ICE bootstrapping rustc with NLL enabled

[nikomatsakis]

When I try to bootstrap rustc with NLL enabled, I get an odd ICE compiling libsyntax_ext:

error: internal compiler error: broken MIR in NodeId(16117) (_368 = move _369): bad assignment (for<'cx, 'r, 's> fn(&'cx mut syntax::ext::base::ExtCtxt<'r>, syntax_pos::Span, &'s [syntax::tokenstream::To\
kenTree]) -> std::boxed::Box<syntax::ext::base::MacResult + 'cx> = for<'r, 's, 't0> fn(&'r mut syntax::ext::base::ExtCtxt<'s>, syntax_pos::Span, &'t0 [syntax::tokenstream::TokenTree]) -> std::boxed::Box<\
syntax::ext::base::MacResult>): RegionsOverlyPolymorphic(BrNamed(crate11:DefIndex(1:1012), 'cx), '_#729r)
   --> src/libsyntax_ext/lib.rs:65:44
    |
65  |                           expander: Box::new($f as MacroExpanderFn),
    |                                              ^^^^^^^^^^^^^^^^^^^^^
...
92  | /     register! {
93  | |         line: expand_line,
94  | |         __rust_unstable_column: expand_column_gated,
95  | |         column: expand_column,
...   |
112 | |         compile_error: compile_error::expand_compile_error,
113 | |     }
    | |_____- in this macro invocation

[Aaron1011]

I'd like to work on this.

[nikomatsakis]

@Aaron1011 any progress? want me to take a look at all?

[Aaron1011]

@nikomatsakis: I haven't yet been able to reproduce this, due to #48129 stopping compilation. I'll try to work around that issue locally, and see if I can reproduce + investigate the original issue.

[Aaron1011]

@nikomatsakis: I ran across another issue while trying to reach the ICE: #48224

[Aaron1011]

@nikomatsakis: Until the intermediate issues are resolved, I don't think I'll be able to reproduce this.

[nikomatsakis]

@Aaron1011 this branch #48372 clears the way

[nikomatsakis]

Hmm, but on that branch I am now encountering the AddAssign problems I guess. So we're still blocked on #48129

[nikomatsakis]

Actually, the issue-48071 branch on my repo reproduces the problem. You have to build like so:

RUSTFLAGS_STAGE_NOT_0='-Znll -Zborrowck=mir -Ztwo-phase-borrows' ./x.py build --stage 2 

[nikomatsakis]

Error that I get is (lightly edited):

error: internal compiler error: broken MIR in NodeId(16117) (_368 = move _369): bad assignment (

for<'cx, 'r, 's> fn(&'cx mut syntax::ext::base::ExtCtxt<'r>, syntax_pos::Span, &'s [syntax::tokenstream::TokenTree]) -> std::boxed::Box<syntax::ext::base::MacResult + 'cx>
for<'r, 's, 't0> fn(&'r mut syntax::ext::base::ExtCtxt<'s>, syntax_pos::Span, &'t0 [syntax::tokenstream::TokenTree]) -> std::boxed::Box<syntax::ext::base::MacResult>): 

RegionsOverlyPolymorphic(BrNamed(crate11:DefIndex(1:1012), 'cx), '_#729r)

Removing explicit paths:

for<'cx, 'r, 's> fn(&'cx mut ExtCtxt<'r>, Span, &'s [TokenTree]) -> Box<MacResult + 'cx>
for<'r, 's, 't0> fn(&'r mut ExtCtxt<'s>, Span, &'t0 [TokenTree]) -> Box<MacResult>)

The problem seems to be the return type.

[nikomatsakis]

Minimized:

#![allow(warnings)]
#![feature(dyn_trait)]
#![feature(nll)]

trait Foo {
    fn foo(&self) { }
}

impl Foo for () {
}

type MakeFooFn = for<'a> fn(&'a u8) -> Box<dyn Foo + 'a>;

fn make_foo(x: &u8) -> Box<dyn Foo + 'static> {
    Box::new(())
}

fn main() {
    let x: MakeFooFn = make_foo as MakeFooFn;
}