Replace CRC-32 with SHA-256 in our macro target #1047
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This PR replaces CRC-32 with SHA-256 in our macro target. We currently use CRC-32 to disambiguate test functions that would otherwise generate identical derived symbol names (using `context.makeUniqueName()`.) By replacing it with the first 64 bits of a SHA-256 hash, we reduce the odds of a collision. We also currently use a 128-bit random number as a unique ID for exit tests during macro expansion (which is as unique as it gets, but unstable.) Replacing this random number with half of a SHA-256 hash allows us to generate _stable_ IDs (that are still statistically unique) which can help when debugging an exit test and may also improve cache quality for tools (e.g. an IDE's symbol cache.) Because there is no SHA-256 implementation available in the Swift standard library or other components we can reliably link to in the macro target, I've borrowed the implementation of SHA-256 in swift-tools-support-core. The original version is [here](https://github.com/swiftlang/swift-tools-support-core/blob/main/Sources/TSCBasic/HashAlgorithms.swift).
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This PR replaces CRC-32 with SHA-256 in our macro target.
We currently use CRC-32 to disambiguate test functions that would otherwise generate identical derived symbol names (using
context.makeUniqueName().) By replacing it with the first 64 bits of a SHA-256 hash, we reduce the odds of a collision.We also currently use a 128-bit random number as a unique ID for exit tests during macro expansion (which is as unique as it gets, but unstable.) Replacing this random number with half of a SHA-256 hash allows us to generate stable IDs (that are still statistically unique) which can help when debugging an exit test and may also improve cache quality for tools (e.g. an IDE's symbol cache.)
Because there is no SHA-256 implementation available in the Swift standard library or other components we can reliably link to in the macro target, I've borrowed the implementation of SHA-256 in swift-tools-support-core. The original version is here.
Checklist: