Execute code block in markdown file

[linux-china]

justfile is very easy, but you know some guys still write code in markdown. For example as following:

```shell {#hello .just}
echo hello
```

With markdown attributes, and #hello is recipe name, and .just means to execute the code with just.

The above code is friendly with most editors, and no break.

Updated on 11/29/2023

[casey]

This is an interesting feature! I'm not totally sold on it, but I'll leave it open in case it's something that a lot of people want and would use.

[runeimp]

@linux-china I love Markdown and have used it for years. But I've never seen anything execute code from a Markdown file. I think it's great for documenting code or creating page content for tools like Hugo, etc. but using it as source for some tool as well is cool sounding but instantly strikes me as impractical. Doesn't mean it's a bad idea I'm just not seeing the utility. Can you list any tools that have this sort of feature? And list a use case where this might be better than just targeting a script?

[chengxuncc]

Might be useful to introduce mask for whom want this feature.

[daniels]

This was my first idea when I just now found out about just. I don't want to duplicate the information I already put into my README.md, but if just could pick up recipes defined in code blocks it would be really useful.

Unlike the original idea here, I would not have expected any different format with extra markdown parsing - just read recipes defined in code blocks marked with ```just. (Nice if multiple code blocks are accepted and merged.)

[linux-china]

This was my first idea when I just now found out about just. I don't want to duplicate the information I already put into my README.md, but if just could pick up recipes defined in code blocks it would be really useful.

Unlike the original idea here, I would not have expected any different format with extra markdown parsing - just read recipes defined in code blocks marked with ```just. (Nice if multiple code blocks are accepted and merged.)

According to markdown attributes, and I think following code block is correct:

```shell {#hello .just}
echo hello
```

#hello is recipe name, and .just means to use just.

[laniakea64]

I don't want to duplicate the information I already put into my README.md, but if just could pick up recipes defined in code blocks it would be really useful.
...
I would not have expected any different format with extra markdown parsing ... (Nice if multiple code blocks are accepted and merged.)

Should be doable already, here's quick attempt at working with the syntax @linux-china demonstrated:

readme_justfile := justfile_directory() / '.readme.just'

readme2justfile:
  #!/usr/bin/env python3
  import re
  recipeStartRx = re.compile(r'^```[a-z]+\s+\{#([a-zA-Z_][a-zA-Z0-9_-]*)\s+\.just\}', re.I)
  recipes = dict()
  with open('README.md', 'r') as readme:
    recipeName = None
    for line in readme:
      if recipeName:
        if line.strip() == '```':
          recipeName = None
        else:
          recipes[recipeName] += '  ' + line
      elif s := recipeStartRx.search(line):
        s=s.group(1)
        recipeName = s
        if recipeName not in recipes:
          recipes[recipeName] = ''
  with open("""{{readme_justfile}}""", 'w') as justfile:
    for recipe, body in recipes.items():
      justfile.write(f'{recipe}:\n{body}\n')

@r *recipe: readme2justfile
  {{quote(just_executable())}} -f {{quote(readme_justfile)}} {{recipe}}

Then you can run just r your_readme_recipe.

It would be more seamless if #1646 were implemented.