getOverlayDatabaseMode: use Feature.OverlayAnalysis

This commit changes getOverlayDatabaseMode so that, when
Feature.OverlayAnalysis is enabled, it calculates the overlay database
mode automatically based on analysis metadata. If we are analyzing the
default branch, use OverlayBase, and if we are analyzing a PR, use
Overlay.

If CODEQL_OVERLAY_DATABASE_MODE is set to a valid overlay database mode,
that environment variable still takes precedence.

Author: cklin

src/config-utils.ts

@@ -5,12 +5,13 @@ import { performance } from "perf_hooks";
 import * as yaml from "js-yaml";
 import * as semver from "semver";
 
+import { isAnalyzingPullRequest } from "./actions-util";
 import * as api from "./api-client";
 import { CachingKind, getCachingKind } from "./caching-utils";
 import { CodeQL } from "./codeql";
 import { shouldPerformDiffInformedAnalysis } from "./diff-informed-analysis-utils";
 import { Feature, FeatureEnablement } from "./feature-flags";
-import { getGitRoot } from "./git-utils";
+import { getGitRoot, isAnalyzingDefaultBranch } from "./git-utils";
 import { Language, parseLanguage } from "./languages";
 import { Logger } from "./logging";
 import {
@@ -743,46 +744,87 @@ function parseQueriesFromInput(
   return trimmedInput.split(",").map((query) => ({ uses: query.trim() }));
 }
 
+/**
+ * Calculate and validate the overlay database mode to use.
+ *
+ * - If the environment variable `CODEQL_OVERLAY_DATABASE_MODE` is set, use it.
+ * - Otherwise, if `Feature.OverlayAnalysis` is enabled, calculate the mode
+ *   based on what we are analyzing.
+ *   - If we are analyzing a pull request, use `Overlay`.
+ *   - If we are analyzing the default branch, use `OverlayBase`.
+ * - Otherwise, use `None`.
+ *
+ * For `Overlay` and `OverlayBase`, the function performs further checks and
+ * reverts to `None` if any check should fail.
+ */
 async function getOverlayDatabaseMode(
   codeql: CodeQL,
   features: FeatureEnablement,
   sourceRoot: string,
   buildMode: BuildMode | undefined,
   logger: Logger,
 ): Promise<OverlayDatabaseMode> {
-  const overlayDatabaseMode = process.env.CODEQL_OVERLAY_DATABASE_MODE;
+  let overlayDatabaseMode = OverlayDatabaseMode.None;
 
+  const modeEnv = process.env.CODEQL_OVERLAY_DATABASE_MODE;
+  // Any unrecognized CODEQL_OVERLAY_DATABASE_MODE value will be ignored and
+  // treated as if the environment variable was not set.
   if (
-    overlayDatabaseMode === OverlayDatabaseMode.Overlay ||
-    overlayDatabaseMode === OverlayDatabaseMode.OverlayBase
+    modeEnv === OverlayDatabaseMode.Overlay ||
+    modeEnv === OverlayDatabaseMode.OverlayBase ||
+    modeEnv === OverlayDatabaseMode.None
   ) {
-    if (buildMode !== BuildMode.None) {
-      logger.warning(
-        `Cannot build an ${overlayDatabaseMode} database because ` +
-          `build-mode is set to "${buildMode}" instead of "none". ` +
-          "Falling back to creating a normal full database instead.",
-      );
-      return OverlayDatabaseMode.None;
-    }
-    if (!(await codeQlVersionAtLeast(codeql, 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.",
+    overlayDatabaseMode = modeEnv;
+    logger.info(
+      `Setting overlay database mode to ${overlayDatabaseMode} ` +
+        "from the CODEQL_OVERLAY_DATABASE_MODE environment variable.",
+    );
+  } else if (await features.getValue(Feature.OverlayAnalysis, codeql)) {
+    if (isAnalyzingPullRequest()) {
+      overlayDatabaseMode = OverlayDatabaseMode.Overlay;
+      logger.info(
+        `Setting overlay database mode to ${overlayDatabaseMode} ` +
+          "because we are analyzing a pull request.",
       );
-      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.",
+    } else if (await isAnalyzingDefaultBranch()) {
+      overlayDatabaseMode = OverlayDatabaseMode.OverlayBase;
+      logger.info(
+        `Setting overlay database mode to ${overlayDatabaseMode} ` +
+          "because we are analyzing the default branch.",
       );
-      return OverlayDatabaseMode.None;
     }
-    return overlayDatabaseMode as OverlayDatabaseMode;
   }
-  return OverlayDatabaseMode.None;
+
+  if (overlayDatabaseMode === OverlayDatabaseMode.None) {
+    return OverlayDatabaseMode.None;
+  }
+
+  if (buildMode !== BuildMode.None) {
+    logger.warning(
+      `Cannot build an ${overlayDatabaseMode} database because ` +
+        `build-mode is set to "${buildMode}" instead of "none". ` +
+        "Falling back to creating a normal full database instead.",
+    );
+    return OverlayDatabaseMode.None;
+  }
+  if (!(await codeQlVersionAtLeast(codeql, 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;
 }
 
 /**