Code annotations for C/C++ not working as expected (by me)

[uwezi]

Description

Quarto version 1.8.25 on Windows 11

I found the closed issue #5060 "Code Annotation for C/C++ & VHDL not handled correctly" when experimenting with Quarto for the very first time. My goal is to include plain C code in my presentation and the annotation feature just looks great.

However using the standard inline comment style in C // is not recognized by the preview and revealjs renderer. It is recognized correctly for C++ code though, here is an example

---
title: "Quarto Basics"
format:
  html:
    code-fold: true
jupyter: python3
code-annotations: hover
---

## C code

```c
#include <avr/io.h> // <1>
int main(void)      // <2>
{
    while (1)       // <3>
    {               // <3>
                    // <3>
    }               // <3>
}
```
1. pre-processor library include
2. main function
3. infinite main loop

## C++ code

```cpp
#include <avr/io.h> // <1>
int main(void)      // <2>
{
    while (1)       // <3>
    {               // <3>
                    // <3>
    }               // <3>
}
```
1. pre-processor library include
2. main function
3. infinite main loop

the revealjs output as screenshots:

However the PDF output shows a different appearance: now the comments have been replaced in both code examples, but the ordered list for the C-code example has not been modified:

[mcanouil]

The standard Inline comment symbol in C is not //. It is only in ANSI C C99 and later.

Quarto uses /* ... */:

• quarto-cli/src/resources/filters/modules/constants.lua

  Line 84 in b89d353

  c = {"/*", "*/"},

---
format: html
code-annottions: true
---

```c
#include <stdio.h>
int main() { /* <1> */
    printf("Hello, World!\n");
    return 0;
}
```

1. This is a comment for line 1.
```

[cderv]

@MrP123 you are suggesting supporting also // as comment for C language ? is that right ?

[MrP123]

@cderv Yes I am.
Or more generally the case that a language can have multiple comment styles. In particular also for the case where one comment style is a line comment like // with only a "start token", and another comment style could be a block comment like /* */ that requires a "start token" and an "end token".
I only had a brief look at how the annotation mechanism works, but right now it seems to me that both types of comments are handled, but not within one language.

[mcanouil]

FWIW, beware that the comment symbol is unfortunately used not only for code-annotations and that it's not following the DRY principle especially when accounting for the "quarto" VSCode/Positron extension.

[cderv]

Thanks for adding precision @MrP123

as mentioned this has implication but if we can help user experience for less trip on this, we'll try to do it.
// seems to be indeed supported by most tool nowadays even for C and not just C++.

If we add it, we'll update here.

Thanks for your feedbacks.

[MrP123]

Thanks for getting back so quickly @cderv
Definitely understandable that this is not as simple of a change as one might think from a quick glance.

FWIW I personally haven't encountered a recent C codebase in the wild that is using a standard pre C99. Even in the context of embedded systems, which is what I tend to do if I am working in C, times have definitely moved on in my experience.

Looking forward to see what you can come up with!