Enable debugging with LLDB (Xcode, Qt Creator, etc)

[bluetarpmedia]

Some changes are needed in order to enable debugging with LLDB (used by Xcode and Qt Creator):

• print line directives before each function definition
• filenames in line directives now have absolute paths

I also tested these changes with Visual Studio and the debugging experience continues to work as before.

[gregmarr]

filenames in line directives now have absolute paths

This is going to break the line directives in reflect.h. It also means that the builds are not reproducible from different directories. I'm surprised that any debugger at this point would be unable to understand relative #line directives. I suspect that this would need to be a switch, like this: https://github.com/hsutter/cppfront/blob/main/source/cppfront.cpp#L139

[gregmarr]

Do you have an example of what was being output that is being suppressed? I know that there are some places where we need to output the same directive multiple times due to intermediate code. It's not 100% clear to me that this will only eliminate truly duplicate line numbers.

[bluetarpmedia]

That code prevents duplicate line directives like this:

#line 11 "C:\\path\\main.cpp2"
#line 11 "C:\\path\\main.cpp2"
auto main() -> int{
 print_menu(2023);
}

But it still allows the same line directive line number to be reused elsewhere, just not immediately on subsequent lines.

This is still allowed:

#line 11 "C:\\path\\main.cpp2"
auto main() -> int;

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

#line 11 "C:\\path\\main.cpp2"
auto main() -> int{
 print_menu(2023);
}

[gregmarr]

Great, thanks for the confirmation.

[bluetarpmedia]

This is going to break the line directives in reflect.h.

I hadn't noticed that, thanks. Fortunately, in this case, the impact will be for cppfront developers themselves using lldb if lldb can't find the reflect.h file. End-users of cppfront won't be affected.

It also means that the builds are not reproducible from different directories. I'm surprised that any debugger at this point would be unable to understand relative #line directives.

Yes, I found that surprising too. Based on my tests (on macOS), lldb uses the current working directory when trying to find a relative filename in a line directive. So if you run your binary from a different working directory then suddenly the debugging experience will fail. Whereas with MSVC I suspect the path to the original source code directory is included in the PDB file, so relative filenames work correctly since the debugger can reconstruct it with the directory from the PDB.

I suspect that this would need to be a switch, like this: https://github.com/hsutter/cppfront/blob/main/source/cppfront.cpp#L139

Good thinking, I'll add that to my PR.

EDIT - Done, see below.

[hsutter]

Looks good, thanks!

[hsutter]

After merging this I re-ran regression tests, and it made incorrect changes... in the first couple of test files I looked at, the #line that used to exist on the function definition was removed (which I think is the opposite of what you wanted, and made the line information incorrect).

So I've reverted this merge... please create a new PR and try running it against all regression tests? Thanks!