[NLL] Improve DefiningTy::Const

[sapphire-arches]

Fixes #47590 by fixing the way DefiningTy represents constants. Previously, constants were represented using just the type of the variable. However, this will fail to capture early-bound regions as NLL inference vars, resulting in an ICE when we try to compute region VIDs a little bit later in the universal
region resolution process. (ref #47590)

[rust-highfive]

Thanks for the pull request, and welcome! The Rust team is excited to review your changes, and you should hear from @michaelwoerister (or someone else) soon.

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[sapphire-arches]

r? @nikomatsakis

[nikomatsakis]

Nice work =)

[nikomatsakis]

@bors r+

[bors]

📌 Commit 2ed3969 has been approved by nikomatsakis

[kennytm]

@bors p=1

Increasing priority of PRs with higher complexity.

[bors]

⌛ Testing commit 2ed39698ca15d9abe947491a56d17d0f2286aed2 with merge 2435c2ced0cb34b039b04033a3419c200d24f406...

[bors]

💔 Test failed - status-travis

[kennytm]

The ui/nll/trait-associated-constant.rs output doesn't match what is shown in this PR on arm-unknown-linux-gnueabihf. The error span ends at the struct name, instead of the }.

This might be due to recent diagnostic changes on master. Try to rebase on latest master and regenerate the *.stderr file?

[00:55:05] ---- [ui] ui/nll/trait-associated-constant.rs stdout ----
[00:55:05] 	diff of stderr:
[00:55:05] 
[00:55:05] 9	note: the lifetime 'c as defined on the impl at 30:1...
[00:55:05] 10	  --> $DIR/trait-associated-constant.rs:30:1
[00:55:05] 11	   |
[00:55:05] -	30 | / impl<'a: 'b, 'b, 'c> Anything<'a, 'b> for FailStruct1 {
[00:55:05] -	31 | |     const AC: Option<&'c str> = None;
[00:55:05] -	32 | |     //~^ ERROR: mismatched types
[00:55:05] -	33 | | }
[00:55:05] -	   | |_^
[00:55:05] +	30 | impl<'a: 'b, 'b, 'c> Anything<'a, 'b> for FailStruct1 {
[00:55:05] +	   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
[00:55:05] 17	note: ...does not necessarily outlive the lifetime 'b as defined on the impl at 30:1
[00:55:05] 18	  --> $DIR/trait-associated-constant.rs:30:1
[00:55:05] 19	   |
[00:55:05] 
[00:55:05] -	30 | / impl<'a: 'b, 'b, 'c> Anything<'a, 'b> for FailStruct1 {
[00:55:05] -	31 | |     const AC: Option<&'c str> = None;
[00:55:05] -	32 | |     //~^ ERROR: mismatched types
[00:55:05] -	33 | | }
[00:55:05] -	   | |_^
[00:55:05] +	30 | impl<'a: 'b, 'b, 'c> Anything<'a, 'b> for FailStruct1 {
[00:55:05] +	   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
[00:55:05] 25	
[00:55:05] 26	error[E0308]: mismatched types
[00:55:05] 27	  --> $DIR/trait-associated-constant.rs:38:5
[00:55:05] 
[00:55:05] 34	note: the lifetime 'a as defined on the impl at 37:1...
[00:55:05] 35	  --> $DIR/trait-associated-constant.rs:37:1
[00:55:05] 36	   |
[00:55:05] -	37 | / impl<'a: 'b, 'b> Anything<'a, 'b> for FailStruct2 {
[00:55:05] -	38 | |     const AC: Option<&'a str> = None;
[00:55:05] -	39 | |     //~^ ERROR: mismatched types
[00:55:05] -	40 | | }
[00:55:05] -	   | |_^
[00:55:05] +	37 | impl<'a: 'b, 'b> Anything<'a, 'b> for FailStruct2 {
[00:55:05] +	   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
[00:55:05] 42	note: ...does not necessarily outlive the lifetime 'b as defined on the impl at 37:1
[00:55:05] 43	  --> $DIR/trait-associated-constant.rs:37:1
[00:55:05] 44	   |
[00:55:05] 
[00:55:05] -	37 | / impl<'a: 'b, 'b> Anything<'a, 'b> for FailStruct2 {
[00:55:05] -	38 | |     const AC: Option<&'a str> = None;
[00:55:05] -	39 | |     //~^ ERROR: mismatched types
[00:55:05] -	40 | | }
[00:55:05] -	   | |_^
[00:55:05] +	37 | impl<'a: 'b, 'b> Anything<'a, 'b> for FailStruct2 {
[00:55:05] +	   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
[00:55:05] 50	
[00:55:05] 51	error: aborting due to 2 previous errors
[00:55:05] 52	

[sapphire-arches]

I have updated the stderr file, tests should pass now.

@kennytm

[kennytm]

@bors r=nikomatsakis

[bors]

📌 Commit e99f8fc has been approved by nikomatsakis

[bors]

⌛ Testing commit e99f8fc with merge fee39ba...

[bors]

☀️ Test successful - status-appveyor, status-travis
Approved by: nikomatsakis
Pushing fee39ba to master...