Disable automatic cache saves for merge queues

README.md

@@ -90,8 +90,8 @@ Have a look under [Advanced Configuration](#advanced-configuration) for detailed
     # Whether to restore the cache if found
     restore-cache: "true"
 
-    # Whether to save the cache after the run
-    save-cache: "true"
+    # Whether to save the cache after the run: true, false, or auto (disabled for merge_group events)
+    save-cache: "auto"
 
     # Suffix for the cache key
     cache-suffix: ""

__tests__/utils/inputs.test.ts

@@ -206,6 +206,51 @@ describe("loadInputs", () => {
     expect(inputs.enableCache).toBe(true);
   });
 
+  it("restores but does not save cache automatically for merge groups", () => {
+    mockInputs["working-directory"] = "/workspace";
+    mockInputs["enable-cache"] = "auto";
+    mockInputs["restore-cache"] = "true";
+    mockInputs["save-cache"] = "auto";
+    process.env.RUNNER_ENVIRONMENT = "github-hosted";
+    process.env.RUNNER_TEMP = "/runner-temp";
+    process.env.GITHUB_EVENT_NAME = "merge_group";
+
+    const inputs = loadInputs();
+
+    expect(inputs.enableCache).toBe(true);
+    expect(inputs.restoreCache).toBe(true);
+    expect(inputs.saveCache).toBe(false);
+    expect(mockInfo).toHaveBeenCalledWith(
+      "Cache saving is disabled for the merge_group event",
+    );
+  });
+
+  it.each([
+    ["true", true],
+    ["false", false],
+  ])("honors save-cache %s for merge groups", (saveCacheInput, expected) => {
+    mockInputs["working-directory"] = "/workspace";
+    mockInputs["save-cache"] = saveCacheInput;
+    process.env.GITHUB_EVENT_NAME = "merge_group";
+
+    const inputs = loadInputs();
+
+    expect(inputs.saveCache).toBe(expected);
+    expect(mockInfo).not.toHaveBeenCalledWith(
+      "Cache saving is disabled for the merge_group event",
+    );
+  });
+
+  it("automatically saves cache for other events", () => {
+    mockInputs["working-directory"] = "/workspace";
+    mockInputs["save-cache"] = "auto";
+    process.env.GITHUB_EVENT_NAME = "push";
+
+    const inputs = loadInputs();
+
+    expect(inputs.saveCache).toBe(true);
+  });
+
   it("uses cache-dir from pyproject.toml when present", () => {
     mockInputs["working-directory"] = createTempProject({
       "pyproject.toml": `[project]

action-types.yml

@@ -33,7 +33,11 @@ inputs:
   restore-cache:
     type: boolean
   save-cache:
-    type: boolean
+    type: enum
+    allowed-values:
+      - "true"
+      - "false"
+      - auto
   cache-suffix:
     type: string
   cache-local-path:

action.yml

@@ -51,8 +51,8 @@ inputs:
     description: "Whether to restore the cache if found."
     default: "true"
   save-cache:
-    description: "Whether to save the cache after the run."
-    default: "true"
+    description: "Whether to save the cache after the run. 'auto' disables saving for merge_group events."
+    default: "auto"
   cache-suffix:
     description: "Suffix for the cache key"
     required: false

docs/caching.md

@@ -139,9 +139,11 @@ By default, the cache will be restored.
 
 ## Save cache
 
-You can also disable saving the cache after the run with the `save-cache` input.
+You can control saving the cache after the run with the `save-cache` input.
 This can be useful to save cache storage when you know you will not use the cache of the run again.
-By default, the cache will be saved.
+By default, `save-cache: auto` saves the cache except for `merge_group` events, where caches created
+for temporary merge queue refs are unlikely to be reused. Cache restoration remains enabled for
+these events. Set `save-cache: true` to save the cache for all events.
 
 ```yaml
 - name: Don't save the cache after the run

src/utils/inputs.ts

@@ -60,7 +60,7 @@ export function loadInputs(): SetupInputs {
   const checksum = core.getInput("checksum");
   const enableCache = getEnableCache();
   const restoreCache = core.getInput("restore-cache") === "true";
-  const saveCache = core.getInput("save-cache") === "true";
+  const saveCache = getSaveCache();
   const cacheSuffix = core.getInput("cache-suffix") || "";
   const cacheLocalPath = getCacheLocalPath(
     workingDirectory,
@@ -189,6 +189,18 @@ function getEnableCache(): boolean {
   return enableCacheInput === "true";
 }
 
+function getSaveCache(): boolean {
+  const saveCacheInput = core.getInput("save-cache");
+  if (saveCacheInput === "auto") {
+    if (process.env.GITHUB_EVENT_NAME === "merge_group") {
+      log.info("Cache saving is disabled for the merge_group event");
+      return false;
+    }
+    return true;
+  }
+  return saveCacheInput === "true";
+}
+
 function getToolBinDir(workingDirectory: string): string | undefined {
   const toolBinDirInput = core.getInput("tool-bin-dir");
   if (toolBinDirInput !== "") {