Added Violet - Python VM written in Swift

[LiarPrincess]

Pull Request Description

Adding Violet - Python VM written in Swift.

Acceptance Criteria

To be accepted into the Swift source compatibility test suite, a project must:

• Be an Xcode or swift package manager project

  Swift Package Manager

• Target Linux, macOS, or iOS/tvOS/watchOS device

  Tested on:

  • macOS
    • Intel
      • 11.6.2 (BigSur) + Xcode 12.4 (Swift 5.3.2)
      • 11.6.2 (BigSur) + Xcode 13.0 (Swift 5.5)
    • Apple
      • ⚠️ Not tested! I don't have M1. ⚠️
  • Ubuntu
    • 21.04 + Swift 5.4.2 - use make test and make pytest
  • Docker
    • swift:latest (5.6.0) - use make docker-test and make docker-pytest
    • swift:5.3.2 - use make docker-test-old and make docker-pytest-old

• Support building on either Linux or macOS

• Maintain a project branch that builds against Swift 4.0 and passes any unit tests

  No Swift 4.0 support, although from what I see there are some other projects (like apple/swift-argument-parser) that only support 5+.

  Our target in project_precommit_check:

  '5.3': {
      'version': 'Apple Swift version 5.3.2 '
                  '(swiftlang-1200.0.45 clang-1200.0.32.28)\n'
                  'Target: x86_64-apple-darwin20.3.0\n',
      'description': 'Xcode 12.4 (contains Swift 5.3.2)',
      'branch': 'swift-5.3-branch'
  }

  We could go as low as swift-argument-parser allows us (from my tests it is 5.3 - I had “SPM was unable to reserve dependency” / build failures on earlier versions). If we removed this dependency then I think that we could go to 5.0 (with some changes in our code).

• Be contained in a publicly accessible git repository

  github.com/LiarPrincess/Violet

• Have maintainers who will commit to resolve issues in a timely manner

  github.com/LiarPrincess. No guarantee of 10+ years of support.

• Be compatible with the latest GM/Beta versions of Xcode and swiftpm

  Not tested on beta. All of the tested configurations were mentioned previously.

• Add value not already included in the suite

  We have things like:

  • Unsafe[Raw/Mutable]Pointers + a lof of pointer arithmetic - most of the Swift projects try to stay away from any Unsafe things, we use them a lot. In Violet a single Python object is represented as an UnsafeRawPointer with manually calculated offsets for fields.
  • ManagedBufferPointer + tagged pointers - this one is not popular among Swift programmers (Array is more common). Our custom BigInt implementation is an union (via tagged pointer) of Int32 (called Smi, after V8) and a heap allocation (magnitude + sign representation) with ARC for garbage collection.
  • Tons of UnicodeScalar and String.UnicodeScalarView (+ SubSequence) - most Swift programmers use default String view (the one with on grapheme clusters).
  • A lot of unit tests that will excise all of the above mentioned features.
  • Quite sizable code base for an open source project (Violet is tiny if we measure it in enterprise scale). This may be helpful then working on Swift incremental compilation - change something in VioletCore and check which modules have been recompiled (I think that @CodaFi worked in this area last year).

• be licensed with one of the following permissive licenses:

  • MIT

• pass ./project_precommit_check script run

  stdout - macOS 11.6.2 (BigSur) on Intel + Xcode 12.4 (Swift 5.3.2)

  michal at michal-macbook in ~/GitHub/Swift-source/swift-source-compat-suite git:(Violet*)
  $ ./project_precommit_check violet --earliest-compatible-swift-version=5.3
  ** CHECK **
  --- Validating violet Swift version 5.3 compatibility ---
  --- Project configured to be compatible with Swift 5.3 ---
  --- Checking violet platform compatibility with Darwin ---
  --- Platform compatibility check succeeded ---
  --- Locating swiftc executable ---
  $ xcrun -f swiftc
  --- Checking installed Swift version ---
  $ '/Volumes/So it was important to treat it carefully/XCode12/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/swiftc' --version
  --- Version check succeeded ---
  --- Executing build actions ---
  $ /Users/michal/GitHub/Swift-source/swift-source-compat-suite/runner.py --swift-branch swift-5.3-branch --swiftc '/Volumes/So it was important to treat it carefully/XCode12/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/swiftc' --projects /Users/michal/GitHub/Swift-source/swift-source-compat-suite/projects.json --include-repos 'path == "violet"' --include-versions 'version == "5.3"' --include-actions 'action.startswith("Build")'
  PASS: violet, 5.3, 8217bf, Swift Package
  ========================================
  Action Summary:
      Passed: 1
      Failed: 0
      XFailed: 0
      UPassed: 0
        Total: 1
  ========================================
  Repository Summary:
        Total: 1
  ========================================
  Result: PASS
  ========================================
  --- violet checked successfully against Swift 5.3 ---
  

Other

Release vs debug

There are some differences between a release and debug configuration in Violet. In PR I submitted:

"actions": [
  {
    "action": "BuildSwiftPackage",
    "configuration": "release"
  },
  {
    "action": "TestSwiftPackage"
  }
]

My intention is:

• build in release - from what I see it would execute: command = [swift, 'build', '--package-path', path, '--verbose', '--configuration', configuration] which is “ok”
• build + unit test in debug - from what I see it would execute: command = [swift, 'test', '-C', path, '--verbose'] which is “ok”

Is my project.json configuration correct for this?

Python tests

We have an additional test suite written in Python where our VM is executing those files. You can run it with make pytest (or make pytest-r for release mode). It returns:

• EXIT_SUCCESS - all tests passed
• EXIT_FAILURE- any of the tests failed

Not sure if you want it, from what I see executables are not supported. Though it is a really good way of checking if Swift runtime is doing what it is supposed to do.

[shahmishal]

@swift-ci test

[shahmishal]

Can we update the version to Swift 5.0? We are trying to keep the version 4.0, 4.2, and 5.0

[shahmishal]

PASS: violet, 5.3, 8217bf, Swift Package

[LiarPrincess]

I will try to downgrade to Swift 5.0 over the weekend.