[BUG] Interpolation lowers unparenthesized

[JohelEGP]

Title: Interpolation lowers unparenthesized.

Minimal reproducer (https://cpp2.godbolt.org/z/nzzPsq8n6):

main: () = {
  "`(0)$`".clear();
}

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: CPP2_UFCS_0(clear, ("`" + cpp2::to_string(0) + "`"));

Actual result and error: "`" + cpp2::to_string(0) + CPP2_UFCS_0(clear, "`");

Cpp2 lowered to Cpp1:

#define CPP2_USE_SOURCE_LOCATION Yes

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


#include "cpp2util.h"



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

auto main() -> int;
  

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

auto main() -> int{
  "`" + cpp2::to_string(0) + CPP2_UFCS_0(clear, "`");
}

Output:

raw.githubusercontent.com/hsutter/cppfront/main/include/cpp2util.h:470:44: warning: unused parameter 'where' [-Wunused-parameter]
  470 | auto assert_in_bounds(auto&& x, auto&& arg CPP2_SOURCE_LOCATION_PARAM_WITH_DEFAULT) -> decltype(auto)
      |                                            ^
raw.githubusercontent.com/hsutter/cppfront/main/include/cpp2util.h:369:76: note: expanded from macro 'CPP2_SOURCE_LOCATION_PARAM_WITH_DEFAULT'
  369 |     #define CPP2_SOURCE_LOCATION_PARAM_WITH_DEFAULT , std::source_location where = std::source_location::current()
      |                                                                            ^
build/main.cpp:19:42: error: use of undeclared identifier 'clear'
   19 |   "`" + cpp2::to_string(0) + CPP2_UFCS_0(clear, "`");
      |                                          ^
build/main.cpp:19:30: note: in instantiation of function template specialization 'main()::(anonymous class)::operator()<const char (&)[2]>' requested here
   19 |   "`" + cpp2::to_string(0) + CPP2_UFCS_0(clear, "`");
      |                              ^
raw.githubusercontent.com/hsutter/cppfront/main/include/cpp2util.h:797:2: note: expanded from macro 'CPP2_UFCS_0'
  797 | }(PARAM1)
      |  ^
1 warning and 1 error generated.

[JohelEGP]

I have always thought that interpolation should use absl::concat.
That would fix the problem.

[hsutter]

Thanks! I might do something similar to absl::StrCat in the future, without an Abseil dependency.

[JohelEGP]

Thank you!
I first rediscovered this issue
when I used one of those functions to color strings (from #831 (comment))
and noticed that only a latter part of the string was colored.

[JohelEGP]

Commit 13826c5 regressed
commit acab5c3 (which didn't add a test).
Although according to commit 3a8874a,

Note that "interpolate('d')$ string".ufcs_call() now requires parens, ("interpolate('d')$ string").ufcs_call()