internal/pkg: make checksum available to cure

This enables deduplication by value as implemented in execArtifact.

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

internal/pkg/exec.go

@@ -13,6 +13,7 @@ import (
 	"strconv"
 	"syscall"
 	"time"
+	"unique"
 
 	"hakurei.app/container"
 	"hakurei.app/container/check"
@@ -37,6 +38,31 @@ type ExecPath struct {
 	W bool
 }
 
+// layers returns pathnames collected from A deduplicated by checksum.
+func (p *ExecPath) layers(f *FContext) []*check.Absolute {
+	msg := f.GetMessage()
+
+	layers := make([]*check.Absolute, 0, len(p.A))
+	checksums := make(map[unique.Handle[Checksum]]struct{}, len(p.A))
+	for i := range p.A {
+		d := p.A[len(p.A)-1-i]
+		pathname, checksum := f.GetArtifact(d)
+		if _, ok := checksums[checksum]; ok {
+			if msg.IsVerbose() {
+				msg.Verbosef(
+					"promoted layer %d as %s",
+					len(p.A)-1-i, reportName(d, f.cache.Ident(d)),
+				)
+			}
+			continue
+		}
+		checksums[checksum] = struct{}{}
+		layers = append(layers, pathname)
+	}
+	slices.Reverse(layers)
+	return layers
+}
+
 // Path returns a populated [ExecPath].
 func Path(pathname *check.Absolute, writable bool, a ...Artifact) ExecPath {
 	return ExecPath{pathname, a, writable}
@@ -299,11 +325,6 @@ func (a *execArtifact) cure(f *FContext, hostNet bool) (err error) {
 
 	temp, work := f.GetTempDir(), f.GetWorkDir()
 	for i, b := range a.paths {
-		layers := make([]*check.Absolute, len(b.A))
-		for j, d := range b.A {
-			layers[j] = f.Pathname(d)
-		}
-
 		if i == overlayWorkIndex {
 			if err = os.MkdirAll(work.String(), 0700); err != nil {
 				return
@@ -316,7 +337,7 @@ func (a *execArtifact) cure(f *FContext, hostNet bool) (err error) {
 				AbsWork,
 				work,
 				tempWork,
-				layers...,
+				b.layers(f)...,
 			)
 			continue
 		}
@@ -333,11 +354,12 @@ func (a *execArtifact) cure(f *FContext, hostNet bool) (err error) {
 			if err = os.MkdirAll(tempWork.String(), 0700); err != nil {
 				return
 			}
-			z.Overlay(b.P, tempUpper, tempWork, layers...)
-		} else if len(layers) == 1 {
-			z.Bind(layers[0], b.P, 0)
+			z.Overlay(b.P, tempUpper, tempWork, b.layers(f)...)
+		} else if len(b.A) == 1 {
+			pathname, _ := f.GetArtifact(b.A[0])
+			z.Bind(pathname, b.P, 0)
 		} else {
-			z.OverlayReadonly(b.P, layers...)
+			z.OverlayReadonly(b.P, b.layers(f)...)
 		}
 	}
 	if overlayWorkIndex < 0 {