WalkHandler: move std::string&& to OnWalkAncient()

Needed if the implementation wants to cull asynchronously.

src/Cull.cxx

@@ -99,7 +99,7 @@ Cull::Start(FileDescriptor root_fd)
 
 void
 Cull::OnWalkAncient(WalkDirectory &directory,
-		    std::string_view filename) noexcept
+		    std::string &&filename) noexcept
 {
 	CullFile(dev_cachefiles, directory.fd, filename);
 }

src/Cull.hxx

@@ -57,6 +57,6 @@ private:
 
 	// virtual methods from WalkHandler
 	void OnWalkAncient(WalkDirectory &directory,
-			   std::string_view filename) noexcept override;
+			   std::string &&filename) noexcept override;
 	void OnWalkFinished(WalkResult &&result) noexcept override;
 };

src/WHandler.hxx

@@ -4,7 +4,7 @@
 
 #pragma once
 
-#include <string_view>
+#include <string>
 
 class FileDescriptor;
 struct WalkDirectory;
@@ -20,7 +20,7 @@ public:
          * unconditionally).
 	 */
 	virtual void OnWalkAncient(WalkDirectory &directory,
-				   std::string_view filename) noexcept = 0;
+				   std::string &&filename) noexcept = 0;
 
 	/**
 	 * The #Walk has finished completely.  This method is allowed

src/Walk.cxx

@@ -110,7 +110,7 @@ Walk::AddFile(WalkDirectory &parent, std::string &&name,
 	      FileTime atime, uint_least64_t size)
 {
 	if (atime < discard_older_than) {
-		handler.OnWalkAncient(parent, name);
+		handler.OnWalkAncient(parent, std::move(name));
 		return;
 	}
 

test/RunWalk.cxx

@@ -38,7 +38,7 @@ struct Instance final : WalkHandler {
 
 	// virtual methods from WalkHandler
 	void OnWalkAncient([[maybe_unused]] WalkDirectory &directory,
-			   std::string_view filename) noexcept override {
+			   std::string &&filename) noexcept override {
 		fmt::print("ancient {:?}\n", filename);
 	}