ICE when proc-macro crate and non proc-macro crate share Cargo project

[SergioBenitez]

This is a regression introduced in a recent nightly.

When a lib and a bin are declared in the same Cargo project, where the lib is of type proc-macro, rustc experiences an ICE with a message of thread 'main' panicked at 'librustc_metadata/creader.rs:520: proc-macro crate not dylib', librustc/session/mod.rs:1281:26. This error does not occur when the proc-macro lib and the bin are split into independent Cargo projects. Running with CARGO_INCREMENTAL=0 does not change the outcome.

Cargo.toml looks as follows:

[package]
name = "demo"
version = "0.0.1"

[lib]
name = "codegen"
proc-macro = true
path = "src/lib.rs"

[[bin]]
name = "main"
path = "src/main.rs"

[dependencies]

src/lib.rs looks as follows:

#![feature(proc_macro)]

extern crate proc_macro;

use proc_macro::TokenStream;

#[proc_macro_attribute]
pub fn demo(_args: TokenStream, input: TokenStream) -> TokenStream {
    input
}

src/main.rs looks as follows:

#![feature(proc_macro)]

extern crate codegen;

use codegen::demo;

#[demo]
fn test() { }

fn main() {
    println!("Hello, world!");
}

The full error log:

❯ rustc --version --verbose
rustc 1.27.0-nightly (e5f80f2a4 2018-05-09)
binary: rustc
commit-hash: e5f80f2a4f016bf724a1cfb580619d71c8fd39ec
commit-date: 2018-05-09
host: x86_64-apple-darwin
release: 1.27.0-nightly
LLVM version: 6.0
❯ RUST_BACKTRACE=1  cargo check -v

Checking demo v0.0.1 (file:///rustc-bug)

Running rustc --crate-name main src/main.rs --crate-type bin --emit=dep-info,metadata -C debuginfo=2 -C metadata=411579df123c68f9 -C extra-filename=-411579df123c68f9 --out-dir /rustc-bug/target/debug/deps -C incremental=/rustc-bug/target/debug/incremental -L dependency=/rustc-bug/target/debug/deps --extern codegen=/rustc-bug/target/debug/deps/libcodegen-c52c60a16469d04d.rmeta

thread 'main' panicked at 'librustc_metadata/creader.rs:520: proc-macro crate not dylib', librustc/session/mod.rs:1281:26

stack backtrace:

0: std::sys::unix::backtrace::tracing::imp::unwind_backtrace

1: std::sys_common::backtrace::print

2: std::panicking::default_hook::{{closure}}

3: std::panicking::default_hook

4: rustc::util::common::panic_hook

5: std::panicking::rust_panic_with_hook

6: std::panicking::begin_panic

7: rustc::session::opt_span_bug_fmt::{{closure}}

8: rustc::ty::context::tls::with_opt::{{closure}}

9: rustc::ty::context::tls::with_context_opt

10: rustc::ty::context::tls::with_opt

11: rustc::session::opt_span_bug_fmt

12: rustc::session::span_bug_fmt

13: rustc_metadata::creader::CrateLoader::resolve_crate

14: <rustc_metadata::creader::CrateLoader<'a> as rustc::middle::cstore::CrateLoader>::process_extern_crate

15: rustc_resolve::build_reduced_graph::<impl rustc_resolve::Resolver<'a>>::build_reduced_graph_for_item

16: <rustc_resolve::build_reduced_graph::BuildReducedGraphVisitor<'a, 'b> as syntax::visit::Visitor<'a>>::visit_item

17: syntax::visit::walk_item

18: <rustc_resolve::build_reduced_graph::BuildReducedGraphVisitor<'a, 'b> as syntax::visit::Visitor<'a>>::visit_item

19: syntax::ext::expand::Expansion::visit_with

20: rustc_resolve::macros::<impl syntax::ext::base::Resolver for rustc_resolve::Resolver<'a>>::visit_expansion

21: syntax::ext::expand::MacroExpander::collect_invocations

22: syntax::ext::expand::MacroExpander::expand

23: syntax::ext::expand::MacroExpander::expand_crate

24: rustc_driver::driver::phase_2_configure_and_expand_inner::{{closure}}

25: rustc::util::common::time

26: rustc_driver::driver::phase_2_configure_and_expand

27: rustc_driver::driver::compile_input

28: rustc_driver::run_compiler_impl

29: <scoped_tls::ScopedKey>::set

30: syntax::with_globals

31: <std::panic::AssertUnwindSafe as core::ops::function::FnOnce<()>>::call_once

32: __rust_maybe_catch_panic

33: rustc_driver::run

34: rustc_driver::main

35: std::rt::lang_start::{{closure}}

36: std::panicking::try::do_call

37: __rust_maybe_catch_panic

38: std::rt::lang_start_internal

39: main

query stack during panic:

end of query stack
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/blob/master/CONTRIBUTING.md#bug-reports
note: rustc 1.27.0-nightly (e5f80f2a4 2018-05-09) running on x86_64-apple-darwin
note: compiler flags: -C debuginfo=2 -C incremental --crate-type bin
note: some of the compiler flags provided by cargo are hidden
error: Could not compile demo.
Caused by:

process didn't exit successfully: rustc --crate-name main src/main.rs --crate-type bin --emit=dep-info,metadata -C debuginfo=2 -C metadata=411579df123c68f9 -C extra-filename=-411579df123c68f9 --out-dir /rustc-bug/target/debug/deps -C incremental=/rustc-bug/target/debug/incremental -L dependency=/rustc-bug/target/debug/deps --extern codegen=/rustc-bug/target/debug/deps/libcodegen-c52c60a16469d04d.rmeta (exit code: 101)

[pietroalbini]

A bisect points at #50345 as the cause of the regression, which is a rollup. The only thing that might make sense in there is the cargo update. cc @alexcrichton

[alexcrichton]

Yep looks like a Cargo regression, looking into it

[alexcrichton]

I believe this should be fixed in rust-lang/cargo#5520