Make error messages clearer for some common problems

1. Clicking on query history menu items when nothing is selected. Error
   message is clearer. It would be better to disable when nothing is
   selected, but waiting on
   microsoft/vscode#99767 to be released.
2. Trying to run query with a missing or invalid qlpack has better
   message.
3. Better hover text for "Open query".

Author: aeisenberg

extensions/ql-vscode/package.json

@@ -304,7 +304,7 @@
       },
       {
         "command": "codeQLQueryHistory.openQuery",
-        "title": "Open Query",
+        "title": "Open the Query that Produced these results",
         "icon": {
           "light": "media/light/edit.svg",
           "dark": "media/dark/edit.svg"

extensions/ql-vscode/src/query-history.ts

@@ -310,6 +310,10 @@ export class QueryHistoryManager extends DisposableObject {
       return;
     }
 
+    if (!finalSingleItem) {
+      throw new Error('No query selected. Select a query history item you have already run and try again.');
+    }
+
     const textDocument = await vscode.workspace.openTextDocument(
       vscode.Uri.file(finalSingleItem.query.program.queryPath)
     );
@@ -398,6 +402,11 @@ export class QueryHistoryManager extends DisposableObject {
     if (!this.assertSingleQuery(finalMultiSelect)) {
       return;
     }
+
+    if (!finalSingleItem) {
+      throw new Error('No query selected. Select a query history item you have already run and try again.');
+    }
+
     this.treeDataProvider.setCurrentItem(finalSingleItem);
 
     const now = new Date();
@@ -440,6 +449,10 @@ export class QueryHistoryManager extends DisposableObject {
       return;
     }
 
+    if (!singleItem) {
+      throw new Error('No query selected. Select a query history item you have already run and try again.');
+    }
+
     const queryName = singleItem.queryName.endsWith('.ql')
       ? singleItem.queryName
       : singleItem.queryName + '.ql';

extensions/ql-vscode/src/run-queries.ts

@@ -345,7 +345,7 @@ async function promptUserToSaveChanges(document: TextDocument): Promise<boolean>
     else {
       const yesItem = { title: 'Yes', isCloseAffordance: false };
       const alwaysItem = { title: 'Always Save', isCloseAffordance: false };
-      const noItem = { title: 'No (run anyway)', isCloseAffordance: false };
+      const noItem = { title: 'No (run version on disk)', isCloseAffordance: false };
       const cancelItem = { title: 'Cancel', isCloseAffordance: true };
       const message = 'Query file has unsaved changes. Save now?';
       const chosenItem = await window.showInformationMessage(
@@ -478,6 +478,10 @@ export async function compileAndRunQueryAgainstDatabase(
   // Figure out the library path for the query.
   const packConfig = await cliServer.resolveLibraryPath(diskWorkspaceFolders, queryPath);
 
+  if (!packConfig.dbscheme) {
+    throw new Error('No dbscheme. Is your qlpack.yml missing or invalid?');
+  }
+
   // Check whether the query has an entirely different schema from the
   // database. (Queries that merely need the database to be upgraded
   // won't trigger this check)