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

[bluetarpmedia]

Debugging with LLDB (used by Xcode and Qt Creator) requires the following:

• Print line directives before each function definition
• Use absolute paths for filenames in line directives

Changes in this PR

1. Print line directives before each function definition
2. Add a new command line option to use absolute paths in line directives (defaults to off). LLDB users will have to turn this on.
3. Update the test-results with the new line directives preceding function definitions

I manually verified the line numbers in the updated test-results and also tested the debugging experience.

The implementation in this PR is significantly simpler than the previous one (#785, now closed) thanks to the recent refactoring that Herb made in to_cpp1.h.

[JohelEGP]

2. LLDB users will have to turn this on.

Is it really an issue with LLDB?
I have no problems debugging with GCC + LLDB.
I do have problems debugging with Clang + LLDB.
The issue seems to be https://stackoverflow.com/questions/20985673/how-to-configure-qt-creator-to-show-c-code-rather-than-disassembler?rq=3.
I've solved it by making the input source to cppfront be an absolute path.

[bluetarpmedia]

I've solved it by making the input source to cppfront be an absolute path.

Yeah, supplying an absolute path as the argument to cppfront solves the problem, but I added the flag so that users (or tools) can still supply a relative path for convenience while ensuring that the line directives are absolute.

[gregmarr]

It still boggles my mind that lldb won't work properly without redundant #line specifiers. They truly are redundant. Every single one of them has absolutely zero effect on the effective line number based on the previous #line specifiers in the file. Has this been reported to lldb as a bug?

[bluetarpmedia]

It still boggles my mind that lldb won't work properly without redundant #line specifiers. They truly are redundant. Every single one of them has absolutely zero effect on the effective line number based on the previous #line specifiers in the file. Has this been reported to lldb as a bug?

I haven't investigated further to find out whether the problem is with clang+lldb or just lldb. What I found on macOS with Xcode and Qt Creator is that the line directives preceding function declarations were not enough for breakpoints and stepping to work, and the workaround I found was to put the directives before each function definition.

[MaxSagebaum]

2. LLDB users will have to turn this on.

Is it really an issue with LLDB? I have no problems debugging with GCC + LLDB. I do have problems debugging with Clang + LLDB. The issue seems to be https://stackoverflow.com/questions/20985673/how-to-configure-qt-creator-to-show-c-code-rather-than-disassembler?rq=3. I've solved it by making the input source to cppfront be an absolute path.

The same issue exists with GDB. I had to copy the regex.h2 from the cppfront source directory to the test directory in order to debug the tests.

[JohelEGP]

GDB

Yeah, that's what I (and QtCreator) use, not LLDB.

[hsutter]

Looks good -- do I need to worry about the 3 failing tests before merging, or are those failures spurious-ish/otherwise-non-blocking?

[bluetarpmedia]

Looks good -- do I need to worry about the 3 failing tests before merging, or are those failures spurious-ish/otherwise-non-blocking?

Those are the same failures happening in ‘main’ and I created #933 to fix that.

[hsutter]

Thanks!