ICE: rustdoc on issue-43106-gating-of-proc_macro_derive.rs: proc-macro derives require a name

[matthiaskrgr]

Code

code from ./src/test/ui/feature-gate/issue-43106-gating-of-proc_macro_derive.rs

// At time of authorship, #[proc_macro_derive = "2500"] will emit an
// error when it occurs on a mod (apart from crate-level), but will
// not descend further into the mod for other occurrences of the same
// error.
//
// This file sits on its own because the "weird" occurrences here
// signal errors, making it incompatible with the "warnings only"
// nature of issue-43106-gating-of-builtin-attrs.rs

#[proc_macro_derive()]
//~^ ERROR the `#[proc_macro_derive]` attribute may only be used on bare functions
mod proc_macro_derive1 {
    mod inner { #![proc_macro_derive()] }
    // (no error issued here if there was one on outer module)
}

mod proc_macro_derive2 {
    mod inner { #![proc_macro_derive()] }
    //~^ ERROR the `#[proc_macro_derive]` attribute may only be used on bare functions

    #[proc_macro_derive()] fn f() { }
    //~^ ERROR the `#[proc_macro_derive]` attribute is only usable with crates of the `proc-macro`

    #[proc_macro_derive()] struct S;
    //~^ ERROR the `#[proc_macro_derive]` attribute may only be used on bare functions

    #[proc_macro_derive()] type T = S;
    //~^ ERROR the `#[proc_macro_derive]` attribute may only be used on bare functions

    #[proc_macro_derive()] impl S { }
    //~^ ERROR the `#[proc_macro_derive]` attribute may only be used on bare functions
}

fn main() {}

Meta

rustc --version --verbose:

rustdoc 1.50.0-nightly (1c389ffef 2020-11-24)
binary: rustdoc
commit-hash: 1c389ffeff814726dec325f0f2b0c99107df2673
commit-date: 2020-11-24
host: x86_64-unknown-linux-gnu
release: 1.50.0-nightly

Error output

warning: Trying to document proc macro crate without passing '--crate-type proc-macro to rustdoc
  |
  = warning: The generated documentation may be incorrect

thread 'rustc' panicked at 'proc-macro derives require a name', src/librustdoc/clean/mod.rs:896:22
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

error: internal compiler error: unexpected panic

note: the compiler unexpectedly panicked. this is a bug.

note: we would appreciate a bug report: https://github.com/rust-lang/rust/issues/new?labels=C-bug%2C+I-ICE%2C+T-compiler&template=ice.md

note: rustc 1.50.0-nightly (1c389ffef 2020-11-24) running on x86_64-unknown-linux-gnu

query stack during panic:
end of query stack
warning: 1 warning emitted

Backtrace

warning: Trying to document proc macro crate without passing '--crate-type proc-macro to rustdoc
  |
  = warning: The generated documentation may be incorrect

thread 'rustc' panicked at 'proc-macro derives require a name', src/librustdoc/clean/mod.rs:896:22
stack backtrace:
   0:     0x7f430fecee30 - std::backtrace_rs::backtrace::libunwind::trace::h746c3e9529d524bc
                               at /rustc/1c389ffeff814726dec325f0f2b0c99107df2673/library/std/src/../../backtrace/src/backtrace/libunwind.rs:90:5
   1:     0x7f430fecee30 - std::backtrace_rs::backtrace::trace_unsynchronized::h86340908ff889faa
                               at /rustc/1c389ffeff814726dec325f0f2b0c99107df2673/library/std/src/../../backtrace/src/backtrace/mod.rs:66:5
   2:     0x7f430fecee30 - std::sys_common::backtrace::_print_fmt::h43f85f9b18230404
                               at /rustc/1c389ffeff814726dec325f0f2b0c99107df2673/library/std/src/sys_common/backtrace.rs:67:5
   3:     0x7f430fecee30 - <std::sys_common::backtrace::_print::DisplayBacktrace as core::fmt::Display>::fmt::hc132ae1a5b5aa7cd
                               at /rustc/1c389ffeff814726dec325f0f2b0c99107df2673/library/std/src/sys_common/backtrace.rs:46:22
   4:     0x7f430ff41c4c - core::fmt::write::hdf023a0036d2a25f
                               at /rustc/1c389ffeff814726dec325f0f2b0c99107df2673/library/core/src/fmt/mod.rs:1078:17
   5:     0x7f430fec09a2 - std::io::Write::write_fmt::h8580846154bcb66a
                               at /rustc/1c389ffeff814726dec325f0f2b0c99107df2673/library/std/src/io/mod.rs:1519:15
   6:     0x7f430fed2a95 - std::sys_common::backtrace::_print::h7ee55fed88d107a3
                               at /rustc/1c389ffeff814726dec325f0f2b0c99107df2673/library/std/src/sys_common/backtrace.rs:49:5
   7:     0x7f430fed2a95 - std::sys_common::backtrace::print::h54a7d3e52a524177
                               at /rustc/1c389ffeff814726dec325f0f2b0c99107df2673/library/std/src/sys_common/backtrace.rs:36:9
   8:     0x7f430fed2a95 - std::panicking::default_hook::{{closure}}::h60921e857bf55a40
                               at /rustc/1c389ffeff814726dec325f0f2b0c99107df2673/library/std/src/panicking.rs:208:50
   9:     0x7f430fed25ea - std::panicking::default_hook::hf0f9afb1017317fc
                               at /rustc/1c389ffeff814726dec325f0f2b0c99107df2673/library/std/src/panicking.rs:225:9
  10:     0x7f431075fbb8 - rustc_driver::report_ice::ha25ae86a5858acc3
  11:     0x7f430fed3396 - std::panicking::rust_panic_with_hook::h8d66bf42b407aaea
                               at /rustc/1c389ffeff814726dec325f0f2b0c99107df2673/library/std/src/panicking.rs:595:17
  12:     0x7f430fed2eb7 - std::panicking::begin_panic_handler::{{closure}}::hde71edcd925d0c5e
                               at /rustc/1c389ffeff814726dec325f0f2b0c99107df2673/library/std/src/panicking.rs:497:13
  13:     0x7f430fecf2ec - std::sys_common::backtrace::__rust_end_short_backtrace::h8a3c7d6cea578919
                               at /rustc/1c389ffeff814726dec325f0f2b0c99107df2673/library/std/src/sys_common/backtrace.rs:141:18
  14:     0x7f430fed2e19 - rust_begin_unwind
                               at /rustc/1c389ffeff814726dec325f0f2b0c99107df2673/library/std/src/panicking.rs:493:5
  15:     0x7f430ff3e031 - core::panicking::panic_fmt::h20225113c4a2f8fd
                               at /rustc/1c389ffeff814726dec325f0f2b0c99107df2673/library/core/src/panicking.rs:92:14
  16:     0x7f430ff3dc13 - core::option::expect_failed::h8be1ca96ca0d69ca
                               at /rustc/1c389ffeff814726dec325f0f2b0c99107df2673/library/core/src/option.rs:1260:5
  17:     0x55a546696a67 - <(&rustc_hir::hir::Item,core::option::Option<rustc_span::symbol::Ident>) as rustdoc::clean::Clean<alloc::vec::Vec<rustdoc::clean::types::Item>>>::clean::h6efe2622d62f0879
  18:     0x55a5467a101f - <alloc::vec::Vec<T,A> as alloc::vec::SpecExtend<T,I>>::spec_extend::hbf27f2437fec8031
  19:     0x55a54671dde8 - <rustdoc::doctree::Module as rustdoc::clean::Clean<rustdoc::clean::types::Item>>::clean::hee8955bac14e83bc
  20:     0x55a54671dd50 - <rustdoc::doctree::Module as rustdoc::clean::Clean<rustdoc::clean::types::Item>>::clean::hee8955bac14e83bc
  21:     0x55a546717153 - rustdoc::clean::utils::krate::h68bb50ab032123ce
  22:     0x55a546492b3b - rustdoc::core::run_global_ctxt::h7cf39be6ea65128e
  23:     0x55a54650cece - rustc_interface::passes::QueryContext::enter::hedb615e17429b641
  24:     0x55a546602917 - rustc_interface::interface::create_compiler_and_run::h25fa5935e40978f2
  25:     0x55a5464a90d3 - rustdoc::main_options::h8a5cda9c1c8c625b
  26:     0x55a5465f3a68 - rustc_span::with_session_globals::h7a83fbbd64fb6823
  27:     0x55a5464da30e - std::sys_common::backtrace::__rust_begin_short_backtrace::h50722f4a01515f7b
  28:     0x55a54660c03a - core::ops::function::FnOnce::call_once{{vtable.shim}}::h22276985fb540191
  29:     0x7f430fee265a - <alloc::boxed::Box<F,A> as core::ops::function::FnOnce<Args>>::call_once::hea1090dbdcecbf5a
                               at /rustc/1c389ffeff814726dec325f0f2b0c99107df2673/library/alloc/src/boxed.rs:1318:9
  30:     0x7f430fee265a - <alloc::boxed::Box<F,A> as core::ops::function::FnOnce<Args>>::call_once::h8d5723d3912bd325
                               at /rustc/1c389ffeff814726dec325f0f2b0c99107df2673/library/alloc/src/boxed.rs:1318:9
  31:     0x7f430fee265a - std::sys::unix::thread::Thread::new::thread_start::hc17a425ca2995724
                               at /rustc/1c389ffeff814726dec325f0f2b0c99107df2673/library/std/src/sys/unix/thread.rs:71:17
  32:     0x7f430fdbe3e9 - start_thread
  33:     0x7f430fba4293 - __GI___clone
  34:                0x0 - <unknown>

error: internal compiler error: unexpected panic

note: the compiler unexpectedly panicked. this is a bug.

note: we would appreciate a bug report: https://github.com/rust-lang/rust/issues/new?labels=C-bug%2C+I-ICE%2C+T-compiler&template=ice.md

note: rustc 1.50.0-nightly (1c389ffef 2020-11-24) running on x86_64-unknown-linux-gnu

query stack during panic:
end of query stack
warning: 1 warning emitted

[matthiaskrgr]

@rustbot label -T-compiler +T-rustdoc

[fanninpm]

Playground link of example

[jyn514]

MCVE:

#![crate_type="proc-macro"]

extern crate proc_macro;
use proc_macro::TokenStream;

#[proc_macro_derive()]
pub fn some_derive(_: TokenStream) -> TokenStream {
    TokenStream::new()
}

Rustc gives the correct error:

error: attribute must have either one or two arguments
 --> proc_macro.rs:6:1
  |
6 | #[proc_macro_derive()]
  | ^^^^^^^^^^^^^^^^^^^^^^

which is emitted from here:

rust/compiler/rustc_builtin_macros/src/proc_macro_harness.rs

Line 120 in 0c11b93

self.handler.span_err(attr.span, "attribute must have either one or two arguments");

So for some reason that pass isn't getting run by rustdoc (probably because of the hackery in

rust/src/librustdoc/core.rs

Lines 457 to 473 in 0c11b93

	// Certain queries assume that some checks were run elsewhere
	// (see https://github.com/rust-lang/rust/pull/73566#issuecomment-656954425),
	// so type-check everything other than function bodies in this crate before running lints.
	// NOTE: this does not call `tcx.analysis()` so that we won't
	// typeck function bodies or run the default rustc lints.
	// (see `override_queries` in the `config`)
	// HACK(jynelson) this calls an _extremely_ limited subset of `typeck`
	// and might break if queries change their assumptions in the future.
	// NOTE: This is copy/pasted from typeck/lib.rs and should be kept in sync with those changes.
	tcx.sess.time("item_types_checking", || {
	for &module in tcx.hir().krate().modules.keys() {
	tcx.ensure().check_mod_item_types(tcx.hir().local_def_id(module));
	}
	});

). The fix is to run that pass.

[jyn514]

Marking as P-low since there are many places where rustdoc assumes its inputs are valid (e.g. all of https://doc.rust-lang.org/nightly/rustdoc/advanced-features.html#interactions-between-platform-specific-docs) and I don't think it's particularly important to handle invalid input, since people learn by running rustc, not rustdoc*.

---

*with the caveat that this only applies to features that are common to rustc and rustdoc; it's very important for rustdoc to handle invalid intra-doc links for example.