为什么带有模板 arguments 的 C++ function 在 clang++ 7 上没有警告“控制到达非无效函数的末尾”？

Question

I noticed that if I compile this

int x() { }

I get a warning, as usual:

$ clang++-7 -pthread -std=c++17 -o main main.cpp
main.cpp:5:11: warning: control reaches end of non-void
      function [-Wreturn-type]
int x() { }
          ^
1 warning generated.

$ ./main

however, if the function takes any template arguments:

template <typename y>
int x() { }

no warnings appear.

$ clang++-7 -pthread -std=c++17 -o main main.cpp
$ ./main

Is this a bug in the compiler?

Answer 1

Until you call (or otherwise odr-use) that function template specialisation, instantiating it, the actual resulting function does not exist, and you won't get any diagnostics about it unless it is syntactically invalid.

We cannot see the rest of your program as you did not think a reproducible example was important, but presumably you did not do this in your program.

Write x<int>(); in your main function and you'll see the warning you wanted.