Show error message when user setting select zero files for download

It is possible to create glob patterns such that no files are selected for download. If this happens, let's tell the user what happended and suggest how to fix it.

Fixes #75

Author: dlech

CHANGELOG.md

@@ -6,6 +6,7 @@ Check [Keep a Changelog](http://keepachangelog.com/) for recommendations on how
 ## Unreleased
 ### Fixed
 - Files are not downloaded when using global launch configuration
+- No indication when zero files are downloaded
 
 ## 1.0.1 - 2019-02-02
 ### Fixed

src/extension.ts

@@ -215,6 +215,24 @@ async function download(folder: vscode.WorkspaceFolder, device: Device): Promise
     }, async (progress, token) => {
         try {
             const files = await vscode.workspace.findFiles(includeFiles, excludeFiles);
+
+            // If there are no files matching the given include and exclude patterns,
+            // let the user know about it.
+            if (!files.length) {
+                const msg = 'No files selected for download. Please check the ev3devBrowser.download.include and ev3devBrowser.download.exclude settings.';
+                // try to make it easy for the user to fix the problem by offering to
+                // open the settings editor
+                const openSettings = 'Open Settings';
+                vscode.window.showErrorMessage(msg, openSettings).then(result => {
+                    if (result === openSettings) {
+                        vscode.commands.executeCommand('workbench.action.openSettings2');
+                    }
+                });
+
+                // "cancel" the download
+                return false;
+            }
+
             const increment = 100 / files.length;
             let fileIndex = 1;
             const reportProgress = (message: string) => progress.report({ message: message });