Replace mustache and fmt::format with std::format.

[ScottBailey]

Mustache fails to test at compile time and could easily be replaced with std::format. Additionally, we are using fmt::format which can be replaced with std::format.

Moving to std::format can only be resolved when we switch to a C++20 minimum compiler spec.

If we'd like to remove Mustache before C++20, we can use fmt::format inseat od std::format and write and additional issue to update to std::format later.

[ScottBailey]

One option is to make the format code look like this:

constexpr std::string_view add_contract_template = {
   "file(GLOB {}-source ${CMAKE_CURRENT_SOURCE_DIR}/../../../apps/{}/*{})\n" // target name, object name, source extension                                
   "add_contract({} {} ${{}-source})\n\n"};                                  // object name, target name, target name                                     

constexpr std::string_view add_library_template = {
   "file(GLOB {}-source ${CMAKE_CURRENT_SOURCE_DIR}/../../../libs/{}/*{})\n\n" // target name, object name, source extension                              
   "add_library({} ${{}-source})\n\n"};                                        // target name, target name                     

Another is to make it look like something like this:

constexpr std::string set_vals = {
   "set(APJ_TARGET_NAME \"{}\")\n"
   "set(APJ_OBJECT_NAME \"{}\")\n"
   "set(APJ_EXT \"{}\")\n"};

constexpr std::string_view add_contract_template = {
   "file(GLOB ${APJ_TARGET_NAME}-source ${CMAKE_CURRENT_SOURCE_DIR}/../../../apps/${APJ_OBJECT_NAME}/*${APJ_EXT})\n"
   "add_contract(${APJ_OBJECT_NAME} ${APJ_TARGET_NAME} ${${APJ_TARGET_NAME}-source})\n\n"};

constexpr std::string_view add_library_template = {
   "file(GLOB ${APJ_TARGET_NAME}-source ${CMAKE_CURRENT_SOURCE_DIR}/../../../libs/${APJ_OBJECT_NAME}/*${APJ_EXT})\n\n"
   "add_library(${APJ_TARGET_NAME} ${${APJ_TARGET_NAME}-source})\n\n"};	

[larryk85]

While I agree that lack of it not verifying during compile time is a nice to have. It seems like much more boiler plate and repetition than just leaving mustache.

It is not clear to me as to what the big value add is with this.

[ScottBailey]

@larryk85 There are two additional issues beyond compile time checking making std::format preferable to Mustache.

The first is that Mustache is a non-standard library that essentially duplicates the functionality of a standard one.

The second issue is it's lack of escape mechanism for braces in the source requiring some workaround for use with cmake files.

Given that we are committed to standard libraries and are already using format, it seems like a no brainer to switch away from Mustache.

I wouldn't bet money on it, but I think the number of lines of code (number of characters even) should be about the same between the two solutions; however, the format code should be more familiar to most of us. Of course, removing the Mustache repo reduces the number of lines of code.

I think this is a positive maintenance improvement.

[ScottBailey]

In fact, here's some sample code, untested but you get the idea.

            // as is with workaround                                                                                                             
            s << temp.render(datum{"obj_name", obj.name()}
                                  ("target_name", target_name(obj))
                                  ("source_ext", system::extension(obj.language()))
                                  ("dollar_brace", "${")); // dollar_brace must be "${" to work around Mustache issue                            

            // first example above                                                                                                               
            std::format_to(std::ostream_iterator<char>(s), temp,
                           target_name(obj), obj.name(), system::extension(obj.language()),
                           obj.name(), target_name(obj), target_name(obj));

            // second example above                                                                                                              
            std::format_to(std::ostream_iterator<char>(s), set_vals, target_name(obj), obj.name(), system::extension(obj.language()));
            s << temp;

[ScottBailey]

Here's the proposed code (#41):

            km::mustache cmake::add_contract_template = {
               "file(GLOB {{target_name}}-source ${CMAKE_CURRENT_SOURCE_DIR}/../../../apps/{{obj_name}}/*{{source_ext}})\n"
               "add_contract({{obj_name}} {{target_name}} {{dollar_brace}}{{target_name}}-source})\n\n"};

            km::mustache cmake::add_library_template = {
               "file(GLOB {{target_name}}-source ${CMAKE_CURRENT_SOURCE_DIR}/../../../libs/{{obj_name}}/*{{source_ext}})\n\n"
               "add_library({{target_name}} {{dollar_brace}}{{target_name}}-source})\n\n"};


            s << temp.render(datum{"obj_name", obj.name()}
                                  ("target_name", target_name(obj))
                                  ("source_ext", system::extension(obj.language()))
                                  ("dollar_brace", "${")); // dollar_brace must be "${" to work around Mustache issue                            

Here's the same code with fmt::format or std::format:

           constexpr std::string_view add_contract_template = {      // 0: object name, 1: target name, 2: source extension                     
               "file(GLOB {1}-source ${CMAKE_CURRENT_SOURCE_DIR}/../../../apps/{0}/*{2})\n"
               "add_contract({0} {1} ${{1}-source})\n\n"};

            constexpr std::string_view add_library_template = {       // 0: object name, 1: target name, 2: source extension                     
               "file(GLOB {1}-source ${CMAKE_CURRENT_SOURCE_DIR}/../../../libs/{0}/*{2})\n\n"
               "add_library({0} ${{1}-source})\n\n"};


            std::format_to(std::ostream_iterator<char>(s), temp,
                  obj.name(),
                  target_name(obj),
                  system::extension(obj.language()));

Really not that much different.

[larryk85]

@larryk85 There are two additional issues beyond compile time checking making std::format preferable to Mustache.

The first is that Mustache is a non-standard library that essentially duplicates the functionality of a standard one.

The second issue is it's lack of escape mechanism for braces in the source requiring some workaround for use with cmake files.

Given that we are committed to standard libraries and are already using format, it seems like a no brainer to switch away from Mustache.

I wouldn't bet money on it, but I think the number of lines of code (number of characters even) should be about the same between the two solutions; however, the format code should be more familiar to most of us. Of course, removing the Mustache repo reduces the number of lines of code.

I think this is a positive maintenance improvement.

I'm not sure what you mean by "mustache is not standard", mustache is a standard for templating. https://github.com/mustache/spec/tree/master/specs.

I'm fine with the removal, but I still don't see the big advantage. Mustache also has far more functionality than fmt. Albeit, we aren't currently using that functionality, it's not a 1-1 replacement per se.

[ScottBailey]

Re standard: https://isocpp.org/

I agree, this is not a 1:1 replacement. And the advantage is minor: one less dependency and one less hackey workaround. (Unless there was an escape mechanism I didn't see. But since no one raised their hand to point to it...)

This was closed in #41.