characters: Some(vec!["(".to_string(), ",".to_string()])
+        }),
         definition_provider: Some(true),
         type_definition_provider: None,
         implementation_provider: None,
diff --git a/crates/ra_lsp_server/src/main_loop/handlers.rs b/crates/ra_lsp_server/src/main_loop/handlers.rs
index ab8be15e9..f65e2a889 100644
--- a/crates/ra_lsp_server/src/main_loop/handlers.rs
+++ b/crates/ra_lsp_server/src/main_loop/handlers.rs
@@ -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,
diff --git a/crates/ra_lsp_server/src/main_loop/mod.rs b/crates/ra_lsp_server/src/main_loop/mod.rs
index 402615e42..f4e7cfc33 100644
--- a/crates/ra_lsp_server/src/main_loop/mod.rs
+++ b/crates/ra_lsp_server/src/main_loop/mod.rs
@@ -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)) => {
diff --git a/crates/ra_lsp_server/src/req.rs b/crates/ra_lsp_server/src/req.rs
index f80957589..1630edf7f 100644
--- a/crates/ra_lsp_server/src/req.rs
+++ b/crates/ra_lsp_server/src/req.rs
@@ -14,6 +14,7 @@ pub use languageserver_types::{
     CompletionParams, CompletionResponse,
     DocumentOnTypeFormattingParams,
     TextDocumentEdit,
+    SignatureHelp, Hover
 };
 
 pub enum SyntaxTree {}