internal/rosa: remove xz utils hack

This replaces all xz invocations with the native decompressor. This also significantly cleans up the Gentoo stage3 bootstrap path.

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

internal/rosa/state.go

@@ -213,10 +213,8 @@ type S struct {
 	// Cached [pkg.Artifact].
 	c [_stageEnd]sync.Map
 
-	// URL of a Gentoo stage3 tarball.
-	gentooStage3 string
-	// Expected checksum of gentooStage3.
-	gentooStage3Checksum pkg.Checksum
+	// Unpacked Gentoo LLVM stage3.
+	gentooStage3 pkg.Artifact
 }
 
 // Clone returns a copy of s.
@@ -485,6 +483,7 @@ func (s *S) getFrame() azalea.Frame {
 			k("gzip"):         pkg.Gzip + compressOffset,
 			k("bzip2"):        pkg.Bzip2 + compressOffset,
 			k("zstd"):         pkg.Zstd + compressOffset,
+			k("xz"):           pkg.XZ + compressOffset,
 		}
 
 		s.frame.Val = map[unique.Handle[azalea.Ident]]any{
@@ -803,6 +802,7 @@ func (s *S) getFrame() azalea.Frame {
 				k("gzip"):  uint32(pkg.Gzip),
 				k("bzip2"): uint32(pkg.Bzip2),
 				k("zstd"):  uint32(pkg.Zstd),
+				k("xz"):    uint32(pkg.XZ),
 			}},
 
 			// high-level helpers
@@ -1372,12 +1372,15 @@ func (s *S) SetSource(fsys fs.FS) error {
 // SetGentooStage3 sets the Gentoo stage3 tarball url and checksum. It panics
 // if given zero values or if these values have already been set.
 func (s *S) SetGentooStage3(url string, checksum pkg.Checksum) {
-	if s.gentooStage3 != "" {
+	if s.gentooStage3 != nil {
 		panic(errors.New("attempting to set Gentoo stage3 url twice"))
 	}
 	if url == "" {
 		panic(errors.New("attempting to set Gentoo stage3 url to the zero value"))
 	}
-	s.gentooStage3, s.gentooStage3Checksum = url, checksum
+	s.gentooStage3 = pkg.NewTar(pkg.NewDecompress(
+		pkg.NewHTTPGet(nil, url, checksum),
+		pkg.XZ,
+	))
 	s.DropCaches(s.Arch(), s.Flags())
 }