fs/Path: add WithSuffix()

src/fs/AllocatedPath.cxx

@@ -48,6 +48,21 @@ AllocatedPath::FromUTF8Throw(std::string_view path_utf8)
 #endif
 }
 
+void
+AllocatedPath::SetSuffix(const_pointer new_suffix) noexcept
+{
+	assert(new_suffix != nullptr);
+	assert(*new_suffix == '.');
+
+	const auto end = value.end();
+	auto begin = end;
+
+	if (auto old = GetSuffix())
+		begin = std::next(value.begin(), old - value.data());
+
+	value.replace(begin, end, new_suffix);
+}
+
 void
 AllocatedPath::ChopSeparators() noexcept
 {

src/fs/AllocatedPath.hxx

@@ -304,6 +304,27 @@ public:
 		return Path{*this}.GetSuffix();
 	}
 
+	/**
+	 * Replace the suffix of this path (or append the suffix if
+	 * there is none currently).
+	 *
+	 * @param new_suffix the new filename suffix (must start with
+	 * a dot)
+	 */
+	void SetSuffix(const_pointer new_suffix) noexcept;
+
+	/**
+	 * Return a copy of this path but with the given suffix
+	 * (replacing the existing suffix if there is one).
+	 *
+	 * @param new_suffix the new filename suffix (must start with
+	 * a dot)
+	 */
+	[[gnu::pure]]
+	AllocatedPath WithSuffix(const_pointer new_suffix) const noexcept {
+		return Path{*this}.WithSuffix(new_suffix);
+	}
+
 	/**
 	 * Returns the filename extension (excluding the dot) or
 	 * nullptr if the path does not have one.

src/fs/Path.hxx

@@ -173,6 +173,16 @@ public:
 	[[gnu::pure]]
 	const_pointer GetSuffix() const noexcept;
 
+	/**
+	 * Return a copy of this path but with the given suffix
+	 * (replacing the existing suffix if there is one).
+	 *
+	 * @param new_suffix the new filename suffix (must start with
+	 * a dot)
+	 */
+	[[gnu::pure]]
+	AllocatedPath WithSuffix(const_pointer new_suffix) const noexcept;
+
 	/**
 	 * Returns the filename extension (excluding the dot) or
 	 * nullptr if the path does not have one.

src/fs/Path2.cxx

@@ -26,6 +26,14 @@ Path::GetDirectoryName() const noexcept
 	return AllocatedPath::FromFS(PathTraitsFS::GetParent(c_str()));
 }
 
+AllocatedPath
+Path::WithSuffix(const_pointer new_suffix) const noexcept
+{
+	AllocatedPath result{*this};
+	result.SetSuffix(new_suffix);
+	return result;
+}
+
 AllocatedPath
 operator/(Path a, Path b) noexcept
 {

test/fs/TestPath.cxx

@@ -96,3 +96,14 @@ TEST(Path, Suffix)
 	EXPECT_STREQ(Path::FromFS(PATH_LITERAL("/foo/.bar.abc")).GetSuffix(), ".abc");
 	EXPECT_STREQ(Path::FromFS(PATH_LITERAL("/foo/.bar.abc.def")).GetSuffix(), ".def");
 }
+
+TEST(Path, WithSuffix)
+{
+	EXPECT_STREQ(Path::FromFS(PATH_LITERAL("foo")).WithSuffix(".abc").c_str(), "foo.abc");
+	EXPECT_STREQ(Path::FromFS(PATH_LITERAL("/foo/bar")).WithSuffix(".abc").c_str(), "/foo/bar.abc");
+	EXPECT_STREQ(Path::FromFS(PATH_LITERAL("/foo.xyz/bar")).WithSuffix(".abc").c_str(), "/foo.xyz/bar.abc");
+	EXPECT_STREQ(Path::FromFS(PATH_LITERAL("/foo.abc/bar.def")).WithSuffix(".xyz").c_str(), "/foo.abc/bar.xyz");
+	EXPECT_STREQ(Path::FromFS(PATH_LITERAL("/foo.abc/bar.def.ghi")).WithSuffix(".xyz").c_str(), "/foo.abc/bar.def.xyz");
+	EXPECT_STREQ(Path::FromFS(PATH_LITERAL("/foo/.bar.abc")).WithSuffix(".xyz").c_str(), "/foo/.bar.xyz");
+	EXPECT_STREQ(Path::FromFS(PATH_LITERAL("/foo/.bar.abc.def")).WithSuffix(".xyz").c_str(), "/foo/.bar.abc.xyz");
+}