feat: expose builder name output

Author: mkusaka

README.md

@@ -60,6 +60,12 @@ This action follows semantic versioning and supports multiple referencing patter
 | `max-parallelism`      | Maximum number of concurrent BuildKit RUN steps. Defaults to the number of vCPUs on the runner                | No       |                |
 | `max-cache-size-mb`    | Amount of build cache to retain after pruning, in MB (e.g., 409600 for 400GB). If not set, pruning is skipped | No       |                |
 
+## Outputs
+
+| Name   | Description  |
+| ------ | ------------ |
+| `name` | Builder name |
+
 ## Example Workflows
 
 ### Basic usage with build-push-action

action.yml

@@ -35,6 +35,9 @@ inputs:
   max-cache-size-mb:
     description: "Amount of build cache to retain after pruning, in MB (e.g., 409600 for 400GB). If not set, pruning is skipped."
     required: false
+outputs:
+  name:
+    description: "Builder name"
 runs:
   using: node24
   main: dist/index.js

dist/index.js

@@ -7,6 +7,7 @@ vi.mock("@actions/core", () => ({
   getInput: vi.fn(),
   getBooleanInput: vi.fn(),
   setFailed: vi.fn(),
+  setOutput: vi.fn(),
   warning: vi.fn(),
   info: vi.fn(),
   debug: vi.fn(),

dist/index.js.map

@@ -718,6 +718,8 @@ void actionsToolkit.run(
             );
           }
         });
+
+        core.setOutput("name", name);
       });
 
       // Print builder info
@@ -738,13 +740,15 @@ void actionsToolkit.run(
             core.info(
               `Found configured builder: ${builder.name} (driver: ${builder.driver})`,
             );
+            core.setOutput("name", builder.name);
           } else {
             // Create a local builder
-            const createLocalBuilderCmd =
-              "docker buildx create --name local --driver docker-container --use";
+            const localBuilderName = "local";
+            const createLocalBuilderCmd = `docker buildx create --name ${localBuilderName} --driver docker-container --use`;
             try {
               await Exec.exec(createLocalBuilderCmd);
               core.info("Created and set a local builder for use");
+              core.setOutput("name", localBuilderName);
             } catch (error) {
               core.setFailed(
                 `Failed to create local builder: ${(error as Error).message}`,