Explain "It is a logic error ... " in HashMap, BTreeMap and others #80657
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A-collections
Area: `std::collection`
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Area: Documentation for any part of the project, including the compiler, standard library, and tools
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Category: An issue proposing an enhancement or a PR with one.
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Relevant to the library API team, which will review and decide on the PR/issue.
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sfackler
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By "unsafe behavior" I assume you mean "Undefined Behavior"? |
camelid
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We must guarantee that there is no UB as a result of nonsense Ord/Hash/PartialEq etc impls, but I do not think we should guarantee anything beyond that. I would be open to a PR making a change improving the wording here. |
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…-ou-se Clarify what the effects of a 'logic error' are This clarifies what a 'logic error' is (which is a term used to describe what happens if you put things in a hash table or btree and then use something like a refcell to break the internal ordering). This tries to be as vague as possible, as we don't really want to promise what happens, except "bad things, but not UB". This was discussed in rust-lang#80657
m-ou-se
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…-ou-se Clarify what the effects of a 'logic error' are This clarifies what a 'logic error' is (which is a term used to describe what happens if you put things in a hash table or btree and then use something like a refcell to break the internal ordering). This tries to be as vague as possible, as we don't really want to promise what happens, except "bad things, but not UB". This was discussed in rust-lang#80657
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In rust-lang/rust#80657 and rust-lang/rust#80681 it is discussed how to clarify/define what a "logic error" is and what are their consequences. The reference should mention them as well. Signed-off-by: Miguel Ojeda <ojeda@kernel.org>
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In various pieces of the documentation that talk about "It is a logic error ...", mostly to change the keys of HashMap/Sets and BTreeMap/Sets, using RefCells or hashing functions which change their behaviour based on global variables.
What does "it is a logic error ... " mean? With some brief playing it appears (to me) that it puts the datastructure in an inconsistent state, where future calls to any member function can return nonsense values.
It appears (from what I can tell) there is no unsafe behaviour, and it isn't possible to make the datastructures call
panic, but I would be happy to say they could panic (saying they won't means checking they can't when someone has already done something stupid).So, I suggest a short extra sentence which just says "These logic errors can lead to incorrect results and panics but not unsafe behaviour"
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