From 2613b9ca2bc0061a584d1218ea0cbb5f9a6175fb Mon Sep 17 00:00:00 2001
From: "Michael B. Gale" <mbg@github.com>
Date: Fri, 9 Oct 2026 23:38:11 +0100
Subject: [PATCH] Fix `flushDiagnostics` not ensuring directories exist

---
 lib/entry-points.js     | 13 +++++++++++--
 src/diagnostics.test.ts |  3 +--
 src/diagnostics.ts      | 16 +++++++++++++---
 3 files changed, 25 insertions(+), 7 deletions(-)

diff --git a/lib/entry-points.js b/lib/entry-points.js
index 54362e40d..7376558e1 100644
--- a/lib/entry-points.js
+++ b/lib/entry-points.js
@@ -173070,6 +173070,7 @@ function flushDiagnostics(action, config) {
   action.logger.debug(
     `Moving ${diagnosticsCount} diagnostic(s) to their respective databases.`
   );
+  const failedFlushDiagnostics = [];
   for (const temporary of temporaryDiagnostics) {
     const directory = getDatabaseDiagnosticsPath(
       config,
@@ -173077,9 +173078,17 @@ function flushDiagnostics(action, config) {
     );
     const filename = import_path2.default.basename(temporary.path);
     const destination = import_path2.default.join(directory, filename);
-    action.fs.renameSync(temporary.path, destination);
+    try {
+      action.fs.mkdirSync(directory, { recursive: true });
+      action.fs.renameSync(temporary.path, destination);
+    } catch (err) {
+      action.logger.warning(
+        `Failed to rename '${temporary.path}' to '${destination}': ${getErrorMessage(err)}`
+      );
+      failedFlushDiagnostics.push(temporary);
+    }
   }
-  temporaryDiagnostics = [];
+  temporaryDiagnostics = failedFlushDiagnostics;
 }
 function makeTelemetryDiagnostic(id, name, attributes, tags) {
   return makeDiagnostic(id, name, {
diff --git a/src/diagnostics.test.ts b/src/diagnostics.test.ts
index e721dfc52..7d898defc 100644
--- a/src/diagnostics.test.ts
+++ b/src/diagnostics.test.ts
@@ -88,9 +88,8 @@ test("addDiagnostic writes temporary diagnostics and flushDiagnostics moves them
     );
   });
 
-  // addDiagnostic
   t.is(existsSync.callCount, 1);
-  t.is(mkdirSync.callCount, 1);
+  t.is(mkdirSync.callCount, 2);
   t.is(writeFileSync.callCount, 1);
   t.is(writeFileSync.args[0].length, 2);
   t.is(writeFileSync.args[0][1], JSON.stringify(diagnostic));
diff --git a/src/diagnostics.ts b/src/diagnostics.ts
index 3563e41f4..a29ef25ec 100644
--- a/src/diagnostics.ts
+++ b/src/diagnostics.ts
@@ -7,7 +7,7 @@ import type { Config } from "./config-utils";
 import type { FileSystem } from "./fs";
 import { Language } from "./languages";
 import { getActionsLogger, type Logger } from "./logging";
-import { getCodeQLDatabasePath } from "./util";
+import { getCodeQLDatabasePath, getErrorMessage } from "./util";
 
 /**
  * Known tags for diagnostics. There is currently only "internal-error",
@@ -304,6 +304,7 @@ export function flushDiagnostics(
     `Moving ${diagnosticsCount} diagnostic(s) to their respective databases.`,
   );
 
+  const failedFlushDiagnostics: TemporaryDiagnostic[] = [];
   for (const temporary of temporaryDiagnostics) {
     // If `temporary.language` is `undefined`, then we didn't have a `config` at the time that
     // `addNoLanguageDiagnostic` was called. In that case, we arbitrarily choose the first
@@ -315,11 +316,20 @@ export function flushDiagnostics(
     const filename = path.basename(temporary.path);
     const destination = path.join(directory, filename);
 
-    action.fs.renameSync(temporary.path, destination);
+    try {
+      action.fs.mkdirSync(directory, { recursive: true });
+      action.fs.renameSync(temporary.path, destination);
+    } catch (err) {
+      action.logger.warning(
+        `Failed to rename '${temporary.path}' to '${destination}': ${getErrorMessage(err)}`,
+      );
+
+      failedFlushDiagnostics.push(temporary);
+    }
   }
 
   // Reset the temporary diagnostics arrays.
-  temporaryDiagnostics = [];
+  temporaryDiagnostics = failedFlushDiagnostics;
 }
 
 /**