Rust rlib vendor snapshot support.

Adds support for snapshotting Rust rlibs. This allows us
vendor-specific code that uses rlib-only linkage until dylib
snapshot support is added.

Bug: 184042776
Test: m nothing # new Soong tests pass
Test: Example test Rust vendor module builds
Test: m dist vendor-snapshot # includes rlibs
Change-Id: I4976d3e1efec0ee778cc97730d45be471dffb678
diff --git a/rust/image.go b/rust/image.go
index 6cfb42c..3b54f12 100644
--- a/rust/image.go
+++ b/rust/image.go
@@ -82,7 +82,12 @@
 }
 
 func (mod *Module) SnapshotVersion(mctx android.BaseModuleContext) string {
-	panic("Rust modules do not support snapshotting: " + mod.BaseModuleName())
+	if snapshot, ok := mod.compiler.(cc.SnapshotInterface); ok {
+		return snapshot.Version()
+	} else {
+		mctx.ModuleErrorf("version is unknown for snapshot prebuilt")
+		return ""
+	}
 }
 
 func (mod *Module) VendorRamdiskVariantNeeded(ctx android.BaseModuleContext) bool {
@@ -110,7 +115,9 @@
 }
 
 func (mod *Module) IsSnapshotPrebuilt() bool {
-	// Rust does not support prebuilts in its snapshots
+	if p, ok := mod.compiler.(cc.SnapshotInterface); ok {
+		return p.IsSnapshotPrebuilt()
+	}
 	return false
 }
 
@@ -220,7 +227,9 @@
 		}
 	}
 	if vendorSpecific {
-		mctx.PropertyErrorf("vendor", "Vendor-only non-rust_ffi Rust modules are not supported.")
+		if lib, ok := mod.compiler.(libraryInterface); ok && lib.buildDylib() {
+			mctx.PropertyErrorf("vendor", "Vendor-only dylibs are not yet supported, use rust_library_rlib.")
+		}
 	}
 
 	cc.MutateImage(mctx, mod)