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dropck: Ignore bounds for traits without any items #24805

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pnkfelix opened this issue Apr 25, 2015 · 1 comment · Fixed by #25113
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dropck: Ignore bounds for traits without any items #24805

pnkfelix opened this issue Apr 25, 2015 · 1 comment · Fixed by #25113

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@pnkfelix
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As stated in RFC 769, the Drop Check rule is supposed to ignore any trait bounds for traits that do not have associated methods (or perhaps that needs to be strengthened to associated items, as implied by this ticket's title).

However, the current dropck implementation is not so general -- I believe it just hard-codes the set of builtin bounds, rather than allowing any empty trait to be ignored.

This is bad because it complicates e.g. adding OIBIT traits to interfaces, since it can cause the dropck rule to start firing (and for new region constraints to be introduced) that can then cause surprising compilation failures.
@pnkfelix pnkfelix mentioned this issue Apr 25, 2015
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(In particular, I discovered this while doing some prototyping work on stabilizing allocators by adding a Raw OIBIT bound as part of some future-proofing plans.)

pnkfelix added a commit to pnkfelix/rust that referenced this issue Apr 28, 2015
@pnkfelix
Generalize dropck to ignore item-less traits.
e166daa 
Fix rust-lang#24805

(see follow-on commit for test.)
pnkfelix added a commit to pnkfelix/rust that referenced this issue Apr 28, 2015
@pnkfelix
Regression tests for rust-lang#24805.
3640a5c 
The new functionality being tested here is that a drop impl bounded by
`UserDefined` does not cause dropck to inject its conservative
constraints on region inference.
@pnkfelix pnkfelix mentioned this issue Apr 28, 2015
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pnkfelix added a commit to pnkfelix/rust that referenced this issue May 5, 2015
@pnkfelix
Generalize dropck to ignore item-less traits.
c76d66e 
Fix rust-lang#24805

(see follow-on commit for test.)
pnkfelix added a commit to pnkfelix/rust that referenced this issue May 5, 2015
@pnkfelix
Regression tests for rust-lang#24805.
f40d9d9 
The new functionality being tested here is that a drop impl bounded by
`UserDefined` does not cause dropck to inject its conservative
constraints on region inference.
@pnkfelix pnkfelix mentioned this issue May 5, 2015
Merged
bors added a commit that referenced this issue May 5, 2015
@bors
Auto merge of #25113 - pnkfelix:dropck-itemless-traits, r=huonw
c0100ce 
Generalize dropck to ignore item-less traits

Fix #24805.

(This is the reopened + rebased version of PR #24898)
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