[BUG] No implicit move or forward on last use in initialization

[JohelEGP]

Title: No implicit move or forward on last use in initialization.

Minimal reproducer (https://cpp2.godbolt.org/z/Pb6YaYvsT):

f: (copy x)    = { _ = x; } // OK, moves.
f: (forward x) = { _ = x; } // OK, forwards.
g: (copy x)    = { i := x; } // Wrong, doesn't move.
g: (forward x) = { i := x; } // Wrong, doesn't forward.
main: () = { }

Commands:

cppfront main.cpp2
clang++18 -std=c++23 -stdlib=libc++ -lc++abi -pedantic-errors -Wall -Wextra -Wconversion -Werror=unused-result -I . main.cpp

Expected result:

auto f(auto x) -> void{static_cast<void>(std::move(x));}// OK, moves.
auto f(auto&& x) -> void{static_cast<void>(CPP2_FORWARD(x)); }// OK, forwards.
auto g(auto x) -> void{auto i {std::move(x)}; }// Wrong, doesn't move.
auto g(auto&& x) -> void{auto i {CPP2_FORWARD(x)}; }// Wrong, doesn't forward.

Actual result and error:

Program returned: 0

auto f(auto x) -> void{static_cast<void>(std::move(x));}// OK, moves.
auto f(auto&& x) -> void{static_cast<void>(CPP2_FORWARD(x)); }// OK, forwards.
auto g(auto x) -> void{auto i {x}; }// Wrong, doesn't move.
auto g(auto&& x) -> void{auto i {x}; }// Wrong, doesn't forward.

Cpp2 lowered to Cpp1:

//=== Cpp2 type declarations ====================================================


#include "cpp2util.h"



//=== Cpp2 type definitions and function declarations ===========================

auto f(auto x) -> void;
auto f(auto&& x) -> void;
auto g(auto x) -> void;
auto g(auto&& x) -> void;
auto main() -> int;


//=== Cpp2 function definitions =================================================

auto f(auto x) -> void{static_cast<void>(std::move(x));}// OK, moves.
auto f(auto&& x) -> void{static_cast<void>(CPP2_FORWARD(x)); }// OK, forwards.
auto g(auto x) -> void{auto i {x}; }// Wrong, doesn't move.
auto g(auto&& x) -> void{auto i {x}; }// Wrong, doesn't forward.
auto main() -> int{}

[hsutter]

Thanks! Repeating rationale here from #792 comment thread: The issue is that I was trying out suppressing move-from-last-use if the last use was in an initializer, because of examples like view: std::span = local_variable; when that was the last use of local_variable, which is an error for an rvalue. But that also suppresses a righteous move in examples like result := local_variable;. So I now agree those should be treated as rvalues too, and if that causes an error for an rvalue because there is no further us of that variable in scope, then the programmer must write an explicit discard of the variable.