Support overlay database creation

This commit adds support for creating overlay-base and overlay
databases, controlled via the CODEQL_OVERLAY_DATABASE_MODE environment
variable.

src/init.ts

@@ -3,15 +3,20 @@ import * as path from "path";
 
 import * as toolrunner from "@actions/exec/lib/toolrunner";
 import * as io from "@actions/io";
+import * as semver from "semver";
 
 import { getOptionalInput, isSelfHostedRunner } from "./actions-util";
 import { GitHubApiCombinedDetails, GitHubApiDetails } from "./api-client";
 import { CodeQL, setupCodeQL } from "./codeql";
 import * as configUtils from "./config-utils";
 import { CodeQLDefaultVersionInfo, FeatureEnablement } from "./feature-flags";
+import { getGitRoot } from "./git-utils";
 import { Language, isScannedLanguage } from "./languages";
 import { Logger } from "./logging";
-import { OverlayDatabaseMode } from "./overlay-database-utils";
+import {
+  CODEQL_OVERLAY_MINIMUM_VERSION,
+  OverlayDatabaseMode,
+} from "./overlay-database-utils";
 import { ToolsSource } from "./setup-codeql";
 import { ZstdAvailability } from "./tar";
 import { ToolsDownloadStatusReport } from "./tools-download";
@@ -80,6 +85,47 @@ export async function initConfig(
   return config;
 }
 
+export async function getOverlayDatabaseMode(
+  codeqlVersion: string,
+  config: configUtils.Config,
+  sourceRoot: string,
+  logger: Logger,
+): Promise<OverlayDatabaseMode> {
+  const overlayDatabaseMode = process.env.CODEQL_OVERLAY_DATABASE_MODE;
+
+  if (
+    overlayDatabaseMode === OverlayDatabaseMode.Overlay ||
+    overlayDatabaseMode === OverlayDatabaseMode.OverlayBase
+  ) {
+    if (config.buildMode !== util.BuildMode.None) {
+      logger.warning(
+        `Cannot build an ${overlayDatabaseMode} database because ` +
+          `build-mode is set to "${config.buildMode}" instead of "none". ` +
+          "Falling back to creating a normal full database instead.",
+      );
+      return OverlayDatabaseMode.None;
+    }
+    if (semver.lt(codeqlVersion, CODEQL_OVERLAY_MINIMUM_VERSION)) {
+      logger.warning(
+        `Cannot build an ${overlayDatabaseMode} database because ` +
+          `the CodeQL CLI is older than ${CODEQL_OVERLAY_MINIMUM_VERSION}. ` +
+          "Falling back to creating a normal full database instead.",
+      );
+      return OverlayDatabaseMode.None;
+    }
+    if ((await getGitRoot(sourceRoot)) === undefined) {
+      logger.warning(
+        `Cannot build an ${overlayDatabaseMode} database because ` +
+          `the source root "${sourceRoot}" is not inside a git repository. ` +
+          "Falling back to creating a normal full database instead.",
+      );
+      return OverlayDatabaseMode.None;
+    }
+    return overlayDatabaseMode as OverlayDatabaseMode;
+  }
+  return OverlayDatabaseMode.None;
+}
+
 export async function runInit(
   codeql: CodeQL,
   config: configUtils.Config,