Persistent collections updates (part 9)

[lorentey]

Add structural union and symmetricDifference implementations. Add combinatorial tests for all these & fix all issues uncovered. Optimize these operations not to copy any data if they end up returning self verbatim.

I think this PR completes all the immediate non-trivial coding work on PersistentSet & PersistentDictionary -- except for dictionary merge operations; those will be relatively straightforward adaptations of union.

I'll still need to add the customary generic overloads for intersection/union/etc that take arbitrary sequences -- but those are mostly trivial.

These types are shaping up pretty well!

Checklist

• I've read the Contribution Guidelines
• My contributions are licensed under the Swift license.
• I've followed the coding style of the rest of the project.
• I've added tests covering all new code paths my change adds to the project (if appropriate).
• I've added benchmarks covering new functionality (if appropriate).
• I've verified that my change does not break any existing tests or introduce unexplained benchmark regressions.
• I've updated the documentation if necessary.

[lorentey]

I don't have any benchmarks this time around; at least not yet. I'm thinking we could demonstrate the superiority of CHAMPs over flat hash tables by looking at how fast PersistentSet.subtracting is when given two sets that are slightly mutated copies of the same original.

[lorentey]

@swift-ci test

[lorentey]

swift-collections/Sources/PersistentCollections/Node/_Bitmap.swift:135:18: warning: instance method '_rank(ofBit:)' cannot be used in an '@inlinable' function because '_CollectionsUtilities' was not imported by this file; this is an error in Swift 6
    _Slot(_value._rank(ofBit: bucket.value))
                 ^

Oops

[lorentey]

@swift-ci test

[lorentey]

Welp

error: emit-module command failed due to signal 6 (use -v to see invocation)error: compile command failed due to signal 6 (use -v to see invocation)/Users/ec2-user/jenkins/workspace/pr-swift-collections-macos/branch-release/1.1/swift-collections/Tests/BitCollectionsTests/BitSetTests.swift: error: file failed to round-trip
Please submit a bug report (https://swift.org/contributing/#reporting-bugs) and include the project and the crash backtrace.
[...]
1.	Apple Swift version 5.8-dev (LLVM ed4d811c2897d77, Swift 8491f52d478aca6)
2.	Compiling with the current language version
3.	While evaluating request ParseSourceFileRequest(source_file "/Users/ec2-user/jenkins/workspace/pr-swift-collections-macos/branch-release/1.1/swift-collections/Tests/BitCollectionsTests/BitSetTests.swift")
4.	With parser at source location: /Users/ec2-user/jenkins/workspace/pr-swift-collections-macos/branch-release/1.1/swift-collections/Tests/BitCollectionsTests/BitSetTests.swift:1278:1
Stack dump without symbol names (ensure you have llvm-symbolizer in your PATH or set the environment var `LLVM_SYMBOLIZER_PATH` to point to it):
0  swift-frontend           0x00000001085f22b7 llvm::sys::PrintStackTrace(llvm::raw_ostream&, int) + 39
1  swift-frontend           0x00000001085f14c5 llvm::sys::RunSignalHandlers() + 85
2  swift-frontend           0x00000001085f2900 SignalHandler(int) + 288
3  libsystem_platform.dylib 0x00007fff20398d7d _sigtramp + 29
4  libdyld.dylib            0x00007fff2036dce8 _dyld_fast_stub_entry(void*, long) + 65
5  libsystem_c.dylib        0x00007fff202a8406 abort + 125
6  swift-frontend           0x0000000104874686 swift::ParseSourceFileRequest::evaluate(swift::Evaluator&, swift::SourceFile*) const + 2454
7  swift-frontend           0x0000000104874b41 swift::SimpleRequest<swift::ParseSourceFileRequest, swift::SourceFileParsingResult (swift::SourceFile*), (swift::RequestFlags)12>::evaluateRequest(swift::ParseSourceFileRequest const&, swift::Evaluator&) + 17
8  swift-frontend           0x00000001046f43d7 llvm::Expected<swift::ParseSourceFileRequest::OutputType> swift::Evaluator::getResultUncached<swift::ParseSourceFileRequest>(swift::ParseSourceFileRequest const&) + 471
9  swift-frontend           0x00000001046f3fcd llvm::Expected<swift::ParseSourceFileRequest::OutputType> swift::Evaluator::getResultCached<swift::ParseSourceFileRequest, (void*)0>(swift::ParseSourceFileRequest const&) + 253
10 swift-frontend           0x00000001046d5cec swift::ParseSourceFileRequest::OutputType swift::evaluateOrDefault<swift::ParseSourceFileRequest>(swift::Evaluator&, swift::ParseSourceFileRequest, swift::ParseSourceFileRequest::OutputType) + 60
11 swift-frontend           0x00000001046cd1c8 swift::SourceFile::getTopLevelDecls() const + 120
12 swift-frontend           0x0000000103fc5ef1 swift::performImportResolution(swift::SourceFile&) + 1169
13 swift-frontend           0x000000010321e9d1 swift::CompilerInstance::performParseAndResolveImportsOnly() + 929
14 swift-frontend           0x000000010321eac3 swift::CompilerInstance::performSema() + 19
15 swift-frontend           0x00000001031b1f38 swift::performFrontend(llvm::ArrayRef<char const*>, char const*, void*, swift::FrontendObserver*) + 3864
16 swift-frontend           0x0000000102fe8d34 swift::mainEntry(int, char const**) + 2932
17 libdyld.dylib            0x00007fff2036ef3d start + 1
18 libdyld.dylib            0x0000000000000033 start + 18446603339975692535
[5/39] Compiling SortedCollectionsTests SortedDictionary Tests.swift
error: fatalError

[lorentey]

Tests/BitCollectionsTests/BitSetTests.swift: error: file failed to round-trip

@DougGregor are you collecting these?

[msteindorfer]

Change List:

• Check / verify potential oversight in structural union.

Otherwise, LGTM.

[lorentey]

It occurs to me we should have in-place mutating variants for formIntersection/formUnion et al., instead of unconditionally delegating to the copying variants. This would be along the lines of remove/removing (which could actually use a bit of refactoring, now that we have Builder -- which is incidentally also badly in need of an interface cleanup). I'm not sure I want to deal with the pain of duplicating & adapting all this code just yet, though.

(Like with remove, we must not call the mutating variants on potentially non-uniquely held nodes to avoid violating the Law of Exclusivity, and unconditionally uniquing nodes along the way would cancel out some/most of the structural benefits.)

[lorentey]

@swift-ci test