Implement variance RFC #738 #22286

nikomatsakis · 2015-02-13T18:13:57Z

This PR:

converts the markers to the new PhantomData/PhantomFn scheme;
corrects various errors in variance inference, which was not always taking the correct things into account;
integrates results variance into trait matching, coherence, subtyping.

This is a [breaking-change]:

The old markers are removed in favor of PhantomData. It is possible to simulate all of the old markers:
- ContravariantLifetime<'a> -> PhantomData<&'a ()> (or just &'a (), actually)
- InvariantLifetime<'a> -> PhantomData<Cell<&'a ()>>
- CovariantType<T> -> PhantomData<T>
- ContravariantType<T> -> PhantomData<fn(T)>
- InvariantType<T> -> PhantomData<Cell<T>>
It is now illegal to have unused type and lifetime parameters. Typically the best fix is either to remove the parameter or to add an instance of PhantomData to your struct (or PhantomFn / MarkerTrait to your trait). See Support variance for type parameters rfcs#738 for more background.
Technically, variance can cause some impls that used to be legal to be illegal due to subtyping. This is highly unlikely to affect you.

Fixes #22212.

rust-highfive · 2015-02-13T18:14:08Z

r? @Aatch

(rust_highfive has picked a reviewer for you, use r? to override)

nikomatsakis · 2015-02-13T18:14:13Z

r? @pnkfelix has been my go-to variance guy.

nikomatsakis · 2015-02-13T18:33:34Z

Grr, something in the last rebase started causing some (minor looking) test failures. I'll track those down.

pkondzior · 2015-02-13T18:47:30Z

src/libarena/lib.rs

@@ -96,7 +96,7 @@ pub struct Arena<'longer_than_self> {
    head: RefCell<Chunk>,
    copy_head: RefCell<Chunk>,
    chunks: RefCell<Vec<Chunk>>,
-    _invariant: marker::InvariantLifetime<'longer_than_self>,
+    _marker: marker::PhantomData<*mut &'longer_than_self()>,


Space after lifetime name is missing ?

nikomatsakis · 2015-02-14T19:02:32Z

Rebased. Make check passes locally now.

frewsxcv · 2015-02-16T04:19:07Z

Needs a rebase

alexcrichton · 2015-02-17T18:56:50Z

src/libcore/marker.rs

+/// FIXME. Better documentation needed here!
+#[cfg(not(stage0))]
+#[lang="phantom_data"]
+pub struct PhantomData<T:?Sized>;


Could you go ahead an mark this #[stable] as well? I think it'd been debated enough that it's probably earned it. (you may want to leave PhantomFn explicitly #[unstable] for now though).

pnkfelix · 2015-02-18T12:18:23Z

@nikomatsakis okay i'm done with the review. Some nits and minor questions, but I would not object to you telling bors that this PR as-is is r=pnkfelix.

into variance inference; fix various bugs in variance inference so that it considers the correct set of constraints; modify infer to consider the results of variance inference for type arguments.

variance or an associated type.

…nd ownership, and also follows the API of `NonZero` a bit more closely. More to do here I think (including perhaps a new name).

… unsafe pointer.

…ters are used.

here. Some of this may have been poorly rebased, though I tried to be careful and preserve the spirit of the test.

…etime`

be migrated to an associated type anyway.

…to the variance analysis.

alexcrichton · 2015-02-18T23:50:03Z

@bors: r=pnkfelix 9f8b9d6

Conflicts: src/librustc/middle/infer/combine.rs src/librustc_typeck/check/wf.rs

alexcrichton · 2015-02-19T21:39:28Z

This was merged in #22541

rust-highfive assigned Aatch Feb 13, 2015

rust-highfive assigned pnkfelix and unassigned Aatch Feb 13, 2015

pkondzior reviewed Feb 13, 2015
View reviewed changes

nikomatsakis force-pushed the variance-4b branch from a325f07 to d910931 Compare February 14, 2015 19:01

nikomatsakis force-pushed the variance-4b branch from d910931 to 048359c Compare February 17, 2015 15:28

alexcrichton reviewed Feb 17, 2015
View reviewed changes

nikomatsakis added 16 commits February 18, 2015 10:24

Introduce the new phantomdata/phantomfn markers and integrate them

2594d56

into variance inference; fix various bugs in variance inference so that it considers the correct set of constraints; modify infer to consider the results of variance inference for type arguments.

Report errors for type parameters that are not constrained, either by

91eedfe

variance or an associated type.

Extend coherence check to understand subtyping.

8c841f2

Rewrite Unique<T> so that it is covariant in T, implies NonZero a…

801bc48

…nd ownership, and also follows the API of `NonZero` a bit more closely. More to do here I think (including perhaps a new name).

Constrain operands to outlive the operation. Fixes rust-lang#21422.

f2529ac

Fallout: Port Vec to use Unique

c5579ca

Fallout: btree. Rephrase invariant lifetime in terms of PhantomData.

b3c00a6

Fallout: port btree to use Unique, some markers.

68ebe64

Fallout: EnumSet, add Marker.

c2891cc

Fallout: RingBuf, use Unique.

8dbdcdb

Fallout: arena needs to use phantomdata since invariantlifetime is gone

2bcf3a4

Fallout: AtomicPtr needs phantom data to indicate that it contains an…

1735e41

… unsafe pointer.

Fallout: iter, add markers or other changes such that all type parame…

d801a4d

…ters are used.

Fallout: docs, elided examples often elided too much.

ef42c2b

Fallout: tests. As tests frequently elide things, lots of changes

872ce47

here. Some of this may have been poorly rebased, though I tried to be careful and preserve the spirit of the test.

Fallout: remove unused type and region parameters.

60f507b

nikomatsakis added 12 commits February 18, 2015 10:25

Fallout: Port slice to use PhantomData instead of `ContravariantLif…

aaf4176

…etime`

Fallout: port libflate to new Unique API

2953710

Fallout: add phantom data to librand

199b992

Fallout: add phantom data to the type inferencer

62b5177

Fallout: extend thread with phantomdata for 'a lifetime

1ed5842

Fallout: add phantomdata for 'a in path

9e0bb52

Fallout: port hashmap to use Unique

ae7c534

Fallout: add phantomdata to hash

6f2a1c9

Fallout: Accepter trait needs phantomdata. This seems like it should

df76442

be migrated to an associated type anyway.

Add regression test for rust-lang#20533. Fixes rust-lang#20533.

d179bb5

Missing test.

e8cb11c

WIP -- improve documentation on the phantom traits

a2393e6

aturon mentioned this pull request Feb 18, 2015

Stabilization for 1.0-beta #22500

Closed

91 tasks

nikomatsakis added 5 commits February 18, 2015 17:14

Add deprecated versions of the old markers and integrate them back in…

d622235

…to the variance analysis.

Try to write some basic docs.

74199c2

Stabilize Send/Sync.

f5491e6

Minor unused imports etc.

cc61f9c

Update tests to use #[feature(rustc_attrs)]

9f8b9d6

nikomatsakis force-pushed the variance-4b branch from 048359c to 9f8b9d6 Compare February 18, 2015 22:32

Mark intentionally buggy test as ignore

2e482cd

alexcrichton added a commit to alexcrichton/rust that referenced this pull request Feb 19, 2015

rollup merge of rust-lang#22286: nikomatsakis/variance-4b

1506b34

Conflicts: src/librustc/middle/infer/combine.rs src/librustc_typeck/check/wf.rs

alexcrichton closed this Feb 19, 2015

alexcrichton mentioned this pull request Feb 19, 2015

Tracking issue for Support variance for type parameters (RFC 738) #22212

Closed

japaric mentioned this pull request Feb 20, 2015

PhantomData not behaving as advertised #22579

Closed

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Implement variance RFC #738 #22286

Implement variance RFC #738 #22286

nikomatsakis commented Feb 13, 2015

rust-highfive commented Feb 13, 2015

nikomatsakis commented Feb 13, 2015

nikomatsakis commented Feb 13, 2015

pkondzior Feb 13, 2015

nikomatsakis commented Feb 14, 2015

frewsxcv commented Feb 16, 2015

alexcrichton Feb 17, 2015

pnkfelix commented Feb 18, 2015

alexcrichton commented Feb 18, 2015

alexcrichton commented Feb 19, 2015

Implement variance RFC #738 #22286

Implement variance RFC #738 #22286

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