Beta ICE: ItemLocalIds not assigned densely

[matklad]

Hi! I am seeing an ICE in rust-analyzer, when updating rustc from rustc 1.31.0-beta.14 to rustc 1.31.0-beta.15 (so, seems pretty bad?).

Error message:

   Compiling ra_syntax v0.1.0 (/home/matklad/projects/rust-analyzer/crates/ra_syntax)               
thread 'main' panicked at 'librustc/hir/map/hir_id_validator.rs:31:                                 
ItemLocalIds not assigned densely in ::grammar[0]::expressions[0]::{{?}}[1]. Max ItemLocalId = 4, missing IDs = ["[local_id: 1, node:unknown node (id=28193)]", "[local_id: 2, node:path segment super (id=28192)]"]; seens IDs = ["(NodeId(28191) use grammar::expressions::{{?}} (id=28191))", "(NodeId(28195) path segment atom (id=28195))", "(NodeId(28194) path segment self (id=28194))"]
HirIdValidator: The recorded owner of path segment super (id=28192) is ::grammar[0]::expressions[0]::{{?}}[1] instead of ::grammar[0]::expressions[0]::{{?}}[2]
HirIdValidator: Same HirId ::grammar[0]::expressions[0]::{{?}}[2]/2 assigned for nodes path segment super (id=28192) and path segment atom (id=92512)
HirIdValidator: The recorded owner of path segment super (id=28192) is ::grammar[0]::expressions[0]::{{?}}[1] instead of ::grammar[0]::expressions[0]::{{?}}[3]
HirIdValidator: Same HirId ::grammar[0]::expressions[0]::{{?}}[3]/2 assigned for nodes path segment super (id=28192) and path segment atom (id=92515)', librustc/util/bug.rs:47:26
note: Run with `RUST_BACKTRACE=1` for 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/blob/master/CONTRIBUTING.md#bug-reports
                                                                                                    
note: rustc 1.31.0-beta.15 (4b3a1d911 2018-11-20) running on x86_64-unknown-linux-gnu               
                                                                                                    
note: compiler flags: -C debuginfo=2 -C incremental --crate-type lib                                
                                                                                                    
note: some of the compiler flags provided by cargo are hidden                                       
                                                                                                    
error: Could not compile `ra_syntax`.                                                               
warning: build failed, waiting for other jobs to finish...
thread 'main' panicked at 'librustc/hir/map/hir_id_validator.rs:31:                                 
ItemLocalIds not assigned densely in ::grammar[0]::expressions[0]::{{?}}[1]. Max ItemLocalId = 4, missing IDs = ["[local_id: 1, node:unknown node (id=28200)]", "[local_id: 2, node:path segment super (id=28199)]"]; seens IDs = ["(NodeId(28198) use grammar::expressions::{{?}} (id=28198))", "(NodeId(28202) path segment atom (id=28202))", "(NodeId(28201) path segment self (id=28201))"]
HirIdValidator: The recorded owner of path segment super (id=28199) is ::grammar[0]::expressions[0]::{{?}}[1] instead of ::grammar[0]::expressions[0]::{{?}}[2]
HirIdValidator: Same HirId ::grammar[0]::expressions[0]::{{?}}[2]/2 assigned for nodes path segment super (id=28199) and path segment atom (id=104341)
HirIdValidator: The recorded owner of path segment super (id=28199) is ::grammar[0]::expressions[0]::{{?}}[1] instead of ::grammar[0]::expressions[0]::{{?}}[3]
HirIdValidator: Same HirId ::grammar[0]::expressions[0]::{{?}}[3]/2 assigned for nodes path segment super (id=28199) and path segment atom (id=104344)', librustc/util/bug.rs:47:26
note: Run with `RUST_BACKTRACE=1` for 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/blob/master/CONTRIBUTING.md#bug-reports
                                                                                                    
note: rustc 1.31.0-beta.15 (4b3a1d911 2018-11-20) running on x86_64-unknown-linux-gnu               
                                                                                                    
note: compiler flags: -C debuginfo=2 -C incremental                                                 
                                                                                                    
note: some of the compiler flags provided by cargo are hidden  

Steps to reproduce:

$ git clone git@github.com:rust-analyzer/rust-analyzer.git
$ cd rust-analyzer
$ git reset --hard 049f8df93cca05af395ce873738dc85d5a25f3fc
$ cargo test

[oli-obk]

probably a backport of whatever is causing #55475

[petrochenkov]

ping @nrc
This is a regression from #54145 that's now in beta.

[matklad]

It's funny how Keep resolved defs in path prefixes is exactly what I was doing in the rust-analyzer's PR that triggered the issue 😆

[nikomatsakis]

Building the beta locally, I get this error, which is a slightly different message

thread 'main' panicked at 'librustc/hir/map/collector.rs:219: inconsistent DepNode for `PathSegment(PathSegment { ident: super#0, id: Some(NodeId(28192)), def: Some(Err), args: None, infer_types: false })`: current_dep_node_owner=::grammar[0]::expressions[0]::{{?}}[2] (DefIndex(0:1648)), hir_id.owner=::grammar[0]::expressions[0]::{{?}}[1] (DefIndex(0:1647))', librustc/util/bug.rs:47:26

[nikomatsakis]

(Though it seems to be related to the same root problem)

[nikomatsakis]

(Ah, this check is only done when debug_assertions are enabled.)

[nikomatsakis]

Minimized reproduction:

mod bar {
    pub(super) use self::baz::{x, y};
//      ^^^^^ assert has to do with this path
//
// the other thing you need is the `{x, y}` part, which I think causes this to expand into
// two copies of the same `pub use` internally

    mod baz {
        pub fn x() { }
        pub fn y() { }
    }
}

fn main() { }

[nikomatsakis]

OK I see the bug I think

[nikomatsakis]

My theory wasn't quite right. Clearly it has something to do with sharing ids. You can see that in some paths, we clone the ids from the visibility kind:

rust/src/librustc/hir/lowering.rs

Lines 3023 to 3028 in 4b3a1d9

	let mut path = path.clone();
	for seg in path.segments.iter_mut() {
	if seg.id.is_some() {
	seg.id = Some(this.next_id().node_id);
	}
	}

But in others, we do not:

rust/src/librustc/hir/lowering.rs

Lines 3111 to 3118 in 4b3a1d9

	hir::VisibilityKind::Restricted { ref path, id: _, hir_id: _ } => {
	let id = this.next_id();
	hir::VisibilityKind::Restricted {
	path: path.clone(),
	id: id.node_id,
	hir_id: id.hir_id,
	}
	}

However, just adding clone operations to both paths didn't quite suffice.