[Project] Css: Tidy up lambdas

CMakeLists.txt

 		"${CMAKE_SOURCE_DIR}/contrib/frozen/include"
 		"${CMAKE_SOURCE_DIR}/contrib/fmt/include"
 		"${CMAKE_SOURCE_DIR}/contrib/doctest"
-		"${CMAKE_BINARY_DIR}/contrib/fu2/include"
+		"${CMAKE_SOURCE_DIR}/contrib/fu2/include"
 		"${CMAKE_BINARY_DIR}/src" #Stored in the binary dir
 		"${CMAKE_BINARY_DIR}/src/libcryptobox")
 

src/libserver/css/css_parser.cxx

 {
 	css_parser parser(pool);
 
-	/*
-	 * We use shared ptr here to avoid std::function limitation around
-	 * unique_ptr due to copyable of std::function
-	 * Hence, to elongate consumed_blocks lifetime we need to copy them
-	 * inside lambda.
-	 */
-	std::shared_ptr<css_consumed_block> consumed_blocks = parser.consume_css_blocks(st);
+	auto &&consumed_blocks = parser.consume_css_blocks(st);
 	const auto &rules = consumed_blocks->get_blocks_or_empty();
 
 	auto rules_it = rules.begin();
 	auto cur = children.begin();
 	auto last = children.end();
 
-	return [cur, consumed_blocks, last](void) mutable -> const css_consumed_block & {
+	/*
+	 * We use move only wrapper to state the fact that the cosumed blocks
+	 * are moved into the closure, not copied.
+	 * It prevents us from thinking about copies of the blocks and
+	 * functors.
+	 * Mutable lambda is required to copy iterators inside of the closure,
+	 * as, again, it is C++ where lifetime of the objects must be explicitly
+	 * transferred. On the other hand, we could move all stuff inside and remove
+	 * mutable.
+	 */
+	return [cur, consumed_blocks = std::move(consumed_blocks), last](void) mutable
+		-> const css_consumed_block & {
 		if (cur != last) {
 			const auto &ret = (*cur);
 

src/libserver/css/css_parser.hxx

 #include <memory>
 #include <string>
 
+#include "function2/function2.hpp"
 #include "css_tokeniser.hxx"
 #include "parse_error.hxx"
 #include "contrib/expected/expected.hpp"
 
 extern const css_consumed_block css_parser_eof_block;
 
-using blocks_gen_functor = std::function<const css_consumed_block &(void)>;
+using blocks_gen_functor = fu2::unique_function<const css_consumed_block &(void)>;
 
 class css_style_sheet;
 auto parse_css(rspamd_mempool_t *pool, const std::string_view &st) ->

src/libserver/css/css_rule.cxx

 }
 
 auto process_declaration_tokens(rspamd_mempool_t *pool,
-								const blocks_gen_functor &next_block_functor)
+								blocks_gen_functor &&next_block_functor)
 	-> css_declarations_block_ptr
 {
 	css_declarations_block_ptr ret;

src/libserver/css/css_rule.hxx

 using css_declarations_block_ptr = std::shared_ptr<css_declarations_block>;
 
 auto process_declaration_tokens(rspamd_mempool_t *pool,
-							 const blocks_gen_functor &next_token_functor)
+								blocks_gen_functor &&next_token_functor)
 	-> css_declarations_block_ptr;
 
 }

src/libserver/css/css_selector.cxx

 namespace rspamd::css {
 
 auto process_selector_tokens(rspamd_mempool_t *pool,
-							 const blocks_gen_functor &next_token_functor)
+							 blocks_gen_functor &&next_token_functor)
 	-> selectors_vec
 {
 	selectors_vec ret;

src/libserver/css/css_selector.hxx

 #include <string>
 #include <optional>
 #include <vector>
-#include <functional>
 #include <memory>
 
+#include "function2/function2.hpp"
 #include "parse_error.hxx"
 #include "css_parser.hxx"
 #include "html_tags.h"
  * Consume selectors token and split them to the list of selectors
  */
 auto process_selector_tokens(rspamd_mempool_t *pool,
-							 const blocks_gen_functor &next_token_functor)
+							 blocks_gen_functor &&next_token_functor)
 	-> selectors_vec;
 
 }