WIP: Upgrade to the new custom preprocessor system

[Michael-F-Bryan]

I'm mainly doing this to see what working with the rust-lang/mdBook#792 will be like. Translating from the previous "wrapped" form to the plugin system was super simple, I essentially reused the existing Mermaid preprocessor and copied the guts from the nop-preprocessor example.

Obviously this won't be ready for other people to use until the custom preprocessor PR makes its way into a release.

How does it look to you @badboy?

[badboy]

It's missing the actual implementation (so probably forgot to commit src/lib.rs?)

[Michael-F-Bryan]

I didn't actually need to touch anything in src/lib.rs. The executable is essentially just a shim which will defer to the mdbook_mermaid::Mermaid preprocessor, so we reuse the existing code.

When I'm writing up a page for the user guide I should probably mention the easiest way to write a custom preprocessor is to implement the Preprocessor trait on your type in lib.rs then for the mdbook-whatever binary you can copy/paste in a program that will pass everything through to the relevant Preprocessor methods.

[badboy]

Oooooh, I see. Even better. I'll check the implementation again.

[Michael-F-Bryan]

@badboy I'm thinking of merging in rust-lang/mdBook#792. Did you get a chance to review this PR?

Any feedback on the general mechanism for custom preprocessors would also be useful.

[badboy]

tl;dr: go for it! Yey, preprocessors!

I haven't given the upstream PR a proper look. This PR is small enough that I'm not worried about the changes.

I do like the idea of simple transformations on JSON (afaik pandoc does it similar). That will allow to have plugins in any language easily (avoids huge and slower-to-compile Rust plugins).
One other thing I have in mind is extracting the basic functionality from mdbook to parse a book (-> smaller dependency for preprocessors). I haven't looked closely into mdbook to see if that would actually make a difference though.

[Michael-F-Bryan]

One other thing I have in mind is extracting the basic functionality from mdbook to parse a book (-> smaller dependency for preprocessors). I haven't looked closely into mdbook to see if that would actually make a difference though.

I'd really like to do this too! At the moment mdbook takes forever to compile due to a large number of dependencies, which in turn have their own dependencies. The core operations are actually really simple and shouldn't require much more than the serde, pulldown-cmark and toml crates.

[Michael-F-Bryan]

@badboy I just pushed 0.2.2 to crates.io with proper custom preprocessor support. That should hopefully make using the mdbook-mermaid preprocessor easier and not require installing from git.

[badboy]

I was nudged enough to finally update this, merged and updated here: https://github.com/badboy/mdbook-mermaid/compare/3cea267..3951f00?diff=unified