extend stable hasher to support CanonicalTy

[nikomatsakis]

Fixes #49043

r? @michaelwoerister

[michaelwoerister]

The Fresh* variants are valid to hash?

[nikomatsakis]

Yes.

[nikomatsakis]

They are not confined to the local tcx:

rust/src/librustc/ty/flags.rs

Lines 112 to 124 in 3b6412b

	match infer {
	ty::FreshTy(_) |
	ty::FreshIntTy(_) |
	ty::FreshFloatTy(_) |
	ty::CanonicalTy(_) => {
	self.add_flags(TypeFlags::HAS_CANONICAL_VARS);
	}
	ty::TyVar(_) |
	ty::IntVar(_) |
	ty::FloatVar(_) => {
	self.add_flags(TypeFlags::KEEP_IN_LOCAL_TCX)
	}

[nikomatsakis]

It just happens that we don't ever put them in query keys right now (and probably never will, but whatever).

[nikomatsakis]

(To be honest, even the TyVar and so forth would be ok to hash -- in the sense that they are "stable-ish" -- it's just that it truly ought to be impossible... it would indicate some other problem if we did see them that would be worth knowing about.)

Well, I take that back. It's a bit dubious given that their meaning depends on the surrounding infcx. Anyway, ought to be impossible. =)

[michaelwoerister]

Thanks for the explanation!

@bors r+

[bors]

📌 Commit f02dc74 has been approved by michaelwoerister

[nikomatsakis]

@bors p=1 -- important regression to button down

[bors]

⌛ Testing commit f02dc74 with merge a5bc1141a0683804890d19bea6a08e3e6d9a0dfb...

[bors]

💔 Test failed - status-travis

[kennytm]

@bors retry

x86_64-gnu-incremental 3-hour timeout, 39 minutes spent in compiling stage1-rustc.

Details

make-prepare                	  72.13
stage0-tidy                 	  71.60
stage0-std                  	  13.79
stage0-rustc                	 989.30
llvm                        	 352.91
stage0-trans-llvm           	  79.50
stage1-std                  	 377.56
stage1-test                 	  29.36
stage1-rustc                	2331.73
stage1-trans-llvm           	 170.96
stage2-rustdoc              	 245.20
stage0-std                  	  58.85
stage0-rustbook             	 145.73
stage2-rustdoc              	 313.87
doc/compiler                	 148.92
stage2-error_index_generator	   6.30
stage0-std                  	  20.38
test/ui                     	 100.33
test/run-pass               	1255.39
test/compile-fail           	 276.29
test/parse-fail             	   6.46
test/run-fail               	  25.33
test/run-pass-valgrind      	   5.62
test/mir-opt                	  27.99
test/codegen                	   7.96
test/codegen-units          	   4.34
test/incremental            	  33.76
test/debuginfo              	  20.12
test/ui-fulldeps            	  32.87
test/run-pass-fulldeps      	 665.77
test/run-fail-fulldeps      	   7.78
test/compile-fail-fulldeps  	 145.30
test/incremental-fulldeps   	   5.47
stage2-rustdoc              	 322.52
test/run-make               	 126.27
...

[bors]

⌛ Testing commit f02dc74 with merge 86091adfe8e5752967963ee8417ce1aa8898cf1a...

[bors]

💔 Test failed - status-travis

[kennytm]

@bors retry

[bors]

⌛ Testing commit f02dc74 with merge 678f786e713c168cbfcd6f1324202514cec7ef45...

[bors]

💔 Test failed - status-travis

[kennytm]

@bors retry

Somethings wrong with Travis.

[bors]

⌛ Testing commit f02dc74 with merge 15add36...

[bors]

☀️ Test successful - status-appveyor, status-travis
Approved by: michaelwoerister
Pushing 15add36 to master...