fs/Traits: add overload GetParent(string_view)

src/fs/Traits.cxx

@@ -84,6 +84,22 @@ GetParentPathImpl(typename Traits::const_pointer p) noexcept
 	return {p, size_t(sep - p)};
 }
 
+template<typename Traits>
+typename Traits::string_view
+GetParentPathImpl(typename Traits::string_view p) noexcept
+{
+	auto sep = Traits::FindLastSeparator(p);
+	if (sep == nullptr)
+		return Traits::CURRENT_DIRECTORY;
+	if (sep == p.data())
+		return p.substr(0, 1);
+#ifdef _WIN32
+	if (Traits::IsDrive(p) && sep == p.data() + 2)
+		return p.substr(0, 3);
+#endif
+	return p.substr(0, sep - p.data());
+}
+
 template<typename Traits>
 typename Traits::const_pointer
 RelativePathImpl(typename Traits::string_view base,
@@ -166,6 +182,12 @@ PathTraitsFS::GetParent(PathTraitsFS::const_pointer p) noexcept
 	return GetParentPathImpl<PathTraitsFS>(p);
 }
 
+PathTraitsFS::string_view
+PathTraitsFS::GetParent(string_view p) noexcept
+{
+	return GetParentPathImpl<PathTraitsFS>(p);
+}
+
 PathTraitsFS::const_pointer
 PathTraitsFS::Relative(string_view base, const_pointer other) noexcept
 {
@@ -210,6 +232,12 @@ PathTraitsUTF8::GetParent(const_pointer p) noexcept
 	return GetParentPathImpl<PathTraitsUTF8>(p);
 }
 
+PathTraitsUTF8::string_view
+PathTraitsUTF8::GetParent(string_view p) noexcept
+{
+	return GetParentPathImpl<PathTraitsUTF8>(p);
+}
+
 PathTraitsUTF8::const_pointer
 PathTraitsUTF8::Relative(string_view base, const_pointer other) noexcept
 {

src/fs/Traits.hxx

@@ -88,6 +88,18 @@ struct PathTraitsFS {
 #endif
 	}
 
+	[[gnu::pure]]
+	static const_pointer FindLastSeparator(string_view p) noexcept {
+#ifdef _WIN32
+		const_pointer pos = p.data() + p.size();
+		while (p.data() != pos && !IsSeparator(*pos))
+			--pos;
+		return IsSeparator(*pos) ? pos : nullptr;
+#else
+		return StringFindLast(p.data(), SEPARATOR, p.size());
+#endif
+	}
+
 	gcc_pure
 	static const_pointer GetFilenameSuffix(const_pointer filename) noexcept {
 		const_pointer dot = StringFindLast(filename, '.');
@@ -106,6 +118,10 @@ struct PathTraitsFS {
 	static constexpr bool IsDrive(const_pointer p) noexcept {
 		return IsAlphaASCII(p[0]) && p[1] == ':';
 	}
+
+	static constexpr bool IsDrive(string_view p) noexcept {
+		return p.size() >= 2 && IsAlphaASCII(p[0]) && p[1] == ':';
+	}
 #endif
 
 	gcc_pure gcc_nonnull_all
@@ -153,6 +169,9 @@ struct PathTraitsFS {
 	gcc_pure gcc_nonnull_all
 	static string_view GetParent(const_pointer p) noexcept;
 
+	[[gnu::pure]]
+	static string_view GetParent(string_view p) noexcept;
+
 	/**
 	 * Determine the relative part of the given path to this
 	 * object, not including the directory separator.  Returns an
@@ -212,6 +231,11 @@ struct PathTraitsUTF8 {
 		return std::strrchr(p, SEPARATOR);
 	}
 
+	[[gnu::pure]]
+	static const_pointer FindLastSeparator(string_view p) noexcept {
+		return StringFindLast(p.data(), SEPARATOR, p.size());
+	}
+
 	gcc_pure
 	static const_pointer GetFilenameSuffix(const_pointer filename) noexcept {
 		const_pointer dot = StringFindLast(filename, '.');
@@ -230,6 +254,10 @@ struct PathTraitsUTF8 {
 	static constexpr bool IsDrive(const_pointer p) noexcept {
 		return IsAlphaASCII(p[0]) && p[1] == ':';
 	}
+
+	static constexpr bool IsDrive(string_view p) noexcept {
+		return p.size() >= 2 && IsAlphaASCII(p[0]) && p[1] == ':';
+	}
 #endif
 
 	gcc_pure gcc_nonnull_all
@@ -277,6 +305,9 @@ struct PathTraitsUTF8 {
 	gcc_pure gcc_nonnull_all
 	static string_view GetParent(const_pointer p) noexcept;
 
+	[[gnu::pure]]
+	static string_view GetParent(string_view p) noexcept;
+
 	/**
 	 * Determine the relative part of the given path to this
 	 * object, not including the directory separator.  Returns an