github · sam-robson · May 14, 2026 · Apr 16, 2026 · Apr 23, 2026 · Apr 24, 2026
@@ -6,13 +6,6 @@ env:
   # Diff informed queries add an additional query filter which is not yet
   # taken into account by these tests.
   CODEQL_ACTION_DIFF_INFORMED_QUERIES: false
-  # Specify overlay enablement manually to ensure stability around the exclude-from-incremental
-  # query filter. Here we only enable for the default code scanning suite.
-  CODEQL_ACTION_OVERLAY_ANALYSIS: true
-  CODEQL_ACTION_OVERLAY_ANALYSIS_JAVASCRIPT: false
-  CODEQL_ACTION_OVERLAY_ANALYSIS_CODE_SCANNING_JAVASCRIPT: true
-  CODEQL_ACTION_OVERLAY_ANALYSIS_STATUS_CHECK: false
-  CODEQL_ACTION_OVERLAY_ANALYSIS_SKIP_RESOURCE_CHECKS: true
 
 on:
   push:
@@ -79,33 +72,13 @@ jobs:
       with:
         version: ${{ matrix.version }}
 
-    # On PRs, overlay analysis may change the config that is passed to the CLI.
-    # Therefore, we have two variants of the following test, one for PRs and one for other events.
-    - name: Empty file (non-PR)
-      if: github.event_name != 'pull_request'
+    - name: Empty file
       uses: ./../action/.github/actions/check-codescanning-config
       with:
         expected-config-file-contents: "{}"
         languages: javascript
         tools: ${{ steps.prepare-test.outputs.tools-url }}
 
-    - name: Empty file (PR)
-      if: github.event_name == 'pull_request'
-      uses: ./../action/.github/actions/check-codescanning-config
-      with:
-        expected-config-file-contents: |
-          {
-            "query-filters": [
-              {
-                "exclude": {
-                  "tags": "exclude-from-incremental"
-                }
-              }
-            ]
-          }
-        languages: javascript
-        tools: ${{ steps.prepare-test.outputs.tools-url }}
-
     - name: Packs from input
       if: success() || failure()
       uses: ./../action/.github/actions/check-codescanning-config

@@ -4,6 +4,7 @@ See the [releases page](https://github.com/github/codeql-action/releases) for th
 
 ## [UNRELEASED]
 
+- For performance and accuracy reasons, [improved incremental analysis](https://github.com/github/roadmap/issues/1158) will now only be enabled on a pull request when diff-informed analysis is also enabled for that run. If diff-informed analysis is unavailable (for example, because the PR diff ranges could not be computed), the action will fall back to a full analysis. [#3791](https://github.com/github/codeql-action/pull/3791)
 - If multiple inputs are provided for the GitHub-internal `analysis-kinds` input, only `code-scanning` will be enabled. The `analysis-kinds` input is experimental, for GitHub-internal use only, and may change without notice at any time. [#3892](https://github.com/github/codeql-action/pull/3892)
 - Added an experimental change which, when running a Code Scanning analysis for a PR with [improved incremental analysis](https://github.com/github/roadmap/issues/1158) enabled, prefers CodeQL CLI versions that have a cached overlay-base database for the configured languages. This speeds up analysis for a repository when there is not yet a cached overlay-base database for the latest CLI version. We expect to roll this change out to everyone in May. [#3880](https://github.com/github/codeql-action/pull/3880)
 

@@ -21,6 +21,7 @@ import { GitVersionInfo } from "./git-utils";
 import { BuiltInLanguage, Language } from "./languages";
 import { getRunnerLogger } from "./logging";
 import { CODEQL_OVERLAY_MINIMUM_VERSION } from "./overlay";
+import * as overlayDiagnostics from "./overlay/diagnostics";
 import { OverlayDisabledReason } from "./overlay/diagnostics";
 import { OverlayDatabaseMode } from "./overlay/overlay-database-mode";
 import * as overlayStatus from "./overlay/status";
@@ -2143,3 +2144,87 @@ test.serial(
     });
   },
 );
+
+test("applyIncrementalAnalysisSettings: no-op when mode is not Overlay and diff ranges are unavailable", async (t) => {
+  const config = createTestConfig({});
+  config.overlayDatabaseMode = OverlayDatabaseMode.None;
+  const codeql = createStubCodeQL({});
+  const logger = getRunnerLogger(true);
+
+  await configUtils.applyIncrementalAnalysisSettings(
+    config,
+    false,
+    codeql,
+    logger,
+  );
+
+  t.is(config.overlayDatabaseMode, OverlayDatabaseMode.None);
+  t.deepEqual(config.extraQueryExclusions, []);
+});
+
+test("applyIncrementalAnalysisSettings: keeps overlay mode and adds exclusions when diff ranges are available", async (t) => {
+  const config = createTestConfig({
+    overlayDatabaseMode: OverlayDatabaseMode.Overlay,
+  });
+  const codeql = createStubCodeQL({});
+  const logger = getRunnerLogger(true);
+
+  await configUtils.applyIncrementalAnalysisSettings(
+    config,
+    true,
+    codeql,
+    logger,
+  );
+
+  t.is(config.overlayDatabaseMode, OverlayDatabaseMode.Overlay);
+  t.deepEqual(config.extraQueryExclusions, [
+    { exclude: { tags: "exclude-from-incremental" } },
+  ]);
+});
+
+test("applyIncrementalAnalysisSettings: disables overlay analysis when diff ranges are unavailable", async (t) => {
+  const config = createTestConfig({
+    overlayDatabaseMode: OverlayDatabaseMode.Overlay,
+  });
+  config.useOverlayDatabaseCaching = true;
+  const codeql = createStubCodeQL({});
+  const logger = getRunnerLogger(true);
+  const addDiagnosticsStub = sinon
+    .stub(overlayDiagnostics, "addOverlayDisablementDiagnostics")
+    .resolves();
+
+  await configUtils.applyIncrementalAnalysisSettings(
+    config,
+    false,
+    codeql,
+    logger,
+  );
+
+  t.is(config.overlayDatabaseMode, OverlayDatabaseMode.None);
+  t.is(config.useOverlayDatabaseCaching, false);
+  t.deepEqual(config.extraQueryExclusions, []);
+  t.true(addDiagnosticsStub.calledOnce);
+  t.is(
+    addDiagnosticsStub.firstCall.args[2],
+    OverlayDisabledReason.DiffInformedAnalysisNotEnabled,
+  );
+});
+
+test("applyIncrementalAnalysisSettings: adds exclusions for diff-informed-only runs", async (t) => {
+  const config = createTestConfig({});
+  config.overlayDatabaseMode = OverlayDatabaseMode.None;
+  const codeql = createStubCodeQL({});
+  const logger = getRunnerLogger(true);
+
+  await configUtils.applyIncrementalAnalysisSettings(
+    config,
+    true,
+    codeql,
+    logger,
+  );
+
+  t.is(config.overlayDatabaseMode, OverlayDatabaseMode.None);
+  t.deepEqual(config.extraQueryExclusions, [
+    { exclude: { tags: "exclude-from-incremental" } },
+  ]);
+});
@@ -31,7 +31,7 @@ import {
   addNoLanguageDiagnostic,
   makeTelemetryDiagnostic,
 } from "./diagnostics";
-import { shouldPerformDiffInformedAnalysis } from "./diff-informed-analysis-utils";
+import { prepareDiffInformedAnalysis } from "./diff-informed-analysis-utils";
 import { EnvVar } from "./environment";
 import * as errorMessages from "./error-messages";
 import { Feature, FeatureEnablement } from "./feature-flags";
@@ -1077,6 +1077,48 @@ function hasQueryCustomisation(userConfig: UserConfig): boolean {
   );
 }
 
+/**
+ * Finalize the incremental-analysis configuration for this run.
+ *
+ * Overlay analysis has only been validated in combination with diff-informed
+ * analysis, so if `Overlay` mode was selected for a pull request but the diff
+ * ranges could not be computed, fall back to a full non-overlay analysis.
+ *
+ * Query exclusions for incremental-only queries are then applied whenever the
+ * diff ranges are available — which, after the fallback above, is exactly the
+ * set of runs where any kind of incremental analysis (overlay or
+ * diff-informed) is in effect.
+ */
+export async function applyIncrementalAnalysisSettings(
+  config: Config,
+  hasDiffRanges: boolean,
+  codeql: CodeQL,
+  logger: Logger,
+): Promise<void> {
+  if (
+    config.overlayDatabaseMode === OverlayDatabaseMode.Overlay &&
+    !hasDiffRanges
+  ) {
+    logger.info(
+      `Reverting overlay database mode to ${OverlayDatabaseMode.None} ` +
+        "because the PR diff ranges could not be computed.",
+    );
+    config.overlayDatabaseMode = OverlayDatabaseMode.None;
+    config.useOverlayDatabaseCaching = false;
+    await addOverlayDisablementDiagnostics(
+      config,
+      codeql,
+      OverlayDisabledReason.DiffInformedAnalysisNotEnabled,
+    );
+  }
+
+  if (hasDiffRanges) {
+    config.extraQueryExclusions.push({
+      exclude: { tags: "exclude-from-incremental" },
+    });
+  }
+}
+
 /**
  * Load and return the config.
  *
@@ -1231,18 +1273,18 @@ 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 hasDiffRanges = await prepareDiffInformedAnalysis(
+    inputs.codeql,
+    inputs.features,
+    logger,
+  );
+
+  await applyIncrementalAnalysisSettings(
+    config,
+    hasDiffRanges,
+    inputs.codeql,
+    logger,
+  );
 
   if (await isTrapCachingEnabled(features, config.overlayDatabaseMode)) {
     const { trapCaches, trapCacheDownloadTime } = await downloadCacheWithTime(