Fall back to non-overlay analysis when diff-informed analysis is unavailable

src/config-utils.test.ts

@@ -2200,3 +2200,68 @@ test.serial(
     });
   },
 );
+
+test("applyIncrementalAnalysisSettings: no-op when mode is not Overlay and diff-informed is unavailable", (t) => {
+  const config = createTestConfig({});
+  config.overlayDatabaseMode = OverlayDatabaseMode.None;
+  const logger = getRunnerLogger(true);
+
+  configUtils.applyIncrementalAnalysisSettings(
+    config,
+    { shouldRun: false, hasDiffRanges: false },
+    logger,
+  );
+
+  t.is(config.overlayDatabaseMode, OverlayDatabaseMode.None);
+  t.deepEqual(config.extraQueryExclusions, []);
+});
+
+test("applyIncrementalAnalysisSettings: keeps overlay mode and adds exclusions when diff-informed analysis shouldn't run", (t) => {
+  const config = createTestConfig({});
+  config.overlayDatabaseMode = OverlayDatabaseMode.Overlay;
+  const logger = getRunnerLogger(true);
+
+  configUtils.applyIncrementalAnalysisSettings(
+    config,
+    { shouldRun: false, hasDiffRanges: false },
+    logger,
+  );
+
+  t.is(config.overlayDatabaseMode, OverlayDatabaseMode.Overlay);
+  t.deepEqual(config.extraQueryExclusions, [
+    { exclude: { tags: "exclude-from-incremental" } },
+  ]);
+});
+
+test("applyIncrementalAnalysisSettings: disables overlay analysis when diff-informed analysis is unavailable", (t) => {
+  const config = createTestConfig({
+    overlayDatabaseMode: OverlayDatabaseMode.Overlay,
+  });
+  const logger = getRunnerLogger(true);
+
+  configUtils.applyIncrementalAnalysisSettings(
+    config,
+    { shouldRun: true, hasDiffRanges: false },
+    logger,
+  );
+
+  t.is(config.overlayDatabaseMode, OverlayDatabaseMode.None);
+  t.deepEqual(config.extraQueryExclusions, []);
+});
+
+test("applyIncrementalAnalysisSettings: adds exclusions for diff-informed-only runs", (t) => {
+  const config = createTestConfig({});
+  config.overlayDatabaseMode = OverlayDatabaseMode.None;
+  const logger = getRunnerLogger(true);
+
+  configUtils.applyIncrementalAnalysisSettings(
+    config,
+    { shouldRun: true, hasDiffRanges: true },
+    logger,
+  );
+
+  t.is(config.overlayDatabaseMode, OverlayDatabaseMode.None);
+  t.deepEqual(config.extraQueryExclusions, [
+    { exclude: { tags: "exclude-from-incremental" } },
+  ]);
+});

src/config-utils.ts

@@ -31,7 +31,10 @@ import {
   addNoLanguageDiagnostic,
   makeTelemetryDiagnostic,
 } from "./diagnostics";
-import { shouldPerformDiffInformedAnalysis } from "./diff-informed-analysis-utils";
+import {
+  type DiffInformedAnalysisPreparation,
+  prepareDiffInformedAnalysis,
+} from "./diff-informed-analysis-utils";
 import { EnvVar } from "./environment";
 import * as errorMessages from "./error-messages";
 import { Feature, FeatureEnablement } from "./feature-flags";
@@ -1076,6 +1079,48 @@ function hasQueryCustomisation(userConfig: UserConfig): boolean {
   );
 }
 
+/**
+ * Finalize the incremental-analysis configuration for this run.
+ *
+ * If overlay mode was selected for a PR but diff-informed analysis should have
+ * run and could not be prepared, fall back to a full non-overlay analysis.
+ * Query exclusions for incremental-only queries are applied only when the final
+ * configuration still uses overlay analysis or the diff ranges are available.
+ *
+ * Note that `overlayDatabaseMode === Overlay` does not imply
+ * `diffInformedAnalysis.shouldRun`. Overlay mode is selected based on language
+ * and feature-flag state and can apply outside of pull-request contexts (e.g.
+ * on branch pushes that build up the overlay cache), whereas diff-informed
+ * analysis only runs for pull requests where we can compute a diff. Each
+ * combination is therefore handled explicitly.
+ */
+export function applyIncrementalAnalysisSettings(
+  config: Config,
+  diffInformedAnalysis: DiffInformedAnalysisPreparation,
+  logger: Logger,
+): void {
+  if (
+    config.overlayDatabaseMode === OverlayDatabaseMode.Overlay &&
+    diffInformedAnalysis.shouldRun &&
+    !diffInformedAnalysis.hasDiffRanges
+  ) {
+    logger.info(
+      "Diff-informed analysis is not available for this pull request. " +
+        `Reverting overlay database mode to ${OverlayDatabaseMode.None}.`,
+    );
+    config.overlayDatabaseMode = OverlayDatabaseMode.None;
+  }
+
+  if (
+    config.overlayDatabaseMode === OverlayDatabaseMode.Overlay ||
+    diffInformedAnalysis.hasDiffRanges
+  ) {
+    config.extraQueryExclusions.push({
+      exclude: { tags: "exclude-from-incremental" },
+    });
+  }
+}
+
 /**
  * Load and return the config.
  *
@@ -1230,18 +1275,13 @@ export async function initConfig(
     );
   }
 
-  if (
-    config.overlayDatabaseMode === OverlayDatabaseMode.Overlay ||
-    (await shouldPerformDiffInformedAnalysis(
-      inputs.codeql,
-      inputs.features,
-      logger,
-    ))
-  ) {
-    config.extraQueryExclusions.push({
-      exclude: { tags: "exclude-from-incremental" },
-    });
-  }
+  const diffInformedAnalysis = await prepareDiffInformedAnalysis(
+    inputs.codeql,
+    inputs.features,
+    logger,
+  );
+
+  applyIncrementalAnalysisSettings(config, diffInformedAnalysis, logger);
 
   if (await isTrapCachingEnabled(features, config.overlayDatabaseMode)) {
     const { trapCaches, trapCacheDownloadTime } = await downloadCacheWithTime(