Doc-examples using `#[doc]` do not have triple backticks stripped before being compiled

[AldaronLau]

Nightly code fails to compile.

Code

I tried this code:

#![cfg_attr(
    feature = "std",
    doc = r#"
        ```rust,no_run
        // Lots of rust code
        ```
    "#
)]

I expected to see this happen: Compiling and working like it does on stable.

Instead, compiler says:

error: unknown start of token: `
   |
24 |     ```
   |     ^
   |
help: Unicode character '`' (Grave Accent) looks like ''' (Single Quote), but it is not
   |
24 |     '``
   |     ^

Version it worked on

It most recently worked on: rustc 1.49.0-nightly (ffa2e7a 2020-10-24)

Version with regression

rustc --version --verbose:

rustc 1.49.0-nightly (cf9cf7c92 2020-11-10)
binary: rustc
commit-hash: cf9cf7c923eb01146971429044f216a3ca905e06
commit-date: 2020-11-10
host: x86_64-unknown-linux-gnu
release: 1.49.0-nightly

[jyn514]

cc @GuillaumeGomez , I think #76154 broke this.

[GuillaumeGomez]

Absolutely!

@Nezeky: Since #76154, we don't allow to "align" comments anymore. You might want to take a look at this blog post.

I'll close this issue and add the label "wont-fix" then.

[juliankrieger]

@GuillaumeGomez How is one sup[posed to combine #![cfg_attr(not(feature = "xxx"), doc = r#" with no_run when backtick compilation no longer works in that case?

[jyn514]

@juliankrieger the 4 space indent is being interpreted as a code block. Then the rust compiler is run on the block and gives an error about the backticks. The fix is to remove (or just decrease) the indentation.

[juliankrieger]

I'm afraid I don't quite understand, can you provide a tiny example that works with no_run? Thanks!

[GuillaumeGomez]

You can't have indented codeblocks with tags.

[jyn514]

@juliankrieger

#![doc = r#"
```rust,no_run
// Lots of rust code
```
"#]

(or use backslashes and \n manually to strip the indentation)