Playground links from code blocks in books need to obey edition2018 flag

[rchaser53]

EDIT: The error here is actually from clicking the playground link, not that there's a problem with the code, or how the book's testpass is running. Original description follows.

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It seems that #![feature(try_blocks)] is not worked now.
link: https://doc.rust-lang.org/unstable-book/language-features/try-blocks.html

[Centril]

This is probably due to compiling the test with Rust 2015; it works on Rust 2018. cc @scottmcm

[scottmcm]

It definitely works in 2018: https://play.rust-lang.org/?version=nightly&mode=debug&edition=2018&gist=e2ca081a42124a7615dd542c3cc36324 See also the run-pass test for it: https://github.com/rust-lang/rust/blob/master/src/test/run-pass/try-block.rs

It was originally marked ignore because of needing 2018 (https://github.com/rust-lang/rust/blob/master/src/test/run-pass/try-block.rs), but was changed to run in 2018 when #54350 made that possible.

So I don't think there's a bug here.

[Centril]

@scottmcm The bug is in the unstable book linking the user towards a 2015 playground instead of a 2018 one.

[scottmcm]

@Centril Ok, renamed the issue and changed the flags. This isn't a testsuite problem, then.

[Centril]

@scottmcm good call :) cc @steveklabnik

[scottmcm]

Related: rust-lang/mdBook#812