Clang: Add support for clang compiler

[hab-0]

The current generated files (c++) are not compatible with the Clang compiler https://clang.llvm.org/.
e.g:
The following syntax used on the Nunavut generated files is not supported by the Clang compiler:
[[deprecated( string-literal )]]

[pavel-kirienko]

The syntax you are referring to is standard per C++14. Clang supports C++14 starting with v3.4. Be sure you are using an up-to-date version of the compiler with the correct flags.

[thirtytwobits]

Sorry @hab-0 , but can you provide the version of clang you are using? We do compile using clang c++14 as part of our CI so it is generally compatible.

[hab-0]

hi @thirtytwobits ,
Mi clang++ version is:

Ubuntu clang version 14.0.0-1ubuntu1.1
Target: x86_64-pc-linux-gnu

Generator:

nunavut-2.0.9 (serialization was enabled)
c++17

I just created a very simple main program which I try to compile with clang++ with the following options:

clang++ -I . -std=c++17 main.cpp -o main

output:

In file included from main.cpp:2:
./uavcan/node/ExecuteCommand_1_0.hpp:125:7: error: misplaced attributes; expected attributes here
struct Request_1_0 final
^
[[deprecated("uavcan.node.ExecuteCommand.Request.1.0 is reaching the end of its life; there may be a newer version available")]]
./uavcan/node/ExecuteCommand_1_0.hpp:331:7: error: misplaced attributes; expected attributes here
struct Response_1_0 final
^
[[deprecated("uavcan.node.ExecuteCommand.Response.1.0 is reaching the end of its life; there may be a newer version available")]]
2 errors generated.

simple-main.zip

tested with same results also with generator version:

nunavut-2.1.1 (serialization was enabled)
c++17 & c++14

IMO, the problem is the way the generator places the "deprecated" attribute.
According to https://en.cppreference.com/w/c/language/struct the syntax is:

struct attr-spec-seq (optional) name (optional) { struct-declaration-list }

while nunavut is generating:

attr-spec-seq (optional) struct name (optional) { struct-declaration-list }

GCC is more tolerant and just gives you a warning that you can easily suppress:

warning: attribute ignored in declaration of ‘struct uavcan::node::ExecuteCommand::Request_1_0’ [-Wattributes]

Clang seems stricter and so far I did not find the way or an option to compile my application (ignoring or suppressing the error: misplaced attributes)

Just for testing, i modified the file with the syntax as follows:
struct [[deprecated("uavcan.node.ExecuteCommand.Response.1.0 is reaching the end of its life; there may be a newer version available")]] Response_1_0 final

Clang++ does complain and the program is compiled without errors.

Could you please let me know if my findings are correct and the code generator should be modified to generate the struct declaration with the syntax?

struct attr-spec-seq (optional) name (optional) { struct-declaration-list }