Show a prompt if we have more than one solution file

This prompt is pretty close to what DevKit does in this same case.

Author: jasonmalinowski

l10n/bundle.l10n.json

@@ -118,6 +118,9 @@
   "View Debug Docs": "View Debug Docs",
   "Ignore": "Ignore",
   "Run and Debug: A valid browser is not installed": "Run and Debug: A valid browser is not installed",
+  "Your workspace has multiple Visual Studio Solution files; please select one to get full IntelliSense.": "Your workspace has multiple Visual Studio Solution files; please select one to get full IntelliSense.",
+  "Choose solution": "Choose solution",
+  "Do not load solutions": "Do not load solutions",
   "Restart Language Server": "Restart Language Server",
   "pipeArgs must be a string or a string array type": "pipeArgs must be a string or a string array type",
   "Name not defined in current configuration.": "Name not defined in current configuration.",

src/lsptoolshost/roslynLanguageServer.ts

@@ -425,6 +425,23 @@ export class RoslynLanguageServer {
                 if (solutionUris) {
                     if (solutionUris.length === 1) {
                         this.openSolution(solutionUris[0]);
+                    } else if (solutionUris.length > 1) {
+                        // We have more than one solution, so we'll prompt the user to use the picker.
+                        const chosen = await vscode.window.showInformationMessage(
+                            vscode.l10n.t(
+                                'Your workspace has multiple Visual Studio Solution files; please select one to get full IntelliSense.'
+                            ),
+                            { title: vscode.l10n.t('Choose solution'), open: true },
+                            { title: vscode.l10n.t('Do not load solutions'), open: false }
+                        );
+
+                        if (chosen) {
+                            if (chosen.open) {
+                                vscode.commands.executeCommand('dotnet.openSolution');
+                            } else {
+                                vscode.workspace.getConfiguration().update('dotnet.defaultSolution', 'disable', false);
+                            }
+                        }
                     } else if (solutionUris.length === 0) {
                         // We have no solutions, so we'll enumerate what project files we have and just use those.
                         const projectUris = await vscode.workspace.findFiles(