[BUG] Explicit discard requirement may be broken?

[Neil Henderson]

Describe the bug
A recent commit may have broken the explicit discard requirement.

To Reproduce
Run cppfront on this code:

m: std::mutex = ();    // <--- Never used again

increment: (inout x) = { x++; }

main: () = {
    v1: std::vector = (11, 22, 33);
    sz:= v1.size();    // <--- Never used again

    value:= 42;
    increment(value);    // <--- inout but never used again
}

There are no errors generated.
Repro on Godbolt which at the time of writing is up-to-date with cppfront's main branch (Build 9318:2141).

[gregmarr]

Something might have updated, because it's erroring now (the error is from clang, not cppfront):

main.cpp2:10:5: error: no matching function for call to 'increment'
   10 |     increment(cpp2::move(value));
      |     ^~~~~~~~~
main.cpp2:3:6: note: candidate function [with x:auto = int] not viable: expects an lvalue for 1st argument
    3 | auto increment(auto& x) -> void{++x; }
      |      ^         ~~~~~~~

Fixing that by adding _ = value; results in:

main.cpp2:7:10: warning: unused variable 'sz' [-Wunused-variable]
    7 |     auto sz {CPP2_UFCS(size)(cpp2::move(v1))}; 
      |          ^~

[Neil Henderson]

Something might have updated, because it's erroring now (the error is from clang, not cppfront):

Yeah, I get subsequent warnings/errors from the compiler, but I'm pretty sure in previous versions of cppfront that cppfront itself produced an error about having to discard the variable.

[gregmarr]

I'm pretty sure in previous versions of cppfront that cppfront itself produced an error about having to discard the variable.

Could be, I don't remember one way or the other.