rust: move crateRootPath to compiler

Test: m nothing
Bug: 309943184
Change-Id: I45028945357c394301d93ca7995a4f9adf281931
diff --git a/rust/compiler.go b/rust/compiler.go
index 9666ce2..98bbcb6 100644
--- a/rust/compiler.go
+++ b/rust/compiler.go
@@ -70,6 +70,8 @@
 
 	unstrippedOutputFilePath() android.Path
 	strippedOutputFilePath() android.OptionalPath
+
+	crateRootPath(ctx ModuleContext) android.Path
 }
 
 func (compiler *baseCompiler) edition() string {
@@ -537,6 +539,15 @@
 	return String(compiler.Properties.Relative_install_path)
 }
 
+func (compiler *baseCompiler) crateRootPath(ctx ModuleContext) android.Path {
+	if compiler.Properties.Crate_root == nil {
+		path, _ := srcPathFromModuleSrcs(ctx, compiler.Properties.Srcs)
+		return path
+	} else {
+		return android.PathForModuleSrc(ctx, *compiler.Properties.Crate_root)
+	}
+}
+
 // Returns the Path for the main source file along with Paths for generated source files from modules listed in srcs.
 func srcPathFromModuleSrcs(ctx ModuleContext, srcs []string) (android.Path, android.Paths) {
 	if len(srcs) == 0 {