Contributing to Swift

A few months ago, I somehow ended up contributing a non-trivial diff to the Swift compiler without much prior experience with C++ and absolutely zero with compilers, and a lot of people have been asking me how I managed to pull that off. This talk will go over how to get up and running with the Swift compiler and how you can contribute too even if it feels completely new and scary!

Transcript

1. Contributing to Swift @ayanonagon
2. Hi! I’m Ayaka.
3. Workflow
4. June 30, 2016
5. #if DC_TARGET_MOBILE #import <UIKit/UIKit.h> @compatibility_alias DCColor UIColor; #else #import <Cocoa/Cocoa.h> @compatibility_alias DCColor NSColor; #endif
10. My job here is done. !
14. Contributing to Swift @ayanonagon
15. 0. Make sure you don’t need to write a proposal for it.
16. 1.Check swift-evolution@swift.org archives 2.Email swift-evolution@swift.org 3.Get a ! from Swift team member 4.Get SR assigned to you.
18. Now what?
19. Fears 1.New codebases 2.Compilers 3.C++
20. I have no idea what I’m doing.
21. Proceed fearlessly!
22. 0.5. Find a mentor My mentor: Robert (aka @_CodaFi)
23. 1. Clone the repo github.com/apple/swift
24. 1. Clone the repo 1.mkdir swift-source (or wherever) 2.cd into swift-source & clone repo 3../swift/utils/update-checkout --clone
26. 2. Get CMake and Ninja
27. » CMake: manages build configurations » Ninja: does the building
30. Homebrew ! brew install cmake ninja
31. 3. Build the project
32. ./swift/utils/build-script -x
35. build/Xcode-DebugAssert/swift-macosx-x86_64/ Swift.xcodeproj
37. 4. Implement the thing
38. 4. Implement the thing !
39. I really have no idea what I’m doing.
40. But… 1.There’s a lot of great existing example code. 2.What’s the worst that can happen?
41. Import @compatibility_alia s as typealias
42. “Where are similar things implemented?”
43. “Where are other Objective-C things pulled into Swift?”
44. ImportDecl.cpp
45. ImportDecl.cpp Decl * VisitObjCCompatibleAliasDecl(const clang::ObjCCompatibleAliasDecl *decl) { // Like C++ using declarations, name lookup simply looks through // Objective-C compatibility aliases. They are not imported directly. return nullptr; }
46. “What behaves similarly to @compatibility_ali as?”
47. “What also gets imported as typealias?”
48. typedef typedef NSString StringCheese;
49. ! " ✨$ !"#$
50. … It builds. !
51. !?
52. !
53. 4. Tests!
54. 1.Write some Objective-C code. 2.Import it from Swift. 3.Make some assertions based on what you would expect.
55. 1.Write some Objective-C code. import Foundation; @compatibility_alias StringCheese NSString;
57. 1.Write some Objective-C code. ✅ 2.Import it from Swift. 3.Make some assertions based on what you would expect.
58. 1.Import it from Swift import CompatibilityAlias
61. test/IDE/Inputs/custom-modules/module.map module CompatibilityAlias { header "CompatibilityAlias.h" export * }
63. 1.Import it from Swift import CompatibilityAlias func dontMove(cheese: StringCheese) -> StringCheese { return cheese }
64. 1.Write some Objective-C code. ✅ 2.Import it from Swift. ✅ 3.Make some assertions based on what you would expect.
65. lit testing It’s lit !
66. // RUN: rm -rf %t // RUN: mkdir -p %t // RUN: %build-clang-importer-objc-overlays // RUN: %target-swift-ide-test(mock-sdk: %clang-importer-sdk-nosource) -I %t -I %S/Inputs/custom-modules // -print-module -source-filename %s -module-to-print=CompatibilityAlias > %t.printed.CompatibilityAlias.txt // RUN: FileCheck %s -check-prefix=PRINT -strict-whitespace < %t.printed.CompatibilityAlias.txt // RUN: %target-parse-verify-swift -sdk %clang-importer-sdk -I %S/Inputs/custom-modules -I %t %s // REQUIRES: objc_interop // PRINT: typealias StringCheese = NSString import CompatibilityAlias func dontMove(cheese: StringCheese) -> StringCheese { return cheese }
67. // PRINT: typealias StringCheese = NSString import CompatibilityAlias func dontMove(cheese: StringCheese) -> StringCheese { return cheese }
68. // RUN: rm -rf %t // RUN: mkdir -p %t // RUN: %build-clang-importer-objc-overlays // RUN: %target-swift-ide-test(mock-sdk: %clang-importer-sdk-nosource) -I %t -I %S/Inputs/custom-modules // -print-module -source-filename %s -module-to-print=CompatibilityAlias > %t.printed.CompatibilityAlias.txt // RUN: FileCheck %s -check-prefix=PRINT -strict-whitespace < %t.printed.CompatibilityAlias.txt // RUN: %target-parse-verify-swift -sdk %clang-importer-sdk -I %S/Inputs/custom-modules -I %t %s // REQUIRES: objc_interop // PRINT: typealias StringCheese = NSString
69. “What also links with an Objective-C module?”
70. swift_newtype
73. Running the Tests
82. ./llvm/utils/lit/lit.py -sv ./build/Ninja- DebugAssert/swift-macosx-x86_64/test-macosx-x86_64/ --filter=compatibility_alias.swift
83. Tests Failed !
84. 6. Debugging
85. LLDB
86. ./llvm/utils/lit/lit.py -sv ./build/Ninja- DebugAssert/swift-macosx-x86_64/test-macosx-x86_64/ --filter=compatibility_alias.swift
89. lldb -- /Users/ayanonagon/swift-source/build/Ninja-DebugAssert/swift-macosx-x86_64/bin/swiftc -frontend -target x86_64-apple-macosx10.9 -module-cache-path '/var/folders/g9/jwhqvm3x1rx65dtfhdrb00dc0000gn/T/swift-testsuite-clang-module-cacheK6GoT_' -sdk /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.12.sdk -parse -verify -disable-objc-attr-requires-foundation-module /Users/ayanonagon/swift-source/swift/test/IDE/compatibility_alias.swift -sdk -enable-source-import -sdk '/Users/ayanonagon/swift-source/swift/test'/Inputs/clang-importer-sdk -I '/Users/ayanonagon/swift-source/swift/test'/Inputs/clang-importer-sdk/swift-modules -I /Users/ayanonagon/swift-source/swift/test/IDE/Inputs/custom-modules -I /Users/ayanonagon/swift-source/build/Ninja-DebugAssert/swift-macosx-x86_64/test-macosx-x86_64/IDE/Output/compatibility_alias.swift.tmp /Users/ayanonagon/swift-source/swift/test/IDE/compatibility_alias.swift
90. !
95. » The secret life of types in Swift by Slava Pestov » Porting the Swift Runtime to Android by Brian Gesiak » Contributing to Open Source Swift by Jesse Squires » Contributing to Swift by Russ Bishop
96. » The secret life of types in Swift by Slava Pestov » Porting the Swift Runtime to Android by Brian Gesiak » Contributing to Open Source Swift by Jesse Squires » Contributing to Swift by Russ Bishop » Contributing to Swift by YOU <3
97. Proceed Fearlessly!
98. Thanks! ? → @ayanonagon