Add threads request to debugger

Summary:
Release note: none

- let UI send threads request
- adapter returns information about the one thread
Closes https://github.com/facebook/prepack/pull/1130

Differential Revision: D6227708

Pulled By: JWZ2018

fbshipit-source-id: 40a14f786842dec01491c03eee49a41a15af98cd

src/debugger/adapter/DebugAdapter.js

@@ -197,6 +197,18 @@ class PrepackDebugSession extends LoggingDebugSession {
       this.sendResponse(response);
     });
   }
+
+  threadsRequest(response: DebugProtocol.ThreadsResponse): void {
+    // There will only be 1 thread, so respond immediately
+    let thread: DebugProtocol.Thread = {
+      id: DebuggerConstants.PREPACK_THREAD_ID,
+      name: "main",
+    };
+    response.body = {
+      threads: [thread],
+    };
+    this.sendResponse(response);
+  }
 }
 
 DebugSession.run(PrepackDebugSession);

src/debugger/mock-ui/UISession.js

@@ -129,8 +129,15 @@ export class UISession {
   }
 
   _processResponse(response: DebugProtocol.Response) {
-    // to be implemented
-    console.log(response);
+    if (response.command === "threads") {
+      this._processThreadsResponse(((response: any): DebugProtocol.ThreadsResponse));
+    }
+  }
+
+  _processThreadsResponse(response: DebugProtocol.ThreadsResponse) {
+    for (const thread of response.body.threads) {
+      this._uiOutput(`${thread.id}: ${thread.name}`);
+    }
   }
 
   // execute a command if it is valid
@@ -167,6 +174,10 @@ export class UISession {
           this._sendBreakpointRequest(filePath, line, column);
         }
         break;
+      case "threads":
+        if (parts.length !== 1) return false;
+        this._sendThreadsRequest();
+        break;
       default:
         // invalid command
         return false;
@@ -256,6 +267,16 @@ export class UISession {
     this._packageAndSend(json);
   }
 
+  _sendThreadsRequest() {
+    let message = {
+      type: "request",
+      seq: this._sequenceNum,
+      command: "threads",
+    };
+    let json = JSON.stringify(message);
+    this._packageAndSend(json);
+  }
+
   // write out a message to the adapter on stdout
   _packageAndSend(message: string) {
     // format: Content-Length: <length> separator <message>