internal/rosa: assume file source is xz-compressed

XZ happens to be the only widely-used format that is awful to deal with, everything else is natively supported.

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

internal/pkg/tar.go

@@ -43,8 +43,7 @@ var _ fmt.Stringer = new(tarArtifactNamed)
 func (a *tarArtifactNamed) String() string { return a.name + "-unpack" }
 
 // NewTar returns a new [Artifact] backed by the supplied [Artifact] and
-// compression method. The source [Artifact] must be compatible with
-// [TContext.Open].
+// compression method. The source [Artifact] must be a [FileArtifact].
 func NewTar(a Artifact, compression uint32) Artifact {
 	ta := tarArtifact{a, compression}
 	if s, ok := a.(fmt.Stringer); ok {

internal/rosa/gnu.go

@@ -639,7 +639,6 @@ func (t Toolchain) newFindutils() (pkg.Artifact, string) {
 		nil, "https://ftpmirror.gnu.org/gnu/findutils/findutils-"+version+".tar.xz",
 		mustDecode(checksum),
 	), &PackageAttr{
-		SourceKind: SourceKindTarXZ,
 		ScriptEarly: `
 echo '#!/bin/sh' > gnulib-tests/test-c32ispunct.sh
 echo 'int main(){return 0;}' > tests/xargs/test-sigusr.c

internal/rosa/rosa.go

@@ -443,11 +443,6 @@ type Helper interface {
 	script(name string) string
 }
 
-const (
-	// SourceKindTarXZ denotes a source tarball to be decompressed using [XZ].
-	SourceKindTarXZ = 1 + iota
-)
-
 // PackageAttr holds build-system-agnostic attributes.
 type PackageAttr struct {
 	// Mount the source tree writable.
@@ -464,8 +459,6 @@ type PackageAttr struct {
 
 	// Passed to [Toolchain.NewPatchedSource].
 	Patches []KV
-	// Kind of source artifact.
-	SourceKind int
 
 	// Dependencies not provided by stage0.
 	NonStage0 []pkg.Artifact
@@ -537,11 +530,6 @@ func (t Toolchain) NewPackage(
 		panic("source must be non-nil")
 	}
 	wantsChmod, wantsWrite := helper.wantsChmod(), helper.wantsWrite()
-	if attr.SourceKind > 0 &&
-		(attr.Writable || attr.Chmod || wantsChmod || wantsWrite || len(attr.Patches) > 0) {
-		panic("source processing requested on a non-unpacked kind")
-	}
-
 	dc := len(attr.NonStage0)
 	if !t.isStage0() {
 		dc += 1<<3 + len(extra)
@@ -560,17 +548,23 @@ func (t Toolchain) NewPackage(
 		paPut(pv)
 	}
 
-	var scriptEarly string
+	var (
+		scriptEarly  string
+		sourceSuffix string
+	)
+
+	if _, ok := source.(pkg.FileArtifact); ok {
+		if attr.Writable || attr.Chmod ||
+			wantsChmod || wantsWrite ||
+			len(attr.Patches) > 0 {
+			panic("source processing requested on a xz-compressed tarball")
+		}
 
-	var sourceSuffix string
-	switch attr.SourceKind {
-	case SourceKindTarXZ:
 		sourceSuffix = ".tar.xz"
 		scriptEarly += `
 tar -C /usr/src/ -xf '/usr/src/` + name + `.tar.xz'
 mv '/usr/src/` + name + `-` + version + `' '/usr/src/` + name + `'
 `
-		break
 	}
 
 	dir := helper.wantsDir()

internal/rosa/strace.go

@@ -11,8 +11,6 @@ func (t Toolchain) newStrace() (pkg.Artifact, string) {
 		nil, "https://strace.io/files/"+version+"/strace-"+version+".tar.xz",
 		mustDecode(checksum),
 	), &PackageAttr{
-		SourceKind: SourceKindTarXZ,
-
 		// patch not possible with nonzero SourceKind
 		ScriptEarly: `
 sed -i 's/off64_t/off_t/g' \