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
   https://github.com/microsoft/vscode/issues/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".

Co-authored-by: Aditya Sharad <6874315+adityasharad@users.noreply.github.com>

extensions/ql-vscode/CHANGELOG.md

@@ -6,6 +6,8 @@
 - Fix bug when removing databases where sometimes the source folder would not be removed from the workspace or the database files would not be removed from the workspace storage location. [#692](https://github.com/github/vscode-codeql/pull/692)
 - Query results with no string representation will now be displayed with placeholder text in query results. Previously, they were omitted. [#694](https://github.com/github/vscode-codeql/pull/694)
 - Add a label for the language of a database in the databases view. This will only take effect for new databases created with the CodeQL CLI v2.4.1 or later. [#697](https://github.com/github/vscode-codeql/pull/697)
+- Add clearer error message when running a query using a missing or invalid qlpack. [#702](https://github.com/github/vscode-codeql/pull/702)
+- Add clearer error message when trying to run a command from the query history view if no item in the history is selected. [#702](https://github.com/github/vscode-codeql/pull/702)
 
 ## 1.3.7 - 24 November 2020
 

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

@@ -172,6 +172,7 @@ class HistoryTreeDataProvider extends DisposableObject implements QueryHistoryDa
  */
 const DOUBLE_CLICK_TIME = 500;
 
+const NO_QUERY_SELECTED = 'No query selected. Select a query history item you have already run and try again.';
 export class QueryHistoryManager extends DisposableObject {
   treeDataProvider: HistoryTreeDataProvider;
   treeView: vscode.TreeView<CompletedQuery>;
@@ -310,6 +311,10 @@ export class QueryHistoryManager extends DisposableObject {
       return;
     }
 
+    if (!finalSingleItem) {
+      throw new Error(NO_QUERY_SELECTED);
+    }
+
     const textDocument = await vscode.workspace.openTextDocument(
       vscode.Uri.file(finalSingleItem.query.program.queryPath)
     );
@@ -398,6 +403,11 @@ export class QueryHistoryManager extends DisposableObject {
     if (!this.assertSingleQuery(finalMultiSelect)) {
       return;
     }
+
+    if (!finalSingleItem) {
+      throw new Error(NO_QUERY_SELECTED);
+    }
+
     this.treeDataProvider.setCurrentItem(finalSingleItem);
 
     const now = new Date();
@@ -440,6 +450,10 @@ export class QueryHistoryManager extends DisposableObject {
       return;
     }
 
+    if (!singleItem) {
+      throw new Error(NO_QUERY_SELECTED);
+    }
+
     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('Could not find a database scheme for this query. Please check that you have a valid qlpack.yml file for this query, which refers to a database scheme either in the `dbscheme` field or through one of its dependencies.');
+  }
+
   // 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)