Disable missing diff-ranges fallback when overlay enabled manually

github · henrymercer · Jun 2, 2026 · May 20, 2026 · May 20, 2026 · May 20, 2026
commit 524532393a46071bdfc81527a811ffa69e16723a
@@ -1044,6 +1044,7 @@ const checkOverlayEnablementMacro = makeMacro({
       | {
           overlayDatabaseMode: OverlayDatabaseMode;
           useOverlayDatabaseCaching: boolean;
+          overlayModeSetExplicitly?: boolean;
         }
       | {
           disabledReason: OverlayDisabledReason;
@@ -1124,7 +1125,13 @@ const checkOverlayEnablementMacro = makeMacro({
         if ("disabledReason" in expected) {
           t.deepEqual(result, new Failure(expected.disabledReason));
         } else {
-          t.deepEqual(result, new Success(expected));
+          t.deepEqual(
+            result,
+            new Success({
+              overlayModeSetExplicitly: false,
+              ...expected,
+            }),
+          );
         }
       } finally {
         // Restore the original environment
@@ -1143,6 +1150,7 @@ checkOverlayEnablementMacro.serial(
   {
     overlayDatabaseMode: OverlayDatabaseMode.Overlay,
     useOverlayDatabaseCaching: false,
+    overlayModeSetExplicitly: true,
   },
 );
 
@@ -1154,6 +1162,7 @@ checkOverlayEnablementMacro.serial(
   {
     overlayDatabaseMode: OverlayDatabaseMode.OverlayBase,
     useOverlayDatabaseCaching: false,
+    overlayModeSetExplicitly: true,
   },
 );
 
@@ -1812,6 +1821,7 @@ checkOverlayEnablementMacro.serial(
   {
     overlayDatabaseMode: OverlayDatabaseMode.Overlay,
     useOverlayDatabaseCaching: false,
+    overlayModeSetExplicitly: true,
   },
 );
 
@@ -1824,6 +1834,7 @@ checkOverlayEnablementMacro.serial(
   {
     overlayDatabaseMode: OverlayDatabaseMode.Overlay,
     useOverlayDatabaseCaching: false,
+    overlayModeSetExplicitly: true,
   },
 );
 
@@ -1920,6 +1931,7 @@ checkOverlayEnablementMacro.serial(
   {
     overlayDatabaseMode: OverlayDatabaseMode.Overlay,
     useOverlayDatabaseCaching: false,
+    overlayModeSetExplicitly: true,
   },
 );
 
@@ -1965,6 +1977,7 @@ checkOverlayEnablementMacro.serial(
   {
     overlayDatabaseMode: OverlayDatabaseMode.Overlay,
     useOverlayDatabaseCaching: false,
+    overlayModeSetExplicitly: true,
   },
 );
 
@@ -2182,33 +2195,64 @@ test("applyIncrementalAnalysisSettings: keeps overlay mode and adds exclusions w
   ]);
 });
 
-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();
+test.serial(
+  "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,
+    );
 
-  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,
+    );
+  },
+);
 
-  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.serial(
+  "applyIncrementalAnalysisSettings: keeps overlay mode when set explicitly and diff ranges are unavailable",
+  async (t) => {
+    const config = createTestConfig({
+      overlayDatabaseMode: OverlayDatabaseMode.Overlay,
+    });
+    config.useOverlayDatabaseCaching = false;
+    config.overlayModeSetExplicitly = 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.Overlay);
+    t.is(config.useOverlayDatabaseCaching, false);
+    t.deepEqual(config.extraQueryExclusions, []);
+    t.true(addDiagnosticsStub.notCalled);
+  },
+);
 
 test("applyIncrementalAnalysisSettings: adds exclusions for diff-informed-only runs", async (t) => {
   const config = createTestConfig({});

@@ -243,6 +243,11 @@ export interface Config {
    */
   useOverlayDatabaseCaching: boolean;
 
+  /**
+   * Whether the overlay database mode was set explicitly.
+   */
+  overlayModeSetExplicitly: boolean;
+
   /**
    * A partial mapping from repository properties that affect us to their values.
    */
@@ -573,6 +578,7 @@ export async function initActionState(
     extraQueryExclusions: [],
     overlayDatabaseMode: OverlayDatabaseMode.None,
     useOverlayDatabaseCaching: false,
+    overlayModeSetExplicitly: false,
     repositoryProperties,
     enableFileCoverageInformation,
   };
@@ -772,6 +778,7 @@ async function checkRunnerResources(
 interface EnabledOverlayConfig {
   overlayDatabaseMode: Exclude<OverlayDatabaseMode, OverlayDatabaseMode.None>;
   useOverlayDatabaseCaching: boolean;
+  overlayModeSetExplicitly: boolean;
 }
 
 /**
@@ -826,6 +833,7 @@ export async function checkOverlayEnablement(
     return validateOverlayDatabaseMode(
       modeEnv,
       false,
+      true,
       codeql,
       languages,
       sourceRoot,
@@ -917,6 +925,7 @@ export async function checkOverlayEnablement(
   return validateOverlayDatabaseMode(
     overlayDatabaseMode,
     true,
+    false,
     codeql,
     languages,
     sourceRoot,
@@ -935,6 +944,7 @@ export async function checkOverlayEnablement(
 async function validateOverlayDatabaseMode(
   overlayDatabaseMode: Exclude<OverlayDatabaseMode, OverlayDatabaseMode.None>,
   useOverlayDatabaseCaching: boolean,
+  overlayModeSetExplicitly: boolean,
   codeql: CodeQL,
   languages: Language[],
   sourceRoot: string,
@@ -1006,6 +1016,7 @@ async function validateOverlayDatabaseMode(
   return new Success({
     overlayDatabaseMode,
     useOverlayDatabaseCaching,
+    overlayModeSetExplicitly,
   });
 }
 
@@ -1080,14 +1091,14 @@ 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.
+ * 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. If the overlay mode was set explicitly, this fallback does
+ * not apply.
  *
- * 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.
+ * 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,
@@ -1097,7 +1108,8 @@ export async function applyIncrementalAnalysisSettings(
 ): Promise<void> {
   if (
     config.overlayDatabaseMode === OverlayDatabaseMode.Overlay &&
-    !hasDiffRanges
+    !hasDiffRanges &&
+    !config.overlayModeSetExplicitly
   ) {
     logger.info(
       `Reverting overlay database mode to ${OverlayDatabaseMode.None} ` +
@@ -1251,14 +1263,18 @@ export async function initConfig(
     logger,
   );
   if (overlayDatabaseModeResult.isSuccess()) {
-    const { overlayDatabaseMode, useOverlayDatabaseCaching } =
-      overlayDatabaseModeResult.value;
+    const {
+      overlayDatabaseMode,
+      useOverlayDatabaseCaching,
+      overlayModeSetExplicitly,
+    } = overlayDatabaseModeResult.value;
     logger.info(
       `Using overlay database mode: ${overlayDatabaseMode} ` +
         `${useOverlayDatabaseCaching ? "with" : "without"} caching.`,
     );
     config.overlayDatabaseMode = overlayDatabaseMode;
     config.useOverlayDatabaseCaching = useOverlayDatabaseCaching;
+    config.overlayModeSetExplicitly = overlayModeSetExplicitly;
   } else {
     const overlayDisabledReason = overlayDatabaseModeResult.value;
     logger.info(

@@ -585,6 +585,7 @@ export function createTestConfig(overrides: Partial<Config>): Config {
       extraQueryExclusions: [],
       overlayDatabaseMode: OverlayDatabaseMode.None,
       useOverlayDatabaseCaching: false,
+      overlayModeSetExplicitly: false,
       repositoryProperties: {},
       enableFileCoverageInformation: true,
     } satisfies Config,