Example programs in 'Rust by Example' return 'undefined' in browser

[bitfield]

Example: https://doc.rust-lang.org/rust-by-example/hello.html

Clicking the 'Run' button to run the code example prints 'undefined' instead of the expected "Hello world!". I looked at a few other examples, but they all fail in the same way.

[kennytm]

This is because play.rust-lang.org recently changed its (private) API. We need to update these lines in mdbook:

https://github.com/rust-lang-nursery/mdBook/blob/29b3ff14c7e47c62f331080e3a92bf5c2484cf52/src/theme/book.js#L112-L119

cc @shepmaster (playground) @mattico @Michael-F-Bryan (mdbook).

[frewsxcv]

Should we look into reverting the play.rust-lang.org API for now? Having it broken for two release cycles seems doesn't seem ideal

[shepmaster]

I've added default values to that API for now. There are zero reliability guarantees for every playground API except /evaluate.json.

[mattico]

mdbook 0.1.10 has a fix for this issue, though most existing documentation will likely not be rebuilt. I'll make sure we switch to the /evaluate.json endpoint for the next release (rust-lang/mdBook#753).

[steveklabnik]

This has been fixed. Closing!