Add a channel for nREPL output to the Output Window

Add a channel to show nREPL output to the user. This channel will be
used for the following:

stdout:

Any stdout messages are sent to the channel.

stderr:

Any stderr messages are sent to the channel, and the channel is brought
to the front to make the user aware.

exit:

If the nREPL closes before be we can load the port, then the exit code
is printed to the nREPL output channel, and the channel is brough to the
front.

Fixes avli#52
Fixes avli#53
Fixed avli#69

Also fixes a bug where the 'Starting nREPL' status message would never
clear if the repl failed to start.

src/cljConnection.ts

@@ -136,12 +136,10 @@ const startNRepl = (): void => {
         .then(connectionInfo => nreplConnection = connectionInfo)
         .then(() => nreplClient.test(nreplConnection))
         .then(stopLoadingAnimation)
-        .then(() => saveConnection(nreplConnection))
-        .catch(({ nreplError }) => {
+        .then(() => saveConnection(nreplConnection), ({ nreplError }) => {
             stopLoadingAnimation();
             if (!nreplError)
                 nreplError = "Can't start nREPL.";
-
             disconnect(false);
             vscode.window.showErrorMessage(nreplError);
         });

src/nreplController.ts

@@ -37,6 +37,10 @@ let nreplProcess: ChildProcess;
 
 const isStarted = () => !!nreplProcess;
 
+// Create a channel in the Output window so that the user
+// can view output from the nREPL session.
+const nreplChannel = vscode.window.createOutputChannel('nREPL');
+
 const start = (): Promise<CljConnectionInformation> => {
     if (isStarted())
         return Promise.reject({ nreplError: 'nREPL already started.' });
@@ -46,30 +50,37 @@ const start = (): Promise<CljConnectionInformation> => {
         detached: !(os.platform() === 'win32')
     });
 
+    // Clear any output from previous nREPL sessions to help users focus
+    // on the current session only.
+    nreplChannel.clear();
+
     return new Promise((resolve, reject) => {
         nreplProcess.stdout.addListener('data', data => {
             const nreplConnectionMatch = data.toString().match(R_NREPL_CONNECTION_INFO);
 
+            // Send any stdout messages to the channel, but do not bring the
+            // channel to the front, since these messages are likely just
+            // informative.
+            nreplChannel.append(data.toString());
+
             if (nreplConnectionMatch && nreplConnectionMatch[1]) {
                 const [host, port] = nreplConnectionMatch[1].split(':');
                 return resolve({ host, port: Number.parseInt(port) });
             }
         });
 
         nreplProcess.stderr.on('data', data => {
-            console.info('nrepl stderr =>', data.toString());
-        });
-
-        nreplProcess.on('exit', (code, signal) => {
-            console.info(`nREPL exit => ${code} / Signal: ${signal}`);
-            stop();
-            return reject();
+            // Log errors and bring panel to the front.
+            nreplChannel.append(data.toString());
+            nreplChannel.show();
         });
 
-        nreplProcess.on('close', (code, signal) => {
-            console.info(`nREPL close => ${code} / Signal: ${signal}`);
-            stop();
-            return reject();
+        nreplProcess.on('exit', (code) => {
+            // nREPL process has exited before we were able to read a host / port.
+            const message = `nREPL exited with code ${code}`
+            nreplChannel.appendLine(message);
+            nreplChannel.show();
+            return reject({ nreplError: message});
         });
     });
 };
@@ -78,12 +89,22 @@ const stop = () => {
     if (nreplProcess) {
         // Workaround http://azimi.me/2014/12/31/kill-child_process-node-js.html
         nreplProcess.removeAllListeners();
-        if(os.platform() === 'win32'){
-            exec('taskkill /pid ' + nreplProcess.pid + ' /T /F')
-        }
-        else {
-            process.kill(-nreplProcess.pid);
+
+        try {
+            // Killing the process will throw an error `kill ESRCH` this method
+            // is invoked after the nREPL process has exited. This happens when
+            // we try to gracefully  clean up after spawning the nREPL fails.
+            // We wrap the killing code in `try/catch` to handle this.
+            if(os.platform() === 'win32'){
+                exec('taskkill /pid ' + nreplProcess.pid + ' /T /F')
+            }
+            else {
+                process.kill(-nreplProcess.pid);
+            }
+        } catch (exception) {
+            console.error("Error cleaning up nREPL process", exception);
         }
+
         nreplProcess = null;
     }
 };