internal/pkg: automatic overlay mount on tmp

This sets up the last Artifact to target /tmp as a writable overlay mount backed by the host side temp directory. This is useful for an Artifact containing source code to be built for another Artifact for example.

Signed-off-by: Ophestra <cat@gensokyo.uk>

internal/pkg/exec_test.go

@@ -11,6 +11,7 @@ import (
 	"testing"
 
 	"hakurei.app/container/check"
+	"hakurei.app/container/fhs"
 	"hakurei.app/container/stub"
 	"hakurei.app/hst"
 	"hakurei.app/internal/pkg"
@@ -189,6 +190,48 @@ func TestExec(t *testing.T) {
 
 			testtoolDestroy(t, base, c)
 		}, pkg.MustDecode("gFT9kprYBqEJKifJIl2sHn_3TgULWVLTU4DrYAHiGcRmcdFRZ0YtjiROW820cAEc")},
+
+		{"overlay temp", nil, func(t *testing.T, base *check.Absolute, c *pkg.Cache) {
+			c.SetStrict(true)
+			testtool, testtoolDestroy := newTesttool()
+
+			msg := message.New(log.New(os.Stderr, "container: ", 0))
+			msg.SwapVerbose(testing.Verbose())
+
+			cureMany(t, c, []cureStep{
+				{"container", pkg.NewExec(
+					t.Context(),
+					msg,
+					0,
+					nil,
+					check.MustAbs("/work"),
+					[]string{"HAKUREI_TEST=1", "HAKUREI_ROOT=1"},
+					check.MustAbs("/tmp/bin/testtool"),
+					[]string{"testtool"},
+
+					pkg.MustPath("/", stubArtifact{
+						kind:   pkg.KindTar,
+						params: []byte("empty directory"),
+						cure: func(c *pkg.CureContext) error {
+							return os.MkdirAll(c.GetWorkDir().String(), 0700)
+						},
+					}),
+					pkg.MustPath("/tmp/", stubArtifact{
+						kind:   pkg.KindTar,
+						params: []byte("empty directory"),
+						cure: func(c *pkg.CureContext) error {
+							return os.MkdirAll(c.GetWorkDir().String(), 0700)
+						},
+					}),
+					pkg.ExecContainerPath{
+						P: fhs.AbsTmp,
+						A: testtool,
+					},
+				), ignorePathname, wantChecksumOffline, nil},
+			})
+
+			testtoolDestroy(t, base, c)
+		}, pkg.MustDecode("_r1IBeMWCkLwQ9Im9w0tV9_CWIOfQlXkkP2CogPHLmZp_AB6W3_8HVZqDV00dNAm")},
 	})
 }