internal/rosa: optionally bypass cross-compilation

Cross-compilation is not applicable to everything, and it is quite
wasteful rebuilding the same thing for every architecture when it is
just using host tools to create arch-independent files.

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

1 files changed, 30 insertions, 5 deletions

diff --git a/internal/rosa/rosa.go b/internal/rosa/rosa.go
index e83d7097..2241788f 100644
--- a/internal/rosa/rosa.go
+++ b/internal/rosa/rosa.go
@@ -267,8 +267,9 @@ function apply {
 	}
 
 	return t.New(name+"-src", Unversioned, nil, &PackageAttr{
-		Paths: paths,
-		Tools: P{_patch},
+		Paths:  paths,
+		Tools:  P{_patch},
+		NoArch: true,
 	}, &GenericHelper{
 		Build: buf.String(),
 	})
@@ -302,7 +303,7 @@ type Helper interface {
 
 // PackageAttr holds build-system-agnostic attributes.
 type PackageAttr struct {
-	// Measure output if populated. Required by [THostNet].
+	// Measure output if populated. Required by HostNet.
 	KnownChecksum *pkg.Checksum
 
 	// Mount the source tree writable.
@@ -337,6 +338,8 @@ type PackageAttr struct {
 	// Whether to create [pkg.KindExecNet] instead of [pkg.KindExec].
 	HostNet bool
 
+	// Whether the [Helper] behaves identically across all architectures.
+	NoArch bool
 	// Inputs added only during cross-compilation.
 	Cross P
 	// Native utilities used by the build process.
@@ -405,6 +408,10 @@ func (t Toolchain) New(
 		attr = new(PackageAttr)
 	}
 
+	if attr.NoArch {
+		t = t.native()
+	}
+
 	if attr.Std && !t.stage.isStd() {
 		panic(BootstrapError(name))
 	}
@@ -640,6 +647,17 @@ ln -s ../bin /usr/`
 	)
 }
 
+// A CrossError refers to a package that does not support cross-compilation and
+// is panicked by the helper implementation.
+type CrossError string
+
+func (e CrossError) Error() string {
+	return "package " + strconv.Quote(string(e)) +
+		" does not support cross-compilation"
+}
+
+var _ error = CrossError("")
+
 // GenericHelper directly passes build script segments for invocations of
 // one-off build scripts too specific to fit into any other [Helper]
 // implementation, but can still benefit from [Toolchain.New].
@@ -677,14 +695,21 @@ func (attr *GenericHelper) wantsDir() (string, bool) {
 }
 
 // script concatenates specified segments.
-func (attr *GenericHelper) script(t Toolchain, _ string) string {
+func (attr *GenericHelper) script(t Toolchain, name string) string {
 	if attr == nil {
 		attr = new(GenericHelper)
 	}
 
 	script := attr.Build
 	if t.cross() {
-		script = attr.Cross + script
+		if attr.Cross == "" {
+			panic(CrossError(name))
+		}
+		cross := attr.Cross
+		if cross == "\x00" {
+			cross = ""
+		}
+		script = cross + script
 	}
 	if t.opts&OptSkipCheck == 0 {
 		script += attr.Check