From 5624ebb7c9aff39e58294745a7ccf81baa04e314 Mon Sep 17 00:00:00 2001
From: Tony <1094086026@qq.com>
Date: Fri, 22 May 2026 08:17:10 +0800
Subject: [PATCH] feat(platforms): fall back to ubuntu-latest image for
 ubuntu-slim runner

GitHub Actions' ubuntu-slim runner (1-vCPU Linux runner, in public
preview since 2025-10-28) uses the same base distro as ubuntu-latest,
so act should resolve it to the same default image instead of
printing 'Skipping unsupported platform'.

Users can still override via -P ubuntu-slim=... like any other
platform.

Fixes #6003
---
 cmd/platforms.go      |  1 +
 cmd/platforms_test.go | 31 +++++++++++++++++++++++++++++++
 2 files changed, 32 insertions(+)
 create mode 100644 cmd/platforms_test.go

diff --git a/cmd/platforms.go b/cmd/platforms.go
index 45724d752dc..aa8a42b7ef6 100644
--- a/cmd/platforms.go
+++ b/cmd/platforms.go
@@ -7,6 +7,7 @@ import (
 func (i *Input) newPlatforms() map[string]string {
 	platforms := map[string]string{
 		"ubuntu-latest": "node:16-buster-slim",
+		"ubuntu-slim":   "node:16-buster-slim",
 		"ubuntu-22.04":  "node:16-bullseye-slim",
 		"ubuntu-20.04":  "node:16-buster-slim",
 		"ubuntu-18.04":  "node:16-buster-slim",
diff --git a/cmd/platforms_test.go b/cmd/platforms_test.go
new file mode 100644
index 00000000000..886518067f5
--- /dev/null
+++ b/cmd/platforms_test.go
@@ -0,0 +1,31 @@
+package cmd
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestNewPlatformsDefaults(t *testing.T) {
+	i := &Input{}
+	platforms := i.newPlatforms()
+
+	// ubuntu-latest must be present and resolve to a default image
+	latest, ok := platforms["ubuntu-latest"]
+	assert.True(t, ok, "ubuntu-latest should be a default platform")
+	assert.NotEmpty(t, latest)
+
+	// ubuntu-slim should fall back to the same image as ubuntu-latest
+	// (GitHub's 1-vCPU runner uses the same base distro, see issue #6003)
+	slim, ok := platforms["ubuntu-slim"]
+	assert.True(t, ok, "ubuntu-slim should be a default platform")
+	assert.Equal(t, latest, slim, "ubuntu-slim should default to the same image as ubuntu-latest")
+}
+
+func TestNewPlatformsUserOverride(t *testing.T) {
+	i := &Input{platforms: []string{"ubuntu-slim=catthehacker/ubuntu:act-latest"}}
+	platforms := i.newPlatforms()
+
+	assert.Equal(t, "catthehacker/ubuntu:act-latest", platforms["ubuntu-slim"],
+		"user-supplied -P value should override the default")
+}