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Panic caused by Markdown in latest nightly #40918

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Panic caused by Markdown in latest nightly#40918
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A-docsArea: Documentation for any part of the project, including the compiler, standard library, and toolsT-rustdocRelevant to the rustdoc team, which will review and decide on the PR/issue.

Description

@SergioBenitez
SergioBenitez
opened on Mar 30, 2017

rustc is panicking on markdown that previously parsed. This appears to be caused by the transition from hoedown to pulldown-cmark (#40912, #40338):

---- src/request/form/from_form_value.rs - request::form::from_form_value::FromFormValue (line 59) stdout ----
	error: unknown start of token: `
 --> <anon>:2:42
  |
2 | A value is validated successfully if the `from_str` method for the given
  |                                          ^

thread 'rustc' panicked at 'Box<Any>', /checkout/src/libsyntax/parse/lexer/mod.rs:81
note: Run with `RUST_BACKTRACE=1` for a backtrace.
thread 'rustc' panicked at 'couldn't compile the test', /checkout/src/librustdoc/test.rs:270

The markdown being referenced in the error looks like this:

/// Rocket implements `FromFormValue` for many standard library types. Their
/// behavior is documented here.
///
///   * **f32, f64, isize, i8, i16, i32, i64, usize, u8, u16, u32, u64**
///
///   **IpAddr, Ipv4Addr, Ipv6Addr, SocketAddrV4, SocketAddrV6, SocketAddr**
///
///     A value is validated successfully if the `from_str` method for the given
///     type returns successfully. Otherwise, the raw form value is returned as
///     the `Err` value.

cc @steveklabnik @GuillaumeGomez

Activity

  1. GuillaumeGomez commented on Mar 30, 2017

    @GuillaumeGomez
    GuillaumeGomez
    on Mar 30, 2017
    Member

    The problem is that this block:

    /// A value is validated successfully if the from_str method for the given
    /// type returns successfully. Otherwise, the raw form value is returned as
    /// the Err value.

    Is considered as code. I wonder what would be a good solution for this (because that's how correct markdown considers this)...

  2. SergioBenitez commented on Mar 30, 2017

    @SergioBenitez
    SergioBenitez
    on Mar 30, 2017
    ContributorAuthor

    I don't think it should be...should it? It wasn't prior to this: https://api.rocket.rs/rocket/request/trait.FromFormValue.html#provided-implementations

  3. GuillaumeGomez commented on Mar 30, 2017

    @GuillaumeGomez
    GuillaumeGomez
    on Mar 30, 2017
    Member

    Yes but before, hoedown wasn't really markdown compliant. You can see by yourself how your code is interpreted by the markdown here.

  4. steveklabnik
    added
    T-rustdocRelevant to the rustdoc team, which will review and decide on the PR/issue.
    A-docsArea: Documentation for any part of the project, including the compiler, standard library, and tools
    on Mar 30, 2017

  5. steveklabnik commented on Mar 30, 2017

    @steveklabnik
    steveklabnik
    on Mar 30, 2017
    Contributor

    (not giving this all the tags because it's linked in to the tracking issue

  6. steveklabnik commented on Mar 30, 2017

    @steveklabnik
    steveklabnik
    on Mar 30, 2017
    Contributor

    rustc is panicking on markdown that previously parsed.

    To be clear, this is a test failure, not an ICE, correct?

    thread 'rustc' panicked at 'couldn't compile the test', /checkout/src/librustdoc/test.rs:270

    that is, this is a test failure.

  7. GuillaumeGomez commented on Mar 30, 2017

    @GuillaumeGomez
    GuillaumeGomez
    on Mar 30, 2017
    Member

    To be clear, this is a test failure, not an ICE, correct?

    Yes.

  8. steveklabnik commented on Mar 30, 2017

    @steveklabnik
    steveklabnik
    on Mar 30, 2017
    Contributor

    Right. So this is more of expected breakages caused by a bugfix.

    @SergioBenitez are you running off rustc master? I wasn't even aware this was in nightly yet, I thought it missed the cutoff. As I mentioned in the other issue, I was planning on publicizing this tomorrow.

  9. SergioBenitez commented on Mar 30, 2017

    @SergioBenitez
    SergioBenitez
    on Mar 30, 2017
    ContributorAuthor

    @steveklabnik Looks like this made it into today's nightly.

    Okay, so after discussing this a bit on IRC and playing with the commonmark.js script, the issue stems from a difference in how hoedown and pulldown-cmark interpret text to be inside of a list item:

    Leading text:

  * List Item Heading

  This is considered to be part of the list item in `hoedown` but not `pulldown-cmark`.

    This is still inside the list item in `hoedown` but is a new code block in `pulldown-cmark`.

    As shown above, text that hoedown treated as being inside of a list item is now treated by pulldown-cmark to be a code block. rustdoc tries to compile each code block as Rust code, and since this is clearly not Rust, compilation fails, and we see the panic! from the failed compilation.

    While this isn't a bug in rustc, it is a breaking change. I'd suggest that a crater run is done to catch any more of these and potentially notify the authors. Alternatively, some of these peculiarities can be "forward-ported" to the new parser.

  10. steveklabnik commented on Mar 30, 2017

    @steveklabnik
    steveklabnik
    on Mar 30, 2017
    Contributor

    Huh. Well, better make that post for sure, I guess. (The nightly)

    Crater wouldn't catch this, it doesn't run tests.

  11. nagisa commented on Mar 30, 2017

    @nagisa
    nagisa
    on Mar 30, 2017
    Member
    ///   * **f32, f64, isize, i8, i16, i32, i64, usize, u8, u16, u32, u64**
///
///     **IpAddr, Ipv4Addr, Ipv6Addr, SocketAddrV4, SocketAddrV6, SocketAddr**
///
///     A value is validated successfully if the `from_str` method for the given
///     type returns successfully. Otherwise, the raw form value is returned as
///     the `Err` value.

    Should work. The prior behaviour seems like a bug to me even considering the original markdown, and I think this is not easily fixable without making the markdown parser non-compliant.

  12. steveklabnik commented on Apr 5, 2017

    @steveklabnik
    steveklabnik
    on Apr 5, 2017
    Contributor

    I'm giving this one a close since it's expected behavior. Thanks all!

  13. steveklabnik
    closed this as completedon Apr 5, 2017
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