Rust 1.18 regression rustc-serialize doc tests have regressed

[alexcrichton]

https://ci.appveyor.com/project/alexcrichton/rustc-serialize/build/1.0.563/job/s4vnewjo4l4448j2

failures:
---- src\base64.rs - base64::DECODE_TABLE (line 333) stdout ----
	error: unexpected close delimiter: `}`
  --> <anon>:21:1
   |
21 | }
   | ^
thread 'rustc' panicked at 'Box<Any>', src\libsyntax\parse\mod.rs:216
note: Run with `RUST_BACKTRACE=1` for a backtrace.
thread 'rustc' panicked at 'couldn't compile the test', src\librustdoc\test.rs:270
failures:
    src\base64.rs - base64::DECODE_TABLE (line 333)
test result: FAILED. 20 passed; 1 failed; 1 ignored; 0 measured

Likely related to #40912

[steveklabnik]

This is basically the same as #40979

https://github.com/rust-lang-nursery/rustc-serialize/blob/master/src/base64.rs#L332-L333

hoedown treated this all as a p tag, pulldown-cmark treats this as a <p><code>

In this case, the code block is invalid. The fix is to either fix that by removing line 352 (and then outdenting all the code), add a function header that accepts ch to make it a different kind of example, or change to rust,ignore so that it's not run as a test.

(I would also add a newline between 32 and 33; that's the whole reason it's ambiguous between implementations anyway, with a blank line, they treat them identically (and it would be the new behavior either way))

[alexcrichton]

@steveklabnik sure yeah, but to put this in perspective: this is invalid TOML that Cargo still accepts with a warning and we even fix bugs in parsing as they arise to ensure we can keep parsing this.

I think we should totally fix the markdown, but I don't think we should immediately start failing so many builds without warning.

[steveklabnik]

so many builds without warning.

I've seen roughly 3 other instances of this so far, and they've all already been fixed. If there's a huge impact, I agree, but I haven't actually seen any evidence of that.

[bluss]

It's a CI failure for rustc-serialize that does not affect anything that depends on rustc-serialize, so impact is very limited in that way

[steveklabnik]

Fix sent: rust-lang-deprecated/rustc-serialize#182