rustc doesn't output anything but exits with 101 and doesn't emit any files

trait Foo {
    type Out;
}

impl<T> Foo for Box<T> {
    type Out where T: Clone = T;
}

fn main() {}

Compiling this code results in no output by rustc. But rustc exits with 101 and does not produce any artifacts. (On Playground)

The error happens with:

rustc 1.27.1 (5f2b325f6 2018-07-07),
rustc 1.27.2 (58cc626de 2018-07-18), and
rustc 1.29.0-nightly (874dec25e 2018-07-21)

$ rustc -Z time-passes a.rs
  time: 0.001	parsing
  time: 0.000	recursion limit
  time: 0.000	crate injection
  time: 0.000	plugin loading
  time: 0.000	plugin registration
  time: 0.000	pre ast expansion lint checks
    time: 0.037	expand crate
    time: 0.000	check unused macros
  time: 0.037	expansion
  time: 0.000	maybe building test harness
  time: 0.000	maybe creating a macro crate
  time: 0.000	creating allocators
  time: 0.000	AST validation
  time: 0.000	name resolution
  time: 0.000	complete gated feature checking
  time: 0.000	lowering ast -> hir
  time: 0.000	early lint checks
  time: 0.000	indexing hir
  time: 0.000	load query result cache
  time: 0.000	looking for entry point
  time: 0.000	looking for plugin registrar
  time: 0.000	loop checking
  time: 0.000	attribute checking
  time: 0.000	stability checking

If I set breakpoints on

rustc::middle::stability::check_unstable_api_usage
rustc_typeck::check_crate
rustc_passes::rvalue_promotion::check_crate

It hits the first two but not the third, seemingly pointing to rustc_typeck::check_crate returning an Err.

The silent exit is a regression. From godbolt,

1.23.0

error: expected `=`, found `where`
 --> <source>:6:14
  |
6 |     type Out where T: Clone = T;
  |              ^^^^^
error[E0046]: not all trait items implemented, missing: `Out`
 --> <source>:5:1
  |
2 |       type Out;
  |       --------- `Out` from trait
...
5 | / impl<T> Foo for Box<T> {
6 | |     type Out where T: Clone = T;
7 | | }
  | |_^ missing `Out` in implementation
error: aborting due to 2 previous errors

exit code = 101

1.24.0–1.25.0

error: cannot continue compilation due to previous error

exit code = 101

1.26.0–1.28.0(beta)

No message, exit code = 101
1.29.0(nightly)

No message, exit code = 1

cc @rust-lang/compiler -- it'd be good to find out why we stopped providing any output at all here

I'm worried it might be one of my parser changes to provide better diagnostics... I would probably check for any odd looking err.cancel().

rust/src/libsyntax/parse/parser.rs

Line 1349 in 11f812a

self.parse_trait_item_assoc_ty()?

rust/src/libsyntax/parse/parser.rs

Lines 4940 to 4963 in 11f812a

    
               /// Parses the following grammar: 
        
               ///     TraitItemAssocTy = Ident ["<"...">"] [":" [GenericBounds]] ["where" ...] ["=" Ty] 
        
               fn parse_trait_item_assoc_ty(&mut self) 
        
                   -> PResult<'a, (Ident, TraitItemKind, ast::Generics)> { 
        
                   let ident = self.parse_ident()?; 
        
                   let mut generics = self.parse_generics()?; 
        
                   // Parse optional colon and param bounds. 
        
                   let bounds = if self.eat(&token::Colon) { 
        
                       self.parse_generic_bounds()? 
        
                   } else { 
        
                       Vec::new() 
        
                   }; 
        
                   generics.where_clause = self.parse_where_clause()?; 
        
                   let default = if self.eat(&token::Eq) { 
        
                       Some(self.parse_ty()?) 
        
                   } else { 
        
                       None 
        
                   }; 
        
                   self.expect(&token::Semi)?; 
        
                   Ok((ident, TraitItemKind::Type(bounds, default), generics)) 
        
               }

It's not the parsing itself, it's that in 1.24 the feature was introduced: #45904.

@estebank

@estebank do you think you see what the problem is?

Calling P-high but we don't yet have an obvious assignee. Still, seems bad that there is no diagnostic output at all! Not a good look.

The core issue is reported in #47206. However, the example here also demonstrates that where clauses aren't being feature gated properly.

I've made #53235 to address the surface problem, which is that you can trigger this on stable, without declaring the generic_associated_types feature. I thought it was better to fix that part of the problem straight away.

Narrowing it down a little more:

rust/src/librustc_typeck/astconv.rs

Lines 1157 to 1163 in 1aa6c23

    
           hir::TyKind::Path(hir::QPath::Resolved(ref maybe_qself, ref path)) => { 
        
               debug!("ast_ty_to_ty: maybe_qself={:?} path={:?}", maybe_qself, path); 
        
               let opt_self_ty = maybe_qself.as_ref().map(|qself| { 
        
                   self.ast_ty_to_ty(qself) 
        
               }); 
        
               self.def_to_ty(opt_self_ty, path, false) 
        
           }

path.def is Def::Err at this point when the where clauses are defined, so something's going wrong before that point.

Rollup merge of rust-lang#53235 - varkor:gat_impl_where, r=estebank

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`rustc` doesn't output anything but exits with 101 and doesn't emit any files #52913

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	/// Parses the following grammar:
	/// TraitItemAssocTy = Ident ["<"...">"] [":" [GenericBounds]] ["where" ...] ["=" Ty]
	fn parse_trait_item_assoc_ty(&mut self)
	-> PResult<'a, (Ident, TraitItemKind, ast::Generics)> {
	let ident = self.parse_ident()?;
	let mut generics = self.parse_generics()?;

	// Parse optional colon and param bounds.
	let bounds = if self.eat(&token::Colon) {
	self.parse_generic_bounds()?
	} else {
	Vec::new()
	};
	generics.where_clause = self.parse_where_clause()?;

	let default = if self.eat(&token::Eq) {
	Some(self.parse_ty()?)
	} else {
	None
	};
	self.expect(&token::Semi)?;

	Ok((ident, TraitItemKind::Type(bounds, default), generics))
	}

	hir::TyKind::Path(hir::QPath::Resolved(ref maybe_qself, ref path)) => {
	debug!("ast_ty_to_ty: maybe_qself={:?} path={:?}", maybe_qself, path);
	let opt_self_ty = maybe_qself.as_ref().map(\|qself\| {
	self.ast_ty_to_ty(qself)
	});
	self.def_to_ty(opt_self_ty, path, false)
	}

rustc doesn't output anything but exits with 101 and doesn't emit any files #52913

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shepmaster commented on Jul 31, 2018

kennytm commented on Aug 1, 2018

1.23.0

1.24.0–1.25.0

1.26.0–1.28.0(beta)

1.29.0(nightly)

Mark-Simulacrum commented on Aug 1, 2018

estebank commented on Aug 1, 2018

estebank commented on Aug 1, 2018

estebank commented on Aug 1, 2018

nikomatsakis commented on Aug 9, 2018

nikomatsakis commented on Aug 9, 2018

varkor commented on Aug 9, 2018

varkor commented on Aug 9, 2018

varkor commented on Aug 9, 2018

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`rustc` doesn't output anything but exits with 101 and doesn't emit any files #52913