[BUG] Short function syntax with multiple return values generates bad code.

[filipsajdak]

Having a single expression function that uses multiple return values syntax compiles to bad cpp1 code.

fun: () -> (i:int) = i = 42;

Steps

tests % cppfront ufcs.cpp2 
ufcs.cpp2... ok (all Cpp2, passes safety checks)

tests % clang++ -std=c++20 -I../cppfront/include ufcs.cpp
tests/ufcs.cpp2:24:47: error: use of undeclared identifier 'i'
[[nodiscard]] auto fun() -> fun__ret { return i.construct(42); }
                                              ^
1 error generated.

Expected result

It should fail on cppfront or compile to correct code like:

[[nodiscard]] auto fun() -> fun__ret{
  cpp2::deferred_init<int> i;
  i.construct(42);
  return  { std::move(i.value()) }; 
}

Actual result/error

cppfront generates bad code that fails to compile:

[[nodiscard]] auto fun() -> fun__ret { return i.construct(42); }

Compiler version

tests % clang++ --version
Apple clang version 14.0.0 (clang-1400.0.29.102)
Target: arm64-apple-darwin21.6.0
Thread model: posix
InstalledDir: /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin