Address review comments

src/config-utils.test.ts

@@ -1253,7 +1253,7 @@ test(
   {
     overlayDatabaseMode: OverlayDatabaseMode.None,
     useOverlayDatabaseCaching: false,
-    disabledReason: OverlayDisabledReason.InsufficientDiskSpace,
+    disabledReason: OverlayDisabledReason.UnableToDetermineDiskUsage,
   },
 );
 
@@ -1679,7 +1679,7 @@ test(
   {
     overlayDatabaseMode: OverlayDatabaseMode.None,
     useOverlayDatabaseCaching: false,
-    disabledReason: OverlayDisabledReason.InsufficientDiskSpace,
+    disabledReason: OverlayDisabledReason.UnableToDetermineDiskUsage,
   },
 );
 

src/config-utils.ts

@@ -702,21 +702,15 @@ async function getOverlayFeatureDisabledReason(
 
 /** Checks if the runner has enough disk space for overlay analysis. */
 function runnerHasSufficientDiskSpace(
-  diskUsage: DiskUsage | undefined,
+  diskUsage: DiskUsage,
   logger: Logger,
   useV2ResourceChecks: boolean,
 ): boolean {
   const minimumDiskSpaceBytes = useV2ResourceChecks
     ? OVERLAY_MINIMUM_AVAILABLE_DISK_SPACE_V2_BYTES
     : OVERLAY_MINIMUM_AVAILABLE_DISK_SPACE_BYTES;
-  if (
-    diskUsage === undefined ||
-    diskUsage.numAvailableBytes < minimumDiskSpaceBytes
-  ) {
-    const diskSpaceMb =
-      diskUsage === undefined
-        ? 0
-        : Math.round(diskUsage.numAvailableBytes / 1_000_000);
+  if (diskUsage.numAvailableBytes < minimumDiskSpaceBytes) {
+    const diskSpaceMb = Math.round(diskUsage.numAvailableBytes / 1_000_000);
     const minimumDiskSpaceMb = Math.round(minimumDiskSpaceBytes / 1_000_000);
     logger.info(
       `Setting overlay database mode to ${OverlayDatabaseMode.None} ` +
@@ -772,6 +766,13 @@ async function getResourceDisabledReason(
   logger: Logger,
   useV2ResourceChecks: boolean,
 ): Promise<OverlayDisabledReason | undefined> {
+  if (diskUsage === undefined) {
+    logger.info(
+      `Unable to determine available disk space for overlay analysis. ` +
+        `Setting overlay database mode to ${OverlayDatabaseMode.None}.`,
+    );
+    return OverlayDisabledReason.UnableToDetermineDiskUsage;
+  }
   if (!runnerHasSufficientDiskSpace(diskUsage, logger, useV2ResourceChecks)) {
     return OverlayDisabledReason.InsufficientDiskSpace;
   }

src/overlay/diagnostics.ts

@@ -26,7 +26,10 @@ export enum OverlayDisabledReason {
   LanguageNotEnabled = "language-not-enabled",
   /** The source root is not inside a git repository. */
   NoGitRoot = "no-git-root",
-  /** Overlay analysis is restricted to code-scanning-only configs but the config uses custom queries or packs. */
+  /**
+   * Overlay analysis is restricted to code-scanning-only configs but the config uses custom
+   * queries or packs, disables default queries, or specifies query filters.
+   */
   NonDefaultQueries = "non-default-queries",
   /** The top-level overlay analysis feature flag is not enabled. */
   OverallFeatureNotEnabled = "overall-feature-not-enabled",