Add warning when using unsupported CLI version

This adds a warning when the user is using an unsupported version of the
CodeQL CLI. The warning is shown once per session, and only if the
version is older than the oldest supported version.

Author: koesie10

extensions/ql-vscode/src/codeql-cli/cli.ts

@@ -1737,6 +1737,10 @@ export function shouldDebugCliServer() {
 }
 
 export class CliVersionConstraint {
+  // The oldest version of the CLI that we support. This is used to determine
+  // whether to show a warning about the CLI being too old on startup.
+  public static OLDEST_SUPPORTED_CLI_VERSION = new SemVer("2.7.6");
+
   /**
    * CLI version where building QLX packs for remote queries is supported.
    * (The options were _accepted_ by a few earlier versions, but only from

extensions/ql-vscode/src/extension.ts

@@ -24,7 +24,7 @@ import {
   activate as archiveFilesystemProvider_activate,
   zipArchiveScheme,
 } from "./common/vscode/archive-filesystem-provider";
-import { CodeQLCliServer } from "./codeql-cli/cli";
+import { CliVersionConstraint, CodeQLCliServer } from "./codeql-cli/cli";
 import {
   CliConfigListener,
   DistributionConfigListener,
@@ -408,6 +408,28 @@ export async function activate(
     codeQlExtension.cliServer.addVersionChangedListener((ver) => {
       telemetryListener.cliVersion = ver;
     });
+
+    let unsupportedWarningShown = false;
+    codeQlExtension.cliServer.addVersionChangedListener((ver) => {
+      if (!ver) {
+        return;
+      }
+
+      if (unsupportedWarningShown) {
+        return;
+      }
+
+      if (CliVersionConstraint.OLDEST_SUPPORTED_CLI_VERSION.compare(ver) < 0) {
+        return;
+      }
+
+      void showAndLogWarningMessage(
+        `You are using an unsupported version of the CodeQL CLI (${ver}). ` +
+          `The minimum supported version is ${CliVersionConstraint.OLDEST_SUPPORTED_CLI_VERSION}. ` +
+          `Please upgrade to the latest version of the CodeQL CLI.`,
+      );
+      unsupportedWarningShown = true;
+    });
   }
 
   return codeQlExtension;