Klammerset: the @@@klammerset construct, its search path, and const correctness

The @@@klammerset system command formally declares a klammerset — a
named, logically related group of klammer definitions — with an
operative, idempotent declaration (:requires and :files load in order
at the declaration point, relative to the declaring file). A bare
symbol given to ktext -k, kdesc --input, or :requires resolves to
x/x.k on the search path: the document's directory, then
KLAMMERTEXT_KLAMMERSETS, then KLAMMERTEXT_HOME; kdesc --klammerset
lists the available sets. sks/sks.k is the first declared klammerset,
so `-k sks` loads the SKS by name. The engine's lookup classes were
renamed *_set → *_registry to keep the two concepts apart, and the
whole C++ tree now follows standard const-correctness conventions.
tst/ gains klammerset_test.sh (18 cases).

(from dev 64b1abf23e56)

sks/document/document_html.cpp

@@ -10,7 +10,7 @@
 #include "show.h"
 #include "file.h"
 
-std::string unescape_newlines(std::string s)
+std::string unescape_newlines(const std::string& s)
 {
     return string_replace(s, " ___NL___ ", "\n");
 
@@ -44,7 +44,7 @@ std::string insert_missing_ids(std::smatch match)
     return result;
 }
 
-std::string insert_ids(std::string html_text)
+std::string insert_ids(const std::string& html_text)
 {
     (void)K::log(3);
     std::string result = html_text;
@@ -154,7 +154,7 @@ std::string Document_class::font_definitions()
     return ss.str();
 }
 
-void Document_class::write_basenames_js_file(std::string filename, std::vector<std::string> basenames)
+void Document_class::write_basenames_js_file(const std::string& filename, const std::vector<std::string>& basenames)
 {
     (void)K::log(3);
     std::string tab("        ");
@@ -202,7 +202,7 @@ std::string Document_class::create_html_output_directories()
     return output_directory;
 }
 
-strings_t get_css_files(strings_t custom_css_files)
+strings_t get_css_files(const strings_t& custom_css_files)
 {
     (void)K::log(3);
     strings_t result = sks_files_of_type("css");
@@ -223,7 +223,7 @@ std::vector<std::string> js_basenames(bool nav)
 
 strings_t Document_class::get_js_files(
     bool nav, bool include_sks_js,
-    std::string pages_basenames_filename)
+    const std::string& pages_basenames_filename)
 {
     (void)K::log(3);
     strings_t result {};
@@ -244,13 +244,13 @@ strings_t Document_class::get_js_files(
 }
 
 
-strings_t link_filenames(strings_t& full_filenames, std::string page_dir)
+strings_t link_filenames(strings_t& full_filenames, const std::string& page_dir)
 {
     strings_t result {};
     fs::path page_dir_path(page_dir);
     // int i = 0;
     std::transform(full_filenames.begin(), full_filenames.end(), std::back_inserter(result),
-                   [&](std::string f) {
+                   [&](const std::string& f) {
                        fs::path full(f);
                        //msg() << i << full << " " << full.filename() << "\n";
                        fs::path path(page_dir_path / full.filename());
@@ -260,8 +260,8 @@ strings_t link_filenames(strings_t& full_filenames, std::string page_dir)
 }
 
 std::pair<std::vector<std::string>, std::vector<std::string>>
-Document_class::html_auxiliary_files(std::string output_directory, std::string pages_basenames_filename,
-                                     std::vector<std::string> custom_css_files)
+Document_class::html_auxiliary_files(const std::string& output_directory, const std::string& pages_basenames_filename,
+                                     const std::vector<std::string>& custom_css_files)
 {
     (void)K::log(3);
     strings_t all_css_files = custom_css_files;
@@ -352,7 +352,7 @@ std::string increment_level(int level, std::vector<int> &levels)
 }
 
 
-std::string extract_id(std::string attr)
+std::string extract_id(const std::string& attr)
 {
     std::smatch match {};
     if (!std::regex_match(attr, match, id_attr_rgx)) {
@@ -362,7 +362,7 @@ std::string extract_id(std::string attr)
 }
 
 std::vector<Heading>
-Document_class::insert_section_numbers(std::string marker, bool add_to_toc)
+Document_class::insert_section_numbers(const std::string& marker, bool add_to_toc)
 {
     std::vector<int> levels(9, 0);
     std::smatch match {};
@@ -407,7 +407,7 @@ Document_class::insert_section_numbers(std::string marker, bool add_to_toc)
     return headings;
 }    
 
-int get_caption_number(std::map<std::string, int>& numbers, std::string label)
+int get_caption_number(std::map<std::string, int>& numbers, const std::string& label)
 {
     int result;
     if (numbers.count(label) == 0) {
@@ -470,7 +470,7 @@ void Document_class::insert_html_caption_numbers()
 
 
 std::vector<std::tuple<std::string, std::string, std::string>>
-Document_class::reference_list(std::string target_marker)
+Document_class::reference_list(const std::string& target_marker)
 {
     std::regex reference_rgx("__REF__");
     std::regex target_rgx("<div id=\"(.*?)\" data-label=\"(.*?)\" class=\"caption_");
@@ -519,7 +519,7 @@ std::map<std::string, std::string> Document_class::id_to_caption_number()
 }
     
 
-std::pair<int, int> offset_spec_to_count(std::string spec)
+std::pair<int, int> offset_spec_to_count(const std::string& spec)
 {
     std::regex rgx(R"((\w+)\s*(\d*))");
     std::smatch match {};
@@ -637,7 +637,7 @@ std::string Document_class::single_page_toc()
 }
 
 
-elements_t Document_class::page(std::string body_text, std::string output_dir, int max_level)
+elements_t Document_class::page(const std::string& body_text, const std::string& output_dir, int max_level)
 {
     (void)K::log(3);
     std::string toc {}; // Calculate
@@ -674,7 +674,7 @@ elements_t Document_class::page(std::string body_text, std::string output_dir, i
     return page;
 }
 
-std::string Document_class::make_single_html_page(std::string output_directory)
+std::string Document_class::make_single_html_page(const std::string& output_directory)
 {
     (void)K::log(3);
     std::stringstream ss {};;
@@ -694,7 +694,7 @@ std::string Document_class::make_single_html_page(std::string output_directory)
 }
 
 std::string Document_class::make_html_navigation_structure(
-    std::string output_directory, std::vector<Heading> headings)
+    const std::string& output_directory, std::vector<Heading> headings)
 {
     msg() << "Navigation format\n";
     std::vector<std::string> pages_basenames {};