ICE with rustdoc json backend

[weiznich]

Code

diesel-rs/diesel@41404e6 using the following command:

RUSTDOCFLAGS='-Z unstable-options --output-format=json' cargo +nightly doc --features "postgres"

produces a internal compiler error inside of rustdoc

Meta

rustdoc +nightly --version --verbose:

rustdoc 1.60.0-nightly (6abb6385b 2022-01-26)
binary: rustdoc
commit-hash: 6abb6385b2cb7249f67b9b3ce7522527767dd907
commit-date: 2022-01-26
host: x86_64-unknown-linux-gnu
release: 1.60.0-nightly
LLVM version: 13.0.0

Error output

thread 'rustc' panicked at 'assertion failed: `(left == right)`
  left: `Item { id: Id("0:23812"), crate_id: 0, name: Some("PgMoney"), span: Some(Span { filename: "diesel/src/pg/types/money.rs", begin: (23, 0), end: (23, 28) }), visibility: Public, docs: Some("Money is represented in Postgres as a 64 bit signed integer.  This struct is a dumb wrapper\ntype, meant only to indicate the integer's meaning.  The fractional precision of the value is\ndetermined by the [`lc_monetary` setting of the database](https://www.postgresql.org/docs/9.6/static/datatype-money.html).\nThis struct is re-exported as `Cents` as a convenient and conventional expression of a typical\nunit of 1/100th of currency. For other names or precisions, users might consider a differently\nnamed `use` of the `PgMoney` struct.\n\n```rust\nuse diesel::data_types::PgMoney as Pence; // 1/100th unit of Pound\nuse diesel::data_types::PgMoney as Fils;  // 1/1000th unit of Dinar\n```"), links: {}, attrs: ["#[diesel(sql_type = Money)]"], deprecation: None, inner: Struct(Struct { struct_type: Tuple, generics: Generics { params: [], where_predicates: [] }, fields_stripped: false, fields: [Id("0:23814")], impls: [Id("a:2:8549-0:23812"), Id("a:2:3022-0:23812"), Id("a:2:8548-0:23812"), Id("a:2:3034-0:23812"), Id("a:2:3063-0:23812"), Id("b:0:542-0:23812"), Id("b:0:559-0:23812"), Id("b:0:549-0:23812"), Id("b:0:1745-0:23812"), Id("b:2:3736-0:23812"), Id("b:2:2951-0:23812"), Id("b:2:2630-0:23812"), Id("b:2:2966-0:23812"), Id("b:2:2955-0:23812"), Id("b:2:2627-0:23812"), Id("b:2:2961-0:23812"), Id("b:5:667-0:23812"), Id("0:23726"), Id("0:23728"), Id("0:23730"), Id("0:23731"), Id("0:23732"), Id("0:23735"), Id("0:23736"), Id("0:23738"), Id("0:23740"), Id("0:23765"), Id("0:23769"), Id("0:23783"), Id("0:23787"), Id("0:23790"), Id("0:23807"), Id("0:8373"), Id("0:8375"), Id("0:8378"), Id("0:8381"), Id("0:8383"), Id("0:8386")] }) }`,
 right: `Item { id: Id("0:23812"), crate_id: 0, name: Some("Cents"), span: Some(Span { filename: "diesel/src/pg/types/money.rs", begin: (23, 0), end: (23, 28) }), visibility: Public, docs: Some("Money is represented in Postgres as a 64 bit signed integer.  This struct is a dumb wrapper\ntype, meant only to indicate the integer's meaning.  The fractional precision of the value is\ndetermined by the [`lc_monetary` setting of the database](https://www.postgresql.org/docs/9.6/static/datatype-money.html).\nThis struct is re-exported as `Cents` as a convenient and conventional expression of a typical\nunit of 1/100th of currency. For other names or precisions, users might consider a differently\nnamed `use` of the `PgMoney` struct.\n\n```rust\nuse diesel::data_types::PgMoney as Pence; // 1/100th unit of Pound\nuse diesel::data_types::PgMoney as Fils;  // 1/1000th unit of Dinar\n```"), links: {}, attrs: ["#[diesel(sql_type = Money)]"], deprecation: None, inner: Struct(Struct { struct_type: Tuple, generics: Generics { params: [], where_predicates: [] }, fields_stripped: false, fields: [Id("0:23814")], impls: [Id("a:2:8549-0:23812"), Id("a:2:3022-0:23812"), Id("a:2:8548-0:23812"), Id("a:2:3034-0:23812"), Id("a:2:3063-0:23812"), Id("b:0:542-0:23812"), Id("b:0:559-0:23812"), Id("b:0:549-0:23812"), Id("b:0:1745-0:23812"), Id("b:2:3736-0:23812"), Id("b:2:2951-0:23812"), Id("b:2:2630-0:23812"), Id("b:2:2966-0:23812"), Id("b:2:2955-0:23812"), Id("b:2:2627-0:23812"), Id("b:2:2961-0:23812"), Id("b:5:667-0:23812"), Id("0:23726"), Id("0:23728"), Id("0:23730"), Id("0:23731"), Id("0:23732"), Id("0:23735"), Id("0:23736"), Id("0:23738"), Id("0:23740"), Id("0:23765"), Id("0:23769"), Id("0:23783"), Id("0:23787"), Id("0:23790"), Id("0:23807"), Id("0:8373"), Id("0:8375"), Id("0:8378"), Id("0:8381"), Id("0:8383"), Id("0:8386")] }) }`', src/librustdoc/json/mod.rs:195:17

Backtrace

stack backtrace:
   0:     0x7fdbf675869c - std::backtrace_rs::backtrace::libunwind::trace::h9c95184963fef745
                               at /rustc/6abb6385b2cb7249f67b9b3ce7522527767dd907/library/std/src/../../backtrace/src/backtrace/libunwind.rs:93:5
   1:     0x7fdbf675869c - std::backtrace_rs::backtrace::trace_unsynchronized::h5d21f8fdfc262588
                               at /rustc/6abb6385b2cb7249f67b9b3ce7522527767dd907/library/std/src/../../backtrace/src/backtrace/mod.rs:66:5
   2:     0x7fdbf675869c - std::sys_common::backtrace::_print_fmt::h6ce732896d3b7bc2
                               at /rustc/6abb6385b2cb7249f67b9b3ce7522527767dd907/library/std/src/sys_common/backtrace.rs:67:5
   3:     0x7fdbf675869c - <std::sys_common::backtrace::_print::DisplayBacktrace as core::fmt::Display>::fmt::h56a1b948079bb60c
                               at /rustc/6abb6385b2cb7249f67b9b3ce7522527767dd907/library/std/src/sys_common/backtrace.rs:46:22
   4:     0x7fdbf67b987c - core::fmt::write::ha787ab3b9068d913
                               at /rustc/6abb6385b2cb7249f67b9b3ce7522527767dd907/library/core/src/fmt/mod.rs:1168:17
   5:     0x7fdbf6747d43 - std::io::Write::write_fmt::h4913c71f24efdd75
                               at /rustc/6abb6385b2cb7249f67b9b3ce7522527767dd907/library/std/src/io/mod.rs:1653:15
   6:     0x7fdbf675cac2 - std::sys_common::backtrace::_print::h8ba799ac9853e240
                               at /rustc/6abb6385b2cb7249f67b9b3ce7522527767dd907/library/std/src/sys_common/backtrace.rs:49:5
   7:     0x7fdbf675cac2 - std::sys_common::backtrace::print::hc1060288e0e5dcfe
                               at /rustc/6abb6385b2cb7249f67b9b3ce7522527767dd907/library/std/src/sys_common/backtrace.rs:36:9
   8:     0x7fdbf675cac2 - std::panicking::default_hook::{{closure}}::h5623b336a8b38b2c
                               at /rustc/6abb6385b2cb7249f67b9b3ce7522527767dd907/library/std/src/panicking.rs:290:50
   9:     0x7fdbf675c6a5 - std::panicking::default_hook::h7f9b0932f349911f
                               at /rustc/6abb6385b2cb7249f67b9b3ce7522527767dd907/library/std/src/panicking.rs:307:9
  10:     0x7fdbf6f39f41 - rustc_driver[d4f1704680c1e064]::DEFAULT_HOOK::{closure#0}::{closure#0}
  11:     0x7fdbe79723f3 - <alloc::boxed::Box<F,A> as core::ops::function::Fn<Args>>::call::h0599b93be78093ff
                               at /rustc/6abb6385b2cb7249f67b9b3ce7522527767dd907/library/alloc/src/boxed.rs:1868:9
  12:     0x7fdbe79aa70c - proc_macro::bridge::client::<impl proc_macro::bridge::Bridge>::enter::{{closure}}::{{closure}}::h45db41ffd4e35ab1
                               at /rustc/6abb6385b2cb7249f67b9b3ce7522527767dd907/library/proc_macro/src/bridge/client.rs:319:21
  13:     0x7fdbe795a920 - std::panicking::update_hook::{{closure}}::hfc35d8f8dfcea4c0
                               at /rustc/6abb6385b2cb7249f67b9b3ce7522527767dd907/library/std/src/panicking.rs:257:41
  14:     0x7fdbf675d2db - std::panicking::rust_panic_with_hook::h87cab73890184b28
                               at /rustc/6abb6385b2cb7249f67b9b3ce7522527767dd907/library/std/src/panicking.rs:695:17
  15:     0x7fdbf675cf97 - std::panicking::begin_panic_handler::{{closure}}::h541a05bf9df15ade
                               at /rustc/6abb6385b2cb7249f67b9b3ce7522527767dd907/library/std/src/panicking.rs:581:13
  16:     0x7fdbf6758b44 - std::sys_common::backtrace::__rust_end_short_backtrace::h18b7b64c8e3dc986
                               at /rustc/6abb6385b2cb7249f67b9b3ce7522527767dd907/library/std/src/sys_common/backtrace.rs:139:18
  17:     0x7fdbf675cca9 - rust_begin_unwind
                               at /rustc/6abb6385b2cb7249f67b9b3ce7522527767dd907/library/std/src/panicking.rs:577:5
  18:     0x7fdbf67242e3 - core::panicking::panic_fmt::h1720bda5e8269e46
                               at /rustc/6abb6385b2cb7249f67b9b3ce7522527767dd907/library/core/src/panicking.rs:135:14
  19:     0x7fdbf67b67b8 - core::panicking::assert_failed_inner::h449b64e1f2903a2a
  20:     0x55fbaa6bbccb - core[66374c829b964992]::panicking::assert_failed::<rustdoc_json_types[fb211a9f4b61a76c]::Item, rustdoc_json_types[fb211a9f4b61a76c]::Item>
  21:     0x55fbaa97d885 - <rustdoc[3bca669b999d636e]::json::JsonRenderer as rustdoc[3bca669b999d636e]::formats::renderer::FormatRenderer>::item
  22:     0x55fbaa978af9 - <rustdoc[3bca669b999d636e]::json::JsonRenderer as rustdoc[3bca669b999d636e]::formats::renderer::FormatRenderer>::item
  23:     0x55fbaa978af9 - <rustdoc[3bca669b999d636e]::json::JsonRenderer as rustdoc[3bca669b999d636e]::formats::renderer::FormatRenderer>::item
  24:     0x55fbaa978af9 - <rustdoc[3bca669b999d636e]::json::JsonRenderer as rustdoc[3bca669b999d636e]::formats::renderer::FormatRenderer>::item
  25:     0x55fbaa99bf7b - rustdoc[3bca669b999d636e]::formats::renderer::run_format::<rustdoc[3bca669b999d636e]::json::JsonRenderer>
  26:     0x55fbaa6dc798 - rustdoc[3bca669b999d636e]::run_renderer::<rustdoc[3bca669b999d636e]::json::JsonRenderer>
  27:     0x55fbaa6f7b4b - <rustc_session[ad3655c0359ac0f8]::session::Session>::time::<core[66374c829b964992]::result::Result<(), rustc_errors[86224a19c1a30ce1]::ErrorReported>, rustdoc[3bca669b999d636e]::main_options::{closure#0}::{closure#0}::{closure#1}::{closure#2}>
  28:     0x55fbaa893885 - <rustc_interface[7eb630a73ce93593]::interface::Compiler>::enter::<rustdoc[3bca669b999d636e]::main_options::{closure#0}::{closure#0}, core[66374c829b964992]::result::Result<(), rustc_errors[86224a19c1a30ce1]::ErrorReported>>
  29:     0x55fbaa91a1cc - rustc_span[342a111d7a8110f2]::with_source_map::<core[66374c829b964992]::result::Result<(), rustc_errors[86224a19c1a30ce1]::ErrorReported>, rustc_interface[7eb630a73ce93593]::interface::create_compiler_and_run<core[66374c829b964992]::result::Result<(), rustc_errors[86224a19c1a30ce1]::ErrorReported>, rustdoc[3bca669b999d636e]::main_options::{closure#0}>::{closure#1}>
  30:     0x55fbaa886277 - rustc_interface[7eb630a73ce93593]::interface::create_compiler_and_run::<core[66374c829b964992]::result::Result<(), rustc_errors[86224a19c1a30ce1]::ErrorReported>, rustdoc[3bca669b999d636e]::main_options::{closure#0}>
  31:     0x55fbaa6de0de - rustdoc[3bca669b999d636e]::main_options
  32:     0x55fbaa6f604d - <scoped_tls[158ee4356b9d3fb1]::ScopedKey<rustc_span[342a111d7a8110f2]::SessionGlobals>>::set::<rustc_interface[7eb630a73ce93593]::util::setup_callbacks_and_run_in_thread_pool_with_globals<rustdoc[3bca669b999d636e]::main_args::{closure#0}, core[66374c829b964992]::result::Result<(), rustc_errors[86224a19c1a30ce1]::ErrorReported>>::{closure#0}::{closure#0}, core[66374c829b964992]::result::Result<(), rustc_errors[86224a19c1a30ce1]::ErrorReported>>
  33:     0x55fbaa8c4b59 - std[ecfd9b74f7001338]::sys_common::backtrace::__rust_begin_short_backtrace::<rustc_interface[7eb630a73ce93593]::util::setup_callbacks_and_run_in_thread_pool_with_globals<rustdoc[3bca669b999d636e]::main_args::{closure#0}, core[66374c829b964992]::result::Result<(), rustc_errors[86224a19c1a30ce1]::ErrorReported>>::{closure#0}, core[66374c829b964992]::result::Result<(), rustc_errors[86224a19c1a30ce1]::ErrorReported>>
  34:     0x55fbaa6f5839 - <<std[ecfd9b74f7001338]::thread::Builder>::spawn_unchecked_<rustc_interface[7eb630a73ce93593]::util::setup_callbacks_and_run_in_thread_pool_with_globals<rustdoc[3bca669b999d636e]::main_args::{closure#0}, core[66374c829b964992]::result::Result<(), rustc_errors[86224a19c1a30ce1]::ErrorReported>>::{closure#0}, core[66374c829b964992]::result::Result<(), rustc_errors[86224a19c1a30ce1]::ErrorReported>>::{closure#1} as core[66374c829b964992]::ops::function::FnOnce<()>>::call_once::{shim:vtable#0}
  35:     0x7fdbf6768e83 - <alloc::boxed::Box<F,A> as core::ops::function::FnOnce<Args>>::call_once::h055a74f58759b602
                               at /rustc/6abb6385b2cb7249f67b9b3ce7522527767dd907/library/alloc/src/boxed.rs:1854:9
  36:     0x7fdbf6768e83 - <alloc::boxed::Box<F,A> as core::ops::function::FnOnce<Args>>::call_once::hb194029d87e03ea5
                               at /rustc/6abb6385b2cb7249f67b9b3ce7522527767dd907/library/alloc/src/boxed.rs:1854:9
  37:     0x7fdbf6768e83 - std::sys::unix::thread::Thread::new::thread_start::h79b5483319eb1ce5
                               at /rustc/6abb6385b2cb7249f67b9b3ce7522527767dd907/library/std/src/sys/unix/thread.rs:108:17
  38:     0x7fdbf63f5927 - start_thread
                               at ./nptl/./nptl/pthread_create.c:435:8
  39:     0x7fdbf64859e4 - __clone
                               at ./misc/../sysdeps/unix/sysv/linux/x86_64/clone.S:100
  40:                0x0 - <unknown>

error: internal compiler error: unexpected panic

[CraftSpider]

This looks like a duplicate of #83720, and as such should be fixed by #93518

[weiznich]

Any news on this? I keep hitting this (with different types) on the current nightly (rustdoc 1.62.0-nightly (34a6c9f26 2022-04-13))

[Enselic]

I don't think this is a duplicate of either #83720 or #83057, because making all modules public and removing all #[doc(inline)] attributes does not get rid of the ICE. This is what I did to try this:

git clone https://github.com/diesel-rs/diesel.git && cd diesel # commit 983209a61 for me

# Make all modules public
git ls-files | grep '\.rs' | xargs perl -pi -e 's/^ *mod /pub mod /'

# Undo partially to fix : error: `proc-macro` crate types currently cannot export any items other than functions tagged with `#[proc_macro]`
git restore diesel_derives/src/lib.rs diesel_migrations/migrations_macros/src/lib.rs 

# Remove all #[doc(inline)]
git ls-files | grep '\.rs$' | xargs perl -pi -e 's/.*#\[doc\(inline\)\]//'

but I still get the same ICE as I get before my changes (in my case it is row_metadata that has duplicate items).

I have tried to debug this further, but no luck so far. I have tried to:

• Systematically remove code from diesel to get the minimal code that can be used to reproduce this, but it turned out to be tricky
• Dump the HIR with cargo +nightly rustc -- -Z unpretty=hir-tree, but that command does not complete for me, it just eats gigs of RAM until I kill it. Edit: This has been fixed by Remove quadratic behaviour from -Zunpretty=hir-tree. #97223
• Build the compiler and rustdoc with tracing, but I get the same problem. rustdoc never completes, it just steadly eats more and more RAM until I have to kill it.

Maybe someone with better knowledge of diesel could help to reduce the code in diesel to a minimal example that can be used to reproduce and debug the ICE?

Disclaimer: My methodology might be flawed, because I'm still no veteran when it comes to debugging problems like these.

[Enselic]

I figured out how to make rustdoc not cause an ICE when generating rustdoc JSON for the main crate diesel/diesel. Maybe this gives someone enough of a clue to figure out what is wrong?

See https://github.com/Enselic/diesel/pull/1/files for the diff that makes rustdoc JSON work. For example, I had to change

impl<T, ST> AsExpression<ST> for T
where
    T: Expression<SqlType = ST>,
    ST: SqlType + TypedExpressionType,
{
    type Expression = Self;

    fn as_expression(self) -> Self {
        self
    }
}

to

impl<T, ST> AsExpression<ST> for T
where
    T: Expression<SqlType = ST>,
    ST: SqlType + TypedExpressionType,
{
    type Expression = T;

    fn as_expression(self) -> T {
        self
    }
}

This fixes the error where one instance of the item with the same ID contains T whereas the other contains Self. But that is just one example.

I haven't yet figured out a minimal way to reproduce. When I rip out this code and put it in a minimal crate, there is no ICE. There is probably some complicated construct that is causing these problems.

CC @aDotInTheVoid who usually is interested in rustdoc JSON stuff.

[aDotInTheVoid]

Started a minification at https://github.com/aDotInTheVoid/diesel-93588, not made much progress.

[Enselic]

I just wanted to add an observation. One of causes of the ICEs is that the typedef item corresponding to type Expression = Self (see #93588 (comment)) also can be represented as type Expression = T, but ends up having the same ID. But, in this context, T and Self is equivalent! So failing on the assert_eq!(old_item, new_item) in src/librustdoc/json/mod.rs doesn't make sense semantically. Because the items are in fact the same.

So to fix this class of ICE problems, it should work to normalise the representation so that the two instance of the same typedef item is the same. This "trick" should in fact fix all cases of ICE in diesel/diesel that I pinpoint with https://github.com/Enselic/diesel/pull/1/files. Because in all cases it is about the same item having different but equivalent representations.

Probably easier said than done to actually implement though... But maybe the code for this already exists for other uses somewhere in the compiler.