NLL diagnostics for ref mut z @ &mut Some(ref a) uses _ as binding name
#67565
Labels
A-diagnostics
Area: Messages for errors, warnings, and lints
A-NLL
Area: Non-lexical lifetimes (NLL)
C-bug
Category: This is a bug.
D-confusing
Diagnostics: Confusing error or lint that should be reworked.
F-bindings_after_at
`#![feature(bindings_after_at)]`
NLL-diagnostics
Working towards the "diagnostic parity" goal
requires-nightly
This issue requires a nightly compiler in some way.
T-compiler
Relevant to the compiler team, which will review and decide on the PR/issue.
Comments
Centril
added
A-diagnostics
Centril
added
A-NLL
|
I feel like the internal use of I feel like internally, we should keep a strong separation between names that we get from the source code being compiled and names being generated by the compiler... |
|
I think this issue is about the narrow issue of why this happens in the case of |
|
@Centril Sure, but I think it stems from a larger problem of undisciplined use of |
|
@mark-i-m I don't mind fixing this by fixing the root cause, but can we discuss the bigger issue in a issue made for that and cc this one? |
InvestigationSource input:#![feature(bindings_after_at)]
fn foo() {
let ref mut _z @ ref _a = &mut 1;
**_z = 0;
}Results in the following MIR:fn foo() -> () {
let mut _0: (); // return place in scope 0 at foo.rs:5:10: 5:10
let _1: &mut &mut i32; // in scope 0 at foo.rs:6:9: 6:28
let _2: &&mut i32; // in scope 0 at foo.rs:6:22: 6:28
let mut _3: &mut i32; // in scope 0 at foo.rs:6:31: 6:37
let mut _4: i32; // in scope 0 at foo.rs:6:36: 6:37
scope 1 {
debug _z => _1; // in scope 1 at foo.rs:6:9: 6:28
debug _a => _2; // in scope 1 at foo.rs:6:22: 6:28
}
bb0: {
StorageLive(_3); // bb0[0]: scope 0 at foo.rs:6:31: 6:37
StorageLive(_4); // bb0[1]: scope 0 at foo.rs:6:36: 6:37
_4 = const 1i32; // bb0[2]: scope 0 at foo.rs:6:36: 6:37
// ty::Const
// + ty: i32
// + val: Value(Scalar(0x00000001))
// mir::Constant
// + span: foo.rs:6:36: 6:37
// + literal: Const { ty: i32, val: Value(Scalar(0x00000001)) }
_3 = &mut _4; // bb0[3]: scope 0 at foo.rs:6:31: 6:37
StorageLive(_1); // bb0[4]: scope 0 at foo.rs:6:9: 6:28
_1 = &mut _3; // bb0[5]: scope 0 at foo.rs:6:9: 6:28
StorageLive(_2); // bb0[6]: scope 0 at foo.rs:6:22: 6:28
_2 = &_3; // bb0[7]: scope 0 at foo.rs:6:22: 6:28
(*(*_1)) = const 0i32; // bb0[8]: scope 1 at foo.rs:7:5: 7:13
// ty::Const
// + ty: i32
// + val: Value(Scalar(0x00000000))
// mir::Constant
// + span: foo.rs:7:12: 7:13
// + literal: Const { ty: i32, val: Value(Scalar(0x00000000)) }
_0 = (); // bb0[9]: scope 0 at foo.rs:5:10: 8:2
StorageDead(_2); // bb0[10]: scope 0 at foo.rs:8:1: 8:2
StorageDead(_1); // bb0[11]: scope 0 at foo.rs:8:1: 8:2
StorageDead(_4); // bb0[12]: scope 0 at foo.rs:8:1: 8:2
StorageDead(_3); // bb0[13]: scope 0 at foo.rs:8:1: 8:2
return; // bb0[14]: scope 0 at foo.rs:8:2: 8:2
}
}And we double check with some debug!("ast_block_stmts: local_decls={:#?}", this.local_decls);
debug!("ast_block_stmts: var_debug_info={:#?}", this.var_debug_info);
debug!("ast_block_stmts: var_indices={:#?}", this.var_indices);using [DEBUG rustc_mir_build::build::block] ast_block_stmts: local_decls=[
LocalDecl {
mutability: Mut,
local_info: Other,
internal: false,
is_block_tail: None,
ty: (),
user_ty: UserTypeProjections {
contents: [],
},
source_info: SourceInfo {
span: foo.rs:5:10: 5:10,
scope: scope[0],
},
},
LocalDecl {
mutability: Not,
local_info: User(
Set(
Var(
VarBindingForm {
binding_mode: BindByReference(
Not,
),
opt_ty_info: None,
opt_match_place: Some(
(
Some(
_3,
),
foo.rs:6:31: 6:37,
),
),
pat_span: foo.rs:6:9: 6:28,
},
),
),
),
internal: false,
is_block_tail: None,
ty: &mut &mut i32,
user_ty: UserTypeProjections {
contents: [],
},
source_info: SourceInfo {
span: foo.rs:6:9: 6:28,
scope: scope[0],
},
},
LocalDecl {
mutability: Not,
local_info: User(
Set(
Var(
VarBindingForm {
binding_mode: BindByReference(
Not,
),
opt_ty_info: None,
opt_match_place: Some(
(
Some(
_3,
),
foo.rs:6:31: 6:37,
),
),
pat_span: foo.rs:6:9: 6:28,
},
),
),
),
internal: false,
is_block_tail: None,
ty: &&mut i32,
user_ty: UserTypeProjections {
contents: [],
},
source_info: SourceInfo {
span: foo.rs:6:22: 6:28,
scope: scope[0],
},
},
LocalDecl {
mutability: Mut,
local_info: Other,
internal: false,
is_block_tail: None,
ty: &mut i32,
user_ty: UserTypeProjections {
contents: [],
},
source_info: SourceInfo {
span: foo.rs:6:31: 6:37,
scope: scope[0],
},
},
LocalDecl {
mutability: Mut,
local_info: Other,
internal: false,
is_block_tail: None,
ty: i32,
user_ty: UserTypeProjections {
contents: [],
},
source_info: SourceInfo {
span: foo.rs:6:36: 6:37,
scope: scope[0],
},
},
]
[DEBUG rustc_mir_build::build::block] ast_block_stmts: var_debug_info=[
VarDebugInfo {
name: "_z",
source_info: SourceInfo {
span: foo.rs:6:9: 6:28,
scope: scope[1],
},
place: _1,
},
VarDebugInfo {
name: "_a",
source_info: SourceInfo {
span: foo.rs:6:22: 6:28,
scope: scope[1],
},
place: _2,
},
]
[DEBUG rustc_mir_build::build::block] ast_block_stmts: var_indices={
HirId {
owner: DefIndex(4),
local_id: 1,
}: One(
_1,
),
HirId {
owner: DefIndex(4),
local_id: 2,
}: One(
_2,
),
}Borrow checking trace:The error comes from We eventually end up in and so it tries to compute The unchanged log output on master is: |
This was referenced Mar 25, 2020
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Context: #66296 (comment)
The
_below should bezinstead.cc @mark-i-m @pnkfelix @matthewjasper
cc #65490
Minimal reproducer:
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