Use BTreeMap for deterministic Into impl order (fixes #48)#49
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The Into derive iterated TypeAttribute.types (a HashMap) to emit one impl block per target. HashMap iteration order is randomized per process, so the generated impls came out in a different order each compile, changing the consuming crate's metadata hash (SVH) build-to-build (rust-lang/rust#89904 class). HashType already implements Ord, so switching types to BTreeMap makes the order deterministic with no other change.
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Fixes #48.
The
Intoderive emits oneimpl Into<…>block per entry ofTypeAttribute.types, which is astd::collections::HashMap.HashMapiteration order is randomized per process (getrandom seed), so the generatedimplblocks come out in a different order on every compile, which changes the consuming crate's metadata hash (SVH). Under content-addressed build systems with a shared cache this causes the same input to produce different artifacts, and mixing a fresh build with a cached dependency fails witherror[E0463]: can't find crate(the proc-macro variant of rust-lang/rust#89904).HashTypealready implementsOrd, so this PR switchesTypeAttribute.typesfromHashMaptoBTreeMap— deterministic iteration order, no other change.Verified: a struct with several
Intotargets, built three times with a clean rebuild each, produced three different.rmetahashes before this change and three identical hashes after.