Allow compare view to work with quick-eval

extensions/ql-vscode/src/compare/compare-view.ts

@@ -175,21 +175,40 @@ export class CompareView extends AbstractWebview<
     const commonResultSetNames = fromSchemaNames.filter((name) =>
       toSchemaNames.includes(name),
     );
+
+    // Fall back on the default result set names if there are no common ones.
+    const defaultFromResultSetName = fromSchemaNames.find((name) =>
+      name.startsWith("#"),
+    );
+    const defaultToResultSetName = toSchemaNames.find((name) =>
+      name.startsWith("#"),
+    );
+
+    if (
+      commonResultSetNames.length === 0 &&
+      !(defaultFromResultSetName || defaultToResultSetName)
+    ) {
+      throw new Error(
+        "No common result sets found between the two queries. Please check that the queries are compatible.",
+      );
+    }
+
     const currentResultSetName =
       selectedResultSetName || commonResultSetNames[0];
     const fromResultSet = await this.getResultSet(
       fromSchemas,
-      currentResultSetName,
+      currentResultSetName || defaultFromResultSetName!,
       from.completedQuery.query.resultsPaths.resultsPath,
     );
     const toResultSet = await this.getResultSet(
       toSchemas,
-      currentResultSetName,
+      currentResultSetName || defaultToResultSetName!,
       to.completedQuery.query.resultsPaths.resultsPath,
     );
     return [
       commonResultSetNames,
-      currentResultSetName,
+      currentResultSetName ||
+        `${defaultFromResultSetName} <-> ${defaultToResultSetName}`,
       fromResultSet,
       toResultSet,
     ];

extensions/ql-vscode/src/view/compare/Compare.tsx

@@ -59,9 +59,7 @@ export function Compare(_: Record<string, never>): JSX.Element {
     return (
       <>
         <div className="vscode-codeql__compare-header">
-          <div className="vscode-codeql__compare-header-item">
-            Table to compare:
-          </div>
+          <div className="vscode-codeql__compare-header-item">Comparing:</div>
           <CompareSelector
             availableResultSets={comparison.commonResultSetNames}
             currentResultSetName={comparison.currentResultSetName}

extensions/ql-vscode/src/view/compare/CompareSelector.tsx

@@ -7,7 +7,8 @@ interface Props {
 }
 
 export default function CompareSelector(props: Props) {
-  return (
+  return props.availableResultSets.length ? (
+    // Handle case where there are shared result sets
     <select
       value={props.currentResultSetName}
       onChange={(e) => props.updateResultSet(e.target.value)}
@@ -18,5 +19,8 @@ export default function CompareSelector(props: Props) {
         </option>
       ))}
     </select>
+  ) : (
+    // Handle case where there are no shared result sets
+    <div>{props.currentResultSetName}</div>
   );
 }