fwcd/gsoc-2022.md

## gsoc-2022.md

      
    Raw
  

              gsoc-2022.md
            
          
    Overview

My Google Summer of Code 2022 project mainly focused on rewriting parts of the SwiftSyntax library using its own SwiftSyntaxBuilder DSL, more specifically, porting the gyb templates in SwiftSyntaxBuilder to type-safe Swift code, written using the library itself. During this bootstrapping process, many improvements to the DSL were added, inconveniences in the (quite large) API surface fixed and thoroughly tested. The result is a robust and ergonomic API for generating Swift code that has proven to be useful in the context of a medium-sized codebase.
The Project: Bootstrapping SwiftSyntaxBuilder

The first step was to set up the build infrastructure. In particular this required adding a new target that, when executed, produced the generated Swift files in SwiftSyntaxBuilder/generated:

  
      flowchart LR
  subgraph Sources
    SwiftSyntax
    SwiftSyntaxBuilder
    generate-swift-syntax-builder
  end
  subgraph Products
    executable(generate-swift-syntax-builder)
  end
  SwiftSyntax -- is used by --> SwiftSyntaxBuilder
  SwiftSyntax -- is used by --> generate-swift-syntax-builder
  SwiftSyntaxBuilder -- is used by --> generate-swift-syntax-builder
  generate-swift-syntax-builder -- compiles to --> executable
  executable -- generates --> SwiftSyntaxBuilder

    
      Loading

  
In the second phase, the project mainly focused on improving the DSL, for example by adding convenience initializers and making sure that trailing closures and result builders make SwiftSyntaxBuilder code both easy to read and write. A specific example of this is the nice duality between trailing closures and generated blocks, which makes use of Swift's expressiveness to model the language itself concisely in the language. For example, consider the following snippet of Swift code:
struct Point {
  let x: Int
  let y: Int
}
In SwiftSyntaxBuilder this would be expressed as:
StructDecl(identifier: "Point") {
  VariableDecl(.let, name: "x", type: "Int")
  VariableDecl(.let, name: "y", type: "Int")
}
The final step consisted of translating the gyb templates to Swift. During this process, many more improvements to the DSL naturally came up and made their way into the project. A detailed breakdown of the PRs to swift-syntax can be found below.
Week 1: 2022/05/30 - 2022/06/06


#456: Extract syntax builder generation templates into separate directory

Week 2: 2022/06/06 - 2022/06/13


#461: Conform Array to various ExpressibleAs protocols in BuildableCollectionNodes

Week 3: 2022/06/13 - 2022/06/20


#464: Add default initialization for EOF token to auto-generate SourceFile convenience initializer
#465: Clean up generation of builder-based convenience initializers

Week 4: 2022/06/20 - 2022/06/27


#473: Automatically generate leading/trailing space trivia for tokens in SyntaxFactory
#474: Add Trivia.isEmpty
#475: Add ability to attach leading trivia directly to buildable nodes

Week 5: 2022/06/27 - 2022/07/04


#477: Migrate examples to Swift snippets
#481: Add --gyb-only flag to build script's generate-source-code
#482: Generate SYNTAX_NODES in SwiftSyntaxBuilderGeneration
#485: Port SyntaxBuildableWrappers to Swift

Week 6: 2022/07/04 - 2022/07/11


#493: Generate TokenSyntax with SwiftSyntaxBuilderGeneration
#495: Generate ExpressibleAsProtocols with SwiftSyntaxBuilderGeneration

Week 7: 2022/07/11 - 2022/07/18


#497: Add SyntaxBuildableType.listBuildable
#498: Generate BuildableBaseProtocols with SwiftSyntaxBuilderGeneration

Week 8: 2022/07/18 - 2022/07/25


#505: Use let bindings in BuildableBaseProtocolsFile
#506: Generate BuildableCollectionNodes with SwiftSyntaxBuilderGeneration
#515: Use .spacedBinaryOperator instead of .identifier in StructTests

Week 9: 2022/07/25 - 2022/08/01


#518: Add a convenience initializer for IfStmt (optionally taking a second trailing builder closure)
#523: Support optional initializer expression in VariableDecl convenience inititializer
#524: Add ExpressibleAsExprBuildable: ExpressibleAsCodeBlockItem
#525: Make OptionalBindingCondition and MatchingPatternCondition expressible as ConditionElement
#526: Make ExprBuildable expressible as InitializerClause
#527: Make SyntaxBuildableType hashable
#530: Make ExprList initializable by result builder
#532: Update links in README
#533: Update SPM instructions to swift-tools-version 5.6

Week 10: 2022/08/01 - 2022/08/08


#540: Add leadingTrivia parameter to the VariableDecl convenience initializer
#542: Migrate from strings to typed buildable nodes in SyntaxBuildableWrappers
#546: Fix documentation for syntax collections in SwiftSyntaxBuilderGeneration
#547: Make TypeBuildable expressible as TypeAnnotation
#548: Fix ArrayExpr in SyntaxBuildableChild
#551: Use the builder-based ParameterClause initializer where possible
#552: Use NilLiteralExpr in BuildableCollectionNodes
#553: Add Child.isGarbageNodes
#555: Generate BuildableNodes with SwiftSyntaxBuilderGeneration

Week 11: 2022/08/08 - 2022/08/15


#571: Port garbage node generation to SwiftSyntaxBuilderGeneration's Node
#573: No longer require trailing space after expression-like keywords
#574: Factor out resultBuilderBaseName
#575: Improve assert statement generation and fix token choices
#576: Add utility property for enclosing a string in backticks
#579: Add convenience initializer for raw string literals
#586: Use explicit return type in Node initializer's flatMap
#587: Generate trailing newlines in SwiftSyntaxBuilderGeneration
#588: Rename SwiftSyntaxBuilderGeneration to generate-swift-syntax-builder

Week 12: 2022/08/15 - 2022/08/22


#610: Add a convenience initializer for TernaryExpr
#611: Generate Format using SwiftSyntaxBuilder
#612: Add += operator for Trivia
#613: Add convenience initializer for computed properties
#615: Add modifiers parameter to VariableDecl convenience init

Week 13: 2022/08/22 - 2022/08/29


#639: Skip leading trivia generation if empty in BuildableNodes
#640: Add convenience initializer for PrefixOperatorExpr
#644: Add attributes to VariableDecl convenience initializers
#645: Factor out all leadingTrivia logic into Format

Week 14: 2022/08/29 - 2022/09/05


#650: Add convenience initializer for CustomAttribute
#666: Make buildable node fields mutable and fix withTrailingComma
#667: Add trailing trivia and with{Leading,Trailing}Trivia to buildable nodes
#685: Exclude gyb_syntax_support from Swift target
#691: Add trailing space to attributes in VariableDecl
#692: Use swift-argument-parser in generate-swift-syntax-builder
#695: Use @_spi(Testing) for Format.indentTrivia

Week 15: 2022/09/05 - 2022/09/12


#708: Remove underscore from _format and make it internal

Side Quest: Extending SourceKit-LSP

In addition to the aforementioned improvements to SwiftSyntax, I also worked on SourceKit-LSP, the language server for Swift: In addition to migrating the inlay hints from my GSoC project last year to upstream LSP inlay hints, I have added two major features to SourceKit-LSP, namely Call Hierarchy and Type Hierarchy. These let the user query caller/callee and subtypes/supertype hierarchies for Swift, thereby making code navigation more convenient.

#570: [5.7] Migrate to upstream inlay hints
#575: Clean up index lookup requests
#578: Implement call hierarchy
#581: Add request structures for type hierarchy
#582: Implement type hierarchy
#584: Include module names in call hierarchy items

Closing Thoughts

As last year, it has been a pleasure working on Swift and its surrounding projects! Robust tooling for Swift source code is essential to many real-world applications and having a production-ready, type-safe DSL for generating Swift code comprises a large part of this goal.
Special thanks to my mentor Alex and the amazing community for the great collaboration, quick reviews, intriguing ideas surrounding this project and SwiftSyntax in general!