limayaml: do not default containerd.user=true on non-Linux guests

FillDefault enabled containerd.user=true whenever the guest arch was
x86_64 or aarch64, with no check on the guest OS. macOS (os: Darwin)
and FreeBSD guests therefore defaulted to containerd.user=true even
though nerdctl is a Linux-only runtime, causing the ~250 MiB nerdctl
archive to be downloaded unnecessarily.

Gate the true default on *y.OS == limatype.LINUX. Behavior for Linux
guests is unchanged; non-Linux guests now default to
containerd.user=false on every architecture. Explicit
containerd.user=true in user YAML is preserved.

Add TestContainerdUserDefaultPerOS covering the Linux/Darwin/FreeBSD
matrix and TestContainerdUserExplicitOverride to lock the override
path.

Fixes #5037

Signed-off-by: gaurav0107 <gauravdubey0107@gmail.com>

Author: gaurav0107

pkg/limayaml/defaults.go

@@ -528,10 +528,17 @@ func FillDefault(ctx context.Context, y, d, o *limatype.LimaYAML, filePath strin
 		y.Containerd.User = o.Containerd.User
 	}
 	if y.Containerd.User == nil {
-		switch *y.Arch {
-		case limatype.X8664, limatype.AARCH64:
-			y.Containerd.User = ptr.Of(true)
-		default:
+		// nerdctl is a Linux-only container runtime; only default
+		// containerd.user=true when the guest OS is Linux. Otherwise
+		// downloading the nerdctl archive (~250 MiB) is wasted I/O.
+		if *y.OS == limatype.LINUX {
+			switch *y.Arch {
+			case limatype.X8664, limatype.AARCH64:
+				y.Containerd.User = ptr.Of(true)
+			default:
+				y.Containerd.User = ptr.Of(false)
+			}
+		} else {
 			y.Containerd.User = ptr.Of(false)
 		}
 	}

pkg/limayaml/defaults_test.go

@@ -887,3 +887,54 @@ func TestMountTagDuplicateLocation(t *testing.T) {
 	tag2 := MountTag(location, "/mnt/home-writable")
 	assert.Assert(t, tag1 != tag2)
 }
+
+// TestContainerdUserDefaultPerOS verifies that FillDefault only enables
+// containerd.user=true on Linux guests. nerdctl is a Linux-only runtime,
+// so non-Linux guests (Darwin, FreeBSD) must default to false regardless
+// of the host architecture. Regression test for issue #5037.
+func TestContainerdUserDefaultPerOS(t *testing.T) {
+	cases := []struct {
+		os   limatype.OS
+		arch limatype.Arch
+		want bool
+	}{
+		{limatype.LINUX, limatype.X8664, true},
+		{limatype.LINUX, limatype.AARCH64, true},
+		{limatype.LINUX, limatype.RISCV64, false},
+		{limatype.LINUX, limatype.ARMV7L, false},
+		{limatype.DARWIN, limatype.AARCH64, false},
+		{limatype.DARWIN, limatype.X8664, false},
+		{limatype.FREEBSD, limatype.X8664, false},
+		{limatype.FREEBSD, limatype.AARCH64, false},
+	}
+	for _, tc := range cases {
+		t.Run(fmt.Sprintf("%s/%s", tc.os, tc.arch), func(t *testing.T) {
+			y := limatype.LimaYAML{
+				OS:   ptr.Of(tc.os),
+				Arch: ptr.Of(tc.arch),
+			}
+			var d, o limatype.LimaYAML
+			FillDefault(t.Context(), &y, &d, &o, "", false)
+			assert.Assert(t, y.Containerd.User != nil, "Containerd.User must be set after FillDefault")
+			assert.Equal(t, *y.Containerd.User, tc.want,
+				"Containerd.User default for OS=%s Arch=%s", tc.os, tc.arch)
+		})
+	}
+}
+
+// TestContainerdUserExplicitOverride verifies FillDefault respects an
+// explicit containerd.user=true value even on non-Linux guests.
+func TestContainerdUserExplicitOverride(t *testing.T) {
+	y := limatype.LimaYAML{
+		OS:   ptr.Of(limatype.DARWIN),
+		Arch: ptr.Of(limatype.AARCH64),
+		Containerd: limatype.Containerd{
+			User: ptr.Of(true),
+		},
+	}
+	var d, o limatype.LimaYAML
+	FillDefault(t.Context(), &y, &d, &o, "", false)
+	assert.Assert(t, y.Containerd.User != nil)
+	assert.Equal(t, *y.Containerd.User, true,
+		"explicit Containerd.User=true must be preserved on non-Linux guests")
+}