feat(lsp): Implement `textDocument/signatureHelp` (#9330)

Co-authored-by: Kitson Kelly <me@kitsonkelly.com>

9 files changed, 382 insertions, 13 deletions

diff --git a/cli/lsp/capabilities.rs b/cli/lsp/capabilities.rs
index 9eed85b73..fb16db88b 100644
--- a/cli/lsp/capabilities.rs
+++ b/cli/lsp/capabilities.rs
@@ -16,6 +16,7 @@ use lspower::lsp::ImplementationProviderCapability;
 use lspower::lsp::OneOf;
 use lspower::lsp::SaveOptions;
 use lspower::lsp::ServerCapabilities;
+use lspower::lsp::SignatureHelpOptions;
 use lspower::lsp::TextDocumentSyncCapability;
 use lspower::lsp::TextDocumentSyncKind;
 use lspower::lsp::TextDocumentSyncOptions;
@@ -69,7 +70,17 @@ pub fn server_capabilities(
         work_done_progress: None,
       },
     }),
-    signature_help_provider: None,
+    signature_help_provider: Some(SignatureHelpOptions {
+      trigger_characters: Some(vec![
+        ",".to_string(),
+        "(".to_string(),
+        "<".to_string(),
+      ]),
+      retrigger_characters: None,
+      work_done_progress_options: WorkDoneProgressOptions {
+        work_done_progress: None,
+      },
+    }),
     declaration_provider: None,
     definition_provider: Some(OneOf::Left(true)),
     type_definition_provider: None,
diff --git a/cli/lsp/language_server.rs b/cli/lsp/language_server.rs
index 6594492a4..1501249e8 100644
--- a/cli/lsp/language_server.rs
+++ b/cli/lsp/language_server.rs
@@ -1705,6 +1705,68 @@ impl Inner {
       }
     }
   }
+
+  async fn signature_help(
+    &self,
+    params: SignatureHelpParams,
+  ) -> LspResult<Option<SignatureHelp>> {
+    if !self.enabled() {
+      return Ok(None);
+    }
+    let mark = self.performance.mark("signature_help");
+    let specifier = utils::normalize_url(
+      params.text_document_position_params.text_document.uri,
+    );
+    let line_index =
+      if let Some(line_index) = self.get_line_index_sync(&specifier) {
+        line_index
+      } else {
+        return Err(LspError::invalid_params(format!(
+          "An unexpected specifier ({}) was provided.",
+          specifier
+        )));
+      };
+    let options = if let Some(context) = params.context {
+      tsc::SignatureHelpItemsOptions {
+        trigger_reason: Some(tsc::SignatureHelpTriggerReason {
+          kind: context.trigger_kind.into(),
+          trigger_character: context.trigger_character,
+        }),
+      }
+    } else {
+      tsc::SignatureHelpItemsOptions {
+        trigger_reason: None,
+      }
+    };
+    let req = tsc::RequestMethod::GetSignatureHelpItems((
+      specifier,
+      line_index.offset_tsc(params.text_document_position_params.position)?,
+      options,
+    ));
+    let res =
+      self
+        .ts_server
+        .request(self.snapshot(), req)
+        .await
+        .map_err(|err| {
+          error!("Failed to request to tsserver: {}", err);
+          LspError::invalid_request()
+        })?;
+    let maybe_signature_help_items: Option<tsc::SignatureHelpItems> =
+      serde_json::from_value(res).map_err(|err| {
+        error!("Failed to deserialize tsserver response: {}", err);
+        LspError::internal_error()
+      })?;
+
+    if let Some(signature_help_items) = maybe_signature_help_items {
+      let signature_help = signature_help_items.into_signature_help();
+      self.performance.measure(mark);
+      Ok(Some(signature_help))
+    } else {
+      self.performance.measure(mark);
+      Ok(None)
+    }
+  }
 }
 
 #[lspower::async_trait]
@@ -1840,6 +1902,13 @@ impl lspower::LanguageServer for LanguageServer {
   ) -> LspResult<Option<Value>> {
     self.0.lock().await.request_else(method, params).await
   }
+
+  async fn signature_help(
+    &self,
+    params: SignatureHelpParams,
+  ) -> LspResult<Option<SignatureHelp>> {
+    self.0.lock().await.signature_help(params).await
+  }
 }
 
 #[derive(Debug, Deserialize, Serialize)]
@@ -2539,6 +2608,80 @@ mod tests {
   }
 
   #[tokio::test]
+  async fn test_signature_help() {
+    let mut harness = LspTestHarness::new(vec![
+      ("initialize_request.json", LspResponse::RequestAny),
+      ("initialized_notification.json", LspResponse::None),
+      (
+        "signature_help_did_open_notification.json",
+        LspResponse::None,
+      ),
+      (
+        "signature_help_request_01.json",
+        LspResponse::Request(
+          1,
+          json!({
+            "signatures": [
+              {
+                "label": "add(a: number, b: number): number",
+                "documentation": "Adds two numbers.",
+                "parameters": [
+                  {
+                    "label": "a: number",
+                    "documentation": "This is a first number."
+                  },
+                  {
+                    "label": "b: number",
+                    "documentation": "This is a second number."
+                  }
+                ]
+              }
+            ],
+            "activeSignature": 0,
+            "activeParameter": 0
+          }),
+        ),
+      ),
+      (
+        "signature_help_did_change_notification.json",
+        LspResponse::None,
+      ),
+      (
+        "signature_help_request_02.json",
+        LspResponse::Request(
+          2,
+          json!({
+            "signatures": [
+              {
+                "label": "add(a: number, b: number): number",
+                "documentation": "Adds two numbers.",
+                "parameters": [
+                  {
+                    "label": "a: number",
+                    "documentation": "This is a first number."
+                  },
+                  {
+                    "label": "b: number",
+                    "documentation": "This is a second number."
+                  }
+                ]
+              }
+            ],
+            "activeSignature": 0,
+            "activeParameter": 1
+          }),
+        ),
+      ),
+      (
+        "shutdown_request.json",
+        LspResponse::Request(3, json!(null)),
+      ),
+      ("exit_notification.json", LspResponse::None),
+    ]);
+    harness.run().await;
+  }
+
+  #[tokio::test]
   async fn test_code_lens_impl_request() {
     let mut harness = LspTestHarness::new(vec![
       ("initialize_request.json", LspResponse::RequestAny),
diff --git a/cli/lsp/tsc.rs b/cli/lsp/tsc.rs
index ef57682f1..5dc7200b7 100644
--- a/cli/lsp/tsc.rs
+++ b/cli/lsp/tsc.rs
@@ -166,16 +166,12 @@ pub async fn get_asset(
   }
 }
 
-fn display_parts_to_string(
-  maybe_parts: Option<Vec<SymbolDisplayPart>>,
-) -> Option<String> {
-  maybe_parts.map(|parts| {
-    parts
-      .into_iter()
-      .map(|p| p.text)
-      .collect::<Vec<String>>()
-      .join("")
-  })
+fn display_parts_to_string(parts: Vec<SymbolDisplayPart>) -> String {
+  parts
+    .into_iter()
+    .map(|p| p.text)
+    .collect::<Vec<String>>()
+    .join("")
 }
 
 fn get_tag_body_text(tag: &JSDocTagInfo) -> Option<String> {
@@ -433,7 +429,7 @@ impl QuickInfo {
   pub fn to_hover(&self, line_index: &LineIndex) -> lsp::Hover {
     let mut contents = Vec::<lsp::MarkedString>::new();
     if let Some(display_string) =
-      display_parts_to_string(self.display_parts.clone())
+      self.display_parts.clone().map(display_parts_to_string)
     {
       contents.push(lsp::MarkedString::from_language_code(
         "typescript".to_string(),
@@ -441,7 +437,7 @@ impl QuickInfo {
       ));
     }
     if let Some(documentation) =
-      display_parts_to_string(self.documentation.clone())
+      self.documentation.clone().map(display_parts_to_string)
     {
       contents.push(lsp::MarkedString::from_markdown(documentation));
     }
@@ -946,6 +942,91 @@ impl CompletionEntry {
   }
 }
 
+#[derive(Debug, Deserialize)]
+#[serde(rename_all = "camelCase")]
+pub struct SignatureHelpItems {
+  items: Vec<SignatureHelpItem>,
+  applicable_span: TextSpan,
+  selected_item_index: u32,
+  argument_index: u32,
+  argument_count: u32,
+}
+
+impl SignatureHelpItems {
+  pub fn into_signature_help(self) -> lsp::SignatureHelp {
+    lsp::SignatureHelp {
+      signatures: self
+        .items
+        .into_iter()
+        .map(|item| item.into_signature_information())
+        .collect(),
+      active_parameter: Some(self.argument_index),
+      active_signature: Some(self.selected_item_index),
+    }
+  }
+}
+
+#[derive(Debug, Deserialize)]
+#[serde(rename_all = "camelCase")]
+pub struct SignatureHelpItem {
+  is_variadic: bool,
+  prefix_display_parts: Vec<SymbolDisplayPart>,
+  suffix_display_parts: Vec<SymbolDisplayPart>,
+  separator_display_parts: Vec<SymbolDisplayPart>,
+  parameters: Vec<SignatureHelpParameter>,
+  documentation: Vec<SymbolDisplayPart>,
+  tags: Vec<JSDocTagInfo>,
+}
+
+impl SignatureHelpItem {
+  pub fn into_signature_information(self) -> lsp::SignatureInformation {
+    let prefix_text = display_parts_to_string(self.prefix_display_parts);
+    let params_text = self
+      .parameters
+      .iter()
+      .map(|param| display_parts_to_string(param.display_parts.clone()))
+      .collect::<Vec<String>>()
+      .join(", ");
+    let suffix_text = display_parts_to_string(self.suffix_display_parts);
+    lsp::SignatureInformation {
+      label: format!("{}{}{}", prefix_text, params_text, suffix_text),
+      documentation: Some(lsp::Documentation::String(display_parts_to_string(
+        self.documentation,
+      ))),
+      parameters: Some(
+        self
+          .parameters
+          .into_iter()
+          .map(|param| param.into_parameter_information())
+          .collect(),
+      ),
+      active_parameter: None,
+    }
+  }
+}
+
+#[derive(Debug, Deserialize)]
+#[serde(rename_all = "camelCase")]
+pub struct SignatureHelpParameter {
+  name: String,
+  documentation: Vec<SymbolDisplayPart>,
+  display_parts: Vec<SymbolDisplayPart>,
+  is_optional: bool,
+}
+
+impl SignatureHelpParameter {
+  pub fn into_parameter_information(self) -> lsp::ParameterInformation {
+    lsp::ParameterInformation {
+      label: lsp::ParameterLabel::Simple(display_parts_to_string(
+        self.display_parts,
+      )),
+      documentation: Some(lsp::Documentation::String(display_parts_to_string(
+        self.documentation,
+      ))),
+    }
+  }
+}
+
 #[derive(Debug, Clone, Deserialize)]
 struct Response {
   id: usize,
@@ -1361,6 +1442,41 @@ pub struct UserPreferences {
   pub provide_refactor_not_applicable_reason: Option<bool>,
 }
 
+#[derive(Debug, Serialize)]
+#[serde(rename_all = "camelCase")]
+pub struct SignatureHelpItemsOptions {
+  #[serde(skip_serializing_if = "Option::is_none")]
+  pub trigger_reason: Option<SignatureHelpTriggerReason>,
+}
+
+#[derive(Debug, Serialize)]
+pub enum SignatureHelpTriggerKind {
+  #[serde(rename = "characterTyped")]
+  CharacterTyped,
+  #[serde(rename = "invoked")]
+  Invoked,
+  #[serde(rename = "retrigger")]
+  Retrigger,
+}
+
+impl From<lsp::SignatureHelpTriggerKind> for SignatureHelpTriggerKind {
+  fn from(kind: lsp::SignatureHelpTriggerKind) -> Self {
+    match kind {
+      lsp::SignatureHelpTriggerKind::Invoked => Self::Invoked,
+      lsp::SignatureHelpTriggerKind::TriggerCharacter => Self::CharacterTyped,
+      lsp::SignatureHelpTriggerKind::ContentChange => Self::Retrigger,
+    }
+  }
+}
+
+#[derive(Debug, Serialize)]
+#[serde(rename_all = "camelCase")]
+pub struct SignatureHelpTriggerReason {
+  pub kind: SignatureHelpTriggerKind,
+  #[serde(skip_serializing_if = "Option::is_none")]
+  pub trigger_character: Option<String>,
+}
+
 /// Methods that are supported by the Language Service in the compiler isolate.
 #[derive(Debug)]
 pub enum RequestMethod {
@@ -1390,6 +1506,8 @@ pub enum RequestMethod {
   GetQuickInfo((ModuleSpecifier, u32)),
   /// Get document references for a specific position.
   GetReferences((ModuleSpecifier, u32)),
+  /// Get signature help items for a specific position.
+  GetSignatureHelpItems((ModuleSpecifier, u32, SignatureHelpItemsOptions)),
   /// Get the diagnostic codes that support some form of code fix.
   GetSupportedCodeFixes,
 }
@@ -1497,6 +1615,15 @@ impl RequestMethod {
         "specifier": specifier,
         "position": position,
       }),
+      RequestMethod::GetSignatureHelpItems((specifier, position, options)) => {
+        json!({
+          "id": id,
+          "method": "getSignatureHelpItems",
+          "specifier": specifier,
+          "position": position,
+          "options": options,
+        })
+      }
       RequestMethod::GetSupportedCodeFixes => json!({
         "id": id,
         "method": "getSupportedCodeFixes",
diff --git a/cli/tests/lsp/signature_help_did_change_notification.json b/cli/tests/lsp/signature_help_did_change_notification.json
new file mode 100644
index 000000000..f88eaa9ff
--- /dev/null
+++ b/cli/tests/lsp/signature_help_did_change_notification.json
@@ -0,0 +1,25 @@
+{
+  "jsonrpc": "2.0",
+  "method": "textDocument/didChange",
+  "params": {
+    "textDocument": {
+      "uri": "file:///a/file.ts",
+      "version": 2
+    },
+    "contentChanges": [
+      {
+        "range": {
+          "start": {
+            "line": 9,
+            "character": 4
+          },
+          "end": {
+            "line": 9,
+            "character": 4
+          }
+        },
+        "text": "123, "
+      }
+    ]
+  }
+}
diff --git a/cli/tests/lsp/signature_help_did_open_notification.json b/cli/tests/lsp/signature_help_did_open_notification.json
new file mode 100644
index 000000000..1ba1f7586
--- /dev/null
+++ b/cli/tests/lsp/signature_help_did_open_notification.json
@@ -0,0 +1,12 @@
+{
+  "jsonrpc": "2.0",
+  "method": "textDocument/didOpen",
+  "params": {
+    "textDocument": {
+      "uri": "file:///a/file.ts",
+      "languageId": "typescript",
+      "version": 1,
+      "text": "/**\n * Adds two numbers.\n * @param a This is a first number.\n * @param b This is a second number.\n */\nfunction add(a: number, b: number) {\n  return a + b;\n}\n\nadd("
+    }
+  }
+}
diff --git a/cli/tests/lsp/signature_help_request_01.json b/cli/tests/lsp/signature_help_request_01.json
new file mode 100644
index 000000000..c3e185e08
--- /dev/null
+++ b/cli/tests/lsp/signature_help_request_01.json
@@ -0,0 +1,19 @@
+{
+  "jsonrpc": "2.0",
+  "id": 1,
+  "method": "textDocument/signatureHelp",
+  "params": {
+    "textDocument": {
+      "uri": "file:///a/file.ts"
+    },
+    "position": {
+      "character": 4,
+      "line": 9
+    },
+    "context": {
+      "triggerKind": 2,
+      "triggerCharacter": "(",
+      "isRetrigger": false
+    }
+  }
+}
diff --git a/cli/tests/lsp/signature_help_request_02.json b/cli/tests/lsp/signature_help_request_02.json
new file mode 100644
index 000000000..c2a6e0abb
--- /dev/null
+++ b/cli/tests/lsp/signature_help_request_02.json
@@ -0,0 +1,14 @@
+{
+  "id": 2,
+  "jsonrpc": "2.0",
+  "method": "textDocument/signatureHelp",
+  "params": {
+    "textDocument": {
+      "uri": "file:///a/file.ts"
+    },
+    "position": {
+      "character": 8,
+      "line": 9
+    }
+  }
+}
diff --git a/cli/tsc/99_main_compiler.js b/cli/tsc/99_main_compiler.js
index 50631e83f..f8eabc890 100644
--- a/cli/tsc/99_main_compiler.js
+++ b/cli/tsc/99_main_compiler.js
@@ -677,6 +677,16 @@ delete Object.prototype.__proto__;
           ),
         );
       }
+      case "getSignatureHelpItems": {
+        return respond(
+          id,
+          languageService.getSignatureHelpItems(
+            request.specifier,
+            request.position,
+            request.options,
+          ),
+        );
+      }
       case "getSupportedCodeFixes": {
         return respond(
           id,
diff --git a/cli/tsc/compiler.d.ts b/cli/tsc/compiler.d.ts
index 4e5dcdb96..7d102eb56 100644
--- a/cli/tsc/compiler.d.ts
+++ b/cli/tsc/compiler.d.ts
@@ -54,6 +54,7 @@ declare global {
     | GetNavigationTree
     | GetQuickInfoRequest
     | GetReferencesRequest
+    | GetSignatureHelpItemsRequest
     | GetSupportedCodeFixes;
 
   interface BaseLanguageServerRequest {
@@ -144,6 +145,13 @@ declare global {
     position: number;
   }
 
+  interface GetSignatureHelpItemsRequest extends BaseLanguageServerRequest {
+    method: "getSignatureHelpItems";
+    specifier: string;
+    position: number;
+    options: ts.SignatureHelpItemsOptions;
+  }
+
   interface GetSupportedCodeFixes extends BaseLanguageServerRequest {
     method: "getSupportedCodeFixes";
   }